Effect of tied-ridging on soil water status of a maize crop under Malawi conditions

Tied-ridging is being promoted in Malawi as a rainwater harvesting techniqu e to reduce drought risk in maize (Zea mays L.) production. Before tied-rid ging can be promoted to subsistence farmers as a viable rainwater harvestin g technique, there is need to evaluate the likely impact of tied-ridging on soil water status acid maize yield. A calibrated field capacity-based wate r balance model (TIEWBM) was used to assess the impact of tied-ridging on s oil water status of a maize crop under Malawi conditions. Effect of tied-ri dging on soil water status was evaluated by simulating seasonal (140 days) changes in retained rainwater, surface runoff, drainage, soil moisture stor age (SMS), waterlogging and actual evapotranspiration (ETa) for 5 soils and 12 rainfall regimes. The simulation results indicate that tied-ridging reduced surface runoff an d this increased retained rainwater within the field. Over 80% of the gaine d rainwater was lost as drainage while the remainder increased SMS and ETa in fine-textured soils (clayey texture) but not in coarse-textured soils (s andy texture). Tied-ridging is not likely to benefit the maize crop in coar se-textured soils regardless of seasonal rainfall amount. Tied-ridging, how ever, is likely to benefit the maize crop in fine-textured soils and for se asonal rainfall between 500-900 mm (drought or dry years). Below 500 mm, th e rainfall is not sufficient to meet maize crop water requirements (CWR) wi th or without tied-ridging. Above 900 mm (normal and wet years), rainfall i s sufficient to meet CWR without tied-ridging making them unnecessary, Furt hermore, in normal or wet years, tied-ridging is likely to lead to waterlog ging in fine but not coarse-textured soils. The results cast doubt on the b enefits of tied-ridging in coarse-textured soils. (C) 2000 Elsevier Science B.V. All rights reserved.