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Soil fertility and climate risks are hampering crop production in the Sahelian region. Because experiments with only a few fertility management options on a limited number of sites and years cannot fully capture the complex and highly non-linear
soil–climate–crop interactions, crop growth simulation models may suitably complement experimental research to support
decision making regarding soil fertility and water management. By means of a long term (23 years) scenario analysis using
the Agricultural Production Systems Simulator (APSIM) model, this study investigates millet response to N in view of
establishing N recommendations better adapted to subsistence small-holder millet farming in the Sahel. Prior to this, the APSIM
model was tested on a rainfed randomized complete block experiment carried out during the 1994 and 1995 cropping
seasons, having contrasting rainfall conditions. The experiment combined, at three levels each, the application of cattle
manure (300, 900 and 2700 kg ha−1), millet residue (300, 900 and 2700 kg ha−1) and mineral fertilizer (unfertilized control,
15 kg N ha−1 + 4.4 kg P ha−1 and 45 kg N ha−1 + 13.1 kg P ha−1) at ICRISAT Sahelian Center, Niger. The model suitably
predicted plant available water PAW and the simulated water and nitrogen stress were in agreement with measurement (water)
and expectation (N) regarding the fertilizer and rainfall conditions of the experiment. APSIM simulations were in satisfactory
agreement with the observed crop growth except for the highest crop residue application rates (>900 kg ha−1). For biomass
and grain yield, the model performance was relatively good in 1994 but biomass yields were slightly overpredicted in 1995.
The model was able to adequately reproduce the average trend of millet grain yield response to N inputs from manure and
fertilizer, and to predict the overall observed higher grain yield in 1995 compared to 1994, despite the better rainfall in 1994.
The 23-year, long term scenario analysis combining different application rates of cattle manure, millet residue and mineral
fertilizer, showed that moderate N application (15 kg N ha−1) improves both the long term average and the minimum yearly
guaranteed yield without increasing inter-annual variability compared to no N input. Although it does imply a lower average
yield than at 30 kg N ha−1, the application of 15 kg N ha−1 appears more appropriate for small-holder, subsistence farmers
than the usual 30 kg N ha−1 recommendation as it guarantees higher minimum yield in worst years, thereby reducing their
vulnerability
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