| Agricultural management practices are crucial to the sequestration of organic carbon in farmland soils.Paddy fields,as special cultivated soils,have a large potential for carbon sequestration.Therefore,studying the carbon sequestration potential of paddy soils under different management practices has double positive significance for mitigating global climate change trends and ensuring food security.In this study,we select paddy soil from 84 counties（cities or districts）in Fujian Province as the research objects,based on agricultural management data from 2016 and meteorological data from 1980 to 2016,the"polygon"of the 1:50,000soil database was used as the minimum unit,adopt DNDC（De Nitrification-De Composition）model,which is now widely used in agroecosystems,to simulate the soil carbon sequestration potential of paddy soils in the province under 16 different agricultural combinations of management measures,including organic fertilizer with straw,nitrogen reduction with organic fertilizer and nitrogen reduction with straw,for the next 37 years from 2017 to 2053.To clarify the effects of the interaction of different management factors on soil organic carbon in paddy fields,to systematically analyze the dynamic changes of organic carbon in Fujian Province,different subclasses,administrative units and landform types under different combinations of management measures,and to propose optimized countermeasures for carbon sequestration management measures in paddy fields,with a view to providing a theoretical basis for the formulation of carbon sequestration and emission reduction policies in paddy ecosystems in Fujian Province.The main results were as follows:（1）Four indicators,correlation coefficient（r）,root mean square error（RMSE）,mean absolute error（MAE）and relative error（E）,were used to verify the simulation effect of the DNDC model based on the measured and simulated values of soil organic carbon of paddy fields in Fujian Province in 2016.From the validation results,the correlation coefficient（r）was 0.41,which reached a highly significant level（P<0.01,n=6880）,the root mean square error（RMSE）was 5.46 g·kg-1,the mean absolute error（MAE）was 4.31 g·kg-1,high agreement between measured and simulated values,and the relative error（E）was-8.18%,which indicated that the DNDC model simulation results are reliable.（2）From 2017 to 2053,the soil of paddy fields in Fujian Province showed“carbon sink”effect under the interaction of each organic fertilizer and straw return,and the carbon sequestration potential increased with the increase of organic fertilizer and straw return.The carbon sequestration rates of paddy soils under conventional management measures,1 time organic fertilizer+30%straw（M1S3）,1 time organic fertilizer+50%straw（M1S5）,1 time organic fertilizer+90%straw（M1S9）,2 times organic fertilizer+30%straw（M2S3）,2 times organic fertilizer+50%straw（M2S5）and 2 times organic fertilizer+90%straw（M2S9）measures were 173,425,602,963,547,725 and 1088 kg C·hm-2·a-1,respectively,and the total carbon sequestration were 11.56,28.34,40.17,64.31,36.54 48.40 and 72.62 Tg C,respectively.From the subclasses of paddy soils,saline paddy soils and salty acid paddy soils had the largest carbon sequestration rates between 515 to 1246 kg C·hm-2·a-1,and percogenic paddy soils and hydromorphic paddy soils had the largest carbon sequestration amounts between 9.00 to 35.64 Tg C.From the administrative regions,both Putian and Quanzhou had the largest carbon sequestration rates in paddy soil,ranging from 547 to 1279kg C·hm-2·a-1,while Quanzhou and Zhangzhou had larger carbon sequestration amounts in paddy soil,ranging from 4.59 to 11.37 Tg C.Among the different landform types,the carbon sequestration rate of paddy soil in the plain-platform was the highest,ranging from 493 to1159 kg C·hm-2·a-1,while the carbon sequestration of paddy soil in the hilly-mountains was the highest,ranging from 14.74 to 38.62 Tg C.M2S9 measures had the highest carbon sequestration potential in the province.（3）Under the combined management measures of reducing nitrogen fertilizer and increasing organic fertilizer application,the soils of paddy fields in Fujian Province still showed“carbon sink”effect from 2017 to2053.the carbon sequestration rates of 0.5 times nitrogen fertilizer+1time organic fertilizer（N0.5M1）,0.5 times nitrogen fertilizer+2 times organic fertilizer（N0.5M2）,0.8 times nitrogen fertilizer+1 time organic fertilizer（N0.8M1）and 0.8 times nitrogen fertilizer+2 times organic fertilizer（N0.8M2）were 262,391,287 and 411 kg C·hm-2·a-1,respectively,and the total carbon sequestration were 17.51,26.11,19.15and 27.43 Tg C,respectively.The effect of nitrogen fertilizer reduction on saline paddy soils and salty acid paddy soils was small,and both had the largest carbon sequestration rates and their increases,ranging from 341 to583 kg C·hm-2·a-1and 55.34%-134.95%,respectively.While percogenic paddy soils and hydromorphic paddy soils sequestered more carbon,together accounting for 82.16%of the total carbon sequestration in the province.Carbon sequestration rates of paddy soil in Putian,Quanzhou and Longyan were the highest,ranging from 359 to 629 kg C·hm-2·a-1.Among them,the paddy soil in Longyan responded less to nitrogen fertilizer reduction and had the largest increase in carbon sequestration rate,ranging from 77.93%to 176.00%.Quanzhou,Zhangzhou and Longyan have a larger amount of carbon sequestraton in paddy soils,together accounting for 51.40%of the total carbon sequestered in the province.The carbon sequestration rate and its increase rate of paddy soil in the plain-platform were the highest,ranging from 342 to 513 kg C·hm-2·a-1and 55.63%to 133.22%,respectively.The highest carbon sequestration was found in the hilly-mountainous paddy soil,which accounted for about 50.56%of the total carbon sequestration in the study area.The highest carbon sequestration potential was found in the province under the N0.8M2 measure.（4）Under the combined management measures of nitrogen reduction and straw application,paddy soil in Fujian Province played a“carbon sink”role from 2017 to 2053.Under the same amount of nitrogen reduction,the carbon sequestration potential increased with the increase of straw return to the field.The carbon sequestration rate of 0.5 times nitrogen fertilizer+30%straw（N0.5S3）,0.5 times nitrogen fertilizer+50%straw（N0.5S5）,0.5 times nitrogen fertilizer+90%straw（N0.5S9）,0.8times nitrogen fertilizer+30%straw（N0.8S3）,0.8 times nitrogen fertilizer+50%straw（N0.8S5）and 0.8 times nitrogen fertilizer+90%straw（N0.8S9）were 242,403,760,287,461 and 823 kg C·hm-2·a-1,respectively,and the total carbon sequestration were 16.14,26.92,50.76,19.19,30.79 and 54.90 Tg C,respectively.Among different paddy soil subclasses,the carbon sequestration rate of saline paddy soils and saline acid paddy soils were the largest,ranging from 300 to 900 kg C·hm-2·a-1,the carbon sequestration rate increase of gleyed paddy soils was the largest,ranging from 43.17%to 473.86%,.The carbon sequestration amount of percogenic paddy soils and hydromorphic paddy soils were the largest,ranging from 5.07 to 26.76 Tg C.Putian and Quanzhou have the largest rates of carbon sequestration in paddy soil,ranging from 321 to921 kg C·hm-2·a-1,while carbon sequestration rates of paddy soil in Nanping and Sanming have the largest increase,ranging from 48.38 to615.15%.The combined carbon sequestration in Zhangzhou,Quanzhou,Nanping and Sanming accounted for 58.97%of the total carbon sequestration in the study area.The carbon sequestration rate of paddy soil in the plain-platform was the highest,ranging from 297 to 851 kg C·hm-2·a-1,the largest amount of carbon sequestration was found in the hilly-mountains paddy soil,ranging from 8.29 to 29.44 Tg C.The province’s carbon sequestration potential was the highest under the N0.8S9 measure.（5）Gray Correlation-Structural Equation Model was used to determine the main driving factors affecting soil organic carbon of paddy fields in Fujian Province and their influence effects.The results showed that initial organic carbon,clay,bulk weight,p H,organic fertilizer,nitrogen fertilizer and annual average temperature were the main driving factors of soil organic carbon of paddy fields in Fujian Province.From the path analysis of the main driving factors of the structural equation model,the absolute values of the path coefficients of initial soil organic carbon,clay and organic fertilizer on the soil carbon sequestration rate of paddy fields in Fujian Province were larger,which were 0.269-0.636,0.388-0.580 and 0.489-0.885,respectively,indicating that the three had a greater degree of influence on the carbon sequestration rate.Initial soil organic carbon had a negative effect on the rate of carbon sequestration in the paddy soils of Fujian Province,while clay and organic fertilizers had a positive effect on the rate of carbon sequestration. |
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