Effect of land use, time since deforestation and management on organic C and N in soil textural fractions

Deforestation and subsequent cultivation practices often result in loss of soil organic matter, in a degree depending on time since deforestation and soil and crop management. A land in North Greece was studied in order to check the influence of land use and management on soil organic C (SOC) and N. Cultivated soils with three dates since deforestation (25, 34 and 72 years) were compared to adjacent undisturbed forest soils. Two management systems were used in the cultivated soils: not irrigated wheat with superficial ploughing and irrigated cotton crop with deeper ploughing alternated with wheat every two years. Soil samples were separated in textural size fractions and organic C and N were analysed. In terms of land use, the most distinctive differences between agricultural and forest plots were found in coarse particulate organic matter (2.8 g kg−1 soil in agricultural land vs 14.8 g kg−1 soil in forest sites), and in the fine sand fraction SOC (8.6 g kg−1 soil in agricultural land vs 40.6 g kg−1 soil in forest sites), and N (1 g kg−1 soil in agricultural land vs 2.4 g kg−1 soil in forest sites), with minimal differences in the clay fraction (15.5 g kg−1 soil in agricultural land vs 21.2 g kg−1 soil in forest sites for SOC, and 2.2 g kg−1 soil in agricultural land vs 2.4 g kg −1 soil in forest sites for N). Time as a factor was significant for all the studied properties regarding the first years following deforestation. Management practices had an effect on SOC and, more pronounced, on N, with the wheat plots showing higher contents. Clay particles present the most stable behavior in terms of SOC (especially regarding time and management as factors) and N (especially regarding land use and time as factors) protection and maintenance.