The potential role of biological inhibition of nitrification in a fallow cropping system: a modelling approach

Abstract To solve fertility problems, most smallholder farmers in sub-Saharan Africa use fallow periods. However, population growth along with land shortage tend to shorten the duration of fallows, resulting in a steady decline in soil fertility. Assuming that nitrogen (N) plays a key role in soil fertility, we designed an ecological model describing N cycle in a cropping system. We examined the impact of different processes involved in N cycle, including mineralization, nitrification and fallow characteristics on the yield of a maize crop in a humid savanna, Côte d’Ivoire. The objective of this study was to explore ways to maintain N supply in N poor soils by identifying the appropriate levers and practices. The model revealed that in low input agricultural systems, soil fertility is maintained by the dynamics of soil organic matter and mineralization. We showed that, variation in nitrification during the cropping cycle (fallow-crop) does not have a significant effect on maize yield. However, with the addition of N fertilizers, reduced nitrification significantly increases crop yield. Indeed, low nitrification increases the efficiency of fertilizer use, which reduces the negative impact of excessive N fertilizer application. Furthermore, legume-based fallow was able to increase maize productivity much more than a nitrification-inhibiting fallow regardless of long duration of fallow periods. Also, the models suggested suggest that using nitrification-inhibiting grasses as cover crops for maize would be beneficial if mineral N fertilizer is used.