Evaluation of Soil Chemical Properties under Paddy Production System in Central Kenya: Soil Exchangeable Cations.

Lowland irrigated schemes contribute the most rice produced in Kenya. However, production is low and highly variable due to management problems. Production could be increased with appropriate soil management which requires that baseline fertility status of the soils and how they vary be known. This study examined the variability of selected soil chemical properties in the Mwea Irrigation Scheme in Central Kenya. Soil samples were collected from the top 0-15 cm depth in August 2013 and 2014 and analysed for pH, electrical conductivity (EC) and the exchangeable cations potassium (K+), calcium (Ca2+), magnesium (Mg2+) and sodium (Na+). Significant variability in soil EC as well as soil cation concentration was observed among units. Overall results showed soil pH ranged from 4.56 (very strongly acidic) to 8.05 (moderately alkaline). Soil EC varied from 0.17 to 1.52 dS m-1 with higher elevation areas recording lower values (< 0.50 dS m-1) and lower elevation areas recording higher EC values (> 0.50 dS m-1). On average, exchangeable Ca2+ was 38.17 cmolc kg-1, Mg2+ 23.80 cmolc kg-1, Na+ 1.24 cmolc kg-1 and K+ 0.35 cmolc kg-1. The soil exchange complex was mainly dominated by Ca2+ and Mg2+ and cation concentration in the soil was in the order Ca2+ > Mg2+ > Na+ > K+. Soil K is low and severe cation imbalances exist with regard to K+ and other cations thus making K+ deficient for plant uptake. Management practices and farming systems which enhance soil K status should be encouraged to help boost and sustain rice yield.