Effect of Organic Fertilizers on Soil Organic Carbon and Risk Trace Elements Content in Soil under Permanent Grassland

The effect of different kinds of organic matter inputs on elemental composition, content, and quality of humic substances was studied on permanent grassland during 2008-2013. The experiment included two organic fertilizer types - compost and slurry, both with the range of stocking rates 0.9, 1.4, and 2.0 livestock units (LU)/ha (corresponding to 54, 84, and 120 kg N/ha, respectively), and control without any fertilizer. The soil was sandy-loam, of Cambisol type, with semi natural permanent grassland. Labile forms and total contents of selected trace elements (Co, Cu, Zn, Cd) and macroelements (Ca, Mg, K, P, and N) were measured. Soil organic matter parameters such as total organic carbon (C-ox), humic substances (HS), humic acid (HA), fluvic acid (FA), and labile carbon forms (hot-water extractable carbon (C-hws), cold water extractable carbon (C-cws)) were determined. Results showed that the greatest content of P, Ca, Mg, and N in the soil was detected by the CO 2.0 treatment. Furthermore, the positive effect of compost on C-ox, C-hws, HA, FA, HS, N and macronutrients was observed. The elemental analysis of humic acids showed lower carbon content and higher oxygen content in HA molecule, which indicated young humic acids, with a lower condensation degree. The content and quality of humic substances strongly influenced the total and labile trace elements content in the soil. Additionally, hot water soluble carbon significantly correlated with plant available forms of Zn, Cu, and Cd.