Potential use of burnt rice husk to substitute for potassium applied for cassava grown in a low K-reserve soil

Abstract

Importance of the work: Burnt rice husk (BRH), a valuable organic amendment that contains high potassium (K), can be a low-cost, alternative source of K for cassava in low K-reserve soils.
Objectives: To investigate the growth, yield and nutrient uptake of cassava in response to the application rate of BRH and K-fertilizer.
Materials & Methods: A field experiment was conducted in a K-deficient sandy soil based on a split plot design with fours levels of BRH applied (0 t/ha, 6.25 t/ha, 12.5 t/ha or 25.0 t/ha) in the main plot and six levels of K fertilizer (0 kg K₂O/ha, 25 kg K₂O/ha, 50 kg K₂O/ha, 75 kg K₂O/ha, 100 kg K₂O/ha or 125 kg K₂O/ha) in the subplot.
Results: The fresh tuber yield (FTY) obtained from the control plot was not significantly different from the plots added with a sole application of BRH or K fertilizer at all rates; however, BRH significantly increased soil K availability. Across all combined rates of BRH and K fertilizer, cassava produced significantly greater FTY by 62.6–170% over the control, where the highest yield was from the plot amended with 12.5 t/ha BRH and 100 kg K₂O/ha. The use of 25.0 t/ha of BRH together with K fertilizer reduced the uptake of Mg and Ca, resulting in a significant adverse decrease in the FTY. There was no clear interactive impact of BRH and K fertilizer on the starch yield and aboveground biomass, though it did stimulate the uptake of some plant nutrients.
Main finding: BRH application increased soil K and partially substituted for applied K in cassava growth; however, K fertilizer was still required when BRH was applied at a low rate (less than 12.5 t/ha).