Isotherm Derivation Of Optimum Potassium Fertilizer Dosages For Maize Farming: Matungulu Sub-County, Machakos, Kenya

ABSTRACT 

Population increase in Matungulu Sub-County in Kenya has led to pressure on arable land where agriculture is the main economic activity. This has caused a gradual shift in land use practices over the years from extensive to intensive agriculture. There has been a decrease in maize yields over the years despite the use of phosphate (P) and nitrogenous (N) fertilizers, which may suggest that the levels of potassium (K) in the soil may be low. Fertilizer application for maize farming in Kenya has been reported to be 12 bags per hectare compared to the recommended 50 bags per hectare. This study sought to determine concentration levels of potassium, organic carbon, phosphorus, nitrogen and soil pH of composite soil samples from five farms. Five composite soil samples were collected at depths of between 0-30 cm from five selected farms that have been consistently under intensive cultivation. Fractionation of potassium was done by sequential extraction of soil samples with distilled water, ammonium acetate and nitric acid. Concentration levels of potassium in the extract were determined using a flame photometer. From potassium concentration levels, thermodynamic parameters were determined. pH meter, colorimeter, nitrogen analyzer, flame photometer, and Bray-1 extractable were used to determine the levels of soil pH, organic carbon, nitrogen, potassium and phosphorus respectively. The relationship between the adsorbed and equilibrated potassium concentration, quantity/intensity were determined by plotting suitable adsorption isotherms. The isotherms were in turn used in determining the buffering capacity of potassium and the concentration levels of potassium adsorbed on non-specific sites in the soil. The basic soil fertility indices were found to be below their critical values except phosphorus. It was also established that the optimum potassium dosage for growing maize in Matungulu sub-County is 4.25 mg/L which was achieved by adding 95mg per kilogram of soil. Potassium concentrations in roots straw and grain were found to be 114.26, 450.28 and 3.034 mg/kg respectively. The soils were found to be acidic despite having sufficient calcium and magnesium above critical levels. They were also found to lack basic soil fertility indices. In view of this findings that soils in Matungulu are highly deficient of potassium, farmers should be advised to incorporate potassium rich fertilizers in their farming. They should also be encouraged to prepare composite manure using maize straws grown in potassium rich soils in order increase high crop yields.