RESIDUE MANAGEMENT EFFECTS ON SUGARCANE YIELD AND SOIL PROPERTIES IN NORTHEASTERN BRAZIL

Sugarcane (Saccharum spp.) production systems commonly include preharvest or postharvest burning to dispose of residue. In northeastern Brazil, no-burn mulching practices are being introduced as a labor-intensive but environmentally more friendly alternative. We examined the effect of burning crop residues on sugarcane yield and C, N, and P cycles. Carbon, N, and P losses during preharvest burning were measured for a sugarcane first ratoon crop. Postharvest burn and mulch treatments were compared for a plant crop grown on an Oxic Haplustult soil. During the preharvest burn of the first ratoon crop, 2600 kg C ha-1, 17 kg N ha-1 and 1 kg P ha-1 were lost by convection. The postharvest burn of the plant crop residue resulted in losses of 4800 kg C ha-1 and 42 kg N ha-1; P losses were undetectable in the burn. The postharvest burn of the plant crop residue had no significant effect on total C or NH4-N plus organic N in soil during the first ratoon crop cycle. Soil pH in the top 7.5 cm layer of soil did not change after the postharvest burn, but increased 1.1 units in the top 1-cm layer. In the unburned mulch treatment, the litter layer did not reduce tillering or N and P uptake. Harvestable cane yield of the first ratoon crop was 17 Mg ha-1 (wet wt.) greater in the mulch than the burn treatment (54 vs. 37 Mg ha-1). This yield response was attributed to increased soil water retention and reduced weed growth under the mulch. In this short-term trial, mulching proved to be an alternative to the traditional burn system.