Effect of Tillage Methods, Farmyard Manure and Potassium Rates on Cassava Yield and Root Quality in Kagera Region, Tanzania

Abstract

A study was conducted in Bukoba, Missenyi and Biharamulo districts in the Kagera region Tanzania during the 2018/19 and 2019/20 cropping seasons to determine the effect of tillage methods, farmyard manure (FYM) and potassium (K) rates on cassava yield and root quality. Three tillage methods (flat tillage, tied ridging and open ridging), 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 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. The plot size was 6 m x 5 m with a spacing of 1 m x 1 m. Root yield ha-1 was collected during harvesting and about 500 g of cassava roots from each treatment were oven-dried at 105 oC to constant weight for determining dry matter content using the equation by [31]. Root starch content in each treatment was determined using the method by [32]. The results indicate that cassava planted on ridges gave significantly (P <.001) higher cassava root yields (18.98 - 34.84 MT ha-1) than flat tillage (16.86 - 29.74 MT ha-1). The combined use of FYM at 4 MT ha-1 or FYM at 8 MT ha-1 and potassium fertilizer at 40, 80 or 120 kg K ha-1 significantly (P <.001) increased cassava root yield (14.56 - 39.94 MT ha-1) as compared to other fertilizer rates (8.90 – 29.63 MT ha-1). In addition, the combined use of inorganic N40P30K120 or the combined use of FYM at 8 MT ha-1 and potassium fertilizer at 80 or 120 kg K ha-1 gave significantly (P <.001) higher starch (28. 04 - 34.06 %) and dry matter (39.57 - 44.93 %) content in cassava roots than other fertilizer rates. Therefore, planting cassava on ridges and the combined use of FYM at 4 MT ha-1 and potassium fertilizer at 40, 80 or 120 kg K ha-1 is desirable for increasing cassava root yield. Moreover, the combined use of inorganic N40P30K120 fertilizers or the combined use of FYM at 8 MT ha-1 and potassium fertilizer at 80 or 120 kg K ha-1 is desirable for increasing the content of starch and dry matter in cassava roots.