Effect of natural phosphate rock enhanced compost on pearl millet-cowpea cropping systems

Phosphorus (P) deficiency is considered as a major soil constraint to increased yields in tropical zones of Africa. Several methods have been tested to improve crop production but little information is available about the usage effect of phosphate rock (PR) and compost on mixed cropping of pearl millet (Pennisetum glaucum L. R. Br.) and cowpea (Vigna unguiculata L. Walp.). In this study, we investigated the effects of different PR application methods on pearl millet (millet) and cowpea cropping systems. This study was carried out at Senegal Agricultural Research Institute during the 2002 and 2003 rainy seasons, and comprised a sole millet, sole cowpea and millet-cowpea intercrop. Treatments were a control (Cont), 3 tons ha ' of compost (Com), 3 tons ha^-1 of phospho-compost (P-Com) and 3 tons ha ' of compost plus Taiba Natural Phosphate (T-Com), replicated 4 times in a randomized complete block design. In sole millet, P-Com significantly increased the total dry weight compared to the control. Although P-Com was beneficial for intercrop millet, its increased yields through T-Com were more significant, giving evidence of the beneficial effect of mixed cropping on the usage of local phosphate rock directly applied to soil. In contrast, such a beneficial effect was not observed for cowpea which was likely not P limited growth. However, although sole crops gave higher yields, the Land Equivalent Ratios (LERs) over the two years indicated a greater advantage of applying treatments in the millet-cowpea intercrops except for P-Com (LER=0.93) which appeared to be more effective in sole cropping systems.