| As the most serious area of soil and water loss in China,Loess Plateau is one of the key areas for ecological conservation and high-quality development in the Yellow River Basin.Food and ecological environment security are seriously threatened by the deterioration of ecological environment due to the soil erosion and its impact on the sustainable development of agriculture.About 333.3 km~2 of land has been renovated in the Hilly-gully Region through the Gully Land Consolidation project(GLC)since 2010,which is of great significance to ensure food security,protect ecological environment and promote regional economic development.However,the realization of the established objectives is seriously restricted by some problems,such as low soil fertility,poor structure and fragile ecosystem.Thus,aiming at the high-quality development of land resources,the study takes the new created land as the research object to explore the influence of biochar on soil structure in the way of combining field sampling with field experiment on the basis of studying the soil natural evolution law of typical(GLC)projects.This project clarified the effect of biochar on soil quality and crop yield under different nitrogen levels.Meanwhile,it revealed the mechanism of increasing productivity of new created land under the combined application of biochar and nitrogen fertilizer.The GLCcould provide scientific basis for increasing productivity of new created land,efficient utilization of resources and sustainable development of ecological environment.The main conclusions are as follows:(1)The evolution law of the soil quality in the typical Gully Land Consolidation project(GLC).Taking Terraces in Nianzhuang watershed of Yan'an as the object,the study adopted the method of substituting space for time to explore the evolution of soil quality and fertility recovery in recent 30 years.The results showed that soil organic carbon(SOC)and total nitrogen(TN)density increased by 47%and 75%respectively,and the average accumulation rates were 317.7 kg/(ha?a)and37.4 kg/(ha?a).SOC and TN density exceeded the level of slope farmland after 10years and increased by 74.0%and 107%after 30 years.Nitrogen is the main limiting factor of soil organic carbon sink in terraced fields on the Loess Plateau.Under the general farming conditions,it takes 3-10 years for the typical project of(GLC)on the Loess Plateau to recover to the level before consolidation,and it takes another20-30 years to reach the level of fertile land.Therefore,it is urgent to explore a new way to improve the productivity of new land in gully regulation.(2)The effects of biochar on soil structure and soil aggregate stability.The effects of biochar from apple branches on soil bulk density,soil aggregate structure and stability were used to explore the mechanism of combined application of biochar and nitrogen fertilizer on soil physical structure.The results showed that the soil bulk density decreased gradually with the increase of biochar application rate,and the soil bulk density of high fertilizer and high carbon treatment was significantly reduced by15.42%compared with the control.When the biochar application rate was 40 t/ha,the content of soil water stable aggregates larger than 0.25 mm increased by 42.18%compared with the control.The application of Biochar also reduced the destruction rate of soil aggregates,but thesoil organic carbon content,mean weight diameter(MWD)and geometric mean diameter(GMD)were significantly increased.Considering the three indicators of aggregate stability,biochar had the best effects on improving the stability of soil aggregates when the amount of biochar was 40 t/ha.(3)The effects of biochar on the quality of soil carbon pool and carbon cycle in the new created land.The project studied the effects of combined application of biochar and nitrogen fertilizer on soil organic carbon,microbial biomass carbon,carbon components and carbon pool management index,whichcan be used to explore the effects of combined application of biochar and nitrogen fertilizer on soil carbon pool quality and soil carbon cycle.The results showed that the active organic carbon in soil increased with the enhanceof biochar application rate,but the carbon pool activity and activity index were decreased.Under the reduction of chemical fertilizer level,when the biochar application rate was 40 t/ha,the management index of the soil carbon pool increased by 80.47%compared with the control.Combined application of biochar and nitrogen fertilizer significantly increased the contents of soil organic carbon and microbial biomass carbon,with the highest increase of 169%and 181%in high carbon treatment,respectively,so the results indicate that the addition of biochar can improve the soil carbon capacity and is conducive to soil carbon sequestration.(4)The effects of biochar on soil fertility and crop yield in new created land.Based on a twoyears field experiment,the effects of biochar on soil fertility of new created land were revealed from the perspective of soil nutrients and biological characteristics,and the effects of biochar on land productivity were characterized from the perspective of crop yield.The results showed that:when the biochar application rate was 40 t/ha,the soil electrical conductivity of low and high fertilizer treatments increased by 123.93%and 102.73%respectively,and the soil cation exchange capacity increased by 123.93%and 102.73%respectively.The application of biochar and nitrogen fertilizer increased soil organic matter content by 1.21?3.64times,total nitrogen by 18.31%?45.34%,ammonia nitrogen and nitrate nitrogen by1.23 times and 5.69 times respectively,total phosphorus and available phosphorus by11.6%?40.11%and 11.16%?151.09%respectively.Biochar also significantly increased the activities of?-glucosidase and n-acetylglucosaminidase,the number of bacteria and actinomycetes in soil by 5.3?8.5 times and 2.78?4.68 times compared with the control,respectively.The results showed that the highest average yield of maize was 13595.98kg/ha,which was 34.24%higher than that of the control group.(5)The effects of biochar on soil fertility and crop yield in new created land.Based on a 2-years field experiment,the effects of biochar on soil fertility of newfarm land were revealed from the perspective of soil nutrients and biological characteristics,and the effects of biochar on land productivity were characterized from the perspective of crop yield.The results showed that:when the biochar application rate was 40 t/ha,the soil electrical conductivity of low and high fertilizer treatments increased by 123.93%and 102.73%respectively,and the soil cation exchange capacity increased by 123.93%and 102.73%respectively.The application of biochar and nitrogen fertilizer increased soil organic matter content by 1.21?3.64 times,total nitrogen by 18.31%?45.34%,ammonia nitrogen and nitrate nitrogen by 1.23 times and 5.69 times respectively,total phosphorus and available phosphorus by 11.6%?40.11%and 11.16%?151.09%respectively.Biochar also significantly increased the activities of?-glucosidase and n-acetylglucosaminidase,the number of bacteria and actinomycetes in soil by 5.3?8.5 times and 2.78?4.68 times compared with the control,respectively.The results showed that the highest average yield of maize was13595.98kg/ha,which was 34.24%higher than that of the control group.Through factor analysis and cluster analysis,the effects of biochar and nitrogen fertilizer on soil quality were evaluated and the optimal ratio was explored.The article took soil21 indexes which reflecting physical,chemical and biological characteristics of soil fertility as evaluation indexes.Three common factors were extracted to evaluate soil quality.Their cumulative contribution rate reached 85.73%.Based on the comprehensive score of factor analysis,the cluster analysis method was used to grade the soil of each treatment.The results showed that the comprehensive score of soil quality of low fertilizer and high carbon treatment was the highest,and the cluster analysis results also showed that the soil fertility of low fertilizer and high carbon treatment represented the highest grade.Considering the economic benefits and comprehensive evaluation of soil quality of biochar and nitrogen fertilizer treatment,we put forward the high-yield and economic high-efficiency utilization models of new land in gully management.In the same year of biochar application,the soil fertility level can recover or even exceed the level before remediation.It is suggested that the economic biochar and fertilization pattern was added 30 t/ha biochar,280 kg/ha nitrogen fertilizer and 140 kg/ha calcium superphosphate. |
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