| The study utilized biogeochemical model DNDC (DeNitrification-DeComposition,9.5),with the database of1:50000for soil-land use according to the measure values of23,869sampling points in year1980and15,948sampling point in year2008, took five typical county (Tong’an, Pucheng, Wuping, Yongding, and Minhou) in different geographic locations from Fujian Province in subtropical regions as the study area, analyzed the change rule of soil organic carbon in Fujian province between1980and2009, explored the "cardon source/sink" effect of20possible scenario in soils of Fujian province from2011to2040. Thereby providing the theoretical foundation for the development of organic carbon management measures. The main research conclusions were as follows.1. According to the verification result at the regional scale, the correlation coefficient between the simulated and the measured values of soils SOC in research region is0.77. The simulated values of soils SOC are strongly correlated to the measured values of soils SOC.The MAE and RMSE is4.35g/kg and3.40g/kg which was less on the small side.The results indicated that DNDC model has a good performance on simulating the SOC dynamics for the soils of Fujian province. According to the verification results from the diverse land-uses, the correlation coefficient between the simulated and the measured values of soils SOC in diverse land-uses,involving irrigated paddy fields,vegetable plots,dry land, irrigated land,rain fed paddy fields, is0.72(n=5559),0.54(n=1137),0.36(n=490),0.15(n=609) and0.39(n=85). The simulated values are strongly correlated to the measured values. The MAE were3.69g/kg,3.75g/kg,4.69g/kg,2.40g/kg and4.33g/kg. The RMSE were4.47g/kg,4.64g/kg,6.00g/kg,3.30g/kg and5.57g/kg. The results indicated that DNDC model has a good performance simulating the SOC dynamics for the diverse land-uses of Fujian province. According to the verification result from the diverse soil groups, the correlation coefficient between the simulated and the measured values of soils SOC in diverse soil groups, involving paddy soils, latosolic red soils, red soils, is0.72(n=7307),0.19(n=371) and0.54(n=150). The simulated values are strongly correlated to the measured values. The MAE were3.59g/kg,5.08g/kg and3.60g/kg. The RMSE were4.62g/kg,6.46g/kg and4.60g/kg. The results indicated that DNDC model has a good performance on simulating the SOC dynamics for paddy soils, latosolic red soils, red soils of Fujian province. The correlation coefficient between the simulated and the measured values of yellow soils SOC is0.12(n=27). The simulated values were not correlated to the measured values. The results indicated that the simulated values were not accurate to yellow soils. According to the verification result from the diverse soil subground, the correlation coefficient between the simulated and the measured values of soils SOC,involving percogenic paddy soils, gleyed paddy soils, hydromorphic paddy soils, submergenic paddy soils and bleached paddy soils, is0.68(n=3262),0.50(n=587),0.58(n=2624),0.29(n=652) and0.69(n=77). The simulated values are strongly correlated to the measured values(p<0.01). The correlation coefficient between the simulated and the measured values of Salinized paddy soils SOC is0.16(n=105). The simulated values are not correlated to the measured values. The results indicated that the simulated values were not accurate to the Salinized paddy soils. Coastal solonchaks, latosolic red soils, red soils, yellow soils and fluvo-aquic soils were the only soil subgrounds of their soil group, the verification result was same to their soil group.2. According to the change of soils organic in Fujian province between1980and2009, the soils in Fujian province showed the weak "cardon source" effect as a whole. The total SOC stock in soils increased7.37Tg and the dSOC is189.72kg/hm2. The total SOC stock in the Paddy soils increased6.81Tg and the dSOC is212.09kg/hm2. The yellow soils, coastal soloncharks,fluvo-aquic soils and Latosolic red soils showed the "cardon source" effect. The dSOC and total SOC stock of these soil types were between30.44-178.9kg/hm2and0.01-0.58Tg respectively. The red soils and fluvo-aquic soils showed the "cardon sink" effect. The dSOC and total SOC stock of these soil types.3. The simulation results of changes of different meteorological factors from2011to2040indicated that, carbon fixation of soil in Fujian province of carbon dioxide (CO2) concentration normal increase, normal increase concentration increased1times and2times3scenarios was7.04Tg,7.08Tg,7.30Tg respectively; carbon fixation of soil in Fujian province of normal rainfall, rainfall increased20%and decreased20%3scenarios was7.04Tg,6.56Tg,7.24Tg respectively; carbon fixation of soil in Fujian province of temperature increased2℃and4℃2scenarios was5.62Tg and4.27Tg respectively, The results indicated that temperature increased in the future had the great impact to the change of SOC.4. The possible scenario of changes of different agricultural management measures from2011to2040indicated that, cultivated soil in Fujian showed the slight "carbon sink" effect when treated without the use of nitrogen fertilizer and0.5times of normal nitrogen fertilizer application, losing carbon respectively1.10Tg and4.95Tg; and when the nitrogen fertilizer application amount reached1.5and2times of normal nitrogen fertilizer application in Fujian Province, it showed the carbon fixation was respectively7.80Tg and7.05Tg. Manure amendment increased double,2times and3times on the basis of the normal treatment scenarios, carbon fixation of cultivated soil in Fujian Province was13.35Tg,19.47Tg and25.67Tg, respectively. When the siraw returning rate increase to50%and90%of normal fertilizer application, carbon fixation of cultivated soil in Fujian Province was respectively18.73Tg and31.62Tg. The tillage changed from the normal current farming to no-tillage, carbon fixation of cultivated soil in Fujian Province was reached9.65Tg. The different processes of one type of a combination of recommended management practices (30%of the straw returning rate,30%of Manure and no-tillage), second type of a combination of recommended management practices (50%of the straw returning rate,50%of Manure and no-tillage) and third type of a combination of recommended management practices (90%of the straw returning rate,90%of Manure and no-tillage) showed that cultivated soil in Fujian showed the huge "carbon sink" effect, carbon fixation was respectively19.95Tg,35.76Tg and65.66Tg. In terms of different agricultural management measures of paddy soils organic carbon in Fujian Province, the order of contribution rate was:third type of a combination of recommended management practices> second type of a combination of recommended management practices> crop biomass returned by90%>one type of a combination of recommended management practices>3times of organic fertilizer>2times of organic fertilizer>crop biomass returned by50%>1time of organic fertilizer>1.5times of nitrogen fertilizer>2times of nitrogen fertilizer>0.5times of nitrogen fertilizer>no nitrogen fertilizer, it indicated that the combination of recommended management practices would pay an important part in the management of organic carbon in Fujian Province in the future. |
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