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 technique to reduce drought risk in maize (Zea mays L.) production. Before tied-ridging can be promoted to subsistence farmers as a viable rainwater harvesting technique, there is need to evaluate the likely impact of tied-ridging on soil water status and maize yield. A calibrated field capacity-based water balance model (TIEWBM) was used to assess the impact of tied-ridging on soil water status of a maize crop under Malawi conditions. Effect of tied-ridging on soil water status was evaluated by simulating seasonal (140 days) changes in retained rainwater, surface runoff, drainage, soil moisture storage (SMS), waterlogging and actual evapotranspiration (ETa) for 5 soils and 12 rainfall regimes. The simulation results indicate that tied-ridging reduced surface runoff and this increased retained rainwater within the field. Over 80% of the gained rainwater was lost as drainage while the remainder increased SMS and ETa in fine-textured soils (clayey texture) but not in coarse-textured soils (sandy texture). Tied-ridging is not likely to benefit the maize crop in coarse-textured soils regardless of seasonal rainfall amount. Tied-ridging, however, is likely to benefit the maize crop in fine-textured soils and for seasonal rainfall between 500–900 mm (drought or dry years). Below 500 mm, the rainfall is not sufficient to meet maize crop water requirements (CWR) with or without tied-ridging. Above 900 mm (normal and wet years), rainfall is sufficient to meet CWR without tied-ridging making them unnecessary. Furthermore, in normal or wet years, tied-ridging is likely to lead to waterlogging in fine but not coarse-textured soils. The results cast doubt on the benefits of tied-ridging in coarse-textured soils.