Combined Use of Organic and Inorganic Nutrient Sources Improved Maize Productivity and Soil Fertility in Southwestern Ethiopia

Declining soil quality is among the factors leading to low crop yields in Sub-Saharan Africa. In this study, a 2 year on farm field experiment was carried out in Ethiopia to test whether integration of organic and inorganic fertilizer inputs increases soil quality, the nutrient balance and maize yields. Treatment combinations included 2 and 4 t ha(-1) of compost (Com) and farm yard manure (FYM), and 50 and 100% of the recommended inorganic fertilizer (RIF). The treatments were laid out on 11 farmer fields where each farm served as a replicate. About 40% yield increase was recorded due to the combined use of 4 t ha(-1) of Com along with 50% RIF compared to the 100% RIF. Soil quality was significantly improved in the top 20 cm of the soil due to application of FYM or Com combined with 50% RIF. Carbon and Nitrogen stocks were respectively 86 and 175% higher in the 4 t Com + 50% RIF compared to the control with no significant variation between farms. Further, the N and P partial balances were between 12.2 and 41.6 kg ha(-1) year(-1) and 10.2 and 17.4 kg ha(-1) year(-1) for N and P, respectively implying that the sites showed N and P-accumulations over the study period. Results suggest that nutrient depletion can be mitigated in smallholder systems through the use of locally available organic inputs, hence longer-term productivity of smallholders can be sustained.