Effects of intergrated soil fertility management and ridging on maize-soybeans yields and selected soil properties in Tharaka-Nithi County, Kenya
Sibomana, Jean Damascene
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Constraints to soil productivity include reduction in soil fertility and lack of adequate soil water conservation techniques due to erratic rainfall in central highlands of Kenya. This study evaluated effects of combining integrated soil fertility management options and tied- ridging on maize-soybean yields and selected soil properties during short rains in 2014 and long rains in 2015 seasons. The study was carried out in Kigogo primary school in Tharaka- Nithi County. The experimental layout was a randomized complete block design replicated 4 times. The treatments were: manure+fertilizer, tithonia+fertilizer, inorganic fertilizer, sole and control under tied ridging or conventional tillage. To evaluate effect of rotation on maize grain yield, 2 test crops: maize and soybean were alternated every season except sole maize treatment which was maintained throughout the trial period. Soil was sampled at 0-20 cm and 20-40 cm depths at the start and end of the study, and analyzed for soil pH, total N, available P, organic C and exchangeable bases. The data was subjected to analysis of variance using Genstat program and means were separated using Fishers’ LSD at p=0.05. Integrated soil fertility management technologies under soil water conservation tillage significantly increased both maize and soybean grain yields during short rains in 2014 (p≤0.037 and p≤0.039 respectively) and only maize grain yield during long rains in 2015 (p≤0.005). Further, tithonia+fertilizer and manure+fertilizer treatments under tied ridging significantly increased maize grain yields and soybean grain yields by 34.8% and 43.5% respectively compared to the control in long rains in 2015. Only tithonia+fertilizer under tied ridging increased significantly soybean grain yields by 57.1% over control in short rains in 2014. Maize grain yield also has increased under maize-soybean rotation by 35.5% over sole maize. The results showed significant decrease in soil pH, available P and total N in mineral fertilizer under tied ridging (p0.05). Soil exchangeable K + , Ca 2+ and Mg 2+ generally increased in most treatments. This study recommends use of combination of either tithonia biomass or manure with inorganic fertilizer under conventional tillage as well as crop rotation to enhance soil fertility and maize-soybean yields in the region.