The Effect of Biochar on Disperse and Mineral-Associated Organic Matter in Soddy-Podzolic Sandy Loam Soil

The effect of biochar applied at the rate of 20 t/ha on content of total organic carbon Corg, dispersed pool carbon, carbon of mineral-associated organic matter, and carbon of the clay fraction of the soil Cclay was studied in a 4-year field experiment. The field experiment was performed at the Agrophysical Station of the Men’kovo Experimental Station (Leningrad oblast). The agricultural plot was occupied by soddy-podzolic sandy loam soil, which differed in the degree of cultivation: medium cultivated (MC) and highly cultivated (HC). The experiment scheme was the following: control (without biochar) and soil with biochar at the rate of 20 t/ha. The Corg content was determined by the Tyurin method. The dispersed pool (POM) and mineral-associated pool (MAOM) were isolated according to the following procedure: 30 mL of sodium hexametaphosphate solution (Na6P6O18) (5 g/L) was added to a soil sample (10 g) passed through a 2-mm mesh sieve and then shaken on a shaker for 15 hours (speed 180 rpm).The resulting suspension was passed through a sieve with a mesh diameter of 0.053 mm. We collected the POM fraction on a sieve and the MAOM fraction under the sieve. The clay fraction of soil was isolated by sedimentation after treating the samples with ultrasound. The purpose of this study is to assess temporary changes in the content of total organic carbon, dispersed pool carbon, carbon of mineral-associated organic matter, and carbon of the clay fraction of the soil when biochar is added to it. As a result of the 4-year experiment with added biochar, there was an increase in Corg by 2.8% in the MC soil and by 21.3% in the HC soil. Biochar application caused a rise in the POM mass by 8% in the MC soil and, on the contrary, a decrease in the POM content by 4% in the HC soil as compared to the control. Biochar contributed to greater carbon content of the dispersed pool. It increased by 15% in the MC soil and by 20.8% in the HC soil as compared to the control. Biochar application resulted in a decrease in the mass of the MAOM pool by 17.6% in the MC soil and in an increase in its content by 16.5% in the HC soil on the fourth year of the experiment. Biochar favored a decrease in the carbon content in the MAOM pool by 20.8% in the MC soil and an increase in its content by 25.5% in the HC soil as compared to the control. Biochar contributed to an increase in the Cclay content recalculated per soil mass by 4% in the MC soil and by 6.8% in the HC soil. The effect of biochar became slighter on the fourth year of the experiment.