Abstract
Sugarcane (Saccharum spp.) harvested without burning provides a substantial amount of remains (trash) on soil profiles which can be decomposed and release nutrients contributing to reduce fertilizer needs. The contribution of nitrogen (N) from sugarcane plant residues and fertilizer in sugarcane nutrition was assessed. Plant cane treatments were micro plots of 15N-labeled urea, sugarcane trash and root system; the last two to simulate the previous crop residues incorporated into the soil after crop renewal. For ratoons, N-ammonium nitrate (N-AN) micro plots, 150 kg ha-1 of N-AN and control (0 kg ha-1) were set up to evaluate the contribution of trash in N supply and quantify the effects of N-fertilizer on N-trash mineralization. The N balances derived from each 15N source were calculated after four crops and resulted in: 15N-urea applied at planting, 31 % was recovered by plant cane, 12 % by the following ratoons, 20 % remained in the soil and 37 % was not found in the soil-system (NOC). For crop residues 15N-trash + roots 26 % was recovered by sugarcane, 51 % remained in soil, and 23 % was NOC. N-fertilizer applied to ratoons nearly doubled the amount of N from green harvest residues recovered by sugarcane; 17 vs. 31 %. Water balances and crop evapotranspiration were correlated with 15N-sources recoveries and cumulative N recovery presented a positive correlation with evapotranspiration (2005 to 2009). The 15N balances indicated that crop residues are supplementary sources of N for sugarcane and may contribute to reduce N fertilizer needs since trash is annually added to the soil.
Highlights
Sugarcane (Saccharum spp.) is a widely known bioenergy crop due to its large biomass production which liaise for global greenhouse gases (GHG) emission targets and benefits preservation of soil and water resources (Macedo et al, 2008).São Paulo State is the largest producer in Brazil, where more than 70 % of the overall sugarcane production is managed as green cane under trash blanket (GCTB) or without trash burning prior to harvest (Lucon and Goldemberg, 2010).The GCTB provides annually 5 to 20 Mg ha–1 of remains which contribute to increase soil carbon (C), organic matter (Dourado Neto et al, 2010) and to enhance soil physico-chemical and biological properties (Spain and Hodgen, 1994)
Plant cane treatments were micro plots of 15Nlabeled urea, sugarcane trash and root system; the last two to simulate the previous crop residues incorporated into the soil after crop renewal
The N balances derived from each 15N source were calculated after four crops and resulted in: 15N-urea applied at planting, 31 % was recovered by plant cane, 12 % by the following ratoons, 20 % remained in the soil and 37 % was not found in the soil-system (NOC)
Summary
Sugarcane (Saccharum spp.) is a widely known bioenergy crop due to its large biomass production which liaise for global greenhouse gases (GHG) emission targets and benefits preservation of soil and water resources (Macedo et al, 2008).São Paulo State is the largest producer in Brazil, where more than 70 % of the overall sugarcane production is managed as green cane under trash blanket (GCTB) or without trash (or straw) burning prior to harvest (Lucon and Goldemberg, 2010).The GCTB provides annually 5 to 20 Mg ha–1 of remains which contribute to increase soil carbon (C), organic matter (Dourado Neto et al, 2010) and to enhance soil physico-chemical and biological properties (Spain and Hodgen, 1994). Sugarcane trash can provide 40 to 120 kg ha–1 of N year–1 (Franco et al, 2010; Oliveira et al, 2002; Robertson and Thorburn, 2007b) and, on average, sugarcane trash contains 450 and 4.5 g kg–1 of C and N, respectively, a C:N ratio about 100:1.
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