field experiment was conducted to study the effect of organic wastes used as soil amendment and
two rates, 312.5 and 625 kg/ha, of 15-15-15 formula chemical fertilizer on soil properties and yield of cassava grown
on Yasothon soil. In this, a split plot of Randomized Complete block design with four replications was employed.
Main plot consisted of organic soil amendments such as no soil amendment (control, T1), 200 kg/rai of cassava stem
base biochar (T2), 6.25 t/ha of cassava starch waste (T3), 6.25 t/ha of cassava peel (T4) and 6.25 t/ha of tails and
stalk (T5). Chemical fertilizer was applied in sub plot of cassava at four months of age. The higher rate of fertilizer
significantly gave higher starch yield (31.3 t/ha) and above ground biomass (9.1 t/ha) than the one with lower rate.
With no statistical differences, cassava yield tended to increase whereas starch content tended to decrease with
increasing amount of chemical fertilizer. Cassava tails and stalk was likely to be the most suitable soil amendment for
increasing cassava yield in this soil, especially when used with the addition of 625 kg/ha 15-15-15 formula chemical
fertilizer, potentially giving the highest fresh root and starch yields of 34.6 and 10.4 t/ha, respectively. Tails and stalk
reduced acidity more effectively than did other soil amendments, particularly when applied with the higher rate of
chemical fertilizer as the soil significantly had the highest soil pH of 6.07. Cassava peel significantly promoted the
highest soil cation exchange capacity of 3.12 cmolc
/kg whereas other soil amendments had no different effect from
the control on this soil property, having values in the range between 1.50-1.66 cmolc
/kg.
Keywords: fertilizer, cassava starch waste, cassava peel, tails and stalk, biochar