Quantitative differentiation between soil organic carbon and biochar carbon in Aridisol

To understand the effect of biochar, identify its presence and quantify its stability in soil, it is necessary to differentiate between the two main sources of carbon. These sources are resident soil organic matter and biochar, which is produced by burning organic matter under low oxygen concentration in a process known as pyrolysis. The present study employs solid-liquid extraction with an alkaline solution, the efficiency of which was improved by a reflux system and quantification using the modified Walkley-Black method, to distinguish the two carbon sources in samples of arid soils from the area surrounding the city of Arica, XV region of Chile. The mean annual precipitation of this area is less than 0.4 mm, and its soils are characterized by high salinity, low organic matter content, high porosity and low bulk density. The values for total extracted organic carbon obtained using this method were very similar to those for the resident soil organic carbon, indicating that the technique extracts mostly resident soil organic carbon and not biochar carbon. Biochar carbon represented less than 6% of the total organic carbon extracted by the method. The results demonstrate that this method can quantitatively differentiate between resident total organic carbon and applied biochar carbon. The method thus represents a valuable alternative to the use of an elemental analyzer. Con el fin de conocer y asimilar el efecto del biochar, su presencia y estabilidad, es necesario diferenciar entre las dos fuentes principales de carbono, que corresponden a la materia organica del suelo y al carbono organico del biochar adicionado. El metodo aplicado es la extraccion solido-liquido con una solucion alcalina, mejorando la eficiencia en un sistema de reflujo y cuantificado por el metodo modificado de Walkley and Black, en muestras de suelos aridos aledanos a la ciudad de Arica, XV region de Chile, con una media anual de precipitaciones inferior a 0,4 mm. Los suelos se caracterizan por tener una alta salinidad, bajo contenido de materia organica, alta porosidad y baja densidad aparente. Los porcentajes de carbono organico total extraido son muy similares a los valores de carbono de origen organico del suelo, lo que evidencia que esta tecnica extrae principalmente el carbono organico del suelo y no el carbono procedente del biochar. En efecto, el carbono del biochar representa menos del 6% del carbono organico extraido por este metodo. Los resultados demuestran que esta metodologia puede diferenciar cuantitativamente entre el carbono organico del suelo y el carbono organico procedente del biochar aplicado. Por lo tanto el metodo representa una valiosa alternativa a la utilizacion de un analizador elemental.