Pyrolysis conditions directly influence biochar properties and, consequently, influence the potential use of biochar. In this study, we evaluated the effects of different pyrolysis temperatures (450, 550, 650, 750, 850, and 950 °C) on the hydrogen potential, electrical conductivity, ash content, yield, volatile matter content, elemental analysis, Fourier-transform infrared spectroscopy results, X-ray diffraction results, scanning electron microscopy results, specific surface area, and micropore volume of eucalyptus wood-derived biochar. The degree of linear association between pyrolysis temperatures and biochar properties was examined using the Pearson correlation coefficient. The results showed a positive correlation of the pyrolysis temperature with the hydrogen potential value, electrical conductivity, and elemental carbon. There was a negative correlation of the pyrolysis temperature with the yield, volatile matter content, elemental oxygen, elemental hydrogen, surface area, aromaticity, hydrophilicity, and polarity indexes. The Fourier-transform infrared spectroscopy data indicated an increase in aromaticity and a decrease in the polarity of high-temperature biochar. The increased pyrolysis temperature caused the loss of cellulose and crystalline mineral components, as indicated by X-ray diffraction analysis and scanning electron microscopy images. These results indicated that changing the pyrolysis temperature enables the production of biochar from the same raw material with a wide range of physicochemical properties, which allows its use in various types of agricultural and environmental activities.

Herbicides with high mobility can leach to deeper layers of the soil and to contaminate underground aquifers. The potential of herbicide leaching in soil can be monitored by chromatography or bioassay methods. This study evaluated the leaching of imazethapyr, imazapic and its commercial mixture (imazethapyr + imazapic) in three tropical soils via a bioassay method. The herbicides were applied in a polyvinyl chloride column and an 80 mm rainfall was simulated. The bioindicator species sorghum (Sorghum vulgare) BRS 655 was sown. Imazethapyr, imazapic and the commercial herbicide mixture showed high leaching in the soils. The presence of imazethapyr and the commercial mixture was detected up to 25 cm deep in Haplic Plinthosol and Oxisol. Imazapic showed less leaching to tree soil, being found at depth 10–15 cm. The pH, texture and iron oxide amount levels affected herbicide leaching. The mobility of the herbicides imazethapyr and imazapic in the Haplic Plinthosol and the Oxisol at depth 25 cm indicates a high risk of groundwater contamination.

This study evaluated the jack bean (Canavalia ensiformis) as a potential remediator of sulfentrazone in the soil. The experiment was conducted under field conditions in a complete randomised block design. The treatments consisted of soils with and without herbicide application as well as the absence and presence of C. ensiformis cultivation associated with incorporation into the soil or the removal of shoots of C. ensiformis. Sorghum was planted as a bioindicator to evaluate the remediation efficiency of jack bean. Sulfentrazone application in areas without C. ensiformis cultivation decreased plants stands, productivity, and height of sorghum compared to treatments where C. ensiformis was cultivated. Sorghum cultivated in succession to C. ensiformis in areas contaminated with sulfentrazone resulted in dry matter production, plants numbers, productivity, and height of sorghum equivalent to uncontaminated areas. The results of this research indicate that the use of jack bean for the bioremediation of sulfentrazone treated soils would provide greater security in the planting of susceptible species in areas where this herbicide has been applied. The cultivation of C. ensiformis in contaminated areas may reduce the risk of environmental impacts caused by sulfentrazone.