Agronomic and Economic Efficiency of Manure and Urea Fertilizers Use on Vertisols in Ethiopian Highlands

Soil fertility depletion is among the major impediments to sustained agricultural productivity especially in the less developed countries because of limited application of fertilizers. Soil fertility maintenance requires a balanced application of inorganic and organic nutrient sources. This study was conducted on a Vertisol in Ethiopia to determine the optimum farm yard manure (M) and nitrogen (N) application rates for maximum return under cereal-pulse-cereal rotation system. The main and interaction effects of M and N significantly affected biomass, grain and straw yields of wheat (Triticum durum) and tef (Eragrostis tef), but the residual effect on chickpea (Cicer arietinum) was not significant. Application of 6 t M ha−1 and 30 kg N ha−1, gave the largest grain yield of both crops but a comparable result was obtained due to 3 t M ha−1 and 30 kg N ha−1. The economic analysis revealed that 6.85 t M ha−1 and 44 kg N ha−1 for wheat, and 4.53 t M ha−1 and 37 kg N ha−1 for tef were the economic optimum rates. The additional benefit obtained due to these rates was about 450 USD ha−1. Therefore, application of the economic optimum combination of both organic and inorganic sources of nitrogen is recommended for use on cereals in the cereal-legume-cereal rotation system.