Using crop simulation model to evaluate influence of water management practices and multiple cropping systems on crop yields: A case study for Ethiopian highlands

Low soil fertility, soil water stress and deteriorating natural resources are among the causal factors to low crop productivity in Africa. In this study, impact of cropping systems and water management practices on yield of different crops were simulated using the Decision Support System for Agrotechnology Transfer-Cropping System Model. The treatments included continuous cropping (monoculture) of three different crops [wheat, WT; barley, BA; chickpea, CP]; and rotation systems (WT-BA, and WT-BA-CP). Crops were treated with three different water management practices (a) rainfed; (b) tied ridging; and (c) irrigation. Five years (2013-2017) average actual yields were obtained and average short-term (2013-2017) and long-term (1984-2019) yield gaps, relative yields and yield changes were calculated. The yield gap (Yg) [the difference between actual (Ya) and simulated rainfed yield (Yw)] for wheat, barley and chickpea were 0.0 to 0.6, 0.1 to 1.7 and 0.2 to 2.1 Mg/ha, respectively. The large Yg value for chickpea was mainly attributed to the water stress. Whereas barley and wheat yield were less affected by the water stress when compared to chickpea. The rotation WT-BA-CP was more responsive to water management than WT-BA. Tied ridging or irrigations can be considered as an option for improving yield in water scarce areas. Chickpea fixed substantial amount of nitrogen (90-246 kg N/ha) in the soil, which could result in yield benefits and reduced use of inorganic nitrogen. Overall, the rotation WT-BA-CP may be a better option than WT-BA or continuous cropping as it can provide multiple benefits via enhanced crop diversity, improved soil fertility and more resilience to pest and diseases. This simulation case study and discussion of results showed the importance of integration of crop rotations with soil and water conservation practices for improving overall yields and contributions to ecological intensification.