Response of Rice to Phosphorus and Potassium Fertilization Based on Nutrient Critical Levels in Plants and Soils of Kilombero Valley

Phosphorus (P) and potassium (K) optimization is crucial for achieving high yields of rice. This study objective was to establish optimum rates and critical concentrations of P and K in soil and rice shoots using soils from Kilombero district, Tanzania. Two-screen house experiment was carried out from December 2013 to May 2014 at Sokoine University of Agriculture (SUA), each using 10 soils collected from different sites in Kilombero valley. The first experiment had varied levels of P, namely 0, 40 and 80 mg kg-1 soil and the second with varied levels of K, namely 0, 200 and 400 mg kg-1 soil. Absolute control treatment was included in both experiments. Rice (variety TXD 306) was grown in pots arranged in a randomized complete block design with three replications. The results showed that soil critical concentration of P was 8.0 mg kg-1 and the shoots- P critical concentration was 0.16%. Established critical concentration of K in soil was 0.2 cmol (+) kg-1 and the shoots- K concentration was 1.4%. Grain yield increased significantly for rice grown in seven and six out of ten soils tested due to an application of P and K, respectively. The study recommends 40 mg P and 400 mg K kg-1 soil as optimum rates for P and K fertilization, respectively in deficient soils, under screen house conditions. A study revealed that eight and nine out of 19 studied soils from Kilombero are deficient in P and K, respectively for rice production. It was concluded that P and K are yield-limiting nutrients and their applications and management are crucial in the paddy soils of Kilombero valley.