Agronomic and economic benefits of primary and secondary micronutrients in selected fertilizer applications in rice production in Uganda

Two sets of trials were conducted during 2020 and 2021 in Amuru sub-county, Amuru District with the following objectives: Set 1 – to determine which secondary and micronutrient limit rice yield; and Set 2 – to compare the yield and economic benefits of applying rice specific NPK blend to application of NP as DAP and urea. Each farmer had one replicate, with other farmers serving as replications. There were 10 to 15 farmers per trial per season. There was a significant increase at p < 5% in grain yield of 2.6 t ha-1 above the control (1.7 t ha-1) with application of a combination of NP with K, Ca, Zn, B and Cu. Omitting either K, Ca, Zn, B or Cu on average resulted in a significant decrease in grain yield (0.74 t ha-1 vs. 4.3 t ha-1 - when all the nutrients were applied) at p < 5% level. The net benefit of adding K, Ca, Zn, B and Cu to NP was Uganda Shillings 1,602,000/=, 739,000/=, 834,315/=, 906,189/=, and 1,057,603/=, respectively. There was a significant increase in rice yield of 1.5 t ha-1 with a benefit to cost ratio of 2 with application of (125 kg DAP + 125 kg urea) ha-1 compared with 2.3 t ha-1 and a B/C of 2.3 with application of (250 kg rice specific NPK + 125 kg urea) ha-1, confirming that rice specific fertilizers are better than application of NP only. The study confirms that micronutrients limit crop yield in Uganda and should be included in balanced fertilizer formulations. Rice specific fertilizers are better than urea and DAP fertilizers recommended by MAAIF.