Temporal Trends of Soil Organic Carbon and Total Nitrogen Losses in Seasonally Frozen Zones of Northeast China: Responses to Long-Term Conventional Cultivation (1965-2010)

Abstract

Knowledge is limited on soil organic carbon (SOC) and total nitrogen (TN) dynamics shaped by seasonal freezing-thawing cycles under long-term conventional cultivation. This study aimed to elaborate temporal variability of SOC and TN in the plow layer of agricultural soils employing a dataset of a long-term observation (1965-2010). Cumulative losses were calculated via mass balance equation. With the aid of the autoregression integrated moving average model (ARIMA), time series of historical and impending variations of SOC and TN levels were simulated and depicted. Results revealed that SOC and TN contents decreased by 15 and 42 %, respectively. Annual nutrient variations exhibited deteriorating tendencies with fluctuations ranging within -745 and 759 kg C ha-1 year-1 and -432 and 35 kg N ha-1 year-1, respectively. SOC presence was strictly regulated by N input following a regional pattern. Chemical fertilization, combined with crop residue compost, boosted SOC and TN enrichment, but raised the loss risks. Involvement of green manure/fallow treatment with 1-year frequency in crop rotations favored SOC and TN sequestration. Paddy management was beneficial for SOC accumulation. ARIMA modeling demonstrated annual release rates of 468 kg C ha-1 for SOC and 214 kg N ha-1 for TN in subsequent 10 years. The generated algorithms provided a tool to estimate regional SOC and TN losses following cultivation, and to evaluate soil fertility.