Nitrogen losses of applied urea in the soil-plant system during two sugar cane cycles

The objective of this work was to quantify the losses of N from the soil-plant system, in the cane plant and sugar cane ratoon-cycle. Two experiments were carried out in 220 L-pots filled with sandy soil. In the experiment with cane plant two factors were studied: two types of sugar cane crop residues incorporated in the soil and four doses of N applied as urea. In the experiment with sugar carte ratoon two forms of urea application on soil surface were studied: over the straw (trash) or uncovered soil, or at a depth of 15 cm, and two potassium sources: KCl or vinasse. Urea labeled with N-15 was used in both experiments. The experimental design was randomized blocks, with three replications. In the cane plant experiment, 12% of the N-urea applied was lost (recovery of 88%), due to denitrification. In the experiment with sugar cane ratoon, when urea was applied in the soil at 15 cm depth, recovery of the N-fertilizer was 81%, while 50% was recovered when urea was applied on the surface. Losses of 50% of the N-urea applied to soil surface were due to ammonia volatilization in the soil, and also to ammonia volatilization through the sugar cane foliage. When urea was applied at 15 cm depth, 19% of the N-urea was lost from plant tops to the atmosphere, being the total loss of N (from urea and other sources assimilated by sugar cane) equivalent to 90 kg ha(-1).