Abstract:
Decline in soil fertility has been found to be the main cause of low rice yields in many soils of Tanzania. The objective of this study was to evaluate the effects of N, P, K and Zn on their uptake by lowland rice (Oryza sativa, L.) grown in nutrient-deficient soils of Same district. Three bulk soil samples, which were low in some macro- and micro-nutrients, were collected from Kisiwani, Ndungu and Kihurio, and used for pot experiments. The response of rice (Oryza sativa, L., cv super SSD5) to N, P, K and Zn was assessed in a glasshouse experiment where plants were grown for 56 days. Plant samples were analysed for N, P, K, Ca, Mg, Zn and Fe after digestion with HNO 3-H20 2. The results showed that N, P and K increased uptake of each mineral nutrient by rice plants, in all the soils used. For example, N alone increased N uptake from 5.8 to 28.4, 8.3 to 37.0, and 3.6 to 14.2 mg/plant in Ndungu, Mbugani and Kimunyu soils, respectively. Zinc, in addition to N, P, and K, increased the nutrient uptake even further. The uptake of each nutrient applied was consistent with the increase in dry matter yields and nutrient concentrations in rice shoots reported earlier. It was thus confirmed that these soils were deficient in N, P and Zn. Iron was required in the Kisiwani (Mbugani) soils, which were severely deficient of this element.
