UNISWA J. of Agric. Vol 14, 2006: 62-69
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Decline in soil fertility has been found to be the main cause of low rice (Oryza sativa L.) yields in many soils cropped to rice in Tanzania. The objective of this study was to evaluate the effects of N, P, K and Zn on shoot dry matter (DM) yields of lowland rice plants grown in some soils of Same district. Three bulk soil samples were collected from Kisiwani (Mbugani), Ndungu and Kihurio (Kimunyu), which were found to be deficient in some macro- and micro-nutrients following laboratory soil analysis, and were used for this pot experiment. The responses of rice variety, super SSD5 to N, P and K, as well as to different levels of Zn, were assessed in a glasshouse experiment where plants were grown for 56 days. The results showed that N, P and K increased rice shoot DM yields in all the soils used, from 0.61, 0.74 and 0.47 in the controls to 3.01, 2.76, and 1.57 g/plant in the highest N:P:K treatments in Ndungu, Mbugani and Kimunyu sites, respectively. It was further revealed that Zn supplementation in addition to NPK also increased rice dry matter yields further, from 3.05, 2.73 and 1.42 in the Zn controls to 4.75, 4.44, and 2.16 g/plant in the 15 kg/ha Zn treatments in Ndungu, Mbugani and Kimunyu sites, respectively. Iron (Fe) was also found to be deficient in Mbugani soils, and Fe supplementation improved plant growth. It is concluded that deficiency of these nutrients was probably a widespread problem in these and other soils cropped to rice in the district.