Abstract

The yield of upland rice (Oryza spp.) per unit area of production in Uganda is low, partly due to low soil fertility, and use of fertilizer and manure is also low. Trials to establish the response of upland rice to applied nutrients and economically optimal nutrient rates (EOR) were determined at Tororo, Kawanda and Kadesok. The increase in paddy yield was in the range of 91 to 173% with application of 50 to 120 kg N ha-1. Application of 10 kg P ha-1 and 20 kg K ha-1 resulted in a 10 to 46% additional increase, respectively. Nitrogen application was profitable for all cost of fertilizer to farm-gate price of produce (CP) ratios, with a three season mean economically optimum nutrient rate (EONR) ranging from 67 to 144 kg ha-1 and CP ratios varying from 2 to 12. Application of 10 kg P and 20 kg K ha-1 together with N reduced the mean EOR to a range of 47 to 97 kg ha-1 depending on the CP ratio. Application of Zn, S, B and Mg together with nitrogen, phosphorus and potassium fertilizer (NPK) increased paddy yield by 19% above the NPK yield of 3.7 t ha-1, indicating that either Mg, S, Zn and B or their combination limit rice production in Uganda. Trace elements were applied as a mixture. There is a need to establish which element limits rice production in addition to the economics of their use. This information is required for fertilizer blending in the region to produce blends of the right formulation. The cost of fertilizers increases with the nutrients applied, which has an implication for the appropriate quantity of fertilizers to be used. To reduce or stop soil degradation from nutrient mining requires interventions at policy level such as fertilizer subsidies, improved market for produce and input supply efficiency, and increased access to extension, information and credit by farmers.

Key words: Economic, fertilizer use, nitrogen, phosphorus, potassium, trace elements, secondary elements.