Effect of Organic Inputs and Mineral Fertilizer on Maize Yield in a Ferralsol and a Nitisol Soil in Central Kenya

Abstract

Declining land productivity is a major problem facing smallholder farmers in Kenya today. This decline primarily results from a reduction in soil fertility caused by continuous cultivation without adequate addition of external nutrient inputs. Improved fertility management combining organic and mineral fertilizer inputs can enable efficient use of the inputs applied and increase overall system’s productivity. Field trials were established at three sites in distinct agro-ecological zones of central Kenya (one site at Machang’a and two sites at Mucwa with different soil fertility status) aiming to determine the effects of various organic sources (tithonia, lantana, mucuna, calliandra and manure) and combinations with mineral N fertilizer on maize grain yield during four consecutive seasons. In Machang’a site, sole manure recorded the highest maize grain yield across the four seasons. In Mucwa poor site, sole tithonia gave the highest maize grain yield during the four seasons, while in Mucwa good site, sole calliandra gave the highest maize grain yields. Generally, the maize grain yields were lower in the treatments with fertilizer alone compared to the treatments with organics across the three sites in the four seasons due to the poorly distributed rainfall. In Machang’a during the SR 2004 and SR 2005 seasons, the treatments with integration of organic and mineral fertilizer inputs were significantly higher than treatment with the sole organics; however, in Mucwa good and poor sites, generally the treatments with sole organics did better than the ones with integration of mineral N fertilizer and organics with the exception of the mucuna treatment which did significantly better in the integration compared to the sole application.