Complementary effects of organic and mineral fertilizers on maize production in the small holder farms of Meru South district, Kenya.
Mutegi, Edwin Mwiti
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The Central highlands of Kenya are generally densely populated and declining land productivity has been a major problem facing the smallholder farmers in the region. This is mainly attributed to the mining of nutrients due to cropping without external addition of adequate nutrients coupled with small land sizes which promotes continuous cropping with limited scope for crop rotation and inadequate soil fertility replenishment. With this background, a study was conducted on the Humic Nitisols in Mucwa location, Meru South District in a complete randomized block design (CRBD) with ten treatments replicated thrice. The general objective of the study was to determine the levels of complementarities between organic and mineral N amendments on maize production. The specific objectives included determination of the influence of organic and mineral N sources on soil chemical properties, maize grain yields, N uptake and to economically evaluate their .profitability. The results obtained revealed that the general soil fertility parameters changed slightly with calcium, magnesium and potassium increasing in all treatments. The organic carbon and total nitrogen was higher in treatments that received sole organic N sources than in sole mineral N and a combination of organic and mineral N sources. The highest maize grain yield of 4.8 t ha-1 and 4.2 t ha-1 were realized from sole application of calliandra during the 2005 short rains and 2006 long rains cropping seasons. The maize grain yield obtained in the organics and/or mineral N soil amendments was higher than the yields obtained where the recommended mineral fertilizers were used alone. Results obtained indicated that the use of either organic or combined organic/mineral N soil amendment were superior to- using mineral N amendment sources alone. The nitrogen (N) concentration in different parts of the maize crop varied, with the grain having the highest N concentration, followed by the stover during the 2005 short rain season. Sole application of calliandra recorded the highest N uptake (170.8 kg N ha") while the control gave the lowest (49.31 kg N ha"), The results on the average benefit-cost analysis was in the order of calliandra > tithonia > manure> Tithonia + 30 kg N ha-1 > calliandra + 30 kg N ha-l> manure + 60 kg N ha-l > 60 kg N ha-l > control> 30 kg N > 90 kg N ha". From the study findings, it's concluded that organic and/or mineral N fertilizers replenish nutrient deficiencies, enhance crop yields with improved N uptake and concentrations than sole mineral N inputs. This is an indication of improved soil properties and less N losses from the soil-plant systems. The organic and/or mineral N sources are also more economically profitable investment amongst the smallholder farmers within the study area.