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 the dynamic interactions between food production and ecosystem services : a case study in Benin
Duku, C. - \ 2017
University. Promotor(en): Lars Hein, co-promotor(en): S.J. Zwart. - Wageningen : Wageningen University - ISBN 9789463431613 - 141
ecosystem services - modeling - food production - case studies - hydrology - irrigation - forests - woodlands - climatic change - nature conservation - food security - benin - ecosysteemdiensten - modelleren - voedselproductie - gevalsanalyse - hydrologie - irrigatie - bossen - bosgebieden - klimaatverandering - natuurbescherming - voedselzekerheid

Given the high levels of food insecurity and the loss of vital ecosystem services associated with deforestation, countries in sub-Saharan Africa (SSA) face a major dilemma. How can they produce enough food in a changing climate to feed an increasing population while protecting natural forests and woodlands that provide a wide array of ecosystem services beneficial to livelihoods? Thus, the objectives of this thesis are twofold. First, to further enhance the understanding of the dynamic interactions between food production, and natural and semi-natural ecosystems with a case study in Benin. Second, to further enhance the understanding of how hydrological ecosystem services can be captured in an accounting framework. Understanding hydrological ecosystem services is key to understanding the multi-directional relationship between food production and ecosystem services supply from natural and semi-natural ecosystems. First, I examine how a spatially explicit ecohydrological model can be used to analyse multiple hydrological ecosystem services in line with the ecosystem accounting framework. The hydrological ecosystem services include crop water supply for rainfed agriculture, household water supply (both groundwater supply and surface water supply), water purification, and soil erosion control. Second, I develop a general modelling approach for analysing the effects of deforestation on the availability of water for irrigation at the watershed level, and I apply the approach to the Upper Oueme watershed in Benin. Third, I analyse the impact of climate change on agricultural intensification options. Finally, I quantify trade-offs between per capita food availability and protecting forests and woodlands at different levels of yield increases taking into account climate change, population growth. This thesis shows that the integration of hydrological ecosystem services into an accounting framework can provide relevant information at appropriate scales suitable for decision-making. It is empirically feasible to distinguish between service capacity and service flow of hydrological ecosystem services. This requires appropriate decisions regarding physical and mathematical representation of ecohydrological processes, spatial heterogeneity of ecosystems, temporal resolution, and required model accuracy. This thesis also shows that opportunities for irrigation expansion depend on conservation of forests and woodlands in the headwaters of the rivers feeding the irrigation scheme. Opportunities for agricultural intensification in SSA are likely to diminish with climate change, hence increasing pressure to expand cultivated areas in order to meet increasing food demand. Climate change will lead to substantial reductions in; exploitable yield gaps for major food crops, rainfed cropland areas that can support the cultivation of two or more crops per year, and water availability for irrigation expansion. Furthermore, in the far future crop yields will have to increase at a faster rate than has been recorded over the past two and half decades in order to maintain current levels of per capita food availability. Failure to achieve the required levels of yield increases is likely to lead to the conversion of substantial areas of forests and woodlands for crop cultivation. Based on the results of this thesis, four main recommendations to help address the dual challenge of food security and ecosystem protection in Benin and the larger SSA region are made: (i) promote a precautionary approach to forest and woodland conservation, (ii) promote cross-sectoral policy coherence and consultations, (iii) promote the development of satellite ecosystem accounts consistent with national accounts, and (iv) identify, evaluate and implement adaptation and resilience measures to reduce agricultural vulnerability to climate change.

SWAP version 4
Kroes, J.G. ; Dam, J.C. van; Bartholomeus, R.P. ; Groenendijk, P. ; Heinen, M. ; Hendriks, R.F.A. ; Mulder, H.M. ; Supit, I. ; Walsum, P.E.V. van - \ 2017
Wageningen : Wageningen Environmental Research (Wageningen Environmental Research report 2780) - 243
agrohydrology - irrigation - drainage - surface water - soil water - water management - simulation models - salinization - agrohydrologie - irrigatie - oppervlaktewater - bodemwater - waterbeheer - simulatiemodellen - verzilting
Theory description and user manual
Role of reservoir operation in sustainable water supply to Subak irrigation schemes in Yeh Ho River Basin
Yekti, Mawiti Infantri - \ 2017
University. Promotor(en): E. Schultz, co-promotor(en): I. Nyoman Norken; László Hayde. - Leiden : CRC Press/Balkema - ISBN 9781138065437 - 250
irrigation systems - irrigation - water supply - sustainability - basin irrigation - indonesia - rivers - irrigatiesystemen - irrigatie - watervoorziening - duurzaamheid (sustainability) - kombevloeiing - indonesië - rivieren

A Subak irrigation scheme, primarily in Bali, Indonesia concerns an irrigation system of which the construction, operation and management are based on agreed principles of technology, management of agriculture and religious community. Subak systems have been well known since the 9th Century. As a manifestation of the Cultural Landscape of Bali Province the Subak schemes are since June, 2012 included in the World Heritage List of UNESCO. These systems are managed by a Subak Association based on the Tri Hita Karana philosophy - harmony between human beings and God, harmony between people and nature, and harmony between people and people.

The problem of insufficient water in the dry season developed in the Yeh Ho River Basin. Because of this the main objective of this study was to develop an optimal reservoir operation strategy in relation to the water supply of the Subak irrigation schemes, capable to support agricultural productivity at upstream, midstream and downstream level. Based on a Generic Algorithm the RIBASIM model was applied using the dependable 80% of discharge and shifting the start of land preparation. The results provide evidence that the cropping pattern of the fifth scenario results in an overall optimal agriculture production of the Subak schemes. The recoverable flow considered in the river basin scheme model plays an important role in the optimisation. Nevertheless, if a normal hydro-climate occurs, the other scenarios, especially the first scenario, can be applied as well. This reflects the applicability of the Tri Hita Karana philosophy on harmony among people and harmony among people and nature.

Optimization of productivity and quality of irrigated tomato (Solanum lycopersicum L.) by smallholder farmers in the Central Rift Valley area of Oromia, Ethiopia
Gemechis, Ambecha O. - \ 2017
University. Promotor(en): Paul Struik, co-promotor(en): B. Emana. - Wageningen : Wageningen University - ISBN 9789463431576 - 262
solanum lycopersicum - irrigation - crop production - optimization - photosynthesis - chlorophyll - gas exchange - water use efficiency - crop yield - ethiopia - irrigatie - gewasproductie - optimalisatie - fotosynthese - chlorofyl - gasuitwisseling - watergebruiksrendement - gewasopbrengst - ethiopië

Tomato (Solanum lycopersicum L.) is a vegetable crop with high potential to contribute to poverty reduction via increased income and food security. It is widely grown by smallholders, has high productivity and its demand is increasing. Ethiopia produced about 30,700 Mg of tomatoes on 5,027 ha annually in 2014/2015. Average yields are only 6.1 Mg ha-1, below the world average yields. There is both a need and a potential to increase tomato production per unit area.

The aim of this thesis is to analyze the irrigated tomato production systems of smallholder farmers in Ethiopia, to survey and characterize the tomato in selected ecoregions and seasons, and to identify yield-limiting or yield-reducing factors and opportunities to enhance yield by using a combination of surveys and field experiments. Field experiments on optimization of yield and quality of field-grown tomato were carried out at Ziway, Ethiopia, for two seasons to study the impact of different irrigation practices applied, based on local empirical practices, deficit irrigation, or crop water requirement.

This thesis begins with a survey of tomato production systems. The survey details the area and production in various zones and for each of these zones yield- determining, yield-limiting, and yield-reducing factors and opportunities for improving yield and quality are indicated. It also avails area, production and yield data for each growing season and typifies the production systems in these zones. Low temperature (cold) from October-January and shortage of improved seeds are recognized as yield-determining factors, whereas insufficient water and nutrient (fertilizer) supply proved to be yield-limiting factors across zones. Late blight (Phytophthora infestans), Fusarium wilt (Fusarium oxysporum) and different pests and weeds are identified as yield-reducing factors in the zones. Experienced growers who have access to extension service recorded significant yield increment. Farmers Research Groups improved actual average yield with the use of improved technology (improved varieties and quality seed), and better efficiencies of water and fertilizer use. This study quantified influences of irrigation systems and strategies on growth-determining tomato features. Variation in irrigation systems and strategies accounted for variation in growth and dry matter accumulation. Greater performance for yield-related traits was obtained with drip irrigation based on crop water requirement for tomato varieties. Examination of plants showed also that local empirical irrigation is responsible for the occurrence of Phytophthora root rot, whereas deficit irrigation proved cause for occurrence of Fusarium wilt (Fusarium oxysporum), blossom end rot and broome rape (Orobanche ramosa) on roots or leaves, stems or fruits.

The experiments on irrigation scheduling with different irrigation systems and strategies gave useful indications on the possibility to improve commercial yield (CY) and water use efficiency. Promising results on CY and agronomical water use efficiency of tomato were achieved with drip irrigation based on crop water requirement, while for the biological water use efficiency higher value was obtained with deficit drip irrigation in both seasons. The findings indicate that the CY was decreased significantly for deficit by 50% in drip irrigation and deficit by 50% in furrow irrigation in both seasons. Mean CY for drip irrigation according to crop water requirement increased by 51% and 56% compared with deficit drip irrigation, whereas furrow irrigation based on crop water requirement increased by 52% and 54% compared with deficit furrow in Experiments 1 and 2, respectively. However, water use efficiency decreased with the increasing water volume.

Simultaneous measurements of rate of photosynthesis based on gas exchange measurements and the thylakoid electron flux based on chlorophyll fluorescence were used to investigate physiological limitations to photosynthesis in leaves of deficit irrigated tomato plants under open field situations. Combined leaf gas exchange/chlorophyll fluorescence measurements differentiated the treatments effectively. Reduction in rate of photosynthesis, stomatal conductance and the maximum quantum efficiency of photosystem II varied across seasons of all varieties, whereas leaf temperature was increased by deficit irrigation in all varieties. Among varieties studied, Miya was found relatively tolerant to deficit irrigation. Stomatal limitation of rate of photosynthesis increased significantly as a result of water stress suggesting a strong influence of the stomatal behaviour.

We also determined the influence of irrigation systems and strategies on water saving and tomato fruit quality. Using deficit drip irrigation was the best management strategy to optimize water use and tomato quality. Fruit dry matter content, acid content and total soluble solids were significantly higher with deficit drip irrigation than with other treatments.

From this thesis it appeared that agro-climatic conditions, access to resources and culture all contribute to the relatively low yields of tomato in the Central Rift Valley of Ethiopia. The thesis also proved that significant advances can be made in yield, quality and resource use efficiency.

Modernisation strategy for National Irrigation Systems in the Philippines : Balanac and Sta. Maria River Irrigation Systems
Delos Reyes, Mona Liza Fortunado - \ 2017
University. Promotor(en): E. Schulz, co-promotor(en): Guillermo Q. Tabios; K. Prasad. - Leiden : CRC Press/Balkema - ISBN 9781138067745 - 416
irrigation systems - crop yield - design - irrigation - water supply - philippines - irrigatiesystemen - gewasopbrengst - ontwerp - irrigatie - watervoorziening - filippijnen

The performance of publicly funded canal irrigation systems or more commonly called national irrigation systems (NIS) in the Philippines remained below expectations despite considerable system rehabilitation and improvement efforts. The continued suboptimal performances were attributed to technical, managerial, institutional and policy issues and constraints, and in recent years, to climate change. Irrigation modernisation is recognized as strategic option to improve the irrigation system performance. It is defined as a process of technical, management and institutional transformation to improve irrigation services to farmers.

The main objective of the research study was to formulate a strategy for developing a modernisation plan for national irrigation systems in the Philippines. The research methodology was framed with deliberately selected assessment and characterization procedures, which were adoptively modified and integrated to critically analyse the state of coherence among the three fundamentals of irrigation system water delivery: design, operation and water supply; and to identify solutions for any inconsistency. It included, among others an analysis of the process, nature and impacts of rehabilitation projects; diagnostic assessment of the irrigation systems; revalidation of design assumptions on water balance parameters; characterization of irrigation management, service and demands; and identification of options for improvements.

The developed methodology for examining the different aspects of planning and operations of NIS with an end view of modernising the systems provides a more comprehensive and applicable methodology for drawing up of a more relevant plan for NIS modernisation. The knowledge gained on case study systems provides a sound basis for planning of appropriate modernisation solutions for the case study systems and in cases of ungauged, small-scale NIS. The methodology developed in this study could serve as a blueprint for modernisation program for NIS.

Agricultural intensification in Nepal, with particular reference to systems of rice intensification
Uprety, Rajendra - \ 2016
University. Promotor(en): Thomas Kuijper, co-promotor(en): Harro Maat. - Wageningen : Wageningen University - ISBN 9789462579651 - 190
rice - oryza sativa - nepal - asia - south asia - intensification - livelihoods - livelihood strategies - farming systems - farming - crop management - fertilizers - nutrients - irrigation - varieties - rijst - azië - zuid-azië - intensivering - middelen van bestaan - strategieën voor levensonderhoud - bedrijfssystemen - landbouw bedrijven - gewasteelt - kunstmeststoffen - voedingsstoffen - irrigatie - rassen (planten)

This thesis deals with agricultural intensification in Nepal. The initial focus of the study was the System of Rice Intensification (SRI), as introduced in Nepal from 2001. The multiple factors affecting SRI adoption, modification and dissemination together with the option to apply SRI in different combinations of its components result in a variety of SRI applications. For the same reason the effect of SRI on overall agricultural and livelihood development of Nepalese farmers has to be evaluated within the variety of farming systems in which it is applied.

Despite government policies to promote rice cultivation, national rice production is declining. Farmer livelihood strategies, as reflected in rice farming systems, and field management strategies were influenced by several agro-ecological and socio-economic factors. Livelihood and field management strategies of rice farmers are interconnected. In the study presented here four livelihood strategies and three kinds of field management strategies are distinguished. Two livelihood strategies can be characterized as more intensive and more productive; the other two are less intensive and less productive. Livelihood strategies are more family resource-based strategies, while farmers’ field management strategies are more context-dependent. Field management strategies were characterized by forms of nutrient management. Intensive management strategies had most similarities with SRI. But rice intensification is not achievable as a general strategy.

Government policies (fertiliser subsidies) encourage increased fertiliser use. Study results didn't show any significant effect of volume of fertilisers on rice yield but the combined use of organic manure and mineral fertilisers resulted in the highest average rice yields. Irrigation management is another important factor for rice production. Field management is influenced by the reliability of water which was better in farmers' managed irrigation system. Choice of rice varieties influenced the overall rice farming system and cropping intensity and preference of varieties for rice cultivation by scientists and by farmers were different in eastern Nepal. Most popular varieties were those not recommended by science and policy and were disseminated farmer to farmer.

The introduction of SRI in Morang district resulted in several changes in rice farming, but only part of the farmers have adopted such technologies, and adoption has been only in part of their fields. Other farmers have incorporated some SRI practices in their conventional practices. After the introduction of SRI, farmers further tested, re-packaged or hybridized SRI methods to make SRI ideas suitable for their agro-ecological and socio-economic environments. In order to reform Nepalese rice farming, we need to recognize that different farmers, with different livelihood strategies, and with access to different kinds of fields, need different forms for agricultural intensification. High-intensive farmers prefer to use modified SRI methods where there is good irrigation and drainage facilities. There are many possibilities for improvement of the existing nutrient management practices of rice farmers in Nepal. Nutrient management will be useful to increase rice production because the majority of farmers currently use fertilisers non-judiciously. The SRI-recommended practices (younger seedlings, early weeding, use of organic manure, and alternate wetting and drying (AWD) irrigation) will be useful to improve the nutrient use efficiency of rice farmers. Cost-reduction strategies and less labour-intensive cultivation practices will be appropriate options to improve existing rice farming system of Nepal. Participatory cultivar selection and dissemination will be better strategies to introduce new, promising rice cultivars among rice farmers.

Crop intensification options and trade-offs with the water balance in the Central Rift Valley of Ethiopia
Debas, Mezegebu - \ 2016
University. Promotor(en): Martin van Ittersum, co-promotor(en): Huib Hengsdijk; Katrien Descheemaeker. - Wageningen : Wageningen University - ISBN 9789462578616 - 178
cropping systems - intensification - water balance - crop production - land use - climatic change - crop yield - water use - irrigation - ethiopia - teeltsystemen - intensivering - waterbalans - gewasproductie - landgebruik - klimaatverandering - gewasopbrengst - watergebruik - irrigatie - ethiopië

The Central Rift Valley (CRV) of Ethiopia is a closed basin for which claims on land and water have strongly increased over the past decade resulting in over-exploitation of the resources. A clear symptom is the declining trend in the water level of the terminal Lake Abyata. The actual productivity of most cereals in the CRV is less than 2 t ha-1 associated with low input use and poor crop management. Consequently, there are two major development objectives in the CRV, i.e. producing sufficient food for the increasing population, while at the same time ensuring efficient use of limited water and land resources under variable and changing climate conditions. The low productive cereal systems and a declining resource base call for options to increase crop productivity and improve resource use efficiency in order to meet the growing demand for food.

In this thesis, the recent impacts were quantified of climate change, land use change and irrigation water abstraction on water availability of Lake Abyata of the CRV. The trends in lake levels, river discharges, basin rainfall, temperature and irrigation development (ca. 1975-2008) were analysed and the additional evapotranspiration loss resulting from temperature change and irrigated land were computed. We also analysed land use change (1990-2007) and the associated changes in runoff. Results showed that temperature has increased over 34 years (p<0.001) whereas annual rainfall has not changed significantly. Consequently, increased evapotranspiration consumed 62 and 145 Mm3 of additional water from lakes and land surface, respectively, during 1990-2007. Furthermore, an estimated 285 Mm3yr-1 of water was abstracted for irrigation in 2009 of which approximately 170 Mm3yr-1 is irrecoverable evapotranspiration loss. In addition, surface runoff has increased in the upper, and decreased in lower sub-basins of the CRV associated with extensive land use change (1990-2007).

We analysed a large number of data from farmers’ fields (>10,000) and experimental data across the CRV from 2004-2009 to quantify the gaps (Yg) between actual (farm) and experimental (water-limited potential - Yw) yields of maize and wheat in homogenous farming zones. We found that the average (2004-2009) yield gap of maize and wheat ranged between 4.2-9.2 t ha-1, and 2.5-4.7 t ha-1, respectively, across farming zones. The actual N and P application in farmers’ fields was low, as about 46% of maize and 27% of wheat fields did not receive fertilisers. We calibrated, validated and used the Agricultural Production System Simulator (APSIM) model to explore intensification options and their trade-offs with water losses through evapotranspiration. Variety selection and N fertilization were more important for yield gap closure than crop residue management and planting density, and the magnitude of their effect depended on soil type and climate. There was a trade-off between intensification and water use through evapotranspiration, as increasing yield comes at the cost of increased transpiration. However, this trade-off can be minimized by choosing location-specific N levels at which both water use efficiency (WUE) and gross margin are maximised. These application rates varied between 75 and 250 kg N ha-1 across locations and soils, and allowed producing 80% of Yw of maize and wheat. Climate change was projected to lower Yw of maize and wheat by ca. 15-25% and 2-30%, respectively, compared to current climate conditions.

An automated gridded simulation framework was developed to scale up the promising intensification options from field scale to basin scale. We then aggregated basin scale production and identified trade-offs between production and water use for different land use scenarios. This procedure allowed designing land use scenarios based on a spatially explicit optimization of WUE and gross margin per grid cell. Consequences of land use scenarios for food production and water use at basin level were evaluated. Results of the different land use scenarios demonstrated that crop intensification options for which WUE and gross margin are maximised can meet the projected food demand (year 2050) of the growing population in the CRV while at the same time saving large areas of the currently cultivated land. In the intensification scenarios total water loss through evapotranspiration from agricultural land is reduced compared with water loss from current cultivated land and low crop productivity levels.

It is concluded that the current land use together with climate change and water abstraction for irrigation negatively affected the basin level water balance in CRV over the past decade. Furthermore, the scope for further expansion of farmland to increase food production is very limited. The focus should, therefore, be towards intensification also because the existing yield gaps are huge and hence the scope for intensification is large. Model-based exploration of intensification options can be used to prioritize promising options, to close the yield gap and for quantifying trade-offs. Scaling up of promising options allows to assess whether the food demand of the growing population can be met while at the same time saving the less productive land and water per unit agricultural product.

Effect of water use by smallholder farms in the Letaba basin : a case study using the SIMGRO model
Querner, E.P. ; Froebrich, J. ; Clercq, Willem de; Jovanovic, Nebo - \ 2016
Alterra, Wageningen-UR (Alterra-report 2715) - 49 p.
hydrology - models - groundwater - surface water - irrigation - farming systems - limpopo - south africa - hydrologie - modellen - grondwater - oppervlaktewater - irrigatie - bedrijfssystemen - zuid-afrika
For the Letaba basin situated in the South African part of the Limpopo basin, a hydrological study was carried out in order to quantify the effect of smallholder farming on river flows. Important was to study the consequences of improved agricultural systems on the river flows, in particular for the Kruger National Park situated in the lower part of the Letaba basin. The SIMGRO model was used in this study, which integrates groundwater and surface water. The model was calibrated, and furthermore a comparison of measured discharges and groundwater levels against calculated discharges and groundwater levels, revealed that the model is suiTable for practical analysis. For the smallholders farms different scenarios were defined with different levels of crop yield. An increase in crop yield has consequences on more water use as irrigation and crop water use. Because the area covering smallholder farming is only 0.5% of the basin, the effects of changes in water use are relatively small. In a scenario, the weather conditions for 2050 were analysed. This reveals that discharges will go down by 30% on average, which means a substantial reduction of the water resources.
Orchideeënteelt moet nog wennen aan hergebruik gietwater : zoektocht naar teeltkundige grenzen
Staalduinen, J. van; Kromwijk, J.A.M. - \ 2015
Onder Glas 2015 (2015)1. - p. 9 - 11.
glastuinbouw - potplanten - orchidaceae - hergebruik van water - afvalhergebruik - drainagewater - emissie - normen - irrigatie - greenhouse horticulture - pot plants - water reuse - waste utilization - drainage water - emission - standards - irrigation
Tot voor kort was hergebruik van gietwater in de teelt van potorchideeën niet aan de orde. Bedrijfshygiëne en de vrees voor teruglopende waterkwaliteit hield verduurzaming van de teelt op dit punt lang tegen. Strengere emissienormen dwingen ook deze gewasgroep om te investeren in waterontsmetting en hergebruik. Dankzij kennisopbouw door een praktijknetwerk en concreet onderzoek koerst de sector naar verduurzaming. Het ‘laaghangende fruit’ is eenvoudig te plukken, maar er moet nog veel gebeuren om aan de normen voor 2015 en 2016 te kunnen voldoen.
Flexibility in land and water use for coping with rainfall variability
Siderius, C. - \ 2015
University. Promotor(en): Ekko van Ierland; Pavel Kabat, co-promotor(en): Petra Hellegers. - Wageningen : Wageningen University - ISBN 9789462576063 - 222
rain - land use - water use - climatic change - food production - sustainable agriculture - irrigation - rainfed agriculture - regen - landgebruik - watergebruik - klimaatverandering - voedselproductie - duurzame landbouw - irrigatie - regenafhankelijke landbouw
Low cost drip irrigation in Burkina Faso : unravelling actors, networks and practices
Wanvoeke, M.J.V. - \ 2015
University. Promotor(en): Margreet Zwarteveen; Charlotte de Fraiture, co-promotor(en): J.P. Venot. - Wageningen University : Wageningen - ISBN 9789462576117 - 144
irrigatie - irrigatiesystemen - kosten - waterbeheer - waterbeleid - druppelbevloeiing - burkina faso - irrigation - irrigation systems - costs - water management - water policy - trickle irrigation

Title: Low cost drip irrigation in Burkina Faso: Unravelling Actors, Networks and Practices

In Burkina Faso, there is a lot of enthusiasm about Low Cost Drip Irrigation (LCDI) as a tool to irrigate vegetables, and thus improve food security, solve water scarcity and reduce poverty. Already for more than ten years, development cooperation donors, policy makers, and kit designers have invested in the technology, funded its dissemination, and encouraged farmers to adopt it. Yet, there are only very few farmers who are using the technology in their fields. This study shows that this is because the funds for paying the technology mostly do not come from them, but from external donors. For LCDI promoters and disseminators, LCDI is also importantly a tool to survive or make profits. For this, they need to continuously re-assert the success of the technology through reports and stories. Farmers agree to play this game, as they hope and do receive other benefits by associating themselves with LCDI projects.

Beter systeem voor bepalen waterschade
Hack-ten Broeke, M.J.D. ; Kroes, J.G. ; Bartholomeus, R. ; Dam, J.C. van; Bakel, J. van - \ 2015
H2O : tijdschrift voor watervoorziening en afvalwaterbehandeling 2015 (2015)oktober. - ISSN 0166-8439 - p. 43 - 46.
waterbeheer - irrigatie - irrigatiebehoeften - oogstschade - regenschade - modellen - scenario-analyse - landbouw - zouttolerantie - water management - irrigation - irrigation requirements - crop damage - rain damage - models - scenario analysis - agriculture - salt tolerance
Een nieuw instrument voor het bepalen van schade bij landbouwgewassen als gevolg van te veel water, te weinig water of te veel zout: hoe moet dat er uitzien? En kan zo’n instrument bruikbaar zijn voor het doorrekenen van klimaatscenario’s? De Waterwijzer Landbouw moet het antwoord worden op deze vragen.
Waterefficiënte en emissieloze kas voor vruchtgroenten werkt : Onderzoekers en partners tonen aan
Rodenburg, J. ; Beerling, E.A.M. - \ 2015
Onder Glas 12 (2015)1. - p. 50 - 51.
glastuinbouw - teeltsystemen - emissiereductie - steenwol - groeimedia - groenten - vruchtgroenten - doelstellingen - waterzuivering - irrigatie - hergebruik van water - greenhouse horticulture - cropping systems - emission reduction - rockwool - growing media - vegetables - fruit vegetables - objectives - water treatment - irrigation - water reuse
2027 komt snel dichterbij. In dat jaar is het (nagenoeg) emissieloos telen verplicht voor alle glastuinbouwbedrijven. Technisch gezien moet dat mogelijk zijn, meent onderzoeker Ellen Beerling. Nu al zijn diverse technieken voorhanden die deze doelstelling voor veel teelten mogelijk maken. Een langdurige praktijkdemonstratie moet aantonen dat emissieloos telen zeer goed mogelijk is.
Water geven naar behoefte komt stapje dichterbij : Het mysterie van de verdwenen stikstof
Kierkels, T. ; Voogt, W. - \ 2015
Onder Glas 12 (2015)5. - p. 20 - 21.
glastuinbouw - potplanten - plantenvoeding - nutriëntenuitspoeling - stikstof - irrigatie - meting - voedingsstoffenbalans - sensors - vochtmeters - waterbehoefte - greenhouse horticulture - pot plants - plant nutrition - nutrient leaching - nitrogen - irrigation - measurement - nutrient balance - moisture meters - water requirements
De variatie in uitspoeling van mineralen is groot tussen verschillende chrysantenbedrijven. Voor een deel ligt dat aan ondernemersbeslissingen. Om goed te kunnen sturen op minimale uitspoeling en maximale productkwaliteit zijn goede tools nodig. Een betere vochtsensor is zeer welkom, geeft teler Jos Ammerlaan aan.
Beheersing emissie grondgebonden kasteelten
Voogt, W. ; Balendonck, J. ; Janse, J. ; Swinkels, G.L.A.M. ; Winkel, A. van - \ 2015
Bleiswijk : Wageningen UR Glastuinbouw (Rapport GTB 1363) - 38
teelt onder bescherming - snijbloemen - emissie - beslissingsondersteunende systemen - biologische landbouw - irrigatie - lysimeters - sensors - water - voedingsstoffenbalans - voedingsstoffen - optimalisatie - protected cultivation - cut flowers - emission - decision support systems - organic farming - irrigation - nutrient balance - nutrients - optimization
To make growers to be in control of the emission, a decision support system is developed for irrigation in soil grown crops. In 2013-2014 the implementation was continued and several greenhouse crops were monitored. As was found earlier, the organic greenhouse growers are able to control irrigation in a way that emission is reduced to a minimum. The results obtained at (conventional) flower growers show sometimes high emission of nitrogen. This is due at one hand to high irrigation surpluses but also to high fertilisation of nitrogen. Better tuning of the water- and nitrogen supply to the crop demand is necessary. For these stapes growers need better soil-moisture sensors.
Water productivity of sunflower under different irrigation regimes on Gezira clay soil, Sudan
Elsheikh, E.R.A. - \ 2015
University. Promotor(en): E. Schultz, co-promotor(en): H.S. Adam; A.M. Haile. - Leiden : CRC Press/Balkema - ISBN 9781138029149 - 162
helianthus annuus - zonnebloemen - irrigatie - irrigatiesystemen - watergebruik - waterbeschikbaarheid - sudan - sunflowers - irrigation - irrigation systems - water use - water availability
Impact of improved operation and maintenance on cohesive sediment transport in Gezira Scheme, Sudan
Osman, I.S.E. - \ 2015
University. Promotor(en): E. Schultz, co-promotor(en): A.K. Osman; F.X. Suryadi. - Leiden : CRC Press/Balkema - ISBN 9781138028807 - 183
sediment - geologische sedimentatie - waterbeheer - irrigatiekanalen - irrigatie - irrigatiewater-toedieningsschema - sudan - geological sedimentation - water management - irrigation channels - irrigation - irrigation scheduling

Efficient operation and maintenance of irrigation schemes are needed for improving the hydraulic performance of the canals, enhancing the crop yields and insuring sustainable production. There is a great need to enhance the researches and for a variety of tools such as water control and regulation equipment, decision support systems, as well as field surveys and valuation techniques. Water management becomes difficult when dealing with sediment transport in irrigation canals. Most of the studies simulate the sediment transport of relatively coarse grain sizes. The sediment problem in irrigation canals becomes more complicated when dealing with cohesive sediment transport. Therefore, more research is needed to enhance the understanding of the behaviour of cohesive sediment transport under a variety of operation conditions.

This study has been carried out in the Gezira Scheme in Sudan. The scheme, which is one of the largest irrigation schemes in the world under a single management, is located in the arid and semi-arid region. The scheme is chosen as a case study since it can act as a model for similar irrigation schemes. The scheme has a total area of 880,000 ha and uses 35% of Sudan’s current allocation of Nile waters. This represents 6 – 7 billion m3 per year. The scheme is irrigated from the Blue Nile River, which is characterized by its high load of fine sediment. The scheme is facing severe sediment accumulation in its irrigation canals, which represents a challenge to those responsible for the operation and maintenance of the canals. Each year large investments are required to maintain and to upgrade the canal system to keep it in an acceptable condition.

A large quantity of cohesive sediment enters the scheme every year. According to previous studies, about 60% of the sediment deposits in the irrigation canals. The sediment accumulation in the canals reduces the canal conveyance capacity, causes irrigation difficulties, creates inequity and inadequate water supply and increases the rate of aquatic weed growth. The sedimentation problems are not only seriously affecting the performance of the irrigation canals, but are also jeopardizing their sustainability, as well as affecting crop production. Two canals in the scheme have been selected to be studied in detail: Zananda Major Canal, which takes water from Gezira Main Canal at 57 km from the offtake at Sennar Dam, and Toman Minor Canal at 12.5 km from the offtake of Zananda Major Canal.

The hypothesis of the study postulates that the operation and maintenance of an irrigation scheme has a major influence on the hydrodynamic behaviour of canals and hence on sediment movement and deposition. The aim of this study was to improve the operation and maintenance procedures for better sediment and water management. This can be achieved through better understanding of the sediment processes in the irrigation canals of the Gezira Scheme and to understand clearly the link between irrigation system operation and resulting system performance in terms of transport of cohesive sediment.

Data collection and field measurements have been conducted during the flood season between June and October in 2011 and 2012. Sediment sampling and water level measurements have been conducted on a daily basis at selected locations. The manually recorded water levels include about 1080 readings per year. In addition about 1290 sediment samples were analysed for different locations during the study period. Cross-sectional surveys have been performed at the beginning and end of the flood season to address the spatial and temporal variation of the sediment deposition in the canals under study and to detect changes in the bed profile. The head regulator and outlet control structures were calibrated by using the measured stage-discharge relationships. More elaboration is given to the properties of cohesive sediment and identification of the dominant factors that cause deposition in irrigation canals. Sediment properties were tested such as grain size distribution, mechanical and physico-chemical properties of the sediment. The irrigation schedules, cropped area and sowing dates for different crops were reported. Other data such as canal design data, historical data of the sediment and flow for certain canals were reviewed.

The analysis of the data indicates a variation of the water level along the canals under study. It should be noted that the operation control in Gezira Scheme is by using upstream control structures. The field data show that the flow release in the system is not regularly adjusted in a systematic way to meet the demand and maintain the required water level. Continuous change in gate setting results in instability of the water level. This situation became worse with more sediment deposition. The water level has been raised far above the design level and there is lapse in working levels especially at the major and minor canals. The rise is found to be about 1.6 and 1.2 m above the design level at the head of the major and minor canals under study. Furthermore, reduction in the water depth has been detected along the canals as result of bed rise and enlarging of canal sections due to improper desilting. The results demonstrate that the supply of water was extremely large during the flood season of 2011 compared to the actual crop water requirement, especially during the period of high sediment concentration. The delivery performance ratio indicated an oversupply at the major canal in 2011 during most of the time. The study also provides some valuable insight into the nature of sediment in Gezira Scheme.

There is a limitation in the existing models that deal with fine sediment transport in irrigation canals. Most of the sediment transport models are developed for estuaries and rivers. Therefore there was a great need to develop a simple but effective numerical model that incorporates control structures to simulate the fine sediment transport in irrigation canals. Although there are similarities between rivers and irrigation canals, irrigation canals are different. The presence of a large number of flow control structures and the high influence of the side banks on the velocity distribution create some differences in both types of channels. Hence, it was important to develop a model dealing with fine sediment in irrigation canals, including different types of hydraulic structures.

In line with this the one dimensional numerical model Fine SEDiment Transport (FSEDT) dealing with fine sediment transport in irrigation canals has been developed. The model has been used as a tool to study the mechanism of water and sediment flow under different operation and maintenance scenarios. The water surface profile has been predicted by using the predictor corrector method to solve the gradually varied flow equation. The prediction of sediment concentration is based on the solution of the one dimensional advection-diffusion equation. The bed material exchange was determined based on the Partheniades (1962) and Krone (1965) equations. The change in bed level was computed based on the sediment mass balance equation that was solved numerically by using the finite difference method. The model has been applied in the Gezira Scheme. On the basis of the field data the model has been calibrated and validated. The predicted bed profiles depict good agreement with the measured ones. The model is capable to predict the bed profile for any period of simulation. The model can predict the sediment concentration hydrograph at different points within a canal reach, in addition to the total volume of the sediment deposition in the reach. The output of the model can be presented in tabular or graphical form.

The sediment transport in the irrigation canals has been simulated by adopting different scenarios. The interrelationship between water flow and sediment transport in the irrigation canals under changing flow conditions has been investigated. Two scenarios of operation were tested at the major canal under study. The model evaluated the indent system that has been applied in Gezira Scheme for many years in regard to sediment deposition. Another proposed scenario based on crop water requirement was also tested. In addition, operation under future changed conditions in case of reduction in the sediment concentration was tested. The different operation scenarios have been compared with the existing condition based on data collected during the flood season in 2011 in terms of sedimentation. Based on this, the following remarks are made:

the effect of varying crest settings of the movable weirs has been investigated and less sediment deposition was found to occur when the crest level was set at its lowest position. The sediment transport in the canals is influenced by the operation of the hydraulic structures, especially upstream of movable weirs. The effect is extended to about 3 km upstream of the weir;

for many years the indent system of water allocation was applied in the Gezira Scheme based on duty and cropped area. However, this system of operation has been absent during the last years. The slope of Zananda Major Canal became 13 cm/km and 18 cm/km for the first and second reaches respectivelycampaigns

the reduction of the water delivery during the period of high concentration between 10 July and 10 August, based on the crop water requirement results in reduction in the sediment deposition by 51 and 55% for the first and second reaches respectively when compared to the situation in 2011;

the reduction of the Blue Nile River sediment concentration by 50% as result of the construction of the Ethiopia Renaissance Dam and/or improvement in the land use has been simulated. The results of the simulation of the suspended sediment transport at the major canal indicate that the deposition will be 74 and 81% lower for the first and second reaches respectively when compared with the situation in 2011.

At the minor canals, the night storage weirs were designed as cross structures. The idea behind the night storage system was to store water during the night by closing all field outlet pipes and the gates of the cross structures along the minor canal at 6:00 pm and releasing them at 6:00 am. Although this system has been vanished to keep pace with crop intensification and to cope with the deterioration of the water supply due to the poor maintenance of the canals, this scenario has also been simulated. The hydrodynamic flow in the canals during the filling time has been simulated by using the DUFLOW model since the model can be applied for unsteady flow. A spreadsheet has been designed to predict the deposition every hour based on the output of the DUFLOW model. The night storage system has been compared with the continuous system regarding the sediment transport in addition to other scenarios. It was found that:

the continuous system reduces the amount of deposited sediment by 55% compared to the night storage system;

about 29% of the sediment was reduced in 2011 when the system was operated based on crop water requirement;

the deposition lightly increased with reduced capacity of the field outlet pipes. The

The main findings and the contributions that are made by this study:

the study comes up with a model dealing with cohesive sediment in irrigation canals for effective sediment and water management, which can be applied widely for similar irrigation schemes dealing with fine sediment;

it is possible to improve the sediment and water management by improving the operation and maintenance. The high irrigation efficiency is tending to mitigate the inflow sediment load and as a consequence less deposition is expected;

the study comes up with strategies of water management that can reduce the deposition in irrigation canals by operating the system continuously based on crop water requirement at the period of high sediment concentration with the field outlet pipes operating at their full capacity.

The absence of proper maintenance activities and water management has a prominent role in increasing the deposition along the irrigation canals in Gezira Scheme. Improving the operation and maintenance is not the only way to mitigate the sedimentation in the irrigation canals. A great consideration needs to be given to improve the design since conditions based on the original design have been changed with time such as the operation system (night storage system, indent system), cropping intensity and geometry of the canals. In other words, rehabilitation of the system will not be one of the solutions to mitigate the accumulation of the deposition along the canals but the system itself needs remodelling. The developed model can be used to assess the new design and to evaluate the proposed management plans in terms of transport of cohesive sediment.

Sustainable use of land and water under rainfed and deficit irrigation conditions in Ogun-Osun River Basin, Nigeria
Adeboye, O.B. - \ 2015
University. Promotor(en): E. Schultz, co-promotor(en): K.O. Adekalu; K. Prasad. - Leiden : CRC Press/Balkema - ISBN 9789462572782 - 237
landgebruik - watergebruik - duurzaamheid (sustainability) - irrigatie - regenafhankelijke landbouw - watertekort - modellen - bodemwaterbalans - gewasopbrengst - nigeria - land use - water use - sustainability - irrigation - rainfed agriculture - water deficit - models - soil water balance - crop yield

Human population is increasing faster than ever in the history. There is an urgent need to scale up food production in order to meet up with food demands, especially in Sub-Saharan Africa. In Ogun-Osun River Basin, Nigeria, more than 95% of the crop production is done under rainfed conditions. Fluctuation in rainfall as a result of climate change is a major challenge in the recent times in the basin. Land productivity can be greatly improved by using affordable water conservation practices by peasant farmers who produce crops in the basin. Similarly, water saving measures would have to be adopted by using drip irrigation and application of water at critical stages of growth of crops. Fertility of the soil needs to be maintained by cultivating crops that naturally replenish soil nutrients. Such measures will go a long way in ensuring sustainable use of land and water in Ogun-Osun River Basin.

An indeterminate cultivar of Soybeans TGX 1448 2E was cultivated at the Teaching and Research Farms of Obafemi Awolowo University, Ile-Ife, Nigeria during the rainy seasons from May to September, 2011 and June to October, 2012. Similarly, the crop was drip irrigated for two dry seasons from February to May in 2013 and from November, 2013 to February, 2014. The purpose of conducting the experiments in the rainy and dry seasons was to compare the yields and their components and to evaluate the performances of the crop in terms of water use and productivity. The experimental field during the dry season was located at about 1 km from the field used during the rainy season due to the nearness to the source of water. During the experiments in the four seasons, key biometric data of the crop were taken from emergence to physiological maturity. The crop cycle during the rainfed experiment lasted for 117 and 119 days in 2011 and 2012 respectively, while in the dry season it lasted for 112 days in the first season and 105 days in the second season. The lengths of the crop cycles in the four seasons differed a little bit. This is attributed to environmental factors such as weather conditions, nutrient availability in the soil and period of cultivation. During the rainy seasons, six water conservation treatments were used namely Tied ridge, Mulch, Soil bund, Tied ridge plus Soil bund, Tied ridge plus Mulch, Mulch plus Soil bund and Direct sowing without water conservation measure (conventional practice), which was the control treatment. The treatments were placed in a randomised complete block design with four replicates in an area of 31 by 52 m (1,612 m2) and standard agronomic measures were taken. Soil water balance approach was used in determining evapotranspiration during the rainfed and irrigation seasons. Seasonal evapotranspiration was partitioned into the productive transpiration from the plants and non-productive evaporation from the soil.

Seasonal average canopy extinction coefficients were 0.46 and 0.51 respectively in the rainy seasons of 2011 and 2012, while in the dry seasons of 2013 and 2013/2014 they were 0.43 and 0.49. The plant height ranged from 51.3 cm for Soil bund to 67.8 cm for the conventional practice in 2011 while in 2012, it ranged from 60.3 cm for Tied ridge plus Soil bund to 80.3 cm for Mulch plus Soil bund. The minimum fraction of Intercepted Photosynthetically Active Radiation was 0.13 during establishment for Tied ridge plus Soil bund while the peak fraction was 0.97 during seed filling for Soil bund during the rainy seasons. Similarly, the minimum and peak leaf area indices were 0.13 m2 m-2 for Tied ridge plus Soil bund during establishment in 2011 and 6.61 m2 m-2 for Soil bund during seed filling in 2012. There were strong and significant correlations between the fraction of Intercepted Photosynthetically Active Radiation and the leaf area indices (LAI) (0.70 ≤ r2 ≤ 0.99) in 2011 and (0.93 ≤ r2 ≥ 0.99) in 2012 by using an exponential model. Seasonal rainfall in 2011 and 2012 was 539 and 761 mm respectively. Seasonal water storages in the soil in 2011 ranged from 407 mm for the conventional practice to 476 mm for Tied ridge plus Mulch, while in 2012 it ranged from 543 mm for Tied ridge to 578 mm for Tied ridge plus Soil bund.

Radiation Use efficiency was determined by plotting dry above ground biomass measured at intervals of seven days against the Daily Photosynthetically Active Radiation from Solar radiation and the Instantaneous Photosynthetically Active Radiation measured near solar noon for all the treatments. For the Photosynthetically Active Radiation obtained from solar radiation, Radiation Use Efficiency of the crop ranged from 1.18 g MJ-1 for Tied ridge to 1.98 g MJ-1 of Intercepted Photosynthetically Active Radiation for Tied ridge plus Soil bund in 2011, while in 2012 it ranged from 1.45 g MJ-1 for Tied ridge to 1.92 g MJ-1 for Mulch. There was no significant difference in the average seasonal Radiation Use Efficiency in the two seasons. By using instantaneous measurement of the Photosynthetically Active Radiation, Radiation Use Efficiency ranged from 0.80 g MJ-1 of Intercepted Photosynthetically Active Radiation for Tied ridge to 1.65 g MJ-1 for Tied ridge plus Soil bund in 2011, while in 2012 it ranged from 0.94 g MJ-1 for Tied ridge to 1.24 g MJ-1 for Soil bund. The two approaches gave relatively similar values of Radiation Use Efficiency. Positive -correlation coefficients (0.50 ≤ r2 ≤ 0.89) were found among the treatments between the dry above ground biomass simulated by using a light model and those measured in the field in the two seasons.

The seasonal crop water use ranged from 311 mm for Mulch plus Soil bund to 406 mm for Tied ridge plus Soil bund in 2011, while in 2012 it ranged from 533 mm for Mulch plots to 589 mm for Soil bund. Seasonal transpiration ranged from 190 mm for Tied ridge plus Mulch to 204 mm for Soil bund in 2011 while in 2012 it ranged from 164 mm for Tied ridge plus Mulch to 195 mm for Mulch plot. Seasonal evaporation was higher in 2012 ranging from 338 mm for Mulch plots to 408 mm for Soil bund while in 2011 it ranged from 311 mm for Mulch plus Soil bund to 406 mm for Tied ridge plus Soil bund. Water storage in the soil and seasonal crop water use are significantly related. Similarly, the seasonal crop water use, Intercepted Photosynthetically Active Radiation and Radiation Use efficiency were highly related for the crop over the two seasons.

Marketable seed yield ranged from 1.68±0.50 t ha-1 for Tied ridge to 2.95±0.30 t ha-1 for Tied ridge plus Soil bund in 2011, while in 2012 the yield ranged from 1.64±0.50 t ha-1 for the conventional practice to 3.25±0.52 t ha-1 for Mulch plus Soil bund. In 2011, seed yield for Tied ridge plus Soil bund was 15.6, 15.9, 25.4, 28.5, 43.1 and 47.1% higher than seed yield for Mulch plus Soil bund, Soil bund, Mulch, Tied ridge plus Mulch, Tied ridge and conventional practice respectively. In 2012, seed yield for Mulch plus Soil bund was 7.4, 21.8, 32.0, 32.3, 43.7 and 49.5% higher than the seed yields for Soil bund, Tied ridge, Mulch, Tied ridge plus Mulch, Tied ridge plus Soil bunds and Direct sowing respectively. Average seasonal seed yield of the crop was significantly related to the Total Intercepted Photosynthetically Active Radiation but not to the Radiation Use Efficiency. Harvest indices ranged from 47.4±4.5% for Tied ridge to 57.6±1.1% for Tied ridge plus Soil bund in 2011 and 53.1±3.0% for Soil bund to 58.1±2.3% for Tied ridge 2012. The highest harvest indices were obtained in Tied ridge plus Soil bund and Tied ridge in 2011 and 2012 respectively. Harvest index was not significantly related to both Intercepted Photosynthetically Active Radiation and Radiation Use Efficiency of the crop.

Average seasonal transpiration efficiencies - the ratio of the dry above ground biomass at harvest to the seasonal transpiration - for all the treatments were 7.0 kg ha-1 mm-1 in 2011 and 14.9 kg ha-1 mm-1 in 2012. Transpiration efficiency of the crop was strongly related to Intercepted Photosynthetically Active Radiation but not to Radiation Use Efficiency under field conditions in the rainy seasons. The peak water productivity for seed was 7.99 kg-1 ha-1 mm-1 in 2011 and 5.76 kg-1 ha-1 mm-1 for Mulch plus Soil bund in 2012. Water productivity for seed was strongly and significantly related to Intercepted Photosynthetically Active Radiation. However, it was not significantly related to Radiation Use Efficiency. These findings will provide information to the crop yield modellers during the simulation of yields of Soybeans under water conservation practices.

The construction of ridges and Soil bund especially for Tied ridge, Mulch plus Soil bund and Tied ridge plus Soil bund increased the average seasonal cost of production by 28.9% compared with Mulch and conventional practice and by 10.1% compared with Soil bund. In addition, economic water productivity was 3.90 US$ ha-1 mm-1 for Mulch plus Soil bund while for Soil bund and conventional practice, it was 3.30 and 2.27 US$ ha-1 mm-1 respectively.

Due to increase in demand for food, there is the need to produce more crop per drop of water under rainfed conditions and to manage water for agriculture at basin scale. The key priority in the study area was to increase the seed yields, water and economic productivity and the financial benefits at the end of a cropping season. The results show that the use of Mulch plus Soil bund had the average maximum transpiration efficiency, seed yield, water and economic productivity, and revenue of 1,630 US$ per ha. By comparing the average seasonal transpiration efficiency, crop water use, yield, water productivity and costs of production for the six conservation practices with those of the conventional practice in the two rainy seasons, Mulch plus Soil bund had the maximum average seed yield, water and economic productivity. Mulch plus Soil bund is hereby recommended for the cultivation of the crop in the study area. Other conservation practices, such as Soil bund, also performed satisfactorily in terms of seed yield and water productivity, although with a slight reduction in revenue. The use of these water conservation practices will not only increase the yields of the crop, but reduce depletion of water in the soil, which could initiate or increase land degradation in the study area to the barest minimum. Hence, sustainability of land and water in Ogun-Osun River Basin can be ensured. These findings demonstrate that land and water productivity of Soybean under rainfed conditions can be significantly improved with water conservation practices under the current fluctuations of rainfall and competition for land resources between agriculture and urban land use in Ogun-Osun River Basin.

Field trials were also conducted for two irrigation seasons from February to May, 2013 and November, 2013 to February, 2014. The crop was planted in a Randomized Complete Block Design with three replicates and in-line drip irrigation was applied to supply water to the crops. Five treatments were selected and these are: (i) full irrigation, skipping of irrigation every other week during (ii) flowering; (iii) pod initiation; (iv) seed filling and (v) commencement of maturity. Biometric data, which are number of leaves, plant height, leaf area indices and dry above ground biomass, were taken and recorded every week from sowing until maturity in the two irrigation seasons. Soil moisture contents were taken at the root zone of the plants prior to irrigation in order to determine the net irrigation water requirements at each stage of growth. Harvest indices were determined for each treatment. Number of pods per plant, number of seeds per pod and yields under each treatment were determined after physiological maturity in each season. Regression equations were generated for: (i) yield; (ii) number of pods per plant; (iii) number of seeds per pod; (iv) number of leaves; (v) seasonal transpiration and leaf area indices. Similarly, regression equations were generated for: (i) plant heights; (ii) seasonal transpiration; (iii) number of pods per plant; (iv) number of seeds per pod; (v) dry above ground biomass. Linear regressions were also fitted to the yield, dry above ground biomass and seasonal crop water use. The crop response factor was determined. Water productivity and Irrigation water productivity were computed and compared for each treatment. Linear models were fitted to the water productivity, irrigation water productivity and harvest index.

Rainfall contribution to the crop water use was 262 and 50 mm for 2013 and 2013/2014 irrigation seasons respectively. Maximum Leaf Area Index in the 2013 irrigation season was 7.10 m2 m-2 for full irrigation during seed filling, while in the 2013/2014 irrigation season, it was 3.44 m2 m-2 for full irrigation during flowering. The dry above ground biomass after maturity ranged from 359 g m-2 where irrigation was skipped every other week at the commencement of maturity to 578 g m-2 for full irrigation. The seed yields ranged from 1.81 t ha-1 when irrigation was skipped every other week during seed filling to 3.11 t ha-1 for full irrigation. Average seasonal seed yield for full irrigation was 18.8, 21.8, 24.4 and 47.9% higher than yields for treatments where irrigation was skipped every other week during flowering, pod initiation, commencement of maturity and seed filling respectively. Seasonal transpiration ranged from 217 mm when irrigation was skipped every other week during seed filling to 409 mm for full irrigation in the 2013 irrigation season, while in the 2013/2014 irrigation season it ranged from 28 mm for the treatment where irrigation was skipped every other week during seed filling to 223 mm for full irrigation. Seasonal crop water use ranged from 463 mm when irrigation was skipped every other week during flowering to 523 mm for full irrigation in the 2013 irrigation season, while in the 2013/2014 irrigation season it ranged from 364 mm when irrigation was skipped every other week during seed filling to 507 mm for full irrigation. Harvest indices ranged from 56.0% when irrigation was skipped during seed filling to 65.9% when irrigation was skipped during flowering in the 2013 irrigation season, while in the 2013/2014 irrigation season, it ranged from 43.2% when irrigation was skipped during seed filling to 63.9% for full irrigation. Water productivity for seed production ranged from 3.89 kg ha mm-1 when irrigation was skipped during seed filling to 5.95 kg ha-1 mm-1 for full irrigation in the 2013 irrigation season while in the 2013/2014 irrigation season, it ranged from 1.93 kg ha mm-1 when irrigation was skipped during seed filling to 3.00 kg ha-1 mm-1 for full irrigation. Irrigation water productivity ranged from 8.90 kg ha mm-1 when irrigation was skipped during seed filling to 14.0 kg ha-1 mm-1 when irrigation was skipped during flowering in 2013, while in the 2013/2014 irrigation season, it ranged from 2.24 kg ha-1 mm-1 when irrigation was skipped during seed filling to 3.32 kg ha-1 mm-1 for full irrigation. Leaf area indices and yield, number of leaves, number of pods per plant, number of seeds per pod and seasonal transpiration were significantly correlated. Similarly, dry above ground biomass and seasonal transpiration, number of pods per plant, number of seeds per pod were significantly correlated. The crop response factor (Ky), a measure of the relative decrease in seed yield due to relative decrease in evapotranspiration, was 2.24. It indicates that the deficit irrigation imposed on the crop was high and that relative decrease in yields due to deficit irrigation was higher than relative decrease in evapotranspiration.

Results show that skipping of irrigation at any growth stage of the crop led to reduction in the leaf area indices, dry above ground biomass and seasonal crop water use. Deficit irrigation had significant effects on both the dry matter and yields. The effect of deficit irrigation was more pronounced on seed yields than on dry matter. Severity of the effects of deficit irrigation depended on the stage of growth and its duration. Deficit irrigation reduced significantly dry matter at flowering and pod initiation. However, deficit irrigation did not affect the plant height. Number of seeds per plant at flowering and commencement of maturity were reduced significantly by deficit irrigation. The number of seeds per pod was significantly reduced when irrigation was skipped at pod initiation only. Seed yields were significantly reduced when irrigation was skipped during seed filling. In the 2013 irrigation season water productivity when irrigation was skipped during flowering was 2.3, 16.1, 23.5, and 36.1% higher than water productivity for full irrigation, when irrigation was skipped during pod initiation, commencement of maturity and seed filling respectively. In the same season, irrigation water productivity when irrigation was skipped during flowering was 15, 20, 29.3 and 36.4% higher than for full irrigation, when irrigation was skipped during pod initiation, commencement of maturity and seed filling respectively. In the 2013/2014 irrigation season, however, water productivity for full irrigation was 8.7, 16.3, 24.7 and 35.7% higher than when irrigation was skipped during pod initiation, commencement of maturity, flowering and seed filling respectively. Similarly, irrigation water productivity was 7.2, 15.4, 24.1 and 32.5% higher than when irrigation was skipped during pod initiation, commencement of maturity, flowering and seed filling respectively. In addition, irrigation water productivity for full irrigation was 24.1 and 32.5% higher than when irrigation was skipped during flowering and seed filling respectively. Stage of growth, its duration, water requirements and seasonal environmental conditions influenced the seasonal water use, water productivity and irrigation water productivity of Soybean. Maximum water productivity and irrigation water productivity were obtained when irrigation was skipped every other week during flowering only in the first season, whereas in the second season full irrigation gave the peak water and irrigation water productivity. This suggests that irrigation water productivity of Soybean can be improved upon by skipping irrigation during flowering and pod initiation.

In this study, the costs of production for all the irrigation scenarios were high. This is due to the high cost of water, which constituted between 54 to 59% of the production cost if water is purchased and cost of drip irrigation equipment, which constituted between 75.6 to 76.7% of the total cost of production if water would be given without financial implication. Under the prevailing price and economic conditions after harvest, the use of in-line drip irrigation does not offer economic benefit to peasant farmers, who are the predominant growers of the crop in the study area. Economic benefit may be achieved after long periods of usage with proper maintenance of the irrigation facilities and elimination of the fixed cost from the total cost of production.

The water driven crop model AquaCrop was calibrated and validated to predict canopy cover, dry above ground biomass, seed yield, evapotranspiration, soil moisture content and water productivity of the crop. The simulated and measured data compare adequately except for water productivity that was over predicted in the validation data set. The AquaCrop model predicted canopy cover with error statistics of 0.93 ≤ E ≤ 0.98 for both full and deficit irrigation and the degree of agreement d = 0.99 with 4.3 ≤ RMSE ≤ 5.9 (root mean square error) for full irrigation while for deficit irrigation, 0.96 ≤ d ≤ 0.99 with 5.3 ≤ RMSE ≤ 5.8. Dry above ground biomass was predicted with error statistics of 0.08 ≤ RMSE ≤ 0.14 t ha-1 with 0.98 ≤ d ≤ 0.99 for full irrigation, while for deficit irrigation it was 0.06 ≤ RMSE ≤ 1.09 t ha-1 with 0.85 ≤ d ≤ 0.99. One in every five predictions of the above ground biomass was outside 20% deviation from the measured values.

The seed yields were predicted with error statistics of RMSE = 0.10 t ha-1 and d = 0.99 and one in five predictions was outside 15% deviation from the measured data. The prediction error statistics for seasonal crop water use for both full and deficit irrigation treatments was 15.4 ≤ RMSE ≤ 58.3 in the two seasons. The AquaCrop model over predicted percolation also in the validation data set. These observations suggest that the percolation components of the model need to be adjusted to ensure better performance. The performance of the AquaCrop model in predicting canopy cover, seed yield and other quantities in this study are commendable and satisfactory.

Specific and distinct features, such as the use of canopy cover rather than leaf area index, make the model suitable for developing countries like Nigeria, where researchers may not have access to state-of-the-art equipment for measuring the leaf area index. Similarly, water productivity that is normalized for atmospheric demand and carbon dioxide concentration and its focus on water makes it suitable for diverse locations. Over the years, it has been observed that no model is universal in its ability to take into consideration all differences in cultivar, environment, weather and management conditions. Other cultivars of Soybeans in Nigeria and other agro-climatic environments need to be tested and fine-tuned in the model, in order to ascertain the accuracy of the model. generally, the model predicted the stated parameters with reasonable degree of accuracy and is hereby recommended for use in Ile-Ife and other parts of Ogun-Osun River Basin and Nigeria.

Although land, water, and economic productivity of the crop were higher where water was conserved under rainfed conditions, treatment of the soil to conserve water and regular maintenance increased the average seasonal cost of production compared with the conventional practice. High cost of production may reduce the benefits obtained by the crop growers, except when there is improvement in the market price. Therefore, sustainable practice of the water conservation measures must be accompanied with lower cost of production. Under irrigation conditions, the land and water productivity are lower compared with rainfed cultivation. The productivity in the dry season reduces with the severity of the water stress. Average crop water productivity and economic water productivity of all the six water conservation measures in the rainy season were higher than with full irrigation in the dry season. The costs of production of the crop in the dry season were significantly above the cost during the rainfed conditions. Higher water productivity under rainfed conditions in this study is in agreement with the finding that in a significant part of the least developed and emerging countries there is larger opportunity for improving water productivity under rainfed conditions compared to irrigated agriculture.

Expansion of arable land may not be feasible in Ile-Ife because of the huge investments involved. Thus, the focus of efforts to expand food production in the area would have to be on raising land productivity on the existing arable lands and improving production efficiencies, outcomes that can only be achieved by using improved cultivars together with improved agronomic practices. Agronomic practices, especially under rainfed conditions, would have to be designed to improve water productivity. Improving water productivity requires vapour shift (transfer) whereby soil physical conditions, soil fertility, crop varieties and agronomy are applied in tandem and managed to shift the evaporation into useful transpiration by plants. During the dry season, the crop would have to be irrigated in order to achieve maximum land and water productivity. Skipping of irrigation during seed filling would have to be avoided in order to prevent significant reduction in yield. Irrigation at the commencement of maturity after the pods have been completely filled with seeds can be skipped. Under water limiting conditions, the amount of water saved by skipping irrigation during flowering, pod initiation, seed filling and maturity can be used for cultivating other crops and thereby increasing the opportunity cost. Incidental rainfall during the dry season would have to be used in order to increase irrigation water productivity of the crop.

Smart irrigation based on soil indicators for moisture, EC and temperature
Balendonck, Jos - \ 2015
irrigation - salinity - temperature - relative humidity - outturn - trickle irrigation - turkey - recirculating systems
Waterbesparing door slimme en betaalbare sensor
Balendonck, J. - \ 2015
Kas techniek 2015 (2015)april. - p. 34 - 37.
teelt onder bescherming - cultuurmethoden - kunststoftunnels - irrigatie - sensors - instrumenten (meters) - waterbehoefte - vochtmeters - watergebruik - efficiëntie - watergebruiksrendement - irrigatiesystemen - protected cultivation - cultural methods - plastic tunnels - irrigation - instruments - water requirements - moisture meters - water use - efficiency - water use efficiency - irrigation systems
Onderzoekers van Wageningen UR Glastuinbouw hebben in het kader van een Partners voor Water-project laten zien dat Turkse telers met behulp van de AquaTag veel efficiënter kunnen irrigeren. Sturen op vochtsensoren is niet nieuw, maar beschikbare sensoren zijn relatief duur en meten alleen lokaal, terwijl het vochtgehalte sterk kan variëren binnen een kraanvak. Met de AquaTag is nu een goedkope en slimme oplossing voor handen.
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