RothC Model Simulation Of Soil Organic Carbon On Farmland Crop Residue In North China

Crop residues?including straw and root?,which is an important source of soil organic carbon and soil nutrient,can supply all kinds of mineral elements needed for plant growth and microbial activity.In addition,it can increase the soil organic carbon content effectively therefore improve soil structure and soil fertility at the same time.However,material properties?lignin content,nitrogen content and so on.?of different crop residues are different,there have been short of systemic research on the carbon efficiency of crop residues and its contribution to soil organic carbon..Our study is based on long-term fertilization experimental sites in China combine with RothC model,which is simple and widely used.The modified model was validated with the data obtained from the short-time decomposition experiment?2012.11-2013.11?and the long-term trial conducted in Zhengzhou?1990-2008?.Finally,the model was applied to five typical long-term experimental sites?in heihe,Helen,Harbin,Gongzhuling,Shenyang?.The objectices were to make it clear of the old new carbon carbon mineralization process and the new carbon forming process after crop residues into the soil under different fertilization management measures and to explore the characteristics of old carbon mineralization and the contributrion to soil organic carbon of different crop residues,which have a great significance to the carbon sequestration and promotion of soil organic carbon.What is more,we explore reclamation of Mollisols in northeast China after returning only root crop from time scale and space scale,which provides theoretical support to Mollisols reclamation and Mollisols protection.The main results and conclusion are followed.?1?The DPM/RPM value of different crop residues in model was depend on the difference of material property of crop residues.Based on the data of the decomposing experiment of material,RothC model was simulated inversely.It showed that DPM/RPM values of wheat root?WR?,wheat straw?WS?,corn root?CR?,corn straw?CS?were 0.89,3.04,4.35 and 3.25,respectively,the root mean square error of model were less than 10%?3.7%-6.0%?,the relative error were less than±5%(-0.2%-2.7%.It is showed that the improved RothC model can be applied to ecplore the contribution of crop residues?root and straw?to soil organic carbon from organic material types.?2?The modified RothC model can be used to explore the contributions of wheat and corn residues to newly-formed SOC in fluvo-aquic soil area whether no fertilization,balanced fertilization or straw returned?RMSE were 4.86%-7.89%,RE were-5.23%-2.20%?.The contribution of wheat residue?50%-71%?to newly-formed SOC was greater than corn residue?22%-40%?in winter wheat-summer corn rotation system in north China whether no fertilization,balanced fertilization or straw returned.The ratio of SOC derived from wheat to newly-formed SOC was greater than the proportion of the carbon input from wheat to total carbon input,instead of the carbon input of corn and its contribution to newly-formed SOC.The carbon efficiency of wheat root?15.5%-17.5%?was more than the carbon efficiency of corn root and corn straw?10.8%-11.4%?,so the application of root residues could promote the soil organic carbon stock.?3?It showed that the RothC model could be applied in nontheast of China.The parametersRMSE and RE of improved RothC were in the range of 12%and+7%respectively in Heihe,Hailun,Harbin,Gongzhuling and Shenyang except for NPKS treatment in Gongzhuling?RMSE=26%,RE=23%?.The reason for that lies in its mulching treatment in Gongzhuling so that far less than the calculated value was taken into the soil and the simulation data of soil organic carbon was overestimated in the NPKS treatment.The root contribution of different crop to SOC was shown as corn root>wheat root>soybean root and the carbon efficiency was shown as wheat root>soybean root>corn root under CK treatment?chemical fertilizer treatment and organic fertilizer treatment;The contribution of different crop residue to SOC was shown as corn straw>wheat straw>soybean straw and the carbon efficiency was shown as wheat root>soybean root>corn root>corn straw>wheat straw>soybean straw under straw returning treatment.?4?The modified RothC model can be used to simulate the trend of SOC of Mollisols in northeast China after its cultivation?only root?.SOC content was at a higher level(120.72 t hm^-2-174.68 t hm^-2)before reclamation,while SOC reduced to 30.06 t hm^-2-57.2 t hm^-2when it was 1980s?returning stubble mainly before 1980s?.SOC decreased in the order:Heihe<Helen<Harbin<Gongzhuling from the space scale,mainly due to the year of the reclamation and geographical location?precipitation and temperature?;In the preceding reclamation ten years from the time scale,SOC fell rapidly and its decline rate at 3.51 t hm^-2y^-1-5.89 t hm^-2y^-1,of which Helen was the largest(5.89 t hm^-2y^-1)while Heihe was the slowest(3.51 t hm^-2y^-1);The delining rate of Mollisols was flatten out with the time.At the same time,the content of SOC was in a state of decline or flat in which with higher organic matter content?Heihe,Helen?under the existing organic material resources?organic manure or straw returned?;the content of SOC with lower organic matter content?Harbin,Gongzhuling?showed a trend of rising under the same organic material resources.It will avoid the decline of SOC after increasing organic material under area with higher organic matter content.