N-NH3 losses from nitrogen sources applied over unburned sugarcane straw

Where sugarcane is harvested without burning, a thick layer of straw remains on the soil. This crop residue modifies the agroecosystem and requires a reformulation of the crop management. Urea is the most common nitrogen source for sugarcane but, when applied on top of the crop residue, NH3-N loss rates are high. This work was carried out under field conditions in the sugarcane production region of Piracicaba, State of Sao Paulo, Brazil, on an Arenic Kanhaplodult, using the third rattoon of the variety SP 80-1842, harvested mechanically without previous burning. The objective of this study was to evaluate the agronomic efficiency of nitrogen sources applied over sugarcane trash by the determination of NH3-N losses by volatilization, crop yield and quality. The nitrogen rate was 100 kg ha(-1). The experimental design was in completely randomized blocks with five replications and five treatments: T0- control, T1- urea, T2- uran, T3- urea + ammonium sulfate, T4- liquid residue enriched with N. Static semi-open NH3 collectors were used to evaluate losses by ammonia volatilization. The results showed that NH3-N losses were higher in T1 and T3 (36 and 35 %, respectively), and lower in T2 and T4 (15 and 9 %, respectively). Sugarcane yields were affected by the nitrogen fertilization as well as by volatilization losses.