No abstract

Designing innovative combinations of techniques to improve the sustainability of a cropping system is a major challenge in many regions of the world. The available techniques are often added together, and assessed for yield only, rather than combined in an integrated approach. We than developed here a methodology to design and assess a sustainable crop management system adapted to a specific set of constraints. Based on the prototyping approach, this methodology takes advantage of expert knowledge on cotton cropping techniques such as no-till, cover crop, varieties and growth regulator, with innovative potential but which are not yet properly simulated by actual crop models. It involves four successive steps: (1) identification of the local sets of constraints to crop production, and selection of relevant criteria for sustainability assessment, (2) elaboration of a cropping system prototype and its assessment indicators adapted to a target set of constraints, (3) on-station assessment and adjustment of the prototype, and (4) on-farm evaluation and adjustment of the prototype. We describe here the methodology, and how its first three steps were implemented to build and test a prototype for late-planted cotton with low input availability in West Africa. A new cropping system was designed, which included new genotypes, increased plant stand, lower rates of fertilisers and the use of herbicides and growth regulators. Fourteen indicators were selected to assess the economic, environmental and social performance of the prototype. The prototype was then tested in Mali, Cameroon, and Benin in 2002 and 2003. Our findings show that this prototype improved farmers' income by about +35% in 2002 and +20% in 2003, and increased labour productivity by about +5 to +20%. It achieved a satisfactory environmental performance, similar to the control, with positive mineral balances. The prototype still requires extra labour, skill and money to implement, and therefore requires further adjustment. sustainable cotton management system / west Africa / prototyping / multi-criteria evaluation

Smallholder farmers in sub‐Saharan Africa (SSA) currently grow rainfed maize with limited inputs including fertilizer. Climate change may exacerbate current production constraints. Crop models can help quantify the potential impact of climate change on maize yields, but a comprehensive multimodel assessment of simulation accuracy and uncertainty in these low‐input systems is currently lacking. We evaluated the impact of varying [CO2], temperature and rainfall conditions on maize yield, for different nitrogen (N) inputs (0, 80, 160 kg N/ha) for five environments in SSA, including cool subhumid Ethiopia, cool semi‐arid Rwanda, hot subhumid Ghana and hot semi‐arid Mali and Benin using an ensemble of 25 maize models. Models were calibrated with measured grain yield, plant biomass, plant N, leaf area index, harvest index and in‐season soil water content from 2‐year experiments in each country to assess their ability to simulate observed yield. Simulated responses to climate change factors were explored and compared between models. Calibrated models reproduced measured grain yield variations well with average relative root mean square error of 26%, although uncertainty in model prediction was substantial (CV = 28%). Model ensembles gave greater accuracy than any model taken at random. Nitrogen fertilization controlled the response to variations in [CO2], temperature and rainfall. Without N fertilizer input, maize (a) benefited less from an increase in atmospheric [CO2]; (b) was less affected by higher temperature or decreasing rainfall; and (c) was more affected by increased rainfall because N leaching was more critical. The model intercomparison revealed that simulation of daily soil N supply and N leaching plays a crucial role in simulating climate change impacts for low‐input systems. Climate change and N input interactions have strong implications for the design of robust adaptation approaches across SSA, because the impact of climate change in low input systems will be modified if farmers intensify maize production with balanced nutrient management.

Potassium deficiency is known to deeply impact dry matter yield through a lower photoassimilates production. The objectives of this study were to find out and classify the principal mechanisms that accounted for the reduction in plant stature. Our approach used the framework of interceptionconversion modelling, with focuses on photosynthesis (gas exchange analysis, Farquhar model), plant-water relations (water potential components), and soluble sugars in leaves. Cotton plants were grown during 7 weeks under glasshouse hydroponic conditions and 4 increasing levels of potassium nutrition (K0, K1, K2 and K3). Sugar started to accumulate in mature leaves of K deficient plants at 20 days after emergence (DAE). This was mainly interpreted as the consequence of a low phloem loading for sucrose. At 40 DAE, leaf area and dry weight were reduced in K0 and K1 treatments compared to K2 and K3. Specific leaf weight was much higher in K deficient plants then in non deficient ones. Photosynthesis was reduced but only for severe deficient treatments (K0) and at the last measuring dates (50 DAE). We venture the hypothesis that sugar accumulation may be the key factor affecting nutrition of the growing organs, and photosynthetic capacity of the unfolded and mature leaves.

Food security in many countries is threatened due to rapid population growth. Rising temperatures and carbon dioxide, rainfall irregularity, and global warming may have serious consequences on rice production and hence food security. However, there is limited knowledge on the precise effects of global warming on crops, in particular on rice which is a major staple crop and contributor to food security. Most reports have focused on irrigated rice in India or China but much less is known about rainfed rice cropping systems in Madagascar. In the Malagasy highlands, the most populated part of Madagascar, land pressure has led to saturation of irrigated lands and the adoption of rainfed cropping systems on hilltops. The present article reports the impact of various climate changes on rice productivity in four cropping systems using the CERES-Rice model. The cropping systems include two tillages components, hand-plowed and no-tillage, and two fertilization rates: low and high nitrogen. A locally adapted rice cultivar was calibrated and validated using a dataset based on experiments conducted over a 6-year period. Daily weather data were generated for a set of 90 virtual years, from 2010 to 2099. Our results show that no-tillage systems have no advantage for climate change issues. Nitrogen was a major constraint for crops in hand-plowed and no-tillage systems. We found negative effects of climate change on soil carbon and nitrogen. By contrast, we found positive effects of temperature and increased CO2 on rice growth. The overall effects on rice yields are positive under the most pessimistic climate change scenarios but we demonstrate that the sustainability of these systems is threatened. (Résumé d'auteur

This article predicts an unexpected positive effect of climate change on cotton production in Cameroon. Global warming could threaten cotton production in Africa due to increasing temperature and CO2, and rainfall uncertainties. This situation is worsened by the fact that most African farmers grow cotton as their cash crop and have few or no possible alternatives. Assessing the impact of climate change on cotton production is therefore critical. Here, we used CROPGRO, a process-based crop model that can simulate the main features of cotton growth and management. We applied this model to two regions in North Cameroon and a set of six regional climate projections combining general climate models and regional climate models from the ENSEMBLES project. The model was calibrated and validated with a data set of observations made in farmer fields from 2001 to 2005 and at an experimental station in 2010. Our results show unexpectedly that climate change from 2005 to 2050 in North Cameroon will have a positive effect on cotton yields with an increase of 1.3 kg ha?1 year?1 in yield, especially if conservation agriculture systems are adopted. The predicted increase of 0.05 °C year?1 in temperature will shorten crop cycles by 0.1 day year?1 with no negative effect on yields. Moreover, the fertilizing effect of CO2 enrichment will increase yields by approximately 30 kg ha?1. The rainfall pattern is likely to change, but the six regional models used to generate future weather patterns did not predict a decrease in rainfall. One model even forecast an increase in rainfall amounts. According to our findings, climate changes in North Cameroon can be anticipated by tailoring alternative cropping systems and adaptation techniques to cope with climate change. (Résumé d'auteur

No abstract

No abstract