| Different land use patterns and fertilization affect soil aggregates and their carbon and nitrogen distribution,nitrogen content and transformation by changing soil microbial environment and the balance of carbon and nitrogen input and output.The characteristics of nitrogen mineralization determine the availability of nitrogen for plant growth in soil,which played an important role in the process of nitrogen cycle in the ecosystem.In this paper,upland,vegetable plots,cropland,woodland,and orchards land in typical black soil area of Jilin Province were selected as the research objects,the composition of aggregates and the distribution of carbon and nitrogen in the 0～20 cm soil layer were studied using the sieving method.And the transformation characteristics of nitrogen forms in different land use types of black soil were studied by the indoor cultivation method.The main results were as follows:(1)Woodland and cropland were dominated by aggregates>2 mm,while 0.25～2 mm aggregates dominated upland,vegetable plots,and orchards land.The mean weight diameter(MWD)and geometric mean diameter(GMD)values were both woodland>cropland>vegetable plots>upland>orchards land.Woodland aggregates had the best stability,followed by cropland,vegetable plots and upland,and orchards land had the worst.(2)The total nitrogen and organic carbon content of the black soil of the five land use modes was 0.25～2 mm granular aggregates,followed by 0.053～0.25 mm,>2 mm,and<0.053 mm particle size aggregates.The total nitrogen and organic carbon content of aggregates with a particle size of 0.25～2 mm and 0.053～0.25 mm were shown as woodland>cropland>vegetable plots>upland>orchards land.The carbon and nitrogen activity of woodland were higher than other land use methods,and it had higher soil fertility.(3)The difference in ammonium nitrogen contents was not significant,but the difference in nitrate nitrogen contents was significant.For the urea treatment,the contents of nitrate nitrogen woodland(129.82 mg·kg-1)and vegetable plots(138.01 mg·kg-1)were significantly higher than those of orchards land(111.89 mg·kg-1)and cropland(105.35 mg·kg-1).The nitrate nitrogen content of upland(126.92 mg·kg-1)was significantly higher than that of cropland.The analysis of the treatment of diammonium phosphate showed:The order of the nitrate nitrogen content of each soil was vegetable plots(160.23 mg·kg-1)>upland(150.00 mg·kg-1)>woodland(140.12 mg·kg1)>orchards land(133.45 mg·kg-1)>cropland(126.70 mg·kg-1).The nitrate nitrogen content of vegetable plots and upland was significantly higher than those of cropland and orchards land.(4)The content of microbial biomass carbon(CM)and microbial biomass nitrogen(NM)in woodland was significantly higher than that of upland and other land use soils with strong disturbance under different land use methods.At the end of cultivation,the differences in CM and NM content among the black soils of each treatment were all expressed as woodland>vegetable plots>cropland>orchards land>upland.(5)Compared with no exogenous nitrogen treatment,the application of exogenous nitrogen can increase the CM and NM content of the black soil in the five land use modes.Under the treatment of urea and diammonium phosphate,the difference of the CM content of the soil in each land use mode was not significant,and the NM content of the soil showed that the treatment of diammonium phosphate>the treatment of urea.(6)The order of the average net mineralization rate(NMR)of upland,vegetable plots,cropland and orchards land from large to small were:treatment 1>treatment 2>control treatment.The NMR of woodland were in the order of treatment 2>treatment 1>control treatment.The order of the net nitrification rate(NR)of upland,cropland and orchards land from large to small were:treatment 1>treatment 2>control treatment,and the NR of woodland and vegetable plots were in the order of treatment 2>treatment 1>control treatment.NMR and NR were negatively correlated with soil C/N,CM,and NM. |
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