RESUMO
Soil carbon (C) determinations have been widely studied due to soil C sequestration that contributes to the mitigation of greenhouse gas emissions and improves soil quality. However, traditional chemical processes for large-scale analysis generate waste, are time-consuming, and have a high cost per measurement. Laser-induced breakdown spectroscopy (LIBS) is a multi-element spectroanalytical technique that allows fast and low-cost analysis, almost no sample preparation is required, and does not generate hazardous chemical waste. Two emission lines are commonly used for LIBS C determination, 193.03 and 247.85 nm. However, Brazilian soils have a high concentration of aluminum (Al) and iron (Fe), directly interfering in those C emission lines. Furthermore, multiple soil textures increase the difficulty of building calibration models due to matrix effects. In the present work, a mathematical model is proposed to quantify the total C in soil samples having different textures bypassing spectral interferences. A LIBS-specific method for removing outliers has been developed with 6% spectrum removal. From the univariate analysis, it was noticed that some results were projections of a 3D surface in a 2D space, so a 3D plane model was obtained with good fits for the evaluated C emission lines, R2 > 0.91, with limits of detection of 0.11% and 0.13% and limits of quantitation of 0.11% and 0.32% for lines 193.03 and 247.85 nm, respectively. Three repetitions were used to test the robustness of the methods and presented an R2 of 0.95 and 0.93, a mean error of about 20.38% and 24.12% for lines 193.03 and 247.85 nm, respectively, and a root mean square error of prediction lower than 0.40% for both lines.
Assuntos
Carbono , Solo , Solo/química , Carbono/análise , Lasers , Análise Espectral/métodos , Ferro/análiseRESUMO
Intensive management of tropical pastures has shown potential for greenhouse gas (GHG) mitigation due to high forage production and C accumulation in the soil. This study aimed to evaluate different pasture management options in relation to their effect on soil C stocks and soil organic matter (SOM) humification. Pastures in four beef cattle production systems were assessed: intensive and irrigated pasture with high stocking rate (IHS); dryland pasture with high stocking rate (DHS); dryland pasture with moderate stocking rate (DMS); degraded pasture (DP). The soil under the native forest was also evaluated and soil carbon stocks from the 0-100 and 0-30 cm layers were assessed. Carbon stocks (0-100 cm) ranged from 99.88 to 142.33 Mg ha1 in DP and DMS, respectively and were, respectively, 14 % and 24 % higher compared to the soil under the forest and indicate the capacity of adequately managed tropical pastures to mitigate GHG emissions from livestock production. Humification indexes indicated the presence of more labile C in pastures with greater C accumulation (DHS and DMS), mainly in the upper soil layers, indicating recent C accumulation resulting from correct management. However, more labile C can be easily lost to the atmosphere as CO2, depending on pasture management. Low C stocks associated with high humification indexes are characteristics of DP in which significant amounts of SOM are lost. It is necessary to develop technologies to improve C sequestration in IHS and results indicate the importance of quantifying C stocks in association with C stability.
Assuntos
Carbono , Ecossistema , Matéria Orgânica , Pastagens , Química do Solo , Espectrometria de FluorescênciaRESUMO
Intensive management of tropical pastures has shown potential for greenhouse gas (GHG) mitigation due to high forage production and C accumulation in the soil. This study aimed to evaluate different pasture management options in relation to their effect on soil C stocks and soil organic matter (SOM) humification. Pastures in four beef cattle production systems were assessed: intensive and irrigated pasture with high stocking rate (IHS); dryland pasture with high stocking rate (DHS); dryland pasture with moderate stocking rate (DMS); degraded pasture (DP). The soil under the native forest was also evaluated and soil carbon stocks from the 0-100 and 0-30 cm layers were assessed. Carbon stocks (0-100 cm) ranged from 99.88 to 142.33 Mg ha1 in DP and DMS, respectively and were, respectively, 14 % and 24 % higher compared to the soil under the forest and indicate the capacity of adequately managed tropical pastures to mitigate GHG emissions from livestock production. Humification indexes indicated the presence of more labile C in pastures with greater C accumulation (DHS and DMS), mainly in the upper soil layers, indicating recent C accumulation resulting from correct management. However, more labile C can be easily lost to the atmosphere as CO2, depending on pasture management. Low C stocks associated with high humification indexes are characteristics of DP in which significant amounts of SOM are lost. It is necessary to develop technologies to improve C sequestration in IHS and results indicate the importance of quantifying C stocks in association with C stability.(AU)