Management effects on nitrogen recovery in a sugarcane crop grown in Brazil

Abstract

The present study's objectives were to quantify the fertilizer-N and residue-N balances of a sugar cane crop under two trash management systems. The fate of nitrogen (N) derived from fertilizer (NdfF) and N derived from residue (NdfR) was studied comparing: (i) the traditional harvest system with trash burning before harvest (“trash burning”) and (ii) an alternative system without trash burning, in which crop residues are left on the soil surface (“trash mulching”). The experiment consisted of three treatments: (i) T1: at planting, the sugarcane crop was fertilized with 63 kg N ha −1 as 15N-labeled ammonium sulfate, and after the 1st harvest received unlabeled trash from T2; (ii) T2: at planting, the crop was fertilized with 63 kg N ha −1 as unlabeled ammonium sulfate. At the 1st harvest time, this treatment received the labeled trash from T1; (iii) T3: at planting, the crop was fertilized with 63 kg N ha −1 as 15N-labeled ammonium sulfate, and every year, immediately before cutting, the crop residues were burnt. After the first harvest fertilizer-N was applied over the total soil area at a rate of 80 kg N ha −1 as unlabeled ammonium sulfate. The results indicated that the trash remaining as a surface blanket resulted in an average N recycling of 105.0 kg ha −1 year −1, while the practice of burning the trash produced an average N loss from the system of 83.5 kg ha −1 year −1. At the first harvest, about 75% of the labeled N was recovered in the soil–plant system. The majority was found in the plant, indicating a high availability of the fertilizer-N for the crop. At the end of the third crop cycle (2nd ratoon crop harvest), the total output of fertilizer-N (export+burning) was 60% for the burnt-trash treatment, and only 42% (export) for the trash-blanket treatment. The N liberated from the residue is mainly immobilized in the soil, reflecting that sugarcane trash is an N source of slow availability to the crop. This study indicated that green cane harvesting followed by mulching leads to a more efficient recycling of the N applied to the system and therefore reducing fertilizer-N needs.