FONTE ALTERNATIVA DE NITROGÊNIO PARA A CANA-DE-AÇÚCAR: IMPACTOS NA QUALIDADE TECNOLÓGICA, NA PRODUTIVIDADE DE COLMOS E EFEITO RESIDUAL

Abstract

The productivity of sugarcane cultivation is directly impacted by the availability of nitrogen (N). However, due to the nitrate leaching and ammonia the volatilization associated with mineral nitrogen fertilization, there is a need to seek more affordable alternatives aligned with sustainable agricultural practices. The use of chicken litter, an organic residue, emerges as a potential source of nitrogen (NO) supply for large-scale crops. The hypothesis tested in this context was the comparative efficacy between using chicken litter as a NO and applying mineral nitrogen (NM), specifically ammonium nitrate. Experiments conducted in the cultivation area of Usina Denusa – Destilaria Nova União S/A, in the Midwest region of Brazil, adopted a 5 x 5 x 2 split-split- plot desigh. The treatments consisted of five NM doses (0; 40; 80; 120 and 160 kg ha-1) and five NO doses (0; 2; 4; 6 and 8 T ha-1), evaluated over two harvests (2019/2020 – plant cane) and (2020/2021 – ratoon cane). In Chapter I, it was observed that the application of different amounts of NM or NO influenced the height and number of tillers of sugarcane plants. In this sense, the assumption that the NO application in this crop, derived from chicken litter, is as effective as the NM application in promoting plant growth was validated. Furthermore, it was found that NM and NO promote an increase in foliar levels of N, P, and K. The NM absence is compensated by the N presence in organic form, while the NO lack is counterbalanced by the NM availability. In addition to stimulating growth, the NO application, up to a dose of 4.8 T ha-1, resulted in an increase in sugarcane productivity. This study also highlighted the regrowth quality, especially for the IACSP95-5094 cultivar, ensuring greater tillering and stem diameters, resulting in increasingly expressive yields in the ratoon cane harvest. In Chapter II, the evaluated variables included N, P, and K levels, technological quality, and sugar production in the stalks. The hypothesis that the chicken litter application for soil fertilization can replace the use of ammonium nitrate to provide N, P, and K to sugarcane plants was confirmed. However, the increase in doses of NO and NM may negatively affect °Brix, apparent sucrose content (POL), and purity of sugarcane juice, the interaction between high doses of NO and NM compromises total sugar recovery. Regarding technological quality, the NO doses application using chicken litter can be combined with NM doses to achieve high sugar yields; a balanced N application (4.2 T ha-1 of NO combined with 120 kg ha-1 of NM) promoted increases in sugar production, reaching the highest average of 22.845 T ha-1. Although excessive doses of N, whether organic or mineral, may compromise the quality of sugarcane juice by reducing sucrose content, understanding these interactions is essential for proper fertilizer management, aiming to optimize not only production but also the quality of sugarcane. In Chapter III, the residual effect of NO and NM doses in the second ratoon crop (2021/2022 harvest) was evaluated, including variables such as plant height, Brix, Pol (percentage of sucrose by mass), purity, fiber, reducing sugars (AR), total recoverable sugars (ATR), and productivity. The results indicated that mineral nitrogen did not generate significant differences, attributed to losses through ammonium nitrate volatilization in the soil. However, organic nitrogen influenced several variables. Plant height responded linearly to increasing doses of organic nitrogen, while Brix and Pol showed complex quadratic responses. A reduction in sucrose quality was observed with higher doses of organic nitrogen, indicating a compromise in sugarcane quality. Despite the increase in productivity with higher doses of organic nitrogen, the results emphasize that an excess of this element reduces the technological quality of sugarcane.