Factor controlling soil organic carbon and total nitrogen dynamics under long-term conventional cultivation in seasonally frozen soils

Abstract

Limited information is available for understanding factors controlled dynamics of soil organic carbon (SOC) and total nitrogen (TN) affected by long-term conventional cultivation in seasonally frozen soils. A 19-year observation in this study was conducted in north-eastern China to evaluate effects and relative importance of potential factors. SOC variation extent was greater relative to global average as per unit of annual mean air temperature and precipitation changed. Increased carbon sequestration was observed in meadow lessive, while slight to moderate declines occurred in meadow-boggy soil and meadow soil. However, no differences in TN were found across soil types. At sites with low slope, carbon and nitrogen sequestration increased, largely due to water movement. Increased biomass with introducing 1-year oilseed rape/fallow in crop rotations could promote SOC and TN accumulation in the long run. Planting proportion of crops could also regulate carbon and nitrogen levels at a farm scale; the optimal ratio was observed in the range of 0.8–1.4. High crop yield was associated with lower carbon and nitrogen levels, and nutrient thresholds of yielding increment were observed as 25.7 g kg^?1 for carbon and 2.6 g kg^?1 for nitrogen. The length of frost-free period or cultivation period could not help sequestrating carbon and nitrogen. Chemical fertilizer with crop residues provoked SOC and TN increments compared with no chemical fertilizer plus little organic manure. Different factors exerted different tendentious influences, leading to subtle differences in SOC and TN variation rates. Accordingly, optimal cultivation strategies could be developed to reduce nutrient losses and mitigate greenhouse gas emissions.