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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Evaluating coffee yield gaps and important biotic, abiotic, and management factors limiting coffee production in Uganda
Wang, N. ; Jassonge, L. ; Asten, P.J.A. van; Mukasa, D. ; Wanyama, I. ; Kagezi, G.H. ; Giller, K.E. - \ 2015
European Journal of Agronomy 63 (2015). - ISSN 1161-0301 - p. 1 - 11.
boundary-line analysis - soil properties
Coffee is Uganda's biggest export commodity, produced mainly by an estimated one million smallholder farmers (1400. m) such as Eastern, Southwest, and Northwest Uganda. Actual yields are far below (
Closing the cassava yield gap: an analysis from small-holder farms in East Africa
Fermont, A.M. van; Asten, P.J.A. van; Tittonell, P.A. ; Wijk, M.T. van; Giller, K.E. - \ 2009
Field Crops Research 112 (2009)1. - ISSN 0378-4290 - p. 24 - 36.
soil fertility - boundary-line - western kenya - management - photosynthesis - productivity - technologies - physiology - disease - tropics
Cassava yields in Africa are small and it remains unclear which factors most limit yields. Using a series of farm surveys and on-farm and on-station trials in Uganda and western Kenya, we evaluated the importance of abiotic, biotic and associated crop management constraints for cassava production in a range of socio-economic settings as found in smallholder farms in the region. Average yields under farmer management were 8.6 t ha(-1),but these were more than doubled to 20.8 t ha(-1) by using improved crop establishment, improved genotypes and 100-22-83 kg ha(-1) of single-nutrient N-P-K fertilizers. A farm survey revealed large yield differences between farms. Less endowed farmers harvested less cassava per unit area than better endowed farmers (difference of 5.9 and 9.7 t ha(-1) in Kenya and Uganda, respectively); differences were associated with less access to labour, poorer soils, and premature harvesting by less endowed farmers. Analysis of 99 on-farm and 6 on-station trials showed that constraints for cassava production varied strongly between sites and years. Poor soil fertility, early water stress and sub-optimal weed management limited cassava production by 6.7, 5.4 and 5.0 t ha(-1), respectively, when improved crop establishment and genotypes were used. Pests and diseases were relatively unimportant, while weed management was particularly important in farmer fields during a dry year in Kenya (yield gap of 11.6 t ha(-1)). The use of complementary analytical tools such as multiple regression and boundary line analysis revealed that many fields were affected by multiple and interacting production constraints. These should be addressed simultaneously if significant productivity improvements are to be achieved. This will be more difficult for less endowed than for better endowed farm households, since the former lack social and financial capital to improve management. (C) 2009 Elsevier B.V. All rights reserved.
Increasing land pressure in East Africa: The changing role of cassava and consequences for sustainability of farming systems
Fermont, A.M. van; Asten, P.J.A. van; Giller, K.E. - \ 2008
Agriculture, Ecosystems and Environment 128 (2008)4. - ISSN 0167-8809 - p. 239 - 250.
soil fertility management - western kenya - gradients - farmers - maize - crops
Increasing land pressure during the past three to four decades has transformed farming systems in the mid-altitude zone of East Africa. Traditional millet-, cotton-, sugarcane- and/or banana-based farming systems with an important fallow and/or grazing component have evolved into continuously cultivated cassava or cassava/maize-based systems. Within three to four decades, cassava cultivation increased from 1¿11 to 16¿55% of cropped fields in our six study sites. Declining soil fertility, and not labour or food shortage, was apparently the primary trigger for this transformation. The land use changes have increased nutrient offtakes and reduced nutrient recycling rates. Cassava and maize now account for 50¿90% of nutrient removal. Whereas single-season fallows were the most important source of nutrient recycling on cropped fields in the past, currently cassava litterfall and maize stover contribute roughly 70% of nutrient recycling, with 50¿70% of N, P and K recycled in cassava litterfall. This may explain why many farmers reason that cassava `rests¿ the soil. With increasing land use pressure farmers progressively use cassava as an `imitation fallow¿ throughout their farm. Farmers increasingly target cassava to poor fertility fields characterized by low pH and available P. High cassava intensities are nonetheless maintained on more fertile fields, probably to guarantee regeneration of soil fertility on all fields. Once cassava is targeted to poor fertility soils, farmers have run out of low-input management options and need to intensify management to maintain system productivity. As cassava is now used by more farmers and on a larger acreage than fallowing in the studied farming systems, cassava cropping could perhaps serve as an excellent entry point to strengthen system sustainability.
Effect of straw application on rice yields and nutrient availability on an alkaline and a pH-neutral soil in a Sahelian irrigation scheme
Asten, P.J.A. van; Bodegom, P.M. van; Mulder, L.M. ; Kropff, M.J. - \ 2005
Nutrient Cycling in Agroecosystems 72 (2005)3. - ISSN 1385-1314 - p. 255 - 266.
flooded soils - ammonia volatilization - nitrogen transformations - urease activity - paddy soil - nitrification - system - denitrification - hydrolysis - dynamics
Like elsewhere in the Sahel, actual rice yields (3-5 t ha-1) are far below yield potential (±8 t ha-1) in an irrigation scheme in central southern Mauritania. Earlier studies showed that yields are especially low on alkaline soils due to N and P deficiency. We investigated the potential of rice straw application as a mean to improve yields and fertilizer efficiency on an alkaline soil (pH 8.2) and a pH-neutral soil (pH 6.2). Application of 5 t straw ha-1 increased yields by 1.1 t ha -1 on average, independent of soil type and fertilizer dose. Contrary to our study, similar studies in Asia showed little short-term effects of straw on yield and N uptake. Straw application improved N availability, but not P availability. The improved N availability was attributed to N mineralized from the straw, from increased mineralization of soil organic matter (SOM) with a low C:N ratio (<7.2) and from increased mineral fertilizer N (urea) recovery efficiency. We deduced that improved N fertilizer recovery upon straw application was due to reduced nitrification-denitrification losses. On the alkaline soil, volatilization was important, but that process seemed unaffected by straw application. We hypothesize that the positive effects of straw application at our study site are due to low soil C content (<43 g kg -1) and low C:N ratio compared to most lowland rice soils in Asia
Using farmer knowledge to combat low productive spots in rice fields of a Sahelian irrigation scheme
Asten, P.J.A. van; Barro, S.E. ; Wopereis, M.C.S. ; Defoer, T. - \ 2004
Land Degradation and Development 15 (2004)4. - ISSN 1085-3278 - p. 383 - 396.
soil organic-matter - west-africa - lowland rice - management - zinc - perceptions - mauritania - fertility - systems - yield
In the oldest sections of Burkina Faso's largest irrigation scheme in the Sourou Valley (13degrees 10'N, 03degrees 30'W) rice (Oryza sativa L.) yields dropped from about 5 to 6 t ha(-1) in the early 1990s, shortly after establishment of the scheme, to 2 to 4 t ha(-1) from 1995 onwards. Farmers blamed this yield decline on the appearance of 2 to 20 m diameter low productive spots. According to farmers and field measurements, the low productive spots decreased yields by 25-50 per cent. The low productive spots are caused by Zn deficiency. Low Zn availability is related to the very low DTPA-extractable Zn content of the soil (0-08-0.46 mg kg(-1)), the alkaline-calcareous character of the soil, the non-application of Zn fertilizers, and a relatively large P fertilizer dose (21 kg P ha(-1)). Farmers were correct in relating the calcareous nature of the soil to the presence of the low productive spots. They were instrumental in identifying application of decomposed organic resources (e.g. rice straw at 5 t ha(-1)) as a short-term solution that increases yields by 1.5 to 2.0 t ha(-1). Application of Zn fertilizer (10 kg Zn ha(-1)) in 29 fanner fields in the 2001 dry season eradicated the low productive spots and increased yields from 3.4 to 6.0 t ha(-1). Although application of Zn fertilizer is strongly recommended, it is not yet available in Burkina Faso. Based on a comparison of fertilizer prices on the world market and the local market, we expect that the use of Zn fertilizers will be highly profitable (cost/value ratiomuch greater than2). Despite the relatively recent introduction of irrigated rice cropping, most farmers showed a good understanding of cropping constraints and possible solutions. Both farmers and researchers mutually benefited from each other's knowledge and observations. Copyright (C) 2004 John Wiley Sons, Ltd.
The effect of irrigated rice cropping on the alkalinity of two alkaline rice soils in the Sahel
Asten, P.J.A. van; Zelfde, J.A. van 't; Zee, S.E.A.T.M. van der; Hammecker, C. - \ 2004
Geoderma 119 (2004)3-4. - ISSN 0016-7061 - p. 233 - 247.
saline-sodic soil - forage cultivation - reclamation - gypsum - dissolution - scheme - crops - field - zone
Irrigated rice cropping is practiced to reclaim alkaline-sodic soils in many parts of the world. This practice is in apparent contrast with earlier studies in the Sahel, which suggests that irrigated rice cropping may lead to the formation of alkaline-sodic soils. Soil column experiments were done with some of Sahel's most alkaline-sodic rice soils from the Office du Niger (Mali) and Foum Gleita (Mauritania). Soils were irrigated using non-saline carbonate-rich irrigation water typical for the Sahel and percolation was maintained at 3-4 mm day(-1). After one cropping season, soils had turned from sodic to non-sodic, and pH had dramatically decreased, most notably in the upper soil layers. The changes were most important in the Office du Niger soil due to its small buffering capacity (small CEC and CaCO3). Alkalinity consumed by above-ground matter of the rice plants (grain and straw) equaled or exceeded alkalinity added via irrigation in a zero percolation scenario. Hence, for a climate and irrigation water that are typical for the Sahel, removal of straw and grain prevents or substantially reduces further alkalinization of the soils if percolation is absent. However, in case of some percolation, straw can best be incorporated in the topsoil of calcareous soils as it accelerates de-alkalinization and de-sodication through increased dissolution of calcite. No evidence was found indicating that ferrolysis altered the short-term alkalinity balance of the studied soils to any extent. Our results are in line with recent field studies and suggest a de-alkalinization of sodic-alkaline flooded (rice) soils in the Sahel. (C) 2003 Elsevier B.V. All rights reserved.
Explaining yield gaps on farmer-identified degraded and non-degraded soils in a Sahelian irrigated rice scheme
Asten, P.J.A. van; Wopereis, M.C.S. ; Haefele, S. ; Isselmou, M.O. ; Kropff, M.J. - \ 2003
Netherlands Journal of Agricultural Science 50 (2003)39541. - ISSN 0028-2928 - p. 277 - 296.
oryza sativa - gewasopbrengst - gewasproductie - gewasteelt - landbouwplantenteelt - kunstmeststoffen - bodemdegradatie - irrigatie - sahel - mauritanië - bodemchemie - oryza sativa - crop yield - crop production - crop management - crop husbandry - fertilizers - soil chemistry - soil degradation - irrigation - sahel - mauritania - boundary line approach - seeded flooded rice - west-africa - transformations - management - fertility - norms
The objective of this study was to identify to what extent rice productivity problems are caused by soil quality problems (soil alkalinity) and to what extent by sub-optimal crop management. The study area used is the Foum Gleita irrigation scheme, Mauritania
Farmers in the Foum Gleita irrigation scheme in southern central Mauritania experienced declining rice yields, and within a decade after its establishment 12% of the scheme's land had been abandoned. Actual rice yields (less than or equal to 4.0 t ha(-1)) are low in comparison with potential yield (ca. 8 t ha(-1)) and with yields elsewhere in the Sahel (4-6 t ha(-1)). Farmers related the productivity problems to salt efflorescences on the soil surface. Rice yields on the 'upper and middle slope' soils were lower (3.4 t ha(-1)) than the yields on soils further down the slope (> 4.2 t ha(-1)). Farmers classified the 'upper and middle slope' soils as degraded, but following the USDA classification the soils could not be classified saline or sodic. Low yields on the 'degraded' soils were related to co-limitation of nitrogen (N) and phosphorus (P), which was due to low soil N supply (ca. 18 kg ha(-1)), low soil P supply (ca. 8 kg ha(-1)), occasional low N fertilizer doses (35 kg N ha(-1)) in combination with low N fertilizer recovery efficiency (0.3 kg kg(-1)), or non-application of P fertilizer. On the 'non-degraded' soils, soil P supply (ca. 16 kg ha(-1)) was higher and N deficiency prevailed despite a higher soil N supply (ca. 32 kg ha(-1)) and a higher N fertilizer recovery efficiency (0.4 kg kg(-1)). Higher contents of carbonate salts in the 'degraded' soils increase soil pH (> 7.5) and are, therefore, likely to contribute to low soil P supply and low N fertilizer recovery efficiency.
Actual and potential salt-related soil degradation in an irrigated rice scheme in the Sahelian zone of Mauritania
Asten, P.J.A. van; Barbi'ro, L. ; Wopereis, M.C.S. ; Maeght, J.L. ; Zee, S.E.A.T.M. van der - \ 2003
Agricultural Water Management 60 (2003)1. - ISSN 0378-3774 - p. 13 - 32.
bodemdegradatie - irrigatie - verzilting - bodemchemie - modellen - rijst - sahel - mauritanië - soil degradation - irrigation - rice - salinization - soil chemistry - models - sahel - mauritania - senegal river delta - alkalinization - valley
Salt-related soil degradation due to irrigation activities is considered a major threat to the sustainability of rice cropping under semi-arid conditions in West Africa. Rice productivity problems related to soil salinity, alkalinity and topographic position were observed in an irrigated rice scheme in southern central Mauritania. Detailed study of soils in a toposequence revealed that highest topsoil salinity and alkalinity were found at the shallow soils (2.5 m) and salinity levels remained low due to leaching. Foum Gleita¿s irrigation water used is amongst the most alkaline in the Sahel. However, no clear indications of secondary salinization or alkalinization due to irrigation activities were observed. A comparison of historical data revealed no significant changes of topsoil salinity and pH over the last 30 years. The PHREEQC 2.0 model was used to study actual and potential development of soil salinity and alkalinity problems, by simulating excessive concentration of the irrigation water through evaporation. The evolution into a strongly sodic-alkaline solution due to precipitation of Mg-calcite and -silicate minerals did not fit with current composition of ground and surface water, which showed geochemical control of alkalinity at high concentrations. Incorporation of cation exchange processes, using a small (1.0 mmolc per 100 g dry soil) but calcium saturated CEC, resulted in a better fit with field data. Results indicate that the soil¿s buffer capacity to counteract alkalinization processes is large. However, the soil water and salt balance needs to be quantified in order to determine development rate and equilibrium levels of soil salinity and alkalinity for different soil type × water management combinations. This study does neither reject the hypothesis that salt-related soil degradation jeopardizes the sustainability of rice cropping in the Sahel, nor does it provide evidence for its verification. However, our results are in line with other studies in west Africa, in that current salt-related production problems are inherited, rather than being induced by irrigated rice cropping.
Soil quality and rice productivity problems in Sahelian irrigation schemes
Asten, P.J.A. van - \ 2003
Wageningen University. Promotor(en): Sjoerd van der Zee; Martin Kropff. - [S.I.] : S.n. - ISBN 9789058088529 - 143
oryza sativa - rijst - gewasproductie - kunstmeststoffen - alkalinisatie - voedingsstoffentekorten - gewasopbrengst - irrigatiewater-toedieningsschema - sahel - mauritanië - burkina faso - mali - bodemkwaliteit - oryza sativa - rice - crop production - fertilizers - alkalinization - nutrient deficiencies - crop yield - irrigation scheduling - sahel - mauritania - burkina faso - mali - soil quality
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