Potencial alelopático de plantas de adubação verde sobre a Cultura do milho e plantas espontâneas

Abstract

The use of cover crops has been a strategy for farmers to reduce the use of synthetic chemical inputs. This work aimed to evaluate the allelopathic potential of cover crops fodder radish, black oats and hairy vetch on maize and weeds Amaranthus spinosus and Ipomoea grandifolia. The work was divided into three experiments. In the first one the allelopathic potential of root exudates of cover crops was evaluated on the germination and growth of weeds and maize. The evaluations were: germination, Germination Rate Index (GRI), growth and dry matter weight of root and shoot, germination, GRI and growth of spiny amaranth, root protrusion, Root Protrusion Rate Index (RPRI) and morning-glory growth. In the second experiment the allelopathic potential of the aqueous extract of the aerial part of cover crops was evaluated in the germination and growth of weeds and maize. For this, the analyzes performed were the same as the first experiment. In the third experiment the objective was to evaluate the allelopathic potential of the degradation of cover crops in emergence and initial development of maize, with the following analyzes: emergence percentage, Emergency Rate Index (ERI), chlorophyll A, B and Total, leaf area and weight of dry matter of maize seedlings. Laboratory bioassays were conducted to evaluate the phytotoxicity of root exudate and aqueous extract and greenhouse bioassay to evaluate the phytotoxicity of straw degradation on the initial development of maize. Black oat root exudation was the one that presented the greatest phytotoxicity to the initial development of the maize seedlings and weeds tested, followed by root exudate of hairy vetch that also presented phytotoxicity to maize and weeds. The aqueous extract that most affected the vigor and germination of maize was hairy vetch, followed by black oat and fodder radish. Low concentrations of aqueous extracts are less phytotoxic to the initial development of maize, and weeds are more sensitive. The highest amount of total phenols is present in hairy vetch (1.23 mg.g-1), followed by fodder radish (0.76 mg.g-1) and black oat (0.4 mg.g-1). Ten phenolic compounds were identified in the aqueous extract, with benzoic and p-coumaric acids being the most frequent, followed by ferulic acid and phydroxybenzoic acid. The different amounts of straw of fodder radish and black oats do not present interference to the emergence and vigor of maize, and the hairy vetch has been shown to be harmful to the initial development of maize, affecting germination and vigor. Further studies should be performed evaluating this field interference and the inhibition of the phenolic compounds found on target plants.