| In addition to its important effect on soil quality and crop productivity, soil organic carbon (SOC) has also been identi?ed as a potential sink for atmospheric CO2. SOC model is a useful tool to simulate SOC dynamics under various fertilizations and straw management, and it also plays an important role in guiding soil fertilization and carbon sequestration. The objectives of the study were: (i) to validate and modify the RothC-26.3 mode(lRothamsted carbon model,version 26.3) to simulate SOC dynamics for typical upland soils in eastern China; (ii) to predict the equlibrium point of SOC under various fertilization; (iii) to recommend the reasonable fertilization practices for soil cultivation and carbon sequestration.Three types of upland soils were chosen in this study, including black soil (Gongzhuling site, Jilin province, one crop a year, continuous maize), fluvo-aquic soil (Zhengzhou site, Henan province, two crops a year, wheat-maize rotation), red soil (Jinxian site, Jiangxi province, two crops a year, maize-maize; Qiyang site, Hunan province, two crops a year, wheat-maize). At each site, eight typical fertilizer treatments (CK,N,NP,NK,NPK,NPKM-NPK+Manure,1.5NPKM-1.5NPK+1.5Manure,NPKS-NPK+Straw)were selected to validate the RothC-26.3 model. Some of the default values of RothC-26.3 model were changed for the simulation of SOC dynamics under straw retention treatment and extremely acidified soil. And using the modified RothC-26.3 model, we predicted SOC dynamics in the future 50 years and the equilibrium point under current fertilizer management conditions. The main results and conclusion showed as follows:(1)The RothC-26.3 model adequately simulated SOC dynamics under no-fertilizer, chemical fertilizer and chemical fertilizer plus manure treatments at Gongzhuling and Zhengzhou sites, however, it overestimated SOC content under straw retention treatment. Crop straw has a higher soluble carbon, lesser lignin content and poorer soil physical protection compared to roots, leading to a faster decomposition rate. So with a great amount of straw retention, the gross turnover rate of inputing carbon will be accelerated. For straw incorporation treatment at Zhengzhou site, the modeling efficiency was improved when the DPM/RPM ratio of inputing carbon was changed from the default value 1.44 to 3.35. While for straw mulching treatment at Gongzhuling site, with an inverse simulation after changing the DPM/RPM ratio to 3.35, only 17% of the mulching straw incorporated with soil.(2) The RothC-26.3 model was satisfied to simulate SOC dynamics at Jinxian site, but underestimated SOC content at Qiyang site, especially for those treatments without manure application. Possible reasons for this phenomenon are the seasonal wet and dry periods, heavy clay content and extreme acid soil conditions, which lead to a inhibited microbial activity and much slower decomposition rate of HUM (humified organic matter) poor. By adjusting the decomposition rate constant of HUM pool, which was set to 0.003 (for CK\N\NP\NK\NPK treatments) and 0.009 (for NPKS\M\NPKM\1.5NPKM treatments) instead of the default value 0.02 yr-1, the SOC values obtained with the calibrated model agreed well with the observed data at Qiyang site. (3) Currently, SOC content is unsaturated in the upland of eastern China. Managements with increasing carbon input, such as straw retention and manure application, are favorite to a higher SOC equilibrium point. Under current management practices, for CK treatment, SOC will continue to lost 2-8 t·hm-2 and reach a equilibrium point of 10-20 t·hm-2 at all the four sites; for NPK and NPKS treatments, SOC will get a higher equilibrium point of 30-50 t·hm-2 and carbon sequestration potential of 8-18 t·hm-2 at Gongzhuling and Zhengzhou sites,but only maintain a stable level with an equilibrium point of 20-24 t·hm-2 at Qiyang and Jinxian sites; for NPK plus manure treatments, SOC will reach an equilibrium point of 45-55 t·hm-2 and sequester an additional 10-20 tC·hm-2 at Zhengzhou and Jinxian sites, while an equilibrium point of 70-100 t·hm-2 and carbon sequestration potential of 30-60 tC·hm-2 at Gongzhuling and Qiyang sites.To sum up, RothC-26.3 model overestimated SOC content of straw retention treatment and underestimated SOC content of extremely acid soil. The calibrated RothC-26.3 model is feasible to simulate and predict SOC dynamics under various fertilizations in the upland of eastern China. Measures with increasing carbon input, such as straw retention and manure application, can lead to a higher equilibrium point of SOC in the upland of eastern China. Chemical fertilizer plus manure is the best fertilizer practice to maintain crop yield and increase carbon sequestration.
|
PDF Full Text Request