Effects of cultivation practices on spatial variation of soil fertility and millet yields in the Sahel of Mali

The article provides a quantitative analysis of temporal variation in fallow characteristics, and spatial variation in fallow distribution, pearl millet (Pennisetum glaucum) yield and soil fertility in three villages in the Bankass area in Sahelian Mali. Plots of 5 m × 5 m along four transects were installed at 10, 50, 100, 200, 500, 1000 and 2000 m from the edge of the village compounds to the outer boundary of the village territory. We found that currently, fallow is practiced only in 'bushfields', which are further than 200 m away from the dwellings. Significant increases in the amount of organic C and soil nutrients (N, P and K) were found with increasing fallow duration. This was due to gradual accumulation of organic matter from fallow vegetation and the presence of leguminous species. Soil nutrients and organic C were higher in homefields (<200 m away from farmer dwellings) than in bushfields. Also, millet grain yields were highly correlated with soil nutrients, and decreased from 1060 kg ha−1 in homefields to 520 kg ha−1 in bushfields. Yields in bushfields ranged from 450 kg ha−1 on fields cultivated for several years to 640 kg ha−1 after 4-7 years of fallow. Regression analysis showed that millet yields were negatively correlated with infestation by the parasitic weed Striga hermonthica. Future research needs to focus on the relationship between Striga infestation and soil factors.