EFFECT OF DIFFERENT CROPPING OPTIONS ON PLANT-AVAILABLE WATER OF SURFACE-DRAINED VERTISOLS IN THE ETHIOPIAN HIGHLANDS

The productivity of the Vertisols in the Ethiopian highlands could be raised by facilitating the removal of excess water from the fields in the main rainy season. This could be accomplished by the introduction of an animal powered broadbed maker (BBM) which shapes the soil into b roadbeds and furrows. Thus with proper drainage, early sowing of crops becomes feasible. This study compared the plant-available water in th e soil layer and the water use efficiency of local wheat and eight oth er cropping options and also assessed the grain and fodder productivit ies. Replacing late-sown local wheat with an early-sown improved wheat variety (ET-13) improved the utilization of the plant-available water during the rainy season and significantly increased grain and straw y ields with a high rate of water use efficiency. The variations of the available moisture in the soil layer between the different cropping op tions tested were small during the rainy months of July and August due to the continuing replenishment of the used water. Differences of pla nt-available water in both upper and lower soil layers for the various cropping options became distinct at the onset of the dry season. Even though results showed that growing of a sequential crop, such as gras s pea, following wheat is possible with a starter irrigation in the dr y season, yields were generally depressed. (C) 1998 Elsevier Science B .V.