Effects of Tillage Practices and Land Use Management on Soil Aggregates and Soil Organic Carbon in the North Appalachian Region, USA

Promoting soil carbon sequestration in agricultural land is one of the viable strategies to decelerate the observed climate changes. However, soil physical disturbances have aggravated the soil degradation process by accelerating erosion. Thus, reducing the magnitude and intensity of soil physical disturbance through appropriate farming/agricultural systems is essential to management of soil carbon sink capacity of agricultural lands. Four sites of different land use types/tillage practices, i） no-till （NT） corn （Zea mays L.） （NTC）, ii） conventional till （CT） corn （CTC）, iii） pastureland （PL）, and iv） native forest （NF）, were selected at the North Appalachian Experimental Watershed Station, Ohio, USA to assess the impact of NT farming on soil aggregate indices including water-stable aggregation, mean weight diameter （MWD） and geometric mean diameter （GMD）, and soil organic carbon and total nitrogen contents. The NTC plots received cow manure additions （about 15 t ha-1） every other year. The CTC plots involved disking and chisel ploughing and liquid fertilizer application （110 L ha-l）. The results showed that both water-stable aggregation and MWD were greater in soil for NTC than for CTC. In the 0-10 cm soil layer, the 〉 4.75-mm size fraction dominated NTC and was 46% more than that for CTC, whereas the 〈 0.25-mm size fraction was 380% more for CTC than for NTC. The values of both MWD and GMD in soil for NTC （2.17 mm and 1.19 mm, respectively） were higher than those for CTC （1.47 and 0.72 mm, respectively） in the 0-10 cm soil layer. Macroaggregates contained 6%-42% and 13%-43% higher organic carbon and total nitrogen contents, respectively, than microaggregates in soil for all sites. Macroaggregates in soil for NTC contained 40% more organic carbon and total nitrogen over microaggregates in soil for CTC. Therefore, a higher proportion of microaggregates with lower organic carbon contents created a carbon-depleted environment for CTC. In contrast, soil for NTC had more aggregation and contained higher organic carbon content within water-stable aggregates. The soil organic carbon and total nitrogen stocks （Mg ha-1） among the different sites followed the trend of NF 〉 PL 〉 NTC 〉 CTC, being 35%-46% more for NTC over CTC. The NT practice enhanced soil organic carbon content over the CT practice and thus was an important strategy of carbon sequestration in cropland soils.