Response of Soil Chemical Properties, Performance and Quality of Sweet Potato (Ipomoea Batatas L.) to Different Levels of K Fertilizer on a Tropical Alfisol

The optimum rate of nutrient must be defined with reference to soil properties for individual crops and soil.

Field experiments were carried out in 2015 and 2016 cropping seasons to determine the various levels (0, 40, 80, 120 and 160 kg ha^-1) of potassium fertilizer (muriate of potash , KCl), on soil chemical properties, leaf nutrient contents, performance and proximate quality of sweet potatoes (Ipomoea batatas L.).

The five treatments were arranged in a randomized complete block design with three replicates.

Studies showed that K fertilizer in both the years significantly influenced N, P and K concentrations compared with the control and also increased the soil concentrations of these nutrients from 0 - 160 kg ha^-1 K fertilizer. However, soil K only increased up to 80 kg ha^-1 fertilizer after which there was a decrease. There was a reduction in the values of Ca and Mg in the soil as the levels of K increased. Leaf nutrient concentration of the sweet potato was consistent with the values of soil chemical properties recorded. 80 kg ha^-1 K fertilizer was observed to be the highest value of sweet potato growth and tuber yield after which there was a reduction. The yield decrease was adduced to excessive K application leading to imbalanced sweet potato plant nutrition compared with N, P, Ca and Mg. K fertilizer significantly influenced moisture, vitamin C and carbohydrate compared with the control. The highest values of fibre and protein were obtained at 80 and 40 kg ha^-1 K fertilizer, respectively. Dry matter and fat contents of the sweet potato reduced by K application from 0 - 160 kg ha^-1 application rate.

For best tuber yield, quality and economic response of K fertilizer to the sweet potato in the agro-ecological zone or in other similar soil conditions elsewhere in the tropics could be achieved by applying 80 kg ha^-1 K fertilizer.