Influence of Grazing Intensity on Organic Carbon Deposition in Pasture Soil

Abstract

The effect of cattle grazing intensity on the deposition of organic carbon (C_org) in pasture soil was studied. The work was carried out in 2010 on soddy-medium podzolic sandy loam soil in Leningrad oblast. Three pasture areas were identified according to grazing intensity: low (section one), medium (section two), and high (section three). C_org and carbon in the clay fraction of the soil (C_clay) were determined according to the Tyurin method. The clay fraction (<1 µm) was isolated using sedimentation and centrifugation. X-ray analysis of soil minerals was carried out in samples of the clay fraction of the soil on a DRON-3M diffractometer, CuKα tube mode 30 mA, 30 kV, from 3.5 to 75°, goniometer rotation speed 1° per minute. The soil of site three was distinguished by the minimum content of C_org in both periods of the survey (May: 16 C g/kg of soil; July: 27.8 C g/kg). The C_org value in the July samples was 1.3 times less compared to site two and 1.2 times less than site one. C_clay values varied in the following range: 40.8–108.9 C g/kg fractions in May and 99.7–140.9 C g/kg fractions in July. The content of C_clay in July samples from site three was 1.3 times higher than the content in samples from site two and 1.4 times from site one. The variation in the enrichment coefficient (E_soc) was 1.78–3.50 in May and 2.89–5.07 in July. Its highest value was recorded for the soil of site three in July and exceeded the values in sites one and two by 1.75 times. The mineral depositing organic matter in the clay fraction of the soil of the site with high grazing intensity was mica with a deficiency of cation (r = 0.90). The increase in grazing intensity led to an increase in the content of C_clay.