Eficiência agronômica das adubações nitrogenadas de plantio e após o primeiro corte avaliada na primeira soca da cana-de-açúcar / Agronomic efficiency of nitrogen fertilization at planting and after the first harvest, evaluated during the first sugarcane ratoon cultivation

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

Renewable energy sources will gradually replace non-renewable sources due to economic sustainability reasons and to the rational use of natural resources. Consequently, this study aimed to investigate sugarcane nitrogen fertilization in detail, which may help the country to become a world model in the production and use of renewable biofuels. The current knowledge about sugarcane responses to N fertilization has been acquired by means of experiments conducted, for their most part, in a single cropping season. The utilization and redistribution of N from the plant cane root system into the above-ground part of ratoon cane, and its influence on ratoon productivity must be studied in greater detail. To achieve that, two experiments were installed, one on a TYPIC HAPLUDOX SOIL and the other on a RHODIC HAPLUDOX SOIL, both in the State of São Paulo. Cultivar SP81-3250 was planted. A completely-randomized-block experimental design was adopted, with four replicates. The plant cane treatments (plots) consisted of three N doses: 40, 80, and 120 kg ha-1, in the form of urea, and a control without N. Ratoon cane sub-treatments, applied as subplots after the plant cane was harvested, consisted of three N doses: 50, 100, and 150 kg ha-1, in the form of ammonium sulfate, and a control without N. From the results obtained, it should be highlighted that, in the ratoon cane cycle, nitrogen fertilization only increased S, Cu, and Mn contents in diagnostic leaves, without significant interaction between plant cane and ratoon cane nitrogen fertilization on the nutrient contents of diagnostic leaves. Biometric evaluations showed that the nitrogen fertilizations increased dry matter production rate in the maximum ratoon cane development season. However, no residual effect of nitrogen fertilization at planting was observed on dry phytomass productivity and on N accumulation in the first ratoon cane cycle, although recovery (%) of urea applied at planting by the above-ground part of the ratoon, on the average of the experiments, was 4.18%, 5.04%, and 3.54% for the N doses of 40, 80, and 120 kg ha-1, respectively. On the average of the experiments, N recovery (%) by ratoon cane from the residual trash resulting from plant cane harvest was 9%. N recovery (kg ha-1) increased in ratoon cane as ratoon dose increased, regardless of plant cane treatment, but nitrogen fertilizer utilization efficiency (%) was identical for both doses. On the average of the experiments, 37% of the nitrogen fertilizer were recovered from the plant, 29% from the soil, and 34% were not recovered. There was no significant interaction between N doses in plant cane and ratoon cane on the technological parameters of the ratoon, but there was a residual effect of nitrogen fertilization at planting on millable cane yield (TSS) in the second harvest. Planting-N recovery by ratoon cane and the resulting yield increase (TSS) confirm that sugarcane plants use the residual N found in root system reserves and in the soil, demonstrating that nitrogen fertilization should not be taken into consideration in just a single cropping cycle.

ASSUNTO(S)

biometria residual effect cana-de-açúcar productivity fertilizantes nitrogenados nitrogen saccharum spp. ratoon cane. adubação sistema radicular. produtividade

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