Efficient phosphorus application strategies for increased crop production in sub-Saharan West Africa

Comparable data are lacking from the range of environments found in sub-Sah aran West Africa to draw more general conclusions about the relative merits of locally available rockphosphate (RockP) in alleviating phosphorus (P) c onstraints to crop growth. To fill this gap, a multi-factorial field experi ment was conducted over 4 years at eight locations in Niger, Burkina Faso a nd Togo. These ranged in annual rainfall from 510 to 1300 mm. Crops grown w ere pearl millet (Pennisetum glaucum L.), sorghum (Sorghum bicolor (L.) Moe nch) and maize (Zea mays L.) either continuously or in rotation with cowpea (Vigna unguiculata. Walp.) and groundnut (Arachis hypogaea L.). Crops were subjected to six P fertiliser treatments comprising RockP and soluble P at different rates and combined with 0 and 60 kg N ha(-1). For legumes, time trend analyses showed P-induced total dry matter (TDM) increases between 28 and 72% only with groundnut. Similarly, rotation-induced raises in cereal TDM compared to cereal monoculture were only observed with groundnut. For c ereals, at the same rate of application, RockP was comparable to single sup erphosphate (SSP) only at two millet sites with topsoil pH-KCI < 4.2 and an nual average rainfall > 600 nim. Across the eight sites NPK placement at 0. 4 g P per hill raised average cereal yields between 26 and 220%. This was c onfirmed in 119 on-farm trials revealing P placement as a promising strateg y to overcome P deficiency as the regionally most growth limiting nutrient constraint to cereals. (C) 2001 Elsevier Science B.V. All rights reserved.