K-cycling under maize cultivation in Togo

The losses of K by leaching below the root zone were almost compensated by rainfall inputs. The main output of K under traditional management was the removal of crop residues. The soil fixes and releases K, probably on the small quantity of interstratified clay minerals. Fixation decreases the availability of K fertilizer by about 15%. Release can explain why crop yields are poorly correlated to exchangeable K in depleted soil. The occurrence of interstratified clay minerals in tropical soils suggests that K fixation and release could be widespread. In the Ferralsols of Togo, K fertilization should compensate removals, with an additional 15% to balance fixation. The quantity of K required to ensure sustainability depends on the fate of residues. The present system of residue removal without fertilization is leading to a drastic reduction of soil K. (authors). 4 refs., 1 fig., 1 tab