Combined Use of Organic and Inorganic Fertilizers Improved Maize (Zea mays) Yield and Soil Organic Carbon Stock in Lowland Dry Areas of Ethiopia

Abstract

Organic fertilizers can improve soil organic matter and enhance the productivity of agricultural soils. Ten treatments consisting of various combinations of vermicompost (VC) or bioslurry compost (BSC) with Urea as sources of recommended N rate, were evaluated to determine the best combination of organic and Urea fertilizers for maize production and soil organic carbon (SOC) stock. The treatments, laid down in randomized complete block design with three replications, were evaluated on fixed-plot during 2020-2022 cropping seasons in Melkassa Agricultural Research Center. Analysis of variance revealed significant (P<0.05) seasonal and treatment differences. The combined application of N equivalence-based 25:75 VC to Urea demonstrated significantly higher above-ground biomass yield. Comparable grain yield was obtained for combined application of VC or BSC with Urea in various proportions as compared to entire application of recommended N rate from Urea. This was in contrast to application of the entire recommended N rate solely from organic sources. Application of organic sources, either alone or in different combinations with Urea, resulted in a 12-14% enhancement in SOC stock compared to using inorganic fertilizer exclusively. Partial budget analysis indicated the highest net benefits (ETB 228,284.1 per ha) and Marginal Rate of Return (MRR=1049.9%) for N equivalence-based 25:75 VC to Urea combinations followed by the entire N application from urea. Thus, combined use of organic and inorganic fertilizers is advised not only for yield improvements but also for their added benefits for soil health and climate change adaptation that are not accounted in the current economic analysis.