Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Modelling of ammonia volatilisation in fertilised and flooded rice systems
    Khairudin, Nurulhuda - \ 2017
    Wageningen University. Promotor(en): Nurul Khairudin, co-promotor(en): Karel Keesman; Mohamad Pauzi Zakaria. - Wageningen : Wageningen University - ISBN 9789462576698 - 209
    oryza - flooded rice - ammonia - volatilization - modeling - dynamic modeling - flooded land - nitrogen - oryza - natte rijst - ammoniak - vervluchtiging - modelleren - dynamisch modelleren - overstroomde gronden - stikstof

    In flooded rice systems that are broadcast with urea, significant amounts of nitrogen (N) may be lost to the atmosphere in the form of ammonia (NH3). Many models with different complexities with regards to describing the process of NH3 volatilisation and the overall N dynamics in the systems are available. However, given the differences in local conditions, both too simple and too complex models may not be able to predict NH3 volatilisation correctly or may lead to large prediction uncertainties. Therefore, the main objective of this thesis is to provide a framework to determine an appropriate process-based model with corresponding uncertainty characteristics for estimating NH3 volatilisation in fertilised and flooded rice systems.

    As a first step in the selection of a model for a specific application, an overview on the modelling concepts and the performance of 14 models developed to simulate N dynamics in flooded soil systems is given. Next, in order to understand differences in modelling concepts for a specific process, co-validation was conducted at single process level: urea hydrolysis, NH3 volatilisation, and floodwater pH. Then, a new process-based model for estimating NH3 volatilisation in fertilised and flooded rice systems, which is of a complexity appropriate for scarce soil N data, is presented and evaluated with field observations. For the flooded rice systems in the Philippines, conceptualisation of the two-step urea hydrolysis, partitioning between ammonium and NH3, and a time-varying rate coefficient of NH3 volatilisation in the proposed model improved the prediction of the net NH3 loss. Subsequently, a set-membership parameter estimation approach with soft-error-bounds was used to characterise the uncertainty in the parameter estimates in the proposed model. The set-membership approach is appropriate for poor quality data sets as it allows simultaneous consideration of the different sources of uncertainty affecting the model prediction, such as uncertainty in the model structure, parameters, and observations. Findings of this study can be used as criteria for stakeholders to make an informed selection of models, to modify the existing models for a specific purpose, and to interpret model-output responses critically.

    Interactions among rice-Xanthomonas-Rhizoctonia and biostimulans : Design of a framword to test the effect of a multiple species control of Xanthomonas and Rhizoctonia in rice
    Wurff, A.W.G. van der; Streminska, M.A. ; Elings, A. - \ 2016
    Bleiswijk : Wageningen UR Glastuinbouw (Report GTB 1390) - 26
    arable farming - rice - oryza - sustainable agriculture - plant protection - biological control - integrated control - xanthomonas - rhizoctonia - indonesia - akkerbouw - rijst - oryza - duurzame landbouw - gewasbescherming - biologische bestrijding - geïntegreerde bestrijding - xanthomonas - rhizoctonia - indonesië
    The Indonesian Ministry of Agriculture has the ambition to boast the sustainable production of rice in order to meet the increasing demand. Resource use efficiency can be improved if production loss owing to plant
    pathogens is resolved. Knowledge on the role of biodiversity on system stability must be translated Agricultural practices. Species with overlap in function may constitute biological control measures to create a resilient system against pathogens. As species may counteract, the approach needs to take into account the diverse effects caused by different pathogens, both above-ground and below-ground. Above-ground as well as belowground biological control may benefit from a multiple species approach. Pest-enemy interactions are often embedded in rich communities of multiple interacting pathogens and natural enemies. Designing IPM for multiple pests requires understanding of all interactions among species, both pests and natural enemies. The goal of the research is to investigate which currently available biological control agents are compatible or even act synergistically in order to build a resilient and sustainable crop protection system against Xanthomonas and Rhizoctonia in rice in Indonesia.
    Subsurface drainage of valley bottom irrigated rice schemes in tropical savannah : case studies of Tiefora and Moussodougou in Burkina Faso
    Keïta, A. - \ 2015
    Wageningen University. Promotor(en): E. Schultz; H. Yacouba. - Leiden : CRC Press/Balkema - ISBN 9789462572638
    oryza - ondergrondse drainage - drainage - irrigatie - rijst - savannen - irrigatiesystemen - waterbeheer - burkina faso - oryza - subsurface drainage - drainage - irrigation - rice - savannas - irrigation systems - water management - burkina faso

    SUMMARY

    The contrasted global population growth with the multiplication of the constraints to developing new irrigation systems puts a special challenge upon human crop production systems that needs to be taken up. The populations in many countries in Asia, Middle East and Africa are expected to double in the coming 50 years. The experience of the green revolution in Asia – during which 70% of food production increase was provided by irrigated agriculture – shows that there is not only a need to strive to increase such crop production systems, but also to improve the production efficiency of existing ones. In fact, as a much worrying case, rice production in valley bottom irrigated lands of African Tropical Savannah is far to yield the expected amount of cereals. One of the major constraints to this production is iron toxicity subsequent to poor drainage conditions. According to Africa Rice, at least 60% of the Tropical Savannah swampy valley bottoms are affected by different degree of iron toxicity. The yield in many areas drops to zero, leaving behind millions of disappointed and impoverished farmers. Therefore, it is not surprising that there is strong research dynamic – ranging from agronomy to microbiology – that strives to propose alleviating solutions to rice iron toxicity. Because prevalent anoxic conditions in the soil combined with iron reducing bacteria development were found a basic contributing factor to iron toxicity,  this research has chosen to investigate subsurface drainage potential contributions to solving this issue.

    Two complementary series of operations – designed within two project- components and focused on five basic questions closely related to the contributing factors to iron toxicity development – were performed. In fact, the research project was implemented in two major components: field surveys and designed experiments. The field surveys investigated iron toxicity triggering or aggravating factors such as clay proportions, ferrous ion Fe2+ concentration, dissolved oxygen, soil acidity or water management. Drawing profit from the knowledge gained in survey research and literature review, two parallel experiments were designed using concrete microplots on one hand and buckets on the other hand, to statistically ascertain the impact of subsurface on soil acidity and ferrous iron concentration changes. All the operations performed within the two components of this research project endeavoured to answer the following five research questions:

     

    1. how is ferrous iron formed and distributed in soils invaded by iron toxicity?
    2. how is clay spread within the valley?
    3. how is soil permeability affected by clay distribution in the valley?
    4. how can water management help improve soil conditions?
    5. what is the impact of subsurface drainage on iron toxicity?

     

    The answers to these research questions – already published or in press – are exposed below, followed by the contribution of this research project in two areas: i) science en engineering, and ii) socio-economy.

    Clay and ferrous iron may deposit in strata

    High ferrous ion Fe2+ concentration, inserted into dense clay strata, constitutes an important threat to rice production in several tropical Savannah valley irrigation schemes  of  West  Africa.  Many  actions  are  currently  undertaken  to  alleviate  iron

     

    toxicity. In this study, we have investigated the presence of clay and ferrous iron stratifications within a typical flood prone valley bottom called Tiefora in Burkina Faso. Taking into account the multiple slopes of the valley, two randomized soil samplings were implemented at various depths. Samples were collected as deep as 500 cm, but especially at 30, 50 and 100 cm. The clay percentage was determined by grain size analysis. Ferrous iron concentrations were obtained through the reflectometric method. The stratifications of clay and ferrous ion Fe2+ were checked using statistical hypothesis testing (ANOVA and Welch t-Test). Clay percentage within the first 100 cm top soil – 28.9% – was found twice higher than in the layers underneath. Furthermore, ferrous iron was mainly located in the top 30 cm, with a mean concentration of 994 mg/l. This ferrous iron concentration is much higher than found at depths 50 and 100 cm underneath (73 mg/l), while the pH of all the three layers is almost neutral. This striking stratification suggests several means of alleviating iron toxicity. Among these means, we propose maintaining wet conditions during the growing period in the irrigated lands in combination with leaching by subsurface drainage in the fallow periods.

     

    Iron toxicity risk is higher in single season irrigation schemes

     

    With the aim of finding the geochemical differences and helping to build alleviating strategies against iron toxicity, two hematite dominant valley bottoms irrigated rice soils were investigated in the Tropical Savannah region of Burkina Faso. The first site was Tiefora, a 16 ha modern double-season irrigated rice scheme and moderately affected by iron toxicity (10% of the area with a toxicity score of 4). The second site was Moussodougou, a 35 ha traditional single-season irrigated rice valley-bottom, with 50% facing more severe iron toxicity (score 7). Nine soil extracts were taken from three depths – 30,  50 and 100 cm – i.e. 27 at Tiefora  and 27 at  Moussodougou.  Five techniques were used to measure the data: i) the ferrous iron concentration was determined using a reflectometer, ii) a pH-meter yielded the pH, iii) clay-proportions were obtained by United States Department of Army (USDA) grain size analysis and densitometry, iv) the organic matter was determined by oven drying and v) the dry bulk density was determined by using undisturbed soil samples. Statistical hypothesis testing of One-way ANOVA and Welch t-test were applied to the data to isolate the similarities and the differences between the two sites. A geochemical analysis followed to find the causes of these differences. The results showed that while oxidation of pyrite leads to a simultaneous increase in Fe2+ concentrations and acidity in the soils of coastal floodplains and  mangroves,  the oxidation of hematite in  Tropical savannah valley

    bottoms decreases Fe2+ but also increases acidity during the dry season. As a consequence, it was found that the single-season irrigation scheme of Moussodougou is significantly (p-value 0.4%) more acidic (pH 5.7) than the double-season system of Tiefora (pH 6.4) with also 750-1800 mg/l higher ferrous ion Fe2+. The ferrous iron reached 3000 mg/l in some layers in Moussodougou. This result is a justification to modernize traditional single-season spate irrigation schemes into double-season irrigated rice schemes.

     

    Subsurface drainage type depends on clay distribution

     

    Waterlogged valley bottom soils of Tropical Savannah are areas where the richest traditional cropping systems are found, but they also face adverse physical and chemical conditions which can drastically drop rice yield. Subsurface drainage has been used for many areas to alleviate waterlogging. However, this drainage is dependent of clay

    distribution, type and location. The current research analysed these factors using the case of Tiefora. For this purpose nine boreholes, with depths from 2 to 6 m, were realised. Some 50 samples of soils were extracted at various depths, based on soil changes in texture and colour. These samples underwent grain-size-analysis. A comparative non-linear regression was performed on the clay distribution. Quadratic regression was the most appropriate. Clay proportions were high - 20-30% in the 2 m topsoil - in the upstream and middle areas. A more important - 30-40% - peak was reached in the downstream area at 1 m-depth, with a much smaller thickness (less than 50 cm) and higher permeability. These results suggest the application of mole drainage in the valley, except downstream where the classical Hooghoudt pipe subsurface drainage can be implemented.

     

    Subsurface drainage cost can be reduced by taking into account permeability distribution in valley

     

    In flood prone Tropical Savannah valley soils very low infiltration rates often result in acidic conditions favourable to high concentrations of metallic ions, toxic for rice. The infiltration rate determination is important in drainage design to reclaim degraded soils. Several studies have addressed the mapping of the infiltration rate. Yet its relationship with the toposequence of the valley is not clarified. This research has investigated such possibility, examining the case of the irrigated rice valley of Tiefora. Nine boreholes – 1 to 5 m deep – were implemented from upstream to downstream. The Lefranc permeability test of under phreatic conditions in waterlogged soils – used when the impervious layer is close to soil surface or absent – was conducted. First, a comparative regression was applied to the data, including all the parameters of the regression curves. In case of dissimilarity of the infiltration processes, the comparison focused on the final permeability. Our results show a permeability increase from upstream (0.10 ± 0.10 cm/hr) to downstream (greater than 20.0 ± 10.0 cm/h in some places). Taking into account such permeability increase in subsurface drainage system design would result in the implementation of more efficient and cost effective systems.

     

    Data based water management can help to reduce water losses and solve water inequity frictions between farmers

     

    Surface irrigation represents more than 99% of the irrigated area in West Africa and generally includes valley bottoms dedicated to irrigated rice production, which are often denounced as water overusing schemes. Surprisingly, there is neither follow up nor analysis of the irrigation water used in these gravity irrigation systems. Such a work was carried out in the case of the 16 ha Tropical Savannah irrigated rice valley bottom scheme of Tiefora. Using the flow equation of the concrete weir at the headwork, daily water use volumes were calculated as time series covering more than one-year period. The moving average trend analysis reveals that during both the rainy season (1200 mm of rainfall) and the dry season (no rainfall), the main canal gate is almost never closed, keeping a minimum discharge of 200 m3/day for 4 ha (50 mm/day versus. a local evapotranspiration of 7 mm/day). That stresses the necessity of a more rigorous water management. Furthermore, the autocorrelation analysis by using the ARIMA model showed that the irrigation cycle that ensures equity in water distribution among farm plots is 20 days instead of five. The knowledge of this fact can defuse potential conflicts about equity among farmers: the lack of water in day 4 may be compensated later during the 20-day cycle. It appeared that a simple water level measuring device – installed at the headwork of the main irrigation canal – can produce a time series to

    which autoregressive moving average model can be applied to yield, at low cost, a thorough assessment of water management in this surface irrigation system.

     

    Subsurface drainage alleviates iron toxicity in mean and long run

     

    Iron toxicity is one of the most important constraints that hinder rice productivity in Tropical Savannah valley bottom irrigated fields, but fortunately that can be alleviated. A too high ferrous iron level in the soil can nullify rice yield. Several research fields – agronomy, pedology through microbiology – strive to provide a solution to this issue. Up to date, the contribution of hydraulics to tackle iron toxicity remained limited. The current research addressed this aspect through controlled experiments on highly ferrous iron contaminated rice hematite soils. Twelve concrete microplots and eight buckets were used to implement two independent designed experiments during a period of 86 days. Drainage and liming were the two factors whose impacts were investigated. Drainage was used with two treatment conditions: 0 mm/day and = 10 mm/day, and liming also had two treatment conditions: Lime- = 0 kg/m² and Lime+ = 1 kg/m² per unit increment increase of the pH. Four different responses in the soil were measured: ferrous ion concentration Fe2+, pH, oxido reduction potential, and the dissolved oxygen. For the rice, toxicity scores of the International Rice Research Institute were followed

    up. The results indicate an increase of Fe2+ from 935 mg/l to more than 1106 mg/l (at 95% of confidence level), but, which is interesting, with a significant decrease of soil acidity from pH 5.6 to 7.3 (95% confidence level). Liming had the same effect in alleviating the acidity. Reduction processes were not hindered by subsurface drainage since the oxydo reduction potential dropped from 84.6 to 9.2 mV, and dissolved oxygen

    moved from 1 mg/l to less than 0.1 mg/l. Despite of the reduction of the acidity, with such a high ferrous iron level as 1106 mg/l, the iron toxicity score reached 7 in the twelve microplots and the rice died. Still, the reduction of soil acidity provides a new insight on the hematite soils behaviour, opposite to the acidification with subsurface drainage in coastal floodplains and mangrove pyrite. Furthermore, it will lead to less ferrous iron intake by rice roots and in such perspective improve the rice yield. Finally, though liming can achieve the same result, subsurface drainage takes the advantage when this mineral is not available or is expensive.

     

    Project outputs for Tiefora farmers

     

    From the investigations and their supporting activities, two major benefits were brought to the farmers of Tiefora. First, in order to alleviated iron toxicity – which is much less severe in this place than in Moussodougou – and improve rice yield (less than 4 tons/ha), it would be essential to apply according the norms of the Institute of Environment and Agricultural Research (IN.ERA) the complex fertilizer NPK. However, this application should go along with making well built bunds around the farm plots in order to confine the fertilizer and make the mineral more available for the rice roots. This  will invigorate the crop  and thus  strengthen  its resistance to iron toxicity. Secondly, the project handed to the farmers’ association of Tiefora three key documents: i) an aerial photo the environment of the valley of Tiefora, including the reservoir, the village, the roads and the irrigated valley, ii) a topographical map of the valley bottom, intended to help in potential engineering works on the irrigation system, and iii) a detailed map of the farm plot system, accompanied with the complete list of the farmers and their farm sizes, and the location of iron intoxicated plots for their daily activities

     

    Project outputs for Moussodougou farmers

     

    Based on the investigation results and due to the severe iron toxicity in Moussodougou, the project provided several advices and handed some key documents to the farmers. Ferrous iron concentration in the soil of Moussodougou can reach 3000 mg/l in many farm plots with acidity as severe as pH 4. Since its incorporation into the soil was found to induce the growth of iron reducing bacteria activity, and given the positive conservation impact of organic matter in lightening the soil structure,  the  project advised the farmers to reduce its use but not to eliminate it completely. In parallel, farmers would have to use the complex NPK as in Tiefora, according to the norms of IN.ERA, but combine it with a careful erection of plot bunds to make the mineral element more available for the rice. Due to the fact that the current single irrigation season during the year in Moussodougou is an aggravating factor of iron toxicity, the project also introduced to the  farmers association its ongoing work of developing sprinkler irrigation from groundwater during the dry season. Finally, the project handed to the farmers’ association the same set of documents as in Tiefora, but related to the valley bottom of Moussodougou.

     

    Other social impacts

     

    In an ultimate effort to share the insights gained about the iron toxicity alleviation process, this research project produced and uploaded onto the social media YouTube several useful videos. The 15 videos uploaded and accessible for everybody, deal with areas as varied as hydrometrics, microbiology, geochemistry and small scale water saving irrigation equipment assembling at village level (without electricity). Many of these videos were very appreciated by the audience. For example, the video of "Innovative irrigation systems in Sub-Saharan Africa (French)" has been viewed/downloaded 500 times/month. Similarly, the video "How to take a sample of disturbed soil or resting in soil immersed at different depths (English)", was viewed/downloaded some 45 times/month. These two videos were classified "creative common" due to their high potential appropriation by third party video productions. Hence, it is expected that the project will have an even higher social impact in the coming months or years.

     

    Molecular regulation of drought tolerance in rice
    Haider, I. - \ 2014
    Wageningen University. Promotor(en): Harro Bouwmeester, co-promotor(en): Carolien Ruyter-Spira; P.B.F. Ouwerkerk. - Wageningen : Wageningen University - ISBN 9789461738431 - 183
    oryza - oryza sativa - oryza glaberrima - plantenfysiologie - droogte - droogteresistentie - stress - moleculaire biologie - plantengroeiregulatoren - oryza - oryza sativa - oryza glaberrima - plant physiology - drought - drought resistance - stress - molecular biology - plant growth regulators

    Abiotic stresses are the primary cause of crop failure worldwide, reducing average yields by more than 50%. Among the various forms of abiotic stress, drought is the most limiting factor for rice productivity. Drought affects about 20% of the total rice cultivation area in Asia. Understanding the various aspects of drought stress, the response and resistance mechanisms in relation to plant growth is therefore of fundamental importance to improve sustainable agriculture.

    Drought tolerance is usually controlled by complex gene networks and engineering of a single gene is unlikely to improve this trait. However, altering the expression of Transcription Factors (TFs) may be a tool for improvement of drought tolerance since they have been shown to activate the expression of multiple genes in a coordinated manner and they are therefore attractive and promising targets for application in molecular breeding or genetic engineering. In addition, studies on TFs will improve our understanding of the physiological and molecular mechanisms of drought tolerance. The overall objective of the work presented in this thesis was to get more detailed insight in the molecular regulation of drought tolerance in rice, with a particular focus on the role of TFs of the homeobox class and two groups of plant hormones, abscisic acid and strigolactones.

    In Chapter 2, I described the isolation and characterisation of the rice Oshox22 gene which is an homeobox gene of the HD-Zip I family. I showed that the expression of Oshox22 is strongly induced by salt stress, abscisic acid (ABA) and polyethylene glycol (PEG) treatment, and weakly by cold stress. Trans-activation assays in yeast and transient expression analyses in rice protoplasts demonstrated that Oshox22 is able to bind to the CAAT(G/C)ATTG element and acts as a transcriptional activator that requires both the HD and Zip domains. Rice plants homozygous for a T-DNA insertion in the promoter region of Oshox22 showedreduced Oshox22 expression and ABA content, decreased sensitivity to ABA, and enhanced tolerance to drought and salt stress in the seedling stage. In contrast, transgenic rice over-expressing Oshox22 showed increased sensitivity to ABA, increased ABA content, and decreased drought and salt tolerances. These results support the conclusion that Oshox22 acts as a negative regulator in stress response. Since reporter gene studies in yeast and rice cells suggested that Oshox22 acts as a transcriptional activator, its function as a negative regulator in stress responses might be explained via activation of other repressors.

    As Oshox22 is highly expressed in developing panicles and grains, in Chapter 4 I investigated the role of Oshox22 in controlling grain length (GL) in rice. We found a stable quantitative trait locus (QTL) for GL on this position in four mapping populations. Sequence analysis of Oshox22 in rice cultivars Bala, Azucena and Nipponbare revealed an extra A base in the Azucena promoter, which is a long grain type rice. Using a PCR-based insertion/deletion (InDel) CAPS maker assay in rice populations and collections, I found an association between the A InDel in the Oshox22 promoter with GL. Furthermore, expression of Oshox22 under the control of a promoterwith the A InDelin Zhonghua 11 (which does not have the A InDel) resulted in a significant increase in GL in Zhongua 11. Scanning electron microscopy revealed that the enhanced GL was caused by an increased cell length in the inner epidermal cells of the lemma. In addition, the data show that there is a tendency for lower expression of Oshox22 when GL increases which would suggest that Oshox22 functions as a repressor of GL.These findings suggest that natural variation in the Oshox22 promoter can be exploited in breeding programmes to modify GL using molecular marker-assisted selection. However, the exact mechanism of regulation of GL by Oshox22 is still not clear. Since Oshox22 is a homeobox gene, it will exert its function via regulation of downstream target genes which we do not know yet. Therefore, more research is needed to elucidate the genetic and biochemical pathways to understand the molecular mechanisms underlying rice GL development and to determine if there are interactions with other known regulators of GL.

    The strigolactones are a relatively new class of plant hormones and a possible role in drought tolerance is unknown. In Chapter 4 of this thesis, I reviewed the various roles that strigolactones (SLs) play both in the rhizosphere and as endogenous plant hormone. In addition, the current knowledge on the SL biosynthetic and downstream signalling pathways and the interactions of SLs with other plant hormones, such as ABA, is described.

    It has been reported that there seems to be a functional link between ABA and SLs but the mechanism of that link remained unknown. In Chapter 5, I studied the intimate relationship between ABA and SL biosynthesis through the further characterisation of β-carotene isomerase D27 in rice. The results show that the ABA content was increased in SL-deficient and -insensitive dwarf (d) rice mutants, d10, d17 and d3 compared with wild type, while it was reduced in d27. In addition, this difference was significantly enhanced by exposure to drought. Interestingly, as a consequence of their enhanced ABA levels, d10, d17 and d3 plants displayed an increased tolerance to drought compared with wild-type plants, while the ABA deficient d27 plants were more drought sensitive. Transient over-expression of OsD27 in Nicotiana benthamianaenhanced both ABA and SL production. However, constitutive over-expression of OsD27 in rice plants showed no significant changes in ABA and SL levelsunder normal conditions. Still, OsD27 over-expression did result in higher SL levels, compared with wild-type plants, under phosphate starvation. This suggests that likewise, OsD27over-expression may only result in increased ABA levels during drought stress conditions. I concluded that the OsD27 gene is involved in SL as well as ABA biosynthesis, and that, depending on the environmental conditions, the expression of the more downstream SL and ABA specific biosynthetic genes determines which of the two and how much is being produced.

    In Chapter 6, I discussed the main findings of this thesis and presented the future perspective of how the knowledge generated in this thesis can contribute to the improvement of drought tolerance and GL in rice.

    An institutional perspective on farmers’ water management and rice production practices in Benin
    Totin, G.G.E. - \ 2013
    Wageningen University. Promotor(en): Leo Stroosnijder; R. Mongbo, co-promotor(en): Barbara van Mierlo; E. Agbossou. - Wageningen : Wageningen UR - ISBN 9789461738103 - 136
    oryza - rijst - gewasproductie - waterbeheer - beleid - benin - oryza - rice - crop production - water management - policy - benin

    This thesis is part of the wider debate about the role of institutions in agricultural innovation processes. It

    investigates how institutions shape rice production in inland valleys in Benin. It starts from a scoping study

    (prior to this research) on smallholder irrigation in Benin, which indicated irrigation water stress as one of

    the main problems in the rice production chain. The authors explain the water scarcity as the consequence

    of poor maintenance of the irrigation canals, whereas others think that is a direct manifestation of climate

    change. It appears that a mono‐technical explanation cannot give a deep enough understanding of the

    existing water problem, which has various dimensions. The thesis therefore assumes that an institutional

    perspective would provide a better insight into the barriers that hinder the efficient use of irrigation water

    in the rice production chain.

    Chapter 1 introduces the main problems teased out in the book. Between 1976 and 1990, the Benin

    government initiated numerous interventions to increase local rice production. These different

    interventions were ineffective because of the many innovation barriers that existed in the rice chain.

    Therefore, the first research question addressed in this research is: what are the constraints in the local rice

    value chain and the opportunities for innovation in the research areas?

    After the 2007 rice crisis, the government introduced a new generation of interventions which

    prioritised the institutional facilities (e.g., subsidies for seeds and loans for fertiliser, market facilities and so

    forth) to support the intensification of local rice production. There have been successful outcomes in terms

    of increased rice yield, rice production and farmers’ income. So, this research is interested in studying the

    effectiveness of the two generations of interventions in the rice value chain. The following research

    question is also addressed: how and to what extent does the new generation of interventions create space

    for rice production in the research areas and overcome the shortcomings of previous interventions?

    Which factors hinder the effective use of irrigation water and the development of the local rice value

    chain in the three research areas are further explored in a diagnostic study and described in Chapter 2. The

    diagnosis indicates that it is not only technical constraints that hinder the local rice production chain;

    rather, a combination of technical and institutional factors affect the development of rice production.

    Moreover, both local and higher level institutional barriers influence negatively the local rice value chain.

    The barriers to innovation include: unclear division of responsibilities for canal maintenance between local

    farmer groups and the government, lack of effective local rules for the distribution of the available water

    and maintenance of the irrigation infrastructures, distrust among farmers and the constraining formal and

    informal credit systems and uncertain market outlets. These constraints reduce rice output and farmers’

    incomes.

    After identifying the main economic, institutional and technical constraints that limited the

    development of the local rice production chain, the study also describes the potential opportunities that

    exist for innovation in the chain. Chapter 2 shows that, from a bio‐technical perspective, in the three

    irrigation schemes, the actual rice output remains far below the estimated potential of the command areas,

    given the water and land available in the inland valleys. It establishes that there is room for a considerable

    increase in rice production and associated incomes. For instance, in Koussin‐Léléand Bamè, farmers have

    lands in the uplands as well as the lowlands. Less than 10% of the potential land is used for rice production.

    Chapter 4 shows an option to improve soil moisture in the uplands and extend rice production in this part

    of the valleys.

    In the research areas, there are differences in the extent to which the rules for collective activities

    are set and followed. The farmers cooperate, for instance, to collectively purchase inputs, make collective

    credit requests or sell collectively the harvested rice. At the start of the study however, not all the farmers

    contributed to the collective cleaning of the canals to increase the water discharge that serves all of them.

    among the farmers, a comparative analysis of the three research areas was conducted, using a framework

    to highlight key contextual differences such as the nature of the resource, the characteristics of the user

    group and farmer‐based institutional arrangements in the geographical areas. The findings of the case

    studies, reported in Chapter 3, draw attention to the balance between water demand and availability, the

    existence of inequities and privileged positions within the groups and the strength of farmers’ group

    organisation and the ability to sanction uncooperative behaviour. The existence of alternative sources of

    livelihood also influenced cooperation. Contrary to our expectations, the analysis shows that the largest

    and most diverse group of farmers appeared best organised and equipped to engage in cooperation. Large,

    diverse farmer groups allow the emergence of institutional arrangements that can overcome social

    dilemma situations and demotivation emanating from customary privileges and exemptions.

    A collaborative action research approach was used to explore the opportunity to expand rice

    production in the upland areas. In Chapter 2, it was already established that rice production could be

    improved for the uplands if there was a better supply of irrigation water. This analysis inspired the action

    research conducted in collaboration with the rice farmers (from the three production research areas), an

    extension agent and a researcher to examine the application of mulch (three doses) and the use of a highyield

    lowland rice variety to replace an upland rice variety (Chapter 4). Multiple methods suggested by both

    the researcher and farmers themselves were used to evaluate the trial results: quantitative evidence was

    combined with qualitative evaluation, using indicators agreed upon by the collaborating group. The results

    show that the lowland rice variety IR‐841 with 10 t ha‐1 ‘rice‐straw’mulch allows farmers to better use

    available water in the upland areas and increase rice yields. Although opting for IR‐841 over the specially

    bred upland variety Nerica‐4 is risky because of its high water demand and the uncertainty in rainfall

    distribution, farmers use IR‐841 for profit maximisation. Beyond its technical output, the joint

    experimentation facilitated the exchange of knowledge, experiences and practices among the involved

    stakeholders.

    Since the rice crisis of 2007, the government of Benin has initiated a variety of short‐and long‐term

    programmes aimed at providing access for farmers to agricultural inputs for local rice intensification.

    Chapter 5 explores the interplay between the external interventions of the government programmes and

    the local actions of farmers, in the three research areas. Using an actor‐oriented perspective combined

    with the timelines of the chronological events, the study concludes that farmers’ local actions interact at

    diverse junctures with the external interventions. The study shows that it is not only external interventions

    that trigger changes; rather, the interaction between external interventions and farmers’ local actions

    makes room for changes to happen. Moreover, the investigations show that, although the same

    institutional conditions (through the different government interventions) were provided to rice farmers in

    the three study areas, located close to one another, there are similar, but also divergent, hence unexpected

    outcomes regarding farmers’ social practices. The most obvious unexpected outcomes of the programme

    interventions are the change from limited collective canal cleaning to individual effective canal cleaning in

    Koussin‐Lélé, the use of pumps in upland areas in Bamèand farmers who changed from growing vegetables

    or maize alone to growing rice in combination with these in Zonmon. The wish to satisfy subsistence

    livelihood needs, the different production options available and natural biophysical conditions (e.g., floods)

    are the main factors that contribute to shaping farmers’ local actions and explain the diversity of practices

    in the three research areas, although they all received the same interventions.

    Chapter 6 provides answers to the research questions formulated in Chapter 1 and reflects on how

    the different results from the thesis contribute to the policy debate about how to improve rice production

    in Benin. Reflection on the sustainability of the current rice intensification policy established that the

    government interventions constitute a “protected space”. However, there is no guarantee that the

    intensification of local rice production will still continue when the supports provided by the government

    projects end. Another limitation of the rice intensification policy is that it relies on the use of the irrigation

    schemes designed for one cropping season in a context where farmers are now producing up to three

    cropping seasons a year. The inadequacy of the irrigation design concept for the intensification of rice

    production might contribute to explaining why some of the farmers are suffering from the lack of irrigation

    water. Moreover, although the inland valleys in Benin are a potential area for rice production, they are also

    complex ecosystems with irregular water supply wherein smallholder farmers must carefully allocate

    available resources.

    The thesis shows the importance of institutions in agricultural production. Many institutional studies

    are about social issues. One of the main contributions of this thesis relates to the points it established by

    linking institutional issues with technical dimensions. Chapters 3 and 4 explain the interrelations between

    institutions and water management practices. The experimental procedure described in Chapter 4 was

    grounded in the institutional context but also has a technical purpose that is, identifying water use options

    that allow the expansion of rice production in the uplands. By exploring a technical issue like water

    management from an institutional perspective, the thesis provides clear understanding of the reasons

    behind farmers’ seemingly illogical or irrational water management practices.

    Comparative and functional analysis of NODULATION SIGNALING PATHWAY 1 (NSP1) and NSP2 in rice and Medicago
    Liu, W. - \ 2013
    Wageningen University. Promotor(en): Ton Bisseling, co-promotor(en): Rene Geurts. - S.l. : s.n. - ISBN 9789461736369 - 147
    oryza - medicago - knobbelvorming - symbiose - genen - rhizobium - wortelknolletjes - stikstoffixatie - oryza - medicago - nodulation - symbiosis - genes - rhizobium - root nodules - nitrogen fixation
    An ecogeographic analysis of Oryza series Sativae in Asia and the Pacific
    Banaticla-Hilario, M.C.N. - \ 2012
    Wageningen University. Promotor(en): Marc Sosef, co-promotor(en): Ronald van den Berg; K.L. McNally. - S.l. : s.n. - ISBN 9789461733788 - 237
    oryza - oryza sativa - oryza nivara - genetische bronnen van plantensoorten - plantengeografie - plantenecologie - diversiteit - in-situ conservering - plantenmorfologie - taxonomie - genetica - genenbanken - azië - oryza - oryza sativa - oryza nivara - plant genetic resources - phytogeography - plant ecology - diversity - in situ conservation - plant morphology - taxonomy - genetics - gene banks - asia

    The non-cultivated speciesof the genus Oryza can provide a genetic arsenal of useful traits for improving the widely cultivated and consumed Asian rice (O. sativa). The diversity of these valuable plant resources must be well understood to ensure their effective in- and ex-situ conservation. In this thesis, we examined the ecogeographic variations within and between the three species of Oryza series Sativae in Asia and the Pacific. We looked at species differentiation from different spatial scales by analysing sympatric accession pairs of O. meridionalis and O. rufipogon and of O. nivara and O. rufipogon.

    We conducted phenotypic analyses in Chapter 2. The strong influence of ecology on species morphology was demonstrated in the ordination and cluster analyses results where O. meridionalis and O. nivara grouped together and were separated from O. rufipogon. We detected greater differentiation of O. nivara and O. rufipogon in South Asia and positive correlations between spatial and intraspecific (interpopulation) morphological distances in continental Asia. We found significant correlations between geoclimatic factors and certain character measurements within species and observed that seedling height, culm number and diameter, leaf size, and anther length exhibit contrasting responses for O. nivara and O. rufipogon. We confirmed significant morphological differences between the three species, between the South and Southeast Asian populations of O. nivara, and between the Australasian and the non-Australasian populations of O. rufipogon and provided botanical descriptions to delineate O. meridionalis, O. nivara and O. rufipogon morphologically.

    In Chapter 3, we genotyped the same set of accessions with 29 SSR markers and applied a variety of methods for genetic diversity analysis. Based on ordination and phylogenetic results, we verified that O. meridionalis is a genetically distinct species and that O. nivara and O. rufipogon overlap genetically across their geographic distribution. However, Bayesian clustering analysis recognized local-scale species separation of O. nivara and O. rufipogon implying stronger interspecific gene flow barriers in smaller spatial units. Concurrently, AMOVA indicated that the bulk (64%) of genetic variation in Asia Pacific series Sativae can be found among accessions and the lesser portions within accessions (26%) and among species (10%). We captured contrasting intraspecific variation patterns for O. nivara and O. rufipogon where the former exhibited low diversity, high population differentiation and isolation by distance mainly in South Asia while the latter displayed high diversity, low population differentiation and isolation by distance primarily in continental Southeast Asia. We established that altitude is correlated negatively to accession diversity and positively to local-scale species differentiation. Using Bayesian inference, we identified eight genetically distinct population groups: C1) Indian and Bangladeshi O. nivara; C2) Cambodian O. nivara; C3) Southeast Asian O. rufipogon; C4) O. meridionalis; C5) Nepalese O. nivara; C6) non-Cambodian Southeast Asian O. nivara; C7) Australasian O. rufipogon; and C8) South Asian O. rufipogon. Cluster analysis grouped the aromatic and japonica cultivar groups of O. sativa with O. rufipogon in South Asia and the indica and aus groups with O. nivara from Thailand and Cambodia, respectively. O. nivara from Nepal seemed genetically isolated from the other population groups. We also detected variation patterns that agreed with the results in Chapter 1 such as the South and Southeast Asian divisions of O. nivara, the divergence of Australasian populations from the rest of O. rufipogon and the greater differentiation of O. nivara and O. rufipogon in South Asia.

    In Chapter 4, we conducted artificial crossing experiments to 15 selected parental accessions of O. meridionalis, O. nivara, and O. rufipogon and assessed the extent of several post-pollination isolating mechanisms in Oryza series Sativae. We observed reproductive incompatibility within and between the inbreeding species O. meridionalis and O. nivara and high intraspecific crossability of the outcrossing O. rufipogon where viable and non-sterile F1 hybrids were produced only by combinations with a parental distance that ranged from 1062 to 3813 kilometers. Insular Southeast Asian and/or Australasian accessions of O. rufipogon were the most reproductively successful parents. O. rufipogon exhibited significant pre-zygotic species isolation (in terms of seed set) and reduced post-zygotic isolation, and seemed symmetrically compatible with O. nivara and asymmetrically compatible with O. meridionalis. We obtained few annual hybrids with relatively high fertilities from crosses between O. rufipogon and O. nivara and numerous perennial hybrids with low fertilities from crosses between O. rufipogon and O. meridionalis. Crossability estimates did not show significant correlations with geographic distance between parents. However, we discerned reduced seed set and F1 fertility in interspecific combinations with sympatric parents compared to crosses with non-sympatric parents, indicative of reinforced species isolation in sympatry. We evaluated the F1 offspring of different cross combinations and found a mixture of intermediate and parental character traits in interspecific hybrids.

    We discussed the taxonomic implications of the research results in Chapter 5 where we specifically dealt with the opposing views of lumping or splitting of O. nivara and O. rufipogon. We concluded that these two taxadeserve to be treated as separate species based on the following biosystematic evidence obtained from the thesis: 1) ecological distinction; 2) considerable prezygotic barriers; 3) opposing patterns of gene flow and genetic variation; 4) local-scale genetic divergence and 5) enhanced reproductive barriers under sympatric conditions. We identified ecogeography as a major driving force in the diversification of Oryza series Sativae in Asia and the Pacific and suggested that ecological speciation gave rise to O. nivara and O. rufipogon. We also presented recognizable geographic races within species.

    Ultimately in Chapter 6, we emphasized the importance of our study in several aspects of rice science and identified results that agreed with prior Oryza diversity studies. At the same time, we presented previously unreported morphological and genetic variation patterns that were established in this thesis. We discussed the possible applications of the research results to wild rice conservation, covering in situ strategies as well as gene bank practices. We also highlighted the potential role of O. nivara in Asian rice domestication where it could have either directly given rise to the indica cultivar group or hybridized/introgressed with migrated japonica cultivars in India, eventually leading to the development of indica.

    Strengthening rice seed systems and agro-biodiversity conservation in West Africa: a socio-technical focus on farmers’ practices of rice seed development and diversity conservation in Susu cross border lands of Guinea and Sierra Leone
    Okry, F. - \ 2011
    Wageningen University. Promotor(en): Paul Richards; Paul Struik, co-promotor(en): Edwin Nuijten; P. van Mele. - [S.l.] : S.n. - ISBN 9789461731111 - 208
    gewassen - oryza - agrobiodiversiteit - zaden - rassen (planten) - zelfvoorzieningslandbouw - west-afrika - guinee - sierra leone - rijst - crops - oryza - agro-biodiversity - seeds - varieties - subsistence farming - west africa - guinea - sierra leone - rice

    Some decades ago it became clear that formal agricultural research institutions - and hence formal interventions in agriculture - were somehow missing their targets for African farmers, mainly because their proposed solutions, and the ways these solutions were developed and introduced to African farming communities, did not match the realities of peasant life. It was recommended that the formal research should consider the wider contexts within which farmers operated to formulate better solutions. These solutions are essential for low-resource farmers facing many (socio-economic and cultural) constraints and having to cope with uncertainties (climate change, market variations, soil degradation, political and social unrest). The research presented in this thesis analyses the functioning of West African rice seed systems with regards to this recommendation. It starts with a regional focus (seven West African coastal countries) and then focuses on specific in-depth field studies undertaken in Guinea (with some comparison from neighbouring Sierra Leone). The study is based on an interdisciplinary approach combining methods from social and natural sciences.

    Findings show that despite efforts from governments, policy makers and formal agricultural research, the informal seed system still predominates, largely because it is the seed system closest to low-resource farmers. The objective of replacing the informal seed system by a formal seed system exclusively promoting improved varieties is a distant prospect. The research shows that local varieties are, to a large extent, superior to improved varieties in the sub-optimal conditions facing most farmers. It is also shown that even when improved varieties suit farmers’ conditions they are often channeled through inappropriate institutional arrangements that block access by low-resource farmers. Formal seed projects often lack follow-up to sustain actions. Innovations are lost between research planning, donor requirements to demonstrate adoption and the realities of peasant coping strategies. It is argued that success indicators in the formal seed system need to be redefined based on a clear conceptual divide between variety dissemination and bulk seed supply. The formal seed system merges these two activities whereas the informal seed system pursues a different path and addresses different procedural constraints. We suggest seed projects should concentrate on variety dissemination and leave bulk seed supply to local seed dealers. The thesis demonstrates that local dealers are effective and more closely in tune with farmer needs.

    The major finding of this thesis is that the informal seed system is closer to farmers, and works well, because it reflects (and is integrated with) local ideas about food security and social solidarity. This social dimension is missing in the formal system, designed and funded by experts who neither live by planting rice nor share in the local sets of assumptions about social reciprocity and obligation. Guinea may be undermining its long-term food security if it continues to seek to replace a social seed system with one driven solely by abstract ideas of economic rationality. The better option, supported by the weight of evidence in this thesis, is to seek complementarity and synergy between the two systems.

    Keywords: Oryza sativa, Oryza glaberrima, food security, formal seed system, informal seed system, varietal diversity, sub-optimal agriculture, small-scale farmers, farmers’ practices, Guinea, Sierra Leone, West Africa.

    Rice genetic resources in postwar Sierra Leone
    Chakanda, R.T.M. - \ 2009
    Wageningen University. Promotor(en): Marc Sosef, co-promotor(en): Ronald van den Berg; Bert Visser. - - 161
    oryza - rice - plant genetic resources - genetic diversity - war - landraces - varieties - phenotypic variation - farming systems - sierra leone - farmers' knowledge - oryza - rijst - genetische bronnen van plantensoorten - genetische diversiteit - oorlog - landrassen - rassen (planten) - fenotypische variatie - bedrijfssystemen - sierra leone - kennis van boeren
    This research presents the effect of the 10-year long civil war in Sierra Leone on rice genetic resources, using farmers and their seed systems in three selected districts as reference points. The war disrupted all forms of production and development in the country and like other sectors of the economy, agricultural production and the conservation of plant genetic resources at the farm level was severely affected. It emerged that farmers’ effectiveness to cultivate and manage their seed systems and the options to grow rice under insecure conditions were disrupted at different levels in the three districts studied. However, the general consequence of the war in all of the districts was that farmers lost considerable amounts of their seed stocks. Total losses for some rice varieties was averted because of the occurrence of a number of varieties in more than one village in the same region, which was a result of farmers seed exchange systems, and also due to farmer movement during the war. The majority of the varieties that were reported lost were actually “dispersed” in the regions, indicating good options for post-war recovery.

    There was little evidence that the genetic composition of rice varieties were significantly altered as a consequence of the war, except for the total loss of upland varieties in one of the districts. The varieties that had the highest survival were those that had wider pre-war distribution, showed plasticity in growing habits wherein they demonstrated the potential to grow in both agro-ecosystems and in the different districts, and the fact that they existed in many different forms.

    Statistical analysis showed a clear distinction between upland and lowland varieties, which demonstrated the effectiveness of farmer selection with regard to the two production ecosystems. This was different for the periods defined as pre-war and post-war. Pre-war varieties were less well defined in this respect. Further to this, there was evidence of a change in rice genetic resources between the pre-war and post-war situations, which was demonstrated in the number of varieties for each of the two ecosystems. Despite these changes, and the losses in seed stocks as a consequence of the war, genetic diversity increased in post-war rice varieties.

    AFLP results indicated that rice varieties in Sierra Leone possess different levels of intra-variety variation, which makes it difficult to identify homogenous genotypes at the seed unit level. This was attributed to genetic exchanges caused by farmers’ practices of growing different varieties in mixtures. The variation however does not alter the profile of inter-variety genetic differences, which remains large enough to distinguish one variety from the other. It demonstrates that the genetic composition of rice varieties remains distinct from one another, and that variety names in Sierra Leone are good indicators for genetic diversity of rice at the farm level.
    Genetic diversity for sustainable rice blast management in China: adoption and impact
    Revilla-Molina, I.M. - \ 2009
    Wageningen University. Promotor(en): Herman van Keulen, co-promotor(en): Lammert Bastiaans. - [S.l.] : S.n. - ISBN 9789085852551 - 130
    oryza - rijst - magnaporthe grisea - plantenziektebestrijding - genetische diversiteit - tussenplanting - gewasproductie - rassen (planten) - teeltsystemen - yunnan - china - oryza - rice - magnaporthe grisea - plant disease control - genetic diversity - interplanting - crop production - varieties - cropping systems - yunnan - china
    Keywords: Disease management, genetic diversity, rice interplanting, competition, resource complementarity, technical efficiency, production function, Magnaporthe grisea

    The experience on rice blast in Yunnan Province, China, is one of the most successful and widely publicized examples of genetic diversification for disease suppression in practice. The wet, cool climate of the province is highly favourable for the development of rice blast epidemics. Before 1998, farmers had to spray fungicides three to eight times per cropping season to successfully grow a crop of glutinous or sticky rice. To reduce farmers’ dependence on these harmful agrochemicals, a team of scientists from the International Rice Research Institute (IRRI) and Yunnan Agricultural University (YAU) initiated a project in Yunnan Province with the objective to explore the possibilities of using biodiversity as a means to control blast outbreaks, and through the associated increase in productivity and income, contribute to poverty alleviation.
    This study focuses on the effects of the developed technology, i.e., interplanting one row of high-value, but blast-susceptible glutinous rice, with four to six rows of blast-resistant hybrid indica rice varieties, on blast management and the socio-economics, i.e., productivity and farm income, as a basis for explaining its adoption.
    In a field experiment in Gejiu, Yunnan Province, it was shown that niche differentiation, leading to resource complementarity between the two rice varieties, was marginal and hardly increased the land productivity of the rice varietal mixtures. Prevention of lodging of glutinous rice appeared an important additional advantage of growing rice in varietal mixtures. Results of farm surveys involving both, adopters and non-adopters, showed that contact with extension workers and farmers’ perceptions of the technology-specific attributes of the rice varietal mixtures were the major factors determining adoption probability and use intensity. Adoption of rice interplanting resulted in increased technical efficiency. Longer farming experience and access to extension agents were both significantly positively correlated with technical efficiency.
    The rice interplanting system in Yunnan has clearly shown that it is possible to combine modern and traditional rice varieties to control blast disease, attain acceptable crop production and provide high-quality food and income for the rural population. The Yunnan experience has also demonstrated that the best way to transfer a technology from concept to actual practice is to strengthen the links among research, extension, policy makers and farmer communities.


    Improvement of water use efficiency in rice and tomato using Arabidopsis wax biosynthetic genes and transcription factors
    Karaba Pradyumna, A. - \ 2007
    Wageningen University. Promotor(en): Evert Jacobsen; A.B. Pereira, co-promotor(en): M. Udayakumar. - [S.l.] : S.n. - ISBN 9789085046387 - 156
    rijst - tomaten - solanum lycopersicum - oryza - watergebruiksrendement - transcriptiefactoren - genen - arabidopsis - droogteresistentie - plantenveredeling - rice - tomatoes - solanum lycopersicum - oryza - water use efficiency - transcription factors - genes - arabidopsis - drought resistance - plant breeding
    Drought is a common occurrence in rainfed agriculture which is mainly dependent on the seasonal rainfall of the region. Many agricultural regions, especially in tropical-subtropical countries, have consistently low rainfall and unlike other abiotic stresses, the water availability directly affects productivity. Therefore, efforts to increase water uptake and/or conservation by the plants under water limiting conditions would lead to increased biomass, which contributes to fruit/grain yield. The threat of global warming and demands of an increasing world population will increase water scarcity, resulting in a growing need for water use efficient and drought tolerant crop plants.Water use efficiency (WUE), the ratio of biomass produced to the water used, is an important crop trait under water limiting and drought affected environments. Variation in WUE could arise either from variation in biomass (determined by the canopy carbon gain via photosynthesis, which is regulated by net carbon assimilation rate and functional leaf area) or through variation in the amount of water lost by transpiration (determined by stomatal conductance, cuticular properties and leaf area).

    Regulatory genes or transcription factors (TF), more specifically AP2/ERF family TF's have been shown to improve stress tolerance by regulating the coordinated expression of several stress related genes in heterologous transgenic plants. Subsequently, in this study an overexpression approach has been employed for the introduction of TFs and a few target drought adaptive genes from Arabidopsis, in rice and tomato to improve WUE.

    Oryza sativa ) cultivation requires two to three times more water when compared to other major food crops such as wheat or maize. Therefore, water deficit is a major constraint for rice production in rainfed areas. Plants develop adaptive strategies towards drought avoidance, such as an extensiveroot system in response to soil drying where the roots of resistant genotypes continue elongation at water potentials that are low enough to inhibit shoot growth completely.

    A previously identified Arabidopsis gene HARDY ( HRD), an AP2/ERF-like transcription factor, on overexpression shows increased leaf mesophyll layers, extended root branching and thickness and confers drought resistance in Arabidopsis (Dixit et al., unpublished). As the gene displayed various features useful for drought/abiotic stress resistance, the gene was transformed into the crop model rice to characterize the drought resistance related phenotype.

    HRDoverexpressors in rice exhibit improved WUE characterized by a higher biomass both with and without drought stress. This improvement in WUE is mostly due to an increase in root biomass under stress, and increases in leaf and shoot biomass without stress. HRD overexpression shows significantly higher net photosynthetic rate, which is exemplified under drought stress conditions. The major contributing factor for higher biomass and WUE, therefore, seems to be higher net carbon assimilation rate due to better mesophyll efficiency in the HRD lines. Higher net photosynthesis and relative quantum yield of PSII at steady state photosynthesis reflect the higher mesophyll capacity in HRD lines. Though the drought stress reduces the efficiency of PSII reaction centre similar to other studies in rice, HRD overexpression maintains higher efficiency of open PSII reactions compared to wild-type, both under well-irrigated and drought conditions, directly indicating the higher photosynthetic efficiency. The increased root biomass due to water deficit is an adaptive response specific to the HRD genotypes, indicating that HRD expression primes the plant to adapt to water deficit by inducing roots to harvest the scarce water.

    Plants lose a large amount of water in form of transpiration during assimilate/photosynthate production. Under water deficit conditions, most of the transpirational loss is due to non-stomatal/cuticular water loss since drought induces decreased stomatal conductance and stomatal closure. Therefore,decreasing transpiration by changing plant cuticular properties has potential applications. In overexpression studies with wax biosynthetic genes, that alter the cuticular properties either by increasing the cuticular waxes or the cutin monomers (resulting in changed characteristics of the cutin matrix), we show reduction in water lost through the cuticle and thus an increase in WUE.

    The variation for cuticular wax in rice has been suggested to be related to drought resistance, indicating that increase in wax content might be used to improve water use and drought resistance. Therefore, overexpression of genes and TFs involved in wax/cuticle biosynthesis holds great promise in reducing unrestricted cuticular water loss. In this study, rice plants overexpressing an ERF/AP2 TF SHN2 gene and a drought adaptive wax biosynthesis gene CER6, a key elongase enzyme in the wax biosynthesis pathway, show increase in WUE and drought resistance.Increased membrane stability under drought stress in theSHN2and CER6 transformants exhibits their increasedcapacity to avoid membrane damage andhelp stabilize the underlying photosynthetic apparatus.SHN2overexpressors show a reduction in transpiration at whole plant level, in both well watered and water deficit conditions. However, CER6 overexpressors did not show any change in transpiration at the whole plant level, probably because the increase in stomatal conductance is compensated by a decrease in cuticle permeability.

    Constitutive expression of stress resistance genes such as TFs has been shown to result in abnormal phenotypes and reduced growth. Therefore, identification of promoters with tissue specificity and stress inducibility is essential. We characterized the CER1 promoter, showing expression in epidermis and young tissue, as well as stress inducibility, and used it in tomato for overexpression studies of CER1 ,an aldehyde decarbonylase. Since the reactions of wax biosynthesis are localized in epidermal cells, the epidermal specific CER6 promoter was used in tomato to drive the expression of SHN1 , an AP2/ERF TF and a few other genes involved in the wax biosynthetic pathway, such as CER6 ,amajor condensing enzymeand WAX2 ,a gene involved inboth cutin and cuticular wax deposition.

    Cuticle and epidermal development are highly integrated and the nature of their interaction is complex, coregulated changes in the epidermis and cuticular permeability are observed in all the tomato transgenics.Overexpressors of the epidermal/cuticle genes changed epidermal cell shape, with SHN1 overexpressors also showing an increase in cell size. All the overexpressors showed a decrease in cuticular permeability of the leaves and fruit. Stomatal index of these overexpressors is reduced compared to wild-type plants under drought stress, which might be due to the stress inducible nature of the promoters. Decrease in transpiration and a resultant increase in WUE is observed in all the overexpressing tomato lines.As crop water loss is driven by the gradient in water vapor concentration between the crop canopy and the atmosphere, increasing leaf surface reflectance as observed for the tomato SHN overexpressors is expected to reduce the surface temperature of the photosynthetic tissue and increase WUE. This mechanism is supported by theSHN1overexpressors that showbetter photosynthetic mesophyll efficiency and higher efficiency of PSII reaction centre in light adapted conditionsunder both well watered and drought conditions.WAX2overexpression results in a 2.6 fold increase in the amount of cutin monomers compared to wild-type, probably responsible for the increased resistance to cuticular water loss from the plant surface. Consequently these lines display better WUE and reduced transpiration, and interestingly better mesophyll efficiency and efficiency of the PSII reaction center compared with wild-type only under drought stress.

    In nature, plants also have to cope with the interaction of multiple stresses that often arise concomitantly with drought, and ultimately involve oxidative stress. Protective responses at the leaf level must then be triggered in response to stress to prevent irreversible damage to the photosynthetic machinery. The molecular understanding of mechanisms involving stress perception, signal transduction, and transcriptional regulation of stress tolerance, may help engineer tolerance to multiple stresses in crop plants. Application of TFs may provide a more adaptive function in improving tolerance, either through protection or repair mechanisms. Advances in the molecular biology of stress responses in tolerant organisms are introducing the potentials of stress tolerance genes in agricultural programmes, not only to ensure survival but also to ensure productivity under drought.
    Functional genomics strategies with transposons in rice
    Greco, R. - \ 2003
    Wageningen University. Promotor(en): Maarten Koornneef, co-promotor(en): A.B. Pereira. - Wageningen : Wageningen Universiteit - ISBN 9789058089168 - 182
    rijst - oryza - genexpressie - transposons - transpositie - transcriptie - mutagenese - genexpressieanalyse - rice - oryza - gene expression - transposable elements - transposition - transcription - mutagenesis - genomics
    Rice is a major staple food crop and a recognizedmonocotylenedousmodel plant from which gene function discovery is projected to contribute to improvements in a variety of cereals like wheat and maize. The recent release of rough drafts of the rice genome sequence for public research provides a vast resource of gene sequences whose functions need to be determined by reverse genetics methods.

    Characterisation of a mutant phenotype is one of the most promising approaches to link gene to function. Based on this assumption, mutagenesis with transposable elements was chosen as a strategy in the research described in this thesis to address gene function in rice (Chapter 2). The well characterized maize Ac/Ds and En/Spm transposon systems were employed asinsertionalmutagens based on their known ability to transpose inheterologousspecies. Transposon insertions can cause a knockout mutation by blocking the correct expression of a gene, which may result in a mutant phenotype. The mutant gene, thus "tagged" by the inserted transposon, can then be isolated by recovering the DNA flanking the insert and lead to the isolation of the wild-type gene. Constructs for knockout mutagenesis were generated which employed the autonomous Ac element and were tested in rice japonica (Chapter 3) andindica(Chapter 4) varieties. However, the utility of knockout mutations is limited, as the majority of them display no obvious phenotype. This may be due to functional redundancy, where one or more other genes can substitute for the same function, to subtle and conditional phenotypes, or to early lethality caused by the mutation. Gene detection strategies have therefore been developed in addition to classical knockout mutagenesis to address the function of genes that do not directly reveal an obvious phenotype when disrupted (Chapter 5). To utilize gene detection, japonica rice was transformed with advanced two-component enhancer trap vectors, consisting of a mobile transposon element ( Ds or I/dSpm ), and the corresponding stabletransposase( Ac or En/Spm ) source under control of theCaMV35S promoter. The mobile transposons contained in this case a GUS marker gene driven by aCaMV35S minimal promoter that could display the pattern of expression of the adjacent trapped gene and thus provide a clue for its function (Chapters 6 and 7). A large number of rice transformants were produced to test the activity of the different transposon constructs, with the final aim of identifying optimal "starter" lines for the development of tagging populations. Among the factors evaluated were the propensity for continuous transposition through successive generations, the ability to generate large numbers of independent inserts in progeny plants and the target-site specificity of insertion. The usefulness of the selectable markers incorporated in the constructs was also assessed.

    The results revealed high mobility of the Ac/Ds system in rice (Chapter 3, 4 and 6), although inactivation of Ds was observed in later generations (from T 2 onward). Nevertheless, the high frequency of independent transposition demonstrated to occur in early generations (T 0 and T 1 ) enabled the production of T 2 and T 3 lines with independent "stabilised„ insertions, which can be used directly for reverse genetics screenings without further need for selection against thetransposasesource. The autonomous Ac transposon, in contrast, does not seem to lose mobility and was shown to efficiently transpose in japonica andindicagenotypes as well, supporting its further use in the establishment of a tagging system in this economically important subspecies. Both Ac and Ds displayed amplification of copy number, which enabled the generation of lines containing multiple transposons. Pilot sequencing of genomic sites flanking the Ac and Ds inserts revealed a preferential insertion of these transposons into genes or gene-rich regions and confirmed their tendency to transpose to linked sites, which makes them suitable for targeted tagging. Preliminary testing of the Ac/Ds enhancer trap lines for their ability to function as "detectors" of gene activity, revealed a low frequency of GUS staining patterns in somatic sectors. More thorough screenings are currently under way to fully evaluate the functionality of the system.

    In contrast to Ac/Ds , the En/Spm system displayed a surprisingly low transposition activity in rice (Chapter 7), restricted to somatic events that were not transmitted to the next generation, in spite of being a well-established mutagenic system inheterologousdicotyledonous species such as Arabidopsis. Transcription analysis of the En/Spm maize element in rice revealed that correct splicing of the element occurs but is not sufficient for transposition ability. Rather, the relative amounts in which the differenttransposaseproducts necessary for transposition are produced seems to be critical and influenced by host factors. In addition, transposition efficiency might be further reduced by the lack of essentialcis-required sequences in the modified I/dSpm version used in this study, although similar constructs were successfully employed in Arabidopsis. Eventually, cross-talk with related endogenous transposable elements may affect the mobility of the maize transposon in rice. Indeed, an interaction of the maizetransposaseswith a rice En/Spm -homologous element was revealed, resulting in the specific suppression of an alternative transcript in the latter (Chapter 8). This finding demonstrates that interference is possible and trans-activation potentially could occur among elements belonging to the same transposon family in different species.

    Based on the results of these analyses, a core collection of knockout and gene detection Ac/Ds lines with active transposition could be selected as a basis for developing populations for (forward and) reverse genetic screenings. The propagation of lines containing multiple transposons and the preferential insertion into gene-rich regions will help reduce the number of plants that would have to be produced in order to saturate the genome with insertions. At present, over 10,000 stabilised T 2Ac/Ds transposon lines are being analyzed in 5 EU laboratories for transposon flanking sequences that by comparison to the complete and annotated rice sequences will reveal tagged genes of interest that can be used for reverse genetics.
    Soil potassium dynamics under intensive rice cropping. A case study in the Mekong Delta, Vietnam
    Nguyen, M.H. - \ 2003
    Wageningen University. Promotor(en): Oene Oenema, co-promotor(en): Bert Janssen. - [S.l.] : S.n. - ISBN 9789058088901 - 203
    rijst - oryza - kalium - voedingsstoffentekorten - intensieve teelt - teeltsystemen - kunstmeststoffen - vietnam - rice - oryza - potassium - nutrient deficiencies - intensive cropping - cropping systems - fertilizers - vietnam
    Keywords:potassium, nutrient budgets, nutrient depletion, fertilizer, kinetics, adsorption,desorption, fixation, release, modeling, rice cropping system,NaTPB-extractable K, NH 4 OAc-extractable K, sedimentation.

               Rice cropping has been greatly intensified in many Asian countries during the last decades to meet the increasing demand for food by the increasing population. There is some concern now that the increased crop yields and nutrient withdrawal, in combination with unbalanced fertilization, lead to potassium (K) depletion of the soil and to K deficiency in rice. However, reports about crop response to K fertilizer application in wetland rice cropping systems show conflicting results, and there are no proper guidelines for K management.

    This study was set-up to increase the understanding of K budgets of rice cropping systems, and of K dynamics in soil, to be able to develop K management schemes for the various rice cropping systems. The study was carried out in the Mekong Delta of Vietnam, a major rice growing area. Field studies have been carried out to quantify the inputs and outputs of K in various rice cropping systems. Kinetics of K adsorption-desorption and of K fixation-release in soil has been studied in the laboratory to understand the behavior of K in soils. Pot experiments have been carried out to study effect of water management, K fertilizer application on soil K pools and K uptake, and examine the rate of changes of various K pools in soil by rice, grown under controlled conditions. Models were used to analyze and predict changes of K pools in soils over time, using rate constants and initial pool sizes as derived from the laboratory and pot experiments.

    K budgets were assessed for areas, representing double and triple rice cropping systems on flooded alluvial soils. Partial K budgets proved inadequate and a differentiation between pools according to the availability of K in sediments was useful. K balances were always positive for total K, and negative forK(NH 4 OAc) unless about 80 kg ha -1 yr -1 fertiliser K was applied, while balances for K(NaTPB) were in between. Removal of rice straw was the largest K output, sedimentation the largest input for total K.

    The order of the amounts of extracted K was 0.01 M CaCl 2 < 1M NH 4 OAc pH 7 < 1 M HNO 3 < 0.2 MNaTPB. All methods were well correlated with plant uptake of K. Simple first order equations adequately described adsorption, fastening and desorption of K. The rate coefficient of K removal withNaTPBdecreased over time and could be accounted for by the Yang and Janssen equation.

     

    In a greenhouse experiment, water management between two successive crops had no influence on soilK(NH 4 OAc) and K(NaTPB), and on K uptake. BecauseK(NaTPB) did not decrease over time, it was concluded that the intermediate pool in a three-pools model could not be assessed by K(NaTPB). Hence the test of athree-poolsmodel failed. 

    Two models were tested using the results of greenhouse experiments. A so-calledSeries model, in which K flows from minerals to an intermediate pool, next to the labile pool of exchangeable K according to first-order kineticswas able to predict the dynamics of soil K pools over time and K uptake in the future.Also areduced Series model with only two pools was well applicable.The so-called Parallel model in which K moves from each of the pools to the solution pool turned out to be useful for a first interpretation of experimental data to identify the sources of K uptake, but it was unable to predict future soil K changes and hence future K uptake.Based on application of the Series model, a decision support system scheme on soil K management was outlined.

    Rice cultivation in the farming systems of Sukumaland, Tanzania : a quest for sustainable production under structural adjustment programmes
    Meertens, H.C.C. - \ 1999
    Agricultural University. Promotor(en): N.G. Röling; J. Brouwer. - Amsterdam : Royal Tropical Institute [etc.] - ISBN 9789058080929 - 192
    rijst - oryza - bedrijfssystemen - landbouwontwikkeling - cultuurmethoden - bodemvruchtbaarheid - kunstmeststoffen - voorlichting - duurzaamheid (sustainability) - tanzania - rice - oryza - farming systems - agricultural development - cultural methods - soil fertility - fertilizers - extension - sustainability - tanzania

    This thesis investigates options for sustainable rice cultivation and general agricultural development in the Mwanza and Shinyanga regions in northwestern Tanzania, often called Sukumaland due to the predominance of Wasukuma people. Generally Sukumaland has a semi-arid climate; agriculture is constrained by unreliable and low rainfall. In the past fifty years the population density has doubled in most parts. This has triggered several changes in farming systems. One important change is a reduction of grasslands in the valleys, due to increased cultivation of rice. Rice cultivation systems in Sukumaland serve here as a case study that allows the investigation of the interplay of social, economic and biophysical sustainability factors at field, farm, watershed and regional/national levels and their importance to the development of sustainable agriculture. Because soil fertility management is currently more important to sustainable rice cultivation in Sukumaland than water use efficiency or pest and disease susceptibility, it is the focus of the investigation.

    Economic reform programmes known as structural adjustment programmes started in Tanzania around 1986, guided by the International Monetary Fund (IMF) and the World Bank. These programmes required drastic changes in Tanzanian national economic policies and had great impact on the marketing of agricultural outputs and inputs. Liberalized markets and private traders were expected to improve the agricultural sector via a much needed intensification of agriculture, involving higher consumption of mineral fertilizers, herbicides and pesticides. However, the `liberalization' of international agricultural trade provided only a limited increase in access to developed country (DC) markets for less developed countries (LDCs) like Tanzania, and included few restrictions on the dumping of agricultural products by DCs. Farmers in LDCs cannot compete with farmers in DCs, and this lack of market opportunities, in combination with low agricultural prices and the low purchasing power of LDC consumers, pose major constraints on LDC food security. Specific data for Tanzania show that for this country the per capita food production increased in the 1970s, stabilized in the 1980s and started to decline in the 1990s. From a national point of view this is obviously not sustainable agricultural development.

    The gradual process of soil nutrient depletion in many parts of sub-Saharan Africa (SSA) is thought to be a reason, though rather hidden, for slow agricultural growth in the face of high increases in population. An integrated nutrient management (INM) strategy, which combines the use of locally available resources with the use of external inputs and includes both management practices to save nutrients from being lost from the system and interventions to add nutrients from outside, has been advocated to increase production and develop sustainable agriculture in SSA. INM methods are one of the important strategies of low external input and sustainable agriculture (LEISA) policies. The LEISA approach is aimed at making optimal use of local available resources, adding limited external inputs and using them in the most efficient way. In managing soil fertility, low inputs of mineral fertilizers must be combined with applications of farmyard manure and, where applicable, green manures, compost, agroforestry and erosion control. The expected result is sustainable increases in production.

    The objective of this thesis is to evaluate whether it is feasible for farm households in the Sukumaland rice cultivation systems to adopt INM and LEISA, given the current economic climate fostered by structural adjustment programmes. More generally, whether farm households in SSA countries can adopt INM/LEISA as a way of generating sustainable agricultural development in the context of liberalization of international agricultural trade, structural adjustment programmes, and fast population growth, is examined. It must be noted that in many locations within Sukumaland, cassava, maize or sorghum are more important food crops than rice; cotton, maize or horticultural crops can be more important cash crops than rice. Just as elsewhere, sustainable agricultural development in Sukumaland depends on the performance of all cropping systems present, and on the interactions of these cropping systems with livestock and other subsystems at the farm level.

    When performance in the food and cash crop sectors of Tanzania and the availability and consumption of agricultural inputs in 1986-1996 are compared with periods prior to IMF/World Bank backed reform, the positive developments of the first five years of reform appear not to be sustainable. At present, rural productivity levels per capita for important food and cash crops are declining. High increases in fertilizer prices and input availability problems in the villages are related to liberalization of agricultural input supply and pricing. The removal of subsidies on agricultural inputs from 1991 onwards is crucial in explaining the decline in production of maize, the main food crop in Tanzania. Structural adjustment programmes usually include far reaching reductions in the role of government. However, adequate government involvement may be necessary to ensure greater use of agricultural inputs and thus improved performance of the agricultural sector in Tanzania.

    In Sukumaland, historical material makes it possible to put current conditions in an historical context. A description of farming systems dynamics in Sukumaland over the past 100 years shows that people were attracted to the area by its low incidence of human and animal diseases. Cultivation was first restricted to the sandy upper parts of slopes because they are easy to prepare by hand hoe. Increases in population density led to enlargements in farm size directed towards the lower parts of slopes. Rice cultivation in these areas reduced grazing space for livestock. Households with large herds migrated to new, tsetse free areas; large farms were made possible by the availability of ploughs and oxen. In the 1950s and 1960s there were strong increases in household income in Sukumaland due to extensive, financially rewarding cotton growing. In the 1970s and 1980s this became much less profitable, leading to diversification in cash crops in accord with agroecological variations and distance to Mwanza town. Ongoing increases in population density caused a decrease in arable land and livestock units per capita, plus shifts in crops grown. Less demanding (cassava) and higher yield (rice, maize, cassava, sweet potatoes) crops were substituted for the traditional crops (sorghum, bulrush millet). These developments varied across the Mwanza and Shinyanga regions, due to differences in population density and agroecological conditions. At present there are signs of agricultural intensification near Mwanza town, while extensive farming dominates in the remaining parts of Sukumaland.

    Recent agricultural surveys conducted in Sukumaland have drawn attention to the importance of rainfed, lowland rice in the farming systems studied. More than a third of rice produced in Tanzania comes from Sukumaland. Farmers increased their rice production quickly when rice cultivation became more profitable in comparison to cotton and other crops, as well as more popular as a food crop because it can produce high amounts of calories on small pieces of land. The strong increase in rice cultivation during the last 25 years is remarkable, given the low and highly unreliable rainfall in Sukumaland. Farmers have developed highly productive rainfed, lowland rice systems solely on the basis of their knowledge of soils, rainfall patterns and topography, and on their experiments with water management systems, cultivars, and planting and land preparation methods. Rice management practices closely follow differences in ecology and household characteristics. Selection of rice cultivars is largely determined by water conditions in the field. The cultivation of rice is more intensive in Mwanza region, where transplanting takes place; on the larger rice fields in Shinyanga region, broadcasting dominates. Households grow rice for both food and cash - mainly for food in Mwanza region and mainly for cash in Shinyanga region. Water and weeds are the major production constraints, but low soil fertility is also a problem on the sandier fields of Mwanza region. Yields have declined due to continuous cultivation, with almost no application of organic or mineral fertilizers. On the more clayey rice fields in Shinyanga region yields are, however, still satisfactory at present due to the relatively short period (10-20 years) of cultivation. However, in one out of three years farmers fail to get food and cash from rice due to insufficient, too late or too unreliable rainfall.

    In response to farmers' complaints about declining rice yields, on-farm soil fertility research was carried out in the rice fields of Sukumaland between 1990 and 1996, using a Farming Systems Research/Extension (FSRE) methodology. The decline was thought to be related to a decrease in soil fertility. On-farm research showed that broadcasting 30 kg N ha -1in the form of urea in wet rice fields at the tillering stage increased rice grain yields by 500-900 kg ha -1in almost every type of rice field cultivated in Sukumaland. Doses higher than 30 kg N ha -1were less economical at 1996 prices for crops and fertilizers. The crop yield response to urea was better when rice plants were at the maximum tillering stage, when water depths were less than 15 cm at application, and when the sand content of fields was higher. The relatively small differences each year in response per field did not justify multiple extension messages. A single dose of 30 kg N ha -1in the form of urea to rice at tillering was thus recommended for Sukumaland as a whole.

    Despite the relatively high average productivity index for a low dose of urea in rice, there was almost no adoption by farmers. The main factors were problems in the availability of urea in villages and decreasing profitability of the rice-urea technology, due to IMF/World Bank instigated reform measures. Non-adoption was also due to absence of real need to use urea on the more clayey rice fields; poor involvement of the extension service; confusing research messages related to rice soil fertility management; the high degree of uncertainty in Sukumaland farming systems; and low participation of farmers during priority setting for on-farm activities. Effective adoption of agricultural technologies generated by an FSRE methodology calls for strong, institutionalized links with the extension service, commodity research and policy makers. Better coordination of activities between donors and governments is an essential precondition to make such links work.

    Failures in the adoption of use of urea in rice encouraged researchers and farmers in Sukumaland to look for alternative ways to improve soil fertility in rice fields. Research has been done on the use of locally available resources such as kraal manure and rice husks, and the introduction of green manure and multipurpose trees as an alternative to urea. The performance of green manures and multipurpose trees was meagre due to limited potential for biomass production in the semi-arid climate. Half of the households in Sukumaland have no easy access to cattle manure, and in any case the quality of the available manure is low, due to open air collection and very low addition of crop residues. The relatively large amount of labour involved in transporting and incorporating bulky organic materials like kraal manure, green manure, rice husks and tree leaves in the relatively far and less easily accessible rice fields is also a serious problem.

    The increase in labour required per hectare is difficult to realize in the thinly populated Shinyanga region, and furthermore is not seen as desirable by households anywhere in Sukumaland, due to the expected decrease in labour productivity. Apart from that, farmers with clayey rice fields see no need to invest so much in soil fertility management. A nutrient balance calculation for the rainfed lowland rice cultivation systems in Sukumaland gave no serious depletion rates for major nutrients, which seems to support the farmers' attitude. Despite massive campaigns promoting the use of organic fertilizers in Sukumaland during the colonial period and recent attempts by the Tanzanian government, the adoption rate is still very low in almost all cropping systems. Only near Mwanza town are farmers applying kraal manure to horticultural crops and, to a lesser extent, maize/cassava fields. The quantities applied are, however, not sufficient to achieve positive nutrient balances on these sandy upland soils.

    A review of the literature suggests that INM/LEISA successes in SSA are characterized by relatively high intensity of land use, high population density, medium to high livestock density, good market access and presence of large urban markets (in particular for horticulture products) in the vicinity. Further, the active support of SSA governments for their agricultural sectors will be needed if sustainable agriculture is to be attained through INM/LEISA approaches, as well as active intervention to protect their agricultural sectors against competition from industrial countries. INM/LEISA approaches are not appropriate for SSA farming systems that lack these characteristics. Several examples from SSA and Asia show that severe dependence on labour-intensive methods may lead to decreases in labour productivity. LEISA advocates seem to be largely unaware that farming methods based primarily on labour-intensive techniques can lead to the impoverishment of farm households. For resource-poor farmers, sustainable agriculture must first of all be socio-economically viable. Insufficient use of external inputs can turn LEISA into a non-sustainable form of agriculture; therefore LEISA advocates should take a critical look at the impact of structural adjustment programmes in SSA.

    The main conclusion of this thesis is that INM/LEISA approaches are currently not an appropriate way to generate sustainable soil fertility management in the rice cultivation systems of Sukumaland. Farmers with rice fields located on fertile clayey soils are still satisfied with their grain yields, and are not yet motivated to invest labour and cash in soil fertility maintenance. However, especially in rice fields located on sandier soils, in the future farmers will have to invest considerably in soil fertility maintenance to achieve sustainable rice cultivation. The current situation in Sukumaland makes such investments highly unlikely. The huge increase in rice cultivation in Sukumaland is on the other hand a good example of farmer adaptation to increasing population densities, changes in market opportunities, and soil fertility advantages in the valleys. Negative nutrient balances furthermore do not always justify recommendations to farmers that involve the immediate use of mineral fertilizers and/or organic fertilizers. More farmer participation, especially in priority setting, is necessary to prevent misunderstandings regarding farmers' objectives.

    Any strategy for future sustainable rice cultivation and agriculture in Sukumaland, including INM or LEISA, must be based on a thorough analysis of biophysical, socio-economic and public policy factors and their linkages. Such a strategy requires a conducive economic and policy environment. In Sukumaland this will require improvements in infrastructure, increased government support to agriculture, reduced taxation in the cotton crop sector, reduced reliance on rice imports, higher population densities, intensive livestock keeping and a greater variety of off-farm employment. A good INM strategy in Sukumaland would then be to use urea in rice, and farmyard manure in the nearby cassava/maize and cotton fields. Without a conducive economic and policy environment, population growth in Sukumaland will lead to an intensification largely based on labour inputs. Instead of agricultural evolution, agricultural involution will be the result.

    This thesis can be orderd: KIT-publisher R.Gunm@kit.nl

    Vergelijkend onderzoek van diverse rijstsoorten
    Ossenkoppele, J.S. ; Pinckaers, V.G.Z. ; Vliege, J.J.M. ; Jong, W.J.H.J. de; Herstel, H. - \ 1982
    Wageningen : RIKILT (Verslag / RIKILT 82.12) - 18
    rijst - oryza - vergelijkend onderzoek - rice - oryza - comparative research
    Door middel van macroscopisch onderzoek nagaan of er verschillen bestaan tussen diverse soorten rijst, die op de Nederlandse markt verkrijgbaar zijn, aan de hand van de interne methoden. 38 monsters rijst werden onderling vergeleken met behulp van de interne methoden, welke beschreven zijn in de inleiding. De volgende rijstprodukten werden bekeken: padie, gedopte rijst, volwitte rijst, rondkorrelige rijst, langkorrelige rijst, breukrijst, verder op groene, krijtachtige, roodgestreepte, gespikkelde, gevlekte en gele korrels. Ook werd er gelet op aanwezigheid van kiemen, glansmiddel en bijmenging.
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