Recycling sugarcane trash to conserve soil organic carbon for sustaining yields of successive ratoon crops in sugarcane

Abstract

Sugarcane trash, a crop residue constituting 10–20% of the weight of cane harvested, was either burnt, removed or retained as mulch in three successive ratoon crops in a field experiment conducted at Lucknow, India, during 1990–1994. Within three years, trash retained as mulch improved the soil organic carbon by 0·13% (on 0·55%), available N by 37 kg ha −1 and available P by 10 kg ha −1, thereby increasing the yield of the third ratoon crop by 1·9% of the yield of the first ratoon crop. On the other hand, trash burning reduced the organic carbon by 0·02%, available N by 15 kg ha −1 and available P by 16 kg ha −1, hence causing a 13·2% reduction in the yield of the third ratoon crop compared to the first one. In the second experiment, during 1992–1994, a first ratoon crop was grown with and without trash mulch in combination with N application at 0, 50, 100, 150, 200 and 250 kg ha −1 as urea (46·4% N). The optimum N dose, worked out from the quadratic response equation, with mulching was 230 kg ha −1 and without mulching, 241 kg ha −1. At optimum rates, yield response per kg of applied N was 328 kg with mulching and 263 kg without mulching. Mulching increased the N uptake and the apparent recovery of applied N by the crop by improving the soil organic carbon by 0·08% and decreasing the soil bulk density by 0·06 g cm −3, compared to no mulching. The concentration of NO 3 −N in the upper soil layer in both experiments increased due to trash mulching, compared to trash burning and no mulching.