Sulphur and Zinc Fertilization Effects on Growth and Yield Response of Rice

Information on critical concentration and optimum rates of fertilizers is very important in the correction of sulphur (S) and zinc (Zn) deficiencies. A study was carried in the screen house experiments to establish optimum rates and critical concentrations of sulphur and zinc in both soil and rice shoots using soils of Kilombero district, Tanzania. Two experiments were conducted, one with varied levels of S and the other with varied levels of Zn. The treatments were absolute control for both experiments, three levels of S namely 0, 20 and 40 mg kg-1 soil and three levels of Zn namely 0, 5 and 10 mg kg-1 soil. Rice (variety SARO-5) was grown in pots arranged in a randomized complete block design with three replications. The results indicated that soil critical concentration of S was 10.0 mg kg-1 and the S critical range in rice shoots was 0.18 to 0.25%. Established critical level of soil Zn was 1.4 mg kg-1 while the Zn shoots critical concentration was 22 mg kg-1. Grain yield was significantly increased for plants grown in eight and three out of ten soils tested due to an application of S and Zn, respectively. Rates of 20 mg S and 5 mg Zn kg-1 soil were optimum rates for soils with low S and Zn, respectively. The results indicated that 17 and 6 out of 19 studied soils of Kilombero had S and Zn concentration below the critical level, respectively. It was concluded that sulphur deficiency was widely spread and its application and management is crucial, while Zn deficiency was an emerging problem in the paddy soils of Kilombero valley.