Effects of Organic Amendments and NPK on Soil Chemical Properties in Kano Plains, Kisumu, Kenya

Agricultural lands in many parts of the world are threatened by soil degradation as indicated by their declining soil organic matter, loss of fertility, and low productivity. Organic amendments have the potential to alter the soil’s chemical characteristics as they can change the biotic and abiotic properties of the soil. The effect of six organic amendments applied each at 8.33 t/ha on the soil chemical characteristics, compared to NPK fertilizer applied at 250 kg/ha was investigated. The experiment was conducted at the Great Lakes University of Kisumu’s agricultural farm at Kibos in Kenya. To determine the effect of the organic amendments on the soil’s chemical characteristics, soil samples were collected once before the application of the organic amendments (initial) and thereafter at the end of every season. The results showed that the organic amendments affected the soil chemical properties. Compared to NPK fertilizer treatment, soil treated with organic amendments showed pH ranges (5.76 to 6.04) above that resulting from NPK application (5.59). All composts increased soil organic carbon (133, 298, 192 and 185%) for Boom Max, Ecoplanting, Evergrow, and Filter mud respectively compared to the initial levels. The total nitrogen was also increased to levels between 0.14 to 0.18 cmol/kg as compared to that of NPK treated plot (0.15cmol/kg), indicating close similarity. Available phosphorus increased by the application of Boom Max, Evergrow, Filter mud and Market waste slurry by 24, 44,39 and 1022% over the NPK effect, while exchangeable potassium increased by 9.5 and 24% by Evergrow and Market waste slurry over the effect of NPK. Exchangeable calcium increased by all the applied organics but only Evergrow and Market waste slurry exceeded that produced by NPK by 7.0 and 18.6% respectively. Likewise, all amendments increased soil exchangeable magnesium except dung slurry, but only market waste slurry exceeded that produced by NPK by 28%. All the amendments increased the cation exchange capacity compared to the original soil CEC but only Evergrow, Filter mud and Market waste slurry raised the soil’s CEC beyond that affected by NPK by 5.5, 10 and 40% respectively.