Avaliação de extrato etanólico de Urochloa ruziziensis no cultivo da soja

Abstract

Soy is the world's main agricultural product, with great socio-economic importance. Its cultivation is often carried out in crop-livestock integration systems and no-till farming, due to its adaptability. In the crop-livestock integration system, several species of forage grasses are used, such as those of the genus Urochloa. U. ruziziensis has been widely adopted in cropping systems due to its characteristics. The objectives of this work were to evaluate soybean growth and soil biology with the application of ethanolic extract of U. ruziziensis. Initially, the extraction of compounds from U. ruziziensis was performed, thus obtaining the crude alcoholic extract, in which the levels of flavonoids, total polyphenols and alkaloids were determined and submitted to evaluation of flavonoid detection by liquid chromatography. Afterwards, an experiment was conducted in the greenhouse of the soil biology laboratory of Unoeste (Campus II), to observe the influence of the extract on soybean (BRS388RR) and soil microbiology. The experiment was characterized by 5 treatments with 5 repetitions each, T1 - 0g, T2 - 5g, T3 - 1g, T4 - 1.5g and T5 - 2g per vase 1, totaling 25 experimental plots, the plants were conducted for 60 days. At the end, the plants were evaluated regarding the development of the plant (plant height, dry mass of the aerial part and root, number of pods per plant and leaf area index of soybeans), the nodulation of the roots and the nutritional state of the leaf were evaluated, and a spectral evaluation and total chlorophyll index was performed. From the spectral evaluation the following spectral indices were calculated for soybean, NDVI, PRI, MCARI and AOKI. The evaluation of soil microbial activity, was performed in two periods (15 and 60 days after sowing), the carbon and nitrogen of the microbial biomass, soil respiration, dehydrogenase enzyme activity and calculated the metabolic quotient was performed. Among the evaluations referring to the extract it was possible to observe the presence of flavonoids in larger quantities; the flavonoids Naringenin and Kaempferol were identified. The extract when applied to soy showed to stimulate the development of the plant generating increases in the height and dry mass of the aerial part, bigger weight of nodules, nodulation and reduction of the fresh mass root of the plants. The highest dosage stood out on foliar nitrogen. The U. ruziziensis extract provided increases in microbial biomass carbon at the highest dosage, as well as increases in respiration, metabolic quotient and dehydrogenase for higher dosage. The spectral signature in soybean showed that there was higher reflectance in the region near R530 and also in the near infrared region (NIR) in treatments with higher doses of extract applied to the soil. The NVDI index showed decreasing responses to increasing dosages and the other indices showed inverse responses, increasing linearly with increasing doses of extract. In the correlation of the spectral indices with the soybean aerial biomass it was verified that the NDVI presented negative correlation and the PRI stood out with positive correlation It was concluded that the extract provided gains in the soybean development and nodulation, not verifying allelopathic effect and being observed alteration of the soybean spectral behavior in function of the extract dosage applied to the soil. The extract did not negatively impact the soil microbiology at the end of the experiment.