Influence of biochar on disperse and mineral-associated organic matterin sod-podzolic sandy loamy soil

In a four-year field experiment, the effect of applying biochar at a dose of 20 t/ha on the content of total organic carbon (TOC), dispersed pool carbon, carbon of mineral-associated organic matter and carbon of the clay fraction of the soil (Cclay) was studied. The field experiment was carried out at the Agrophysical Station of the Menkovo Experimental Station (Leningrad Region). The agricultural plot is occupied by sod-podzolic sandy loamy soil, which differed in the degree of cultivation: medium cultivated (MC) and highly cultivated (HC). Experiment scheme: control (without biochar) and soil with biochar at a dose of 20 t/ha. The content of Corg was determined using the Tyurin method. Isolation of the dispersed pool (POM) and mineral-associated pool (MAOM) was carried out according to the following procedure. 30 ml of sodium hexametaphosphate solution (Na6P6O18) (5 g/l) was added to a soil sample weighing 10 g, passed through a sieve with 2 mm mesh, then shaken on a shaker for 15 hours (speed 180 rpm). The resulting suspension was passed through a sieve with a hole diameter of 0.053 mm. The POM fraction was collected on a sieve, and the MAOM fraction was collected under the sieve. Isolation of the clay fraction of the soil was carried out by sedimentation after treating the samples with ultrasound. As a result of a 4-year experiment, when biochar was added, there was an increase in Corg content in medium cultivated soil by 2.8%, in highly cultivated soil by 21.3%. An increase in the mass of POM in the variant with biochar of medium cultivated soil by 8% was observed; in highly cultivated soil with biochar, on the contrary, a decrease in the POM content by 4% was observed, compared to the control. Biochar contributed to increasing the carbon content of the dispersed pool. The carbon content in the dispersed pool of MC soil increased by 15%, and of HC soil by 20.8%, compared to the control. The addition of biochar led to a decrease in the mass of the MAOM pool in the 4th year of the study in medium cultivated soil by 17.6%, and an increase in its content in highly cultivated soil by 16.5%. Biochar contributed to a decrease in the carbon content in the MAOM pool in MC soil by 20.8%, and an increase in its content in HC soil by 25.5%, compared to the control option. Biochar contributed to an increase in the content Cclay in terms of soil weight in medium cultivated soil by 4%, in highly cultivated soil by 6.8%. In the fourth year of the experiment, the effect of biochar weakened.