Long-term effects of organic and mineral fertilizer application on physical soil properties and maize yield in western Kenya

Abstract: To evaluate the effects of long-term application of organic and mineral fertilizers on maize yield and soil properties and further to investigate differences in soil fertility gradients, the Tropical Soil Biology and Fertility Institute of the International Centre for Tropical Agriculture (TSBF-CIAT) conducted an 8- year experiment on 12 farms in the districts Nyalgunga, Nyabeda and Vihiga in the Western Province of Kenya. The study was designed as a split plot model where each farm was split into high and low fertility plots on which the following treatments were applied: T2 – no fertilizer application (control), T4 – application of farmyard manure (FYM) alone and T5 – combined application of FYM, Mavuno fertilizer and top dressing. In scope of this thesis the physical soil properties such as bulk density (BD), soil texture , infiltration rate (IF) and aggregate stability (AS) as well as the soil organic carbon content in the soil (OC) were determined. Further Crop Evapotranspiration (ETc) and Water use efficiency were analyzed. The ETc, varied between 2.34 and 4.84 mm/day and was highest during the development and late stage of the growing season. The rainfall was able to cover the water crop requirements of maize in all locations. Maize yield was highest at T5, followed by T4 and T2. Further, yield was strongly affected by the clay content and soil type and resulted in significant differences between the locations (Nyalgunga > Nyabeda > Vihiga). Other physical soil parameters (IF, BD, AS) did not influenced the maize yield. IF varied between 1.3 and 9.1m/day. BD was generally low with an overall mean of 1.16 g/cm³. The Aggregate stability was widely ranged and significantly higher in Nyabeda and on T4. OC was significantly higher on T5. The results indicated that mineral fertilizers contribute more to the increase of OC than organic fertilizers and that OC might not be the main driver of aggregation in tropical soils. AS seemed to be positive affected by organic fertilizers but IF and BD were not influenced by, nether organic or inorganic fertilizers. The results did not indicate any differences between high and low fertility plots, nether in maize yield nor in any of the physical soil properties.