Effects of Residue Management on Nitrogen Losses from Surface and Sub-surface Water in Sugarcane.

This study examined the effect of three different management plans of nitrogen losses from surface runoff and sub-surface water in sugarcane (Saccharum officinarum L.) fields for 3 years. Nitrogen losses of applied fertilizer and compost were evaluated from conventional, compost, and green cane trash blanket (GCTB) treatments. The conventional treatment was adapted as a burning GCTB after harvesting with the chopper harvester. The compost treatment was based on 5443 kg ha^-1 of compost (dry weight basis) applied at 8 weeks prior to planting and then every spring. The GCTB treatment was adapted GCTB raked off row top into wheel furrow within 10 days after harvest. Automatic refrigerated sampler (ISCO 3700FR) and flowmeter (ISCO 4230) with bubble sensors were installed nearby the H-flume which collected runoff. Pan lysimeters (66 cm by 71 cm) were installed horizontally under undisturbed soils at approximately 60 cm below the furrow to collect leachate. All of the runoff water and leachate samples were collected and TN, NO₃/NO₂-N, NH₄-N were measured. The concentration of TN and NO₃/NO₂-N in the compost treatment was significantly higher than the concentration from the conventional and the GCTB treatments. However, the means of TN and NO₃/NO₂-N from the GCTB treatment were not significantly different with the means from the conventional treatment. In the conventional treatment, there were 1.6, 2.6, and 5.7 times more losses with the burning procedure in TN, NO₃/NO₂-N, and NH₄-N, respectively. There were significant differences among the treatments in mean leaching losses by monthly consideration. On an average of 3 years, mean leaching losses in NO₃/NO₂-N were 0.36, 0.82, and 0.10 kg ha^-1 for the conventional, compost, and GCTB treatment, respectively. The annual surface runoff and leaching losses of NO₃/NO₂-N in GCTB treatment during the study were significantly reduced compared to the loss from the conventional treatment.