Dynamic Modeling For Soil Organic Carbon And Its Application Under Intensive Cropping Systems In The Huang-Huai-Hai Plain Of China

Carbon and nitrogen cycles are very important to agricultural productivity and global climate stability. These processes are also strongly affected by intensive farming practices. The Huang-Huai- Hai Plain is often referred to be China's breadbasket with the winter wheat followed by summer com in one year as its main cropping system. The sustainable utilization of agricultural soils in this area affects China's food security. The understanding and management of soil organic matter (SOM) dynamics have been a focus of most important scientific issues. In this paper, focusing on the soil organic carbon dynamics, the accumulation rule of SOM was studied systematically in the Huang-Huai-Hai Plain of China. The main results are listed below:CQESTR is a daily time step model with cumulative degree-days as its driving force, and the water factor was generalized at the 7 sufficiently irrigated sites in the Huang-Huai-Hai Plain. Based on the relevant short- and mid-term buried organic material trial data, the original CQESTR model was modified according to four stages of biomass decomposition. The modified CQESTR model was validated using independent data from the 7 long-term (10-20-year) soil fertility trials in this region. Regression analysis on 1151 pairs of simulated and observed SOM data gave slope coefficient of 0.990 and correlation coefficient (r2) of 0.910 (p < 0.01). The modified model was able to predict the mineralization of crop residue, organic amendment, and native SOM. Further analysis showed that the SOM mineralization rate (MR) in the plough layer increased with increasing annual organic inputs, e.g., MR increased by 0.22% when annual crop yield increased by 1 t hm^-2, suggesting improvement in SOM quality. The value of MR ranged from 2.16% to 5.95% in the 76 treatments. On average, the minimum MR is 54.2% of maximum MR at the respective sites. Quantity and quality of SOM will rise upon the increment of inorganic manure and/or organic manure applied. The inter-annual mean carbon dioxide flux (F_CO2) mineralized from organic compounds in the plough layer ranges from 337.1 g CO₂ m^-2 a^-1 to 2144.3.7 g CO₂ m^-2 a^-1. Averagely, the minimum F_CO2 is 31.9% of maximum F_CO2 at the respective sites. The annual apparent soil respiration efflux also reflected the degree of SOM mineralization and inorganic nitrogen mineralized in the plough layer. These results suggested that the modified model was simple but valuable in predicting SOM trends and soil carbon sequestration at a single agricultural field.A process-based ecosystem model was established to describe soil water, nitrogen, and carbon dynamics of plants and soils for terrestrial ecosystem in Hunag-Huai-Hai Plain. In the model, the leaf area index (LAI), crop coefficients, and root penetration and distribution were simulated for the winter wheat and summer corn double cropping system. The soil water, soil heat sub-modules were validated using the experiment data at the Quzhou Station. It was found that the simulated soil water content and soil temperature were fitted well with the observed values. Thus, the joint model could be used to evaluate water use efficiency (WUE) and daily dynamics of soil water content. Under the winter wheat-summer corn double cropping system at the 7 selected sites, soil water use efficiency in the control treatments was 0.22⁰.56 kg m^-3 for wheat and 0.58⁰.91 kg m^-3 for corn. On average, thesoil water use efficiency for summer corn was higher than that for winter wheat. The sub-carbon turnover module was calibrated to part of the SOM data from the 7 selected sites. Through the validation of 948 pairs of observed and fitted SOM independent data from the 7 experiments, the joint model provided estimates with a 95% confidence interval of 1.89 g kg"1, the slop coefficient of 1.017 and regression coefficient r2 of 0.911(p<0.01). As far as the comparison between fitted and observed SOM values were concerned, the joint model performed as good as the modified CQESTR model.Statistical analysis on crop yield and SOM showed an increase of 1 t hm'2 soil carbon in SOM for sandy loams to loamy clays in the plough layer might increase annual crop yield by 442.2-952.9 kg hm'2 in the Huang-Huai-Hai Plain. This relationship was based on the critical SOM value of 15.2 g kg'1 in the plough layer, beyond which the annual crop yield reached a stable level. SOM dynamics were simulated by the use of modified CQESTR model. The results showed that, under the cropping system of 3 crops (winter wheat-summer com/spring corn) in 2 years in the fulvo-aquic soil in Beijing, 3937.5 kg hm"2 chicken feces returning to the filed with annual crop yield of 20000 kg hm'2 in 2 years could maintain SOM at a level of 13.1 g kg"1. Under winter wheat-summer corn double cropping system in the fulvo-aquic soils at the Hengshui, Xinji and Zhengzhou, chemical NP or NPK applied together with organic manure (the amount of N, P, K and organic amendment were 100-300 kg hm"2, 120-150 kg hm'2, 82.5 kg hm"2-150 kg hm"2 and 1500 kg hm"2 respectively) could increase SOM steadily and will reach a level of 15.2 g kg"1 in 2050, while annual crop yield maintains 8000-12000 kg hm"2.