Ponto ideal de colheita de cinco híbridos comerciais de milho

Abstract

The objective of this work was to determine the ideal harvesting point of five commercial hybrids of corn. The work was conducted in a commercial farming area, at Fazenda Renascer, in Astorga - Paraná, during the autumn/fall of 2007 and the summer harvest of 2007/2008. The corn grains samples, harvested in five distinguished periods and in five replications, were collected in the field and taken to the laboratory, where they were disposed in a completely randomized design. The data were submitted to analyses of variance and regression. The corn grains characteristics evaluated were: physiologic maturity; moisture content; dry mass; commercial classification; density and porosity; mechanical damages and sanity. The endosperm solidification line had shown appropriated and easy detection of the physiologic maturity of the corn grains, unlike the black layer. The physiologic maturity of the grains, in autumn/fall harvest, happened with medium humidity of 25.4%, while in the summer harvest, on the hybrid 2B710 it happened on the humidity of 25.5% and on the hybrids 2B707 and Impact the grains were already physiologically mature. In general, after the physiologic maturity, there was a reduction of the dry mass due to the decreasing grain moisture in the appraised hybrids in the two periods studied, being that fact attributed to the breathing process of the grains. The bulk and real densities presented elevation because of the decrease of moisture influenced above all by the reduction of individual volume of the grains, whereas the porosity had decreased. The percentages of impurities were smaller with the reduction of moisture, while the averaged grains and grains damaged by insects increased, independently of hybrid and of appraised period. The more relevant mechanical damages (endosperm scratched and fragmentation of the grains) had also increased with the reduction of moisture, independently of the grains texture. In the evaluation of the sanitary quality of the corn grains, the genera Fusarium presented increasing incidence due to moisture increasing, whereas Aspergillus spp. and Penicillium spp. had their incidences decreased. It was observed that the possible production of aflatoxins, associated to corn grains still in the field. However, the anticipation of the harvest, followed by immediate drying processes assure the sanitary quality of the corn grains. The moisture content between 22.0% and 26.0% allowed the best physical and sanitary quality of the corn grains, but the best financial return was obtained for grains harvested at 24.0% moisture content.