Performance of in situ rainwater conservation tillage techniques on dry spell mitigation and erosion control in the drought-prone North Wello zone of the Ethiopian highlands

Grain production shortfalls in northern Ethiopia are commonly associated with occurrence of intra-seasonal dry spells or droughts and rapid land degradation which adversely impact crop yields. Suitable practices that use available rainwater more efficiently to mitigate impact of dry spells on crops and that protect soil are needed to stabilize and improve grain yields in the predominately rainfed agriculture. During three cropping seasons on-farm experiments tested conservation tillage techniques implemented with oxen-drawn plows on clay loam soil. Tested tillage techniques are subsoiling, open and tied ridges, no till, and conventional tillage with the local maresha plow (the control). Effectiveness in improving root zone soil moisture, limiting soil erosion, and improving sorghum (Sorghum bicolor (L.) Moench.) and chickpea (Cicer arietinum L.) grain yield were determined. Results demonstrate that performance of the tillage techniques varied with seasonal rainfall distribution and intensity and land slope gradient. Tied and open ridge increased seasonal root zone soil moisture 15-24%. Subsoiling slightly (3%) increased and no till slightly decreased soil moisture but were not statistically different from conventional tillage. Tied ridge and no till significantly reduced seasonal soil loss by up to 11 Mg ha(-1) during seasons with moderate intensity storms, but during a season with high intensity storms tied ridge on over 9% slope gradient increased soil loss (up to 35 Mg ha(-1)). The increased soil disturbance of subsoiling led to higher soil loss rates (up to 32 Mg ha(-1)) than conventional tillage during all seasons. Grain yield decreased and runoff and erosion rates increased rapidly with increasing land slope gradient. During a season with moderate intensity rainfall open and tied ridge increased sorghum yield by 67-73% over the control (730 kg ha-1) while no till decreased yield by 25%. During a season when high intensity rainfall events damaged the ridges, subsoiling had the best sorghum yield with 42% increase over the control (1430 kg ha(-1)). Poor early season rainfall and fungus attacks resulted in low chickpea yields (200-320 kg ha(-1)) and statistically insignificant differences between tillage methods. Overall results of the study suggest that on slopes below 8% gradient oxen-drawn ridge tillage and subsoiling, to a lesser degree, can effectively improve conditions that mitigate impact of short dry spells especially during seasons with less intense rainfall events. (c) 2007 Published by Elsevier B.V.