Nitrogen cycling in sugarcane

Abstract

Sugarcane has been grown extensively in Brasil for more than 50 years, and in the northeast from the time Brasil was discovered. Use of N-fertilizer started in the 1940’s with applications of sodium nitrate, and little yield improvement was obtained in most cases. Average yield is around 70 t ha-1 yr-1 (4-harvest mean), with the first harvest 1.5 year from planting and a ratoon harvest each year thereafter. Nitrogen responses are obtained only with ratoon crops. Nitrogen inputs to the plant come from native soil-N, fertilizer-N, and biological fixation. Sources of loss include N-leaching from leaves and decomposing roots and loss of stems and leaves at harvest. There are technical and economic problems with returning factory waste (vinhoto) to the fields as fertilizer. A reasonably conservative estimate of biological nitrogen fixation holds that 17% of total plant nitrogen is fixed by the plant, or 16.6kg N ha-1 for a harvest of 70 × 103kg ha-1. Rotation and intercropping of legumes with sugarcane could increase N2-fixation by 35 kg N ha-1 yr-1 (soybean rotation) and 25 kg N ha-1 yr-1 (Phaseolus beans intercropping).