Vertisols in the Ethiopian Highlands: Interaction between Land Use Systems, Soil Properties, and Different Types of Fertilizer Applied to Teff and Wheat

Vertisols are among the most extensive soil types in the Ethiopian highlands, occurring in a wide range of agro-ecological zones where complex crop-livestock-based farming systems are practiced. Sustainable soil management on vertisols always meets with physical characteristics that are driven by clay mineralogy, swelling, shrinking, and risk of temporary waterlogging. The latter causes substantial spatial variability and turns vertisols into obnoxious study material, when compared to other soil classification orders. In this study, we have explored soil properties across different farming systems using soil profile and analytical data generated by the CASCAPE project; an action research project funded by the Dutch government for capacity building on the scaling up of evidence-based best practices for increased agricultural production in Ethiopia. In addition, the effects of variations in vertisol properties on crop yield and fertilizer response were examined through fertilizer trials in different locations. Teff (Eragrostis teff Zucc.) and wheat (Triticum aestivium), the two cereal crops commonly grown on vertisols, were used as test crops. Five treatments of NPSZnB-nitrogen, phosphorous, sulfur, zinc and boron containing blend (50, 100, 150, 200 and 300 kg/ha)-and two treatments comparing NPS and diammonium phosphate (DAP) with the blend containing Zn and B were included in a randomized complete block design with three replications. Results revealed that soil quality was generally poor under the highland cereal systems, i.e., sorghum-teff-livestock mixed system (FS1) and wheat-maize-teff-barley-livestock system (FS2) compared to the enset-coffee-cereal-livestock complex system (FS3), which cannot only be attributed to geological history, but also to the way the land use systems have shaped the soils. The emerging differences in soil properties significantly (p < 0.01) affected crop yields. The soil properties that had the largest influence on teff and wheat yield were soil pH, organic carbon (OC), available sulfur (S), exchangeable potassium (K) and some micronutrients (B, Fe, Mn and Cu). Teff grain and biomass yield were inversely related, unlike wheat. Regarding the rate of fertilizer application, wheat responded significantly up to the highest level (300 kg/ha), but teff yield leveled off earlier. The blend fertilizers did not perform any better than NPS or DAP alone. Given the extent and the importance of vertisols in Ethiopian agriculture, comprehensive future outlooks are needed, including the options for cluster farming and mechanization to realize economies of scale and more efficient use of capital and labor inputs.