Decomposition of and nutrient release from ruminant manure on acid sandy soils in the Sahelian zone of Niger, West Africa

In ago-pastoral systems of the semi-arid West African Sahel, targeted appli cations of ruminant manure to the cropland is a widespread practice to main tain soil productivity. However, studies exploring the decomposition and mi neralisation processes of manure under farmers' conditions are scarce. The present research in south-west Niger was undertaken to examine the role of micro-organisms and meso-fauna on in situ release rates of nitrogen (N), ph osphorus (P) and potassium (K) from cattle and sheep-goat manure collected from village corrals during the rainy season. The results show that (1) mac ro-organisms played a dominant role in the initial phase of manure decompos ition; (2) manure decomposition was faster on crusted than on sandy soils; (3) throughout the study N and P release rates closely followed the dry mat ter decomposition; (4) during the first 6 weeks after application the K con centration in the manure declined much faster than N or P. At the applied d ry matter rate of 18.8 Mg ha(-1), the quantities of N, P and K released fro m the manure during the rainy season were up to 10-fold larger than the ann ual nutrient uptake of pearl millet (Pennisetum glaucum L.), the dominant c rop in the traditional agro-pastoral systems. The results indicate consider able nutrient losses with the scarce but heavy rainfalls which could be all eviated by smaller rates of manure application. Those, however, would requi re a more labour intensive system of corralling or manure distribution. (C) 2001 Elsevier Science B.V. All rights reserved.