Profitability of Using Different Rates of Farmyard Manure and Potassium Fertilizer for Cassava Production in Bukoba, Missenyi and Biharamulo Districts, Tanzania

The resolution of using or not using a particular technology in crop production is governed by the profitability of that technology being used. A study was conducted in Bukoba, Missenyi and Biharamulo districts in the Kagera region during the 2018/19 and 2019/20 cropping seasons to determine the economic benefit of using different rates of farmyard manure (FYM) and potassium (K) fertilizer in cassava production. One village potential for cassava production was selected in each district for establishment of cassava trials. Three tillage methods [flat tillage, tied ridging and open ridging] and eleven fertilizer rates [FYM at 4 or 8 MT ha-1, N40P30 + K at 40, 80 or 120 kg ha-1, FYM at 4 or 8 MT ha-1 + K at 40, 80 or 120 kg ha-1] and the control, were arranged in a Randomized Complete Block Design (RCBD) with three replications using a split-plot design. Tillage methods were the main plots and fertilizer rates were the subplots. Cassava yields (MT ha-1) were collected at harvesting (12 months after planting). Partial budget analysis was carried out to estimate the gross values using the adjusted yields at market price for cassava and fertilizers. Costs and benefits were calculated on a hectare basis, in Tanzania Shillings (TShs) ha-1, and converted to USD ha-1 based on the prevailing exchange rate of 1 USD, equivalent to 2 300 TShs. All variable costs were summed up to total variable cost (TVC). The net benefits (NB) [gross benefit (GB) - TVC] ha-1 of the tested treatments were calculated and used to assess the profitability of each treatment. Moreover, the benefit-cost ratios (BCR) [net benefit ÷ TVC] of the tested treatments were compared to the acceptable value of greater than 2 for the technology to be adopted by farmers. The results indicated that in both cropping seasons, and in all studied sites, all the tested fertilizer types and rates gave acceptable BCR of greater than 2, implying that all the fertilizer types and rates could be used for cassava production in the study area. The results on net benefit indicated that the combined use of FYM at 8 MT ha-1 and potassium fertilizer at 80 kg K ha-1 gave higher net benefit (3 020 500 – 9 168 000 TShs ha-1 (1 313.3 – 3 986.1 USD ha-1) than the other fertilizer types and rates (1 915 000 – 9 024 500 (832.6 – 3 923.7 USD ha-1) and is therefore, desirable for increasing cassava root yield and net benefit. However, for the resource-poor farmers, the combined use of farmyard manure at 8 MT ha-1 and potassium fertilizer at 40 kg K ha-1 can still be adopted because, for some reason, not all the famers can afford the best treatment.