Effect of organic and inorganic ammendments on soil chemical and maize yield characteristics in Zimbabwe

Performance evaluation of five treatments on soil chemical characteristics and yield of maize was carried out in Lower Gweru, Zimbabwe. The treatments were gypsum, mopane ash, green manure, combined gypsum and green manure (green manure + gypysum) and an unamended control treatment. The treatments were set up in a complete Randomised Block Design (CRBD) with five blocks and slope was used as the blocking factor. Results indicate that a combination of gypsum and green manure and gypsum do not differ significantly in reducing excessive sodium (Na+), pH, sodium absorption rate (SAR) and exhangeable sodium percentage (ESP). The combination of green manure and gypsum was the most effective in reducing Na+ (36%), SAR (79%), ESP (37%) and increased maize yield to 2 t/ha (122%). Green manure reduced Na+, pH, SAR and ESP by 15, 7, 68 and 15%, respectively and increased electrical conductivity (EC) and yields by 147 and 100%, respectively. Mopane ash significantly reduced SAR and ESP by 65 and 12%, respectively whilst increasing EC and yield by 166 and 55%. Although Mopane ash reduced Na+ to 8.1 and pH value to 8, the reduction was not significantly different from the control. A combination of gypsum and green manure, and green manure and Mopane ash cost effectively improved some soil characteristic and yield of maize when used to amend sodic soils in lower Gweru Zimbabwe. Amongst these amendments, a combination of gypsum and green manure outperformed the other amendments in improving maize yield.