The Kano Close-Settled zone (CSZ) has been the site of an intensive farming system for many years, and for the last 30 years at least, all available land has been under annual cultivation. Observers have wondered at the apparent sustainability of this farming system. This paper presents the results of a two year case study into soil fertility management by three farmers within the Kano CSZ. Fertilizer use (inorganic and manure), harmattan dust deposition, and biological nitrogen fixation by leguminous crops were quantified at the field level. Chemical analysis of the main inputs to the farming system and harvested products enabled a nutrient balance for the farming system to be calculated. The balance varied according to farmer management of individual fields, especially application of traditional and inorganic fertilizers, and the effect of rainfall on the size of the harvest, which is the main determinant of nutrient removal from fields. The results were used to develop a model of nutrient cycling within the farming system. The key to the farming system is the integration of crop and livestock production. Small ruminants consume crop residues, in particular those of groundnuts and cowpeas, which are good quality fodder. The fixed nitrogen in the residues of leguminous crops is converted to manure, which is transported with compound waste back to farmer fields for use as fertilizer. Legume grains are sold, earning cash which farmers may use to purchase inorganic fertilizer if they wish. Cations and micronutrients are added to the system when harmattan dust is deposited on farmer fields during the dry season. This study shows that despite being one of the most densely populated areas in semi-arid West Africa, such an intensive farming system can be both productive and sustainable. Analysis of the conditions specific to this system found that the key elements for its success included high labour availability, plentiful livestock, and recycling of nutrients through the use of crop residues as livestock fodder. These findings contrast with those of other workers who suggest that such intensive farming over a long period is not possible in similar parts of West Africa, without large areas of rangeland to support the system. The author demonstrates how increasing population densities and labour availability contribute to the processes necessary to support sustainable agricultural intensification, such as the increasing use of crop residues to feed livestock, and the eventual shift to full crop-livestock integration. In conclusion, the author recommends that the sustainability of such intensive systems can be further supported through promoting legume cultivation and the keeping of small ruminants.
Harris, F. 1996. Intensification of agriculture in semi-arid areas: Lessons learned from the Kano close-settles zone, Nigeria. Gatekeeper Series No 59. London: Sustainable Agriculture Programme, International Institute for Environment and Development.