Adubação nitrogenada, época de colheita e armazenamento sobre a qualidade dos grãos de dois híbridos de arroz

Abstract

Rice (Oryza sativa L.) plays an important role in human nutrition by providing a diet rich in carbohydrates, as well as proteins, mineral salts, and B complex vitamins. Given population growth, the increase in demand for food will be one of the biggest future challenges. As a result, new technologies have been developed by professionals and researchers in the field, such as hybrid rice cultivars. These cultivars have high productivity as their main characteristic, compared to conventional cultivars. Nitrogen management is a practice widely used in rice crops, as it is considered a limiting nutrient for crop development and grain productivity. Given the above, the objective of this work was to evaluate the influence of different doses of nitrogen, harvest time, and storage time on the physical-chemical and technological properties of two hybrid rice cultivars: XP 123 and LD 522 CL. The dissertation was divided into two studies. In the first study, the influence of fertilization with different doses of nitrogen (0, 60, 120, and 180 kg.ha-1) and harvest time (humidity of 26 and 20%) was evaluated. Plant height, productivity, proximal composition, thousand-grain weight, whole-grain yield, white profile, the incidence of defects and texture variables, thermal properties, paste properties, and relative crystallinity were analyzed. Productivity increased in the second harvest for the LD 522 CL cultivar. Whole grain yield was higher in the second harvest for both cultivars. The protein content was reduced with the increase in the N dose. The amylose content varied, being higher in the higher doses of N. The highest incidence of opaque grains occurred in the second harvest moment, as well as, for the second harvest, the white profile was better for both cultivars. The cooking time was shorter for the XP 123 cultivar (on average 13 minutes) compared to the LD 522 CL cultivar (16 minutes). Thermal and pasting properties varied between cultivars, and relative crystallinity increased with increasing N fertilization. PCA analysis demonstrated a strong negative interaction between amylose and cooking time. In the second study, changes in the cooking behavior of cultivars throughout storage were investigated, being analyzed every 2 months for 6 months at 26°C. The whole grain yield, cooking time, gravimetric and volumetric yield, and grain release after cooking were analyzed. Overall, integer re-yielding was not influenced by storage time. Cooking time increased over time for both cultivars. Gravimetric and volumetric yields varied between cultivars, showing a decrease after 6 months of storage for cultivar LD 522 CL. Storage time favored increased releaseability for both cultivars.