Modelling the impact of nitrification inhibition in a fallow-based West African corn cropping system

To solve soil fertility problems, most smallholder farmers in sub-Saharan Africa use fallow periods. However, population growth along with land shortage tends to shorten the duration of fallows, resulting in a steady decline in soil fertility. Although nitrogen (N) plays a key role in soil fertility, current methods for maintaining N supply in cropping systems are inadequate, especially in N poor soils. Addressing this issue is crucial for improving agricultural productivity and reducing environmental impact. The objective of this study was to explore innovative ways to maintain N supply in N poor soils by identifying the appropriate levers and practices. We designed a general model describing N cycle in a cropping system in a humid savanna in Ivory Coast. We examined the impact of different processes involved in N cycle, including mineralization, nitrification, and fallow characteristics on the yield of a crop such as corn. Our study innovatively assesses the benefits of incorporating nitrification inhibition into traditional African cropping systems and provides a modelling tool to assess its impact. The model confirms that in low input agricultural systems, soil fertility is maintained by the increase in soil organic matter during fallow and its subsequent mineralization. We showed that variation in nitrification during the cropping cycle (fallow-crop) does not have a significant effect on corn yield. However, with the addition of N fertilizers, nitrification inhibition significantly increases crop yield. Indeed, nitrification inhibition increases the efficiency of fertilizer use, which reduces losses of N fertilizer. Furthermore, legume-based fallow is able to increase corn productivity much more than a nitrification-inhibiting fallow regardless of the length of fallow periods. Finally, the models suggest that using nitrification-inhibiting grasses as cover crops for corn would be beneficial if mineral N fertilizer is used.