Qualidade de arroz dos cultivares INOV CL e IRGA 424 RI: efeitos da umidade de colheita, da densidade de semeadura e da dose de nitrogênio em cobertura

Abstract

The knowledge and the application of good agricultural practices have contributed to the increase in productivity and profitability of rice crops. In Brazil, the cultivar IRGA 424 RI has been the most sown. Among hybrid cultivars, INOV CL corresponds to about 4% of the total cultivated area in the South Zone of Rio Grande do Sul. The objective of this study was to evaluate the effects of sowing density, nitrogen coverage and moisture content of harvest on the quality of rice grains of the cultivars INOV CL and IRGA 424 RI. For this, the work was divided into two studies. In Study 1, the INOV CL and IRGA 424 RI genotypes had their panicles evaluated in three parts (basal, median, and upper), where the physicochemical and polishing properties of the grains were evaluated in two harvesting stages. Head rice yield, weight of a thousand grains and percentage of chalky grains, amylose content, starch extraction, molecular size distribution (HPSEC-RI), thermal properties of rice starch, relative crystallinity (X-ray diffraction), viscoamylographic profile and protein content and extraction were evaluated. In Study 2, where the objective was to specifically evaluate the effects of sowing density and nitrogen dose on the industrial quality of the grains from INOV CL and IRGA 424 RI cultivars, the weight of a thousand grains and the industrial and cooking properties were analyzed. In relation to Study 1, the best grain yield and the lowest percentage of chalky grains were obtained when the panicles were harvested at the ideal stage of maturation with 22% moisture content. The amylose content and starch structure of the INOV CL and IRGA 424 RI cultivars did not differ between the harvest times studied. Regarding the position in the panicle, only the strain IRGA 424 RI presented grains from the position of the upper panicle with higher amylose content than those from the basal position, regardless of the harvest time studied. Regarding the results obtained in Study 2, it was found that: (a) the INOV CL genotype was more sensitive to the management adopted for the weight of a thousand grains, percentage of whole grains and degree of polishing and cooking yield; (b) the percentage of chalky grains and “white bellies” decreased with the increase in nitrogen fertilization for both genotypes; (c) the increase in nitrogen fertilization in coverage increased the percentage of translucency; (d) the degree of whiteness decreased in the second harvest for both genotypes and increased their vitricity; (e) the cooking time for the INOV CL genotype decreased in Crop 2 for all densities, whereas for IRGA 424 RI the shorter cooking time was observed in Crop 1 when a higher dose of nitrogen was used and in Crop 2 there was less time cooking at densities of 75 and 100 kg/ha; (f) the INOV CL genotype showed lower gravimetric yield in Crop 2 and higher volumetric yield when the dose of 130 kg N/ha was used for the same crop.