Desempenho fotossintético e eficiência de herbicidas em Urochloa plantaginea (POACEAE) submetidas às diferentes condições hídricas do solo e doses de nitrogênio

Abstract

The species Urochloa plantaginea naturaly native from upland areas, has been demonstrating high occurrence in flooded areas at rice crop in Rio Grande do Sul state of Brazil. There is little information related to specific interactions between this environment and the species. The objective of this work was to comprehend the morphophysiological characteristics of the species in diferent water regimes of the soil and the interaction between nitrogen fertilization and herbicides. Two experiments were carried out under greenhouse conditions in 2016 and 2017. The first one consisted of evaluating the responses of a U. plantaginea population from upland and lowland areas submitted to three soil water conditions: 50 and 100% of soil water retention capacity and water depth of 5 cm. Photosynthetic parameters, lipid peroxidation and morphological aspects were evaluated. The second experiment was composed of a 2x3x4 trifactorial, with the following factors: soil water conditions (100% of soil water retention capacity and water depth of 5 cm), nitrogen doses (zero, 80.0 and 160.0 kg of a.i. ha -1) and herbicides doses (zero; ½ of labeled dose, labeled dose, 2 times labeled dose). The herbicides used were cyhalofop-butyl, imazethapyr and imazapyr + imazapic, where phytotoxicity and dry mass were evaluated at 28 days after application. It is concluded that the populations showed differential behaviors related to the morphophysiology in the water conditions evaluated. The low land population evidenced to be in a process of adaptation to the flooded environment, presenting characteristics favorable to its development. The interactions between nitrogen doses, herbicide doses and soil water conditions varied according to the herbicide in question. Nitrogen fertilization optimized alexander grass control using cyhalofop-butyl and imazapyr + imazapic herbicides in the two water conditions evaluated. In the case of imazethapyr, 100% of soil WRC was more efficient without the presence of nitrogen fertilizer, and the inverse occurred at flooded condition since 35.0 g of a.i. ha-1. It is evident the diversity of the responses of alexander grass plants to the conditions of management commonly imposed and the control complexity of this species in rice cultivation.