ABSTRACT
This study evaluated the long-term effect of biochar application on the sorption and desorption of thiamethoxam in a Haplic Plinthosol. The experiment was conducted in a randomized block design with combination of doses of mineral fertilizer NPK (0 and 300 kg·ha-1 formula 05-25-15) and biochar (0, 16 and 32 Mg ha-1). Deformed soil samples were collected in the field from the 0-0.10 m layer of all plots to determine the sorption and desorption of the thiamethoxam insecticide in the soil; fulvic acid (FA), humic acid (AH) and humin (HUM) carbon contents; and total organic carbon. The Batch slurry method was used to evaluate sorption and desorption. The Freundlich isotherm adequately described thiamethoxam sorption in all treatments. The application of biochar increased the sorption (Kfs) and decreased the desorption (Kfd) of thiamethoxam. The sorption intensity (1/n) showed reduction characteristics as the soil concentration of thiamethoxam increased. Biochar has a sorption effect on the soil through covalent bonds and H-bonds with the insecticide molecules, thereby indirectly increasing the sorption potential in the chemical fractions of the organic matter of soil. The application of 32 Mg ha-1 of biochar significantly reduced thiamethoxam in the soil solution. Altogether, the present study reveals that biochar application in soil is a promising tool for mitigating the contaminant potential of thiamethoxam in subsurface waters.
Subject(s)
Insecticides , Soil Pollutants , Adsorption , Carbon/chemistry , Charcoal/chemistry , Soil/chemistry , Soil Pollutants/analysis , ThiamethoxamABSTRACT
The objective of this research was to assess the emission of nitrous oxide (N2O) from soil amended with biochar in the culture of upland rice. The experiment was conducted in the field in a Cerrado Haplic Plinthosol under randomized block experimental design. The treatments consisted of fertilization with 100 kg N ha(-1) split into two applications, 60% at sowing and 40% at 45 days after crop emergence, combined with four doses of biochar (0, 8, 16 and 32 Mg ha(-1)), with four replications. The application of N and the emission of N2O, moisture retention and soil temperature, respiration (C-CO2), microbial biomass carbon in the soil (C-SMB), total nitrogen (TN), pH and agronomic efficiency in N use (AENu) were evaluated five years after the application of biochar. There was a significant correlation of the application of biochar with moisture retention (r = 0.94**), N2O emission (r = 0.86**) and soil pH (r = 0.65*), and N2O emissions showed a positive correlation (p < 0.05) with soil moisture (r = 0.77**) and pH (r = 0.66*). Thus the highest N2O emissions were observed shortly after N fertilization and in the treatments with 32 Mg ha(-1) of biochar. Despite the higher N2O emissions from the application of 32 Mg ha(-1) of biochar, the emission factor was lower (0.81%) than the maximum recommended by the IPCC. The higher N2O emissions with application of biochar are offset by more efficient use of N and consequently the possibility of reduction of applied doses.
Subject(s)
Charcoal , Nitrous Oxide/analysis , Soil/chemistry , Biomass , Carbon/analysis , Denitrification , Nitrification , Nitrogen/metabolism , Oryza/metabolismABSTRACT
O uso do consórcio entre plantas de cobertura e culturas anuais, no Cerrado, tem sido prática cada vez mais difundida, pela possibilidade de implantação das forrageiras durante o desenvolvimento das culturas anuais, através da diferença de profundidade e sistema de semeadura. Objetivou-se, neste trabalho avaliar a emergência e algumas características agronômicas de quatro espécies de plantas de cobertura, em diferentes profundidades, visando ao seu emprego na consorciação e sobressemeadura em culturas anuais. O experimento foi conduzido em casa-de-vegetação, no delineamento experimental de blocos ao acaso, em arranjo fatorial 4 x 7, composto pelas plantas de cobertura Brachiaria brizantha, B. decumbens, B. ruziziensis e Panicum maximum cv. Tanzânia, e por seis profundidades de semeadura e um sistema de cobertura de sementes (0 sem cobertura, 0 com cobertura, 1, 4, 8, 10 e 15 cm). As sementes foram semeadas em vasos e as plantas cultivadas por 40 dias. Avaliou-se o índice e o tempo de emergência, a altura de plantas, a fitomassa verde e seca da parte aérea, a área foliar, a fitomassa seca radicular e a densidade de comprimento radicular. O maior desenvolvimento das plantas estudadas foi detectado nas semeaduras até 1 cm de profundidade. O P. maximum não apresentou aptidão para uso em consórcio com culturas anuais.Não se recomenda a semeadura das plantas de cobertura a partir de 10 cm.
The use of the consortium between cover crops and annual crops in the Cerrado, is an increasingly widespread practice, because of the possibility of deployment of cover crops during the development of annual crops by the difference in depth and seeding system. The objective was to evaluate the emergency and some agronomic characteristics of four species of cover crops at different seeding depths, to use them in consortium and oversown in annual crops. The experiment was conducted in a greenhouse, and the experimental design of randomized blocks in factorial arranged 4 x 7, where it was four cover crops: Brachiaria brizantha, B. decumbens, B. ruziziensis and Panicum maximum cv. Tanzania, and six depths of sowing and a cover of seed system (0 cm without any mulch, 0 cm with a mulch of soybean leaves, 1, 4, 8, 10 and 15 cm). The cover crops were cropped in vase for 40 days. We evaluated emergence index, emergence time, plant height, green biomass and dry biomass of the above-ground part, leaf area, root dry biomass and root length density. The largest development of the cover crops was detected in the sowing up to 1 cm of depth. The P. maximum showed no ability to use in consortium with annual crops. The sowing of the cover crops from 10 cm is not recommended.
