Abstract
The great difficulty of incorporation of N fertilizers into the "green sugarcane" system causes concern and since urea is the most commonly used source, there is the risk of loosing NH3 through volatilization. For this reason, a field experiment was undertaken (in a Hapludox Typic) with the objective of evaluating the agronomic efficiency of ammonium chloride on stubble of the second ratoon (SP89 1115), as well as its residual effect on the subsequent cycle (third ratoon). The experimental design was randomized blocks with four replications. Treatments consisted of three N rates (60, 120 and 180 kg ha-1 N) in the form of NH4Cl, in addition to a control treatment without the addition of N fertilizer. The ratoon cane of the second cutting was harvested in November 2006 and the treatments were applied in December 2006. The second ratoon was harvested mechanically in November 2007 and in December 2007, 450 kg ha-1 of the NPK mixture 20-05-19 was applied, providing 90, 22 and 86 kg ha-1 N, P2O5 and K2O, respectively, for the purpose of evaluating the effect of residual-N from the treatments implanted in December 2006. An increase in the rates of N-NH4Cl had a positive effect on the leaf concentrations of P, Mg and S. Stalk yield (MSS - Mg ha-1 of sugarcane stalks) and sugar (MSH - Mg ha-1 of sucrose) in the November 2006 harvest responded linearly to the increase of N doses in the form of NH4Cl. In relation to the effect of residual-N in the 2007/2008 harvest, it was observed, in general, that the concentrations of macronutrients in the sugarcane leaf +1 were within the range considered adequate in the state of São Paulo, Brazil. The residual-N of the NH4Cl doses resulted in a significant reduction in stalk (MSS) and sugar (MSH) production. It may be concluded that the NH4Cl source at a dose of 120 kg ha-1 N in ratoon fertilization of the second cutting was agronomically efficient, presenting, however, less efficiency of residual-N in the subsequent cycle.
Highlights
The changes in the sugarcane harvesting system, from the former straw removal by burning to mechanically harvested “green cane”, are an irreversible process foreseen in the legislation of the sugar-alcohol sector
The difficulty of fertilization is increased, due to the need of incorporating the fertilizers during cultivation, especially in the case of sugarcane harvested mechanically without straw removal, where a significant quantity of residues (10 to 30 Mg ha-1) is left on the soil surface (Franco et al, 2007). This difficulty causes concern, bearing in mind that urea is the fertilizer used in greatest quantity for being inexpensive, increasing the risks of N-NH3 losses through volatilization when applied to strawcovered soil surfaces
The sugarcane cultivar used was SP89 1115 and the soil classified as a Typic Hapludox, with the following chemical properties in the arable layer (0–25 cm): pH (CaCl2) = 4.4; SOM (g dm-3) = 32.3; P resin = 11.7; S-SO4 = 50.3; K = 1.8; Ca = 20; Mg = 9.7; H + Al = 69; Al = 5; SB = 31.5; CEC = 101 and V % = 31
Summary
The changes in the sugarcane harvesting system, from the former straw removal by burning to mechanically harvested “green cane”, are an irreversible process foreseen in the legislation of the sugar-alcohol sector. These changes represent advantages with regard to soil conservation, moisture retention and nutrient recycling, among others. The difficulty of fertilization is increased, due to the need of incorporating the fertilizers during cultivation, especially in the case of sugarcane harvested mechanically without straw removal (burning), where a significant quantity of residues (10 to 30 Mg ha-1) is left on the soil surface (Franco et al, 2007). The presence of straw covering the soil modifies the agrisystem, requiring a reformulation of the N fertilization management
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