| In the process of globalization,agricultural land use was mainly influenced by agricultural products price,yield,relative polices resulting in frequent change of land use.Cropping system conversion represents the main change of land use in agricultural production.This study collected soil samples in mollisols region of Songne Plain by gridding location,following soil samples recollection and famer household survey,then estibilished a systematic analysis methods to understand the change of soil organic carbon and soil acidification.We also build a systematic analysis method by using RUSEL model to evaluated soil erosion.Optimized management practices were proposed for soil improvement in mollisols region of Songnen Plain.The main results are as follows:(1)From year of 2005 to 2014,the main reason of cropping system conversion was the net benefit gap between soybeans and corn in term of yield and cost in Songnen Plain.The increase of density and accumulation temperature of varieties of soybeans was lower than those of com.The yield of corn increased from 5.05 Mg ha-1 to 6.14 Mg ha-1,meanwhile the soybean yield almost did not change.With the same growth rate of prices and cost,the siginificant increase of corn yield was the main reason for widening the benefit gap between soybeans and corn.The decrease of soybean benfit influenced the farmer’s plant decision,which led to the cropping system conversion from soybeans to corn.(2)A decrease of Soil organic carbon(SOC)was found by 11.9%in mollisols region of Songnen Plain from 2005 to 2014.However,the changing gap of SOC in different cropping systems is siginificant.SOC decreased by 37.7%and 13.6%in soybean monocropping system(S-S)and soybean and corn break crop system(S-C)respectively but increased by 12.3%in com monocropping system(C-C).The initial SOC level determine the increase or decrease of SOC,but the decrease mignitude was mainly determined by carbon input in different cropping systems.The conversion from low biomass crop(soybeans)to high biomass crop(corn)could maintain or increase the SOC in this area.(3)A decreae of soil pH was found by 0.27 from 2005 to 2014,showing a trend of acidification in mollisols region of Songnen Plain.Speicificly soil pH was decreased by 0.16,0.30 and 0.25 in S-S,C-C and S-C respectively.Though the system analysis of net H+ production in plan-soil system,the results showed that cron production area has a greater soil acidification than soybean production area,due to more H+ production from nitrogen cycling in C-C(91.3 kmol ha-1)than that in S-S(25.5 kmol ha-1)in ten years.(4)Soil erosion of Keshan County was 1.58 million ton in year of 2016,which was deceased by 0.12 million ton(7.3%)than that in 2011.The change of vegetation cover rate and management was the dominant reason of soil erosion decrease in conversion area.The cropping system conversion from soybeans to corn in July led to 45.8%of decreased soil erosion in this County,due to higher cover rate of corn than that of soybeans in July.In terms of space dimension,the cropping system conversion from soybeans to corn in areas with 1-2 gradients led to 35.3%of soil erosion decrease in this County.(5)Other impacts such as soil nutrient,soil water,soil enzyme activity,water quality,biodiversity and food security in different cropping systems should be considered when evaluating the sustainable development of mollisols besides SOC,soil acidification and soil erosion.According to our study,the S-C gained the greatest integrated soil quality followed.Therefore,measures as increasing plant density,using high density cultivated varieties,increasing straw return rate and rhizobia inoculation and balanced fertilization should be adopted in the break crop system.Other effective practices including lime application,conservation tillage,cover crops,and biochar application are also important for achieving soil quality improvement,farmer benefit and agricultural sustainable development in mollisols. |
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