Alterações no metabolismo, nos componentes de produção e na qualidade fisiológica de sementes de arroz em função da aplicação de herbicidas e nitrogênio.

Abstract

The weed control in rice is done mainly through the use of herbicides, which, even though selective, may cause phytotoxicity and trigger oxidative stress process. Thus, the aim of the study was to evaluate possible changes in the secondary metabolism and physiological seed quality in response to oxidative stress caused by herbicides and evaluate the recovery of phytotoxicity by nitrogen fertilization. The first experiment consisted of the oxyfluorfen, oxadiazon and pendimethalin (pre-emergence), imazapic + imazapyr, quincloraq, bentazon, cyhalofop-butyl, penoxsulan, bispyribac-sodium and carfentrazone-ethyl (post-emergence). Oxyfluorfen, pendimethalin and carfentrazone-ethyl herbicides resulted in lower net photosynthesis, increased sub stomatal CO2 , lower efficiency of water use and carboxylation. Greater lipid peroxidation was observed when applied the oxyfluorfen, carfentrazone-ethyl and bispyribac-sodium herbicides, while the same did not generate H2O2 accumulation. The pre-emergent herbicides and post-emergent herbicide bentazon and carfentrazone-ethyl activated enzymes of the antioxidant system. The application of carfentrazone-ethyl, in general, resulted in degradation of photosynthetic pigments. The second experiment was carried out in the field and consisted of clomazone, oxadiazon and pendimethalin (pre-emergence), imazapic + imazapyr, quincloraq, bentazon, penoxsulan, bispyribac-sodium and carfentrazone-ethyl (post-emergence). The oxadiazon and pendimethalin herbicides applied in pre-emergence and bispyribac-sodium and carfentrazone-ethyl, post-emergence, reduced dry matter of leaves of rice plants. All herbicides applied in pre-emergence showed higher grain yield compared to control. For post-emergence herbicides, the highest and lowest yield was observed when used quincloraq and bispyribac-sodium, respectively. The use of clomazone and pendimethalin resulted in higher germination rate index for rice seed. The third experiment was carried out in the field in split plots, where plots had nitrogen application date (without nitrogen, 100% before the water intake, 50% before and 50% after the water intake and 100% after the water intake) and composed of herbicides subplots (control, quincloraq, bentazon, bispyribac-sodium and carfentrazone-ethyl). The smaller statures were due to non-application of nitrogen or when the application of 100% of the nitrogen was carried out after the entry of water. The application of 100% of the nitrogen prior to the entry of water resulted in a greater phytotoxicity caused by the herbicide bispyribac -sodium, while most of bentazon phytotoxicity was observed when nitrogen was applied after the whole water intake. The application of nitrogen before water intake resulted in higher number of tillers per plant. The quincloraq herbicide and nitrogen application before and the splitting of nitrogen water intake resulted in higher grain yield.