Effects of NP Fertilisers and Manure Application on Maize-bean Yields, and Soil Nitrogen Mineralisation in Machakos County, Eastern Kenya

The inherent poor fertility of soils in Kenya constitute a major constrain to sustainable smallholders agriculture and more especially in arid and semi-arid parts of the country. The solution herein lies in the efficient use of nutrients and good management of soil moisture content. This study investigates the effects of manure and fertiliser application on maize-bean intercrop yields, fertiliser use efficiency, nitrogen mineralisation potentials and predicts the long-term soil fertility sustainability. The experiments are being conducted in the laboratory and in the field. Soils will be sampled from a layer of 0-60cm soil profile (0-20, 20-40, 40-6 cm soil depth) for soil physic-chemical and biological properties analysis. Soil sampling will be done at the start and end of each season for two seasons. Maize and beans will be planted as an intercrop in plots measuring 4.5x 4.5 m with a of spacing of 75 x 60 cm for maize and 20 cm for beans which will be planted between maize rows. NP fertilisers will be applied at three levels (0, 50 and 75 kg/ha), and manure at three levels (0, 5 and 10 ton/ha). P fertiliser and manure will be applied at planting while N fertiliser will be top-dressed four weeks after planting. Maize and bean grains will be dried after harvest and weighed at 12.5 % moisture content. Data will besubjected to analysis of variance using the general linear model of the SAS software. Treatment differences will be examined using Tukey-Kramer significant difference (HSD) test. Regression and correlation analyses between various variables will be done to show different interactions. Expected outputs of this study include improved crop yields, proper management of inputs, improved nutrient use efficiency and nitrogen mineralisation potential of the Katumani luvisols documented.