Weed management on Vertisols for small-scale farmers in Ghana

Abstract

Vertisols and vertic clays represent a vast crop production resource (300 million hectares world-wide) that is underutilized, mainly because of problems with soil physical characteristics (particularly relating to water) and weeds. These montmorillonitic clays are generally more fertile and have higher water-holding capacities than many tropical soils, but they are difficult to manage as they are very sticky when wet and hard and cloddy when dry. Research in Ghana has shown that it is technically possible to increase crop yields by 90% in normal wet seasons by using raised (camber) beds to control water, but further increases in yield potential are prevented by highpopulations of Cyperus rotundus L. and Imperata cylindrica (L.) Raeuschel. These challenges have been addressed by research on farms and on a research station to determine the effectiveness of glyphosate and camber beds for weed and water management and crop production in maize-based farming systems. Field trials have shown that tuber populations of C. rotundus could be reduced by 95% after glyphosate at 1.8 kg a.e. ha-1 was applied at the beginning of four cropping seasons during 1997 and 1998. The combination of glyphosate for weed control and camber beds to shed excess water produced maize grain yields of 3.5 t ha-1 - a significant increase over the typical yields of ∼1.0 t ha-1 withtraditional methods ofhoe-weeding onflat land. Economic evaluations have shown that the returns to small-scale farmers could be considerably increased by the use of glyphosate for weed control.