Secondary metabolites of Urochloa ruziziensis on growth, nodulation, and spectral responses of soybean

Abstract

Ruzigrass (Urochloa ruziziensis) is a widely cultivated plant alongside soybeans, particularly in integrated crop and livestock systems, due to its fast growth and adaptability to different conditions. This study aimed to assess the impact of secondary metabolites found in ethanolic extract from ruzigrass on soybean growth, nodulation, spectral responses, and soil microbiological attributes. The ethanolic extract of ruzigrass presents total concentration of flavonoids (852.5 µg g−1), including naringenin and kaempferol. Increasing doses (100, 200, 300, and 400 kg ha−1) of the extract were then applied to the soil in a greenhouse to cultivate soybean plants. The spectral analysis indicated that higher doses of ruzigrass extract enhanced photochemical reflectance, chlorophyll absorption, and total chlorophyll indices. However, the normalized differential vegetative index decreased in response to the treatments. Generally, increasing doses of ruzigrass extract led to linear improvements in plant height, leaf area, shoot dry mass, pod count, nodule count, nitrogen content, and soil microbial activity. On the other hand, root dry massand relative chlorophyll content decreased with higher doses of the extract. In conclusion, the application of Urochloa ruziziensis extract, containing secondary metabolites caused a reduction in root development and an increase in spectral indices related to abiotic stresses in soybeans. There was an increase in the biological attributes of the soil with a significant, increasing linear adjustment in the doses of ruzigrass extract applied, as well as in the soybean production components.