Nutrient cycling in sugarcane. V. Potassium balance during four cropping periods

Abstract

The balance of K in 12 field plots equally fertilized with K, 83 kg/ha per cycle, was followed by determining periodically plant and soil extractable K. For plant-cane, inputs of K in rain water and outputs through deep drainage were measured. During this cycle, fertilizer inputs and decreases in extractable K did not compensate K absorption by plants (174 kg/ha). Of this amount, 88 kg/ha were exported by the canes, 77 kg/ha returned to the soils as ashes and 9 kg/ha remained in the below-ground biomass. Deep drainage losses, 7 kg/ha, were overcompensated by rainwater input, 18 kg/ha. Potassium absorption by the ratoons was smaller than inputs from fertilizer and ashes. For the four cycles, a favorable balance of fertilizer inputs (332 kg/ha) versus cane outputs (170 kg/ha) resulted in increases in ashes (117 kg/ha) plus soil extractable K (66 kg/ha). The K balance in the soil would be closed considering the release of 28 kg/ha of K by the non-exchangeable fraction.