| The primary condition to ensure national food security is to ensure sustainable agricultural development.It is very important to explore the changes of physical properties and organic carbon components of different types of soils with the increase of hydrotillage years in the northern cold region to ensure sustainable agricultural development.Heilongjiang Province is one of the major grain-producing areas in China.In this study,three typical paddy soils(meadow soil,meadow black soil and gleyic alba soil)in Sanjiang Plain of Heilongjiang Province were selected as the research objects,and the dry tillage soil without rice planting was used as the control.The hardness,bulk density,three-phase composition,total porosity,saturated water conductivity,particle composition,microaggregates,total organic carbon,carbohydrate carbon,humus carbon and mineralizable carbon contents of surface layer,plough bottom layer and core layer under different hydrotillage years were determined.The purpose of this study was to understand the evolution of soil physical properties and organic carbon components in paddy fields during different years of rice planting,and to provide theoretical basis and reference for ensuring the sustainable utilization of soil resources.The five to six years after the conversion from dry tillage to hydrotillage were regarded as the initial stage of hydrotillage.The main research results and conclusions were as follows:(1)In the early stage of transferring from dry tillage to water tillage,the hardness of all soil layers decreased by 3.68%-16.97%,the bulk density of all soil layers increased by1.87%-40.85%,and the bulk density of all soil layers decreased by 1.72%-11.84% in meadow soil and gley clay.The solid phase of meadow soil increased by 40.08% in heart soil,the liquid phase decreased by 25.00%-53.38%,and the gas phase increased by 58.59% in plough bottom.Solid phase of meadow black soil increased by 3.76% in plough layer,liquid phase increased by21.28%-34.76% in all soil layers,and gas phase increased by 4.32% in plough layer.The solid phase increased by 14.23%-32.81%,the gas phase decreased by 41.67%-89.35%,and the liquid phase increased by 32.19% in the plough layer.The total porosity of meadow soil and gley slurry decreased by 2.34%-34.66%,and the total porosity of meadow black soil increased by1.63%-19.13%.The saturated water conductivity of plough bottom decreased by 2.41%-21.40%,while the saturated water conductivity of plough bottom increased by 8.20%-28.86%.In the meadow soil and the meadow black soil,the particle composition of less than 2μm decreased in the surface layer,the particle composition of 2-20μm decreased in the heart layer,and the particle composition of 20-200μm decreased in the plow bottom.The particle composition of0-20μm in gley alba soil increased in all soil layers,and the particle composition of 20-200μm decreased in all soil layers.The composition of microaggregates less than 1μm and 10-250μm in the surface layer of the three soils decreased,and the composition of microaggregates 0-10μm in the plow bottom decreased.The contents of microaggregates smaller than 1μm and 10-50μm in the meadow soil core decreased,the contents of microaggregates in 1-10μm and 250-2000μm in the meadow black soil core decreased,and the contents of microaggregates in 0-10μm in the gley white slurry soil core increased.(2)In the early stage of transforming from dry tillage to water tillage,the total organic carbon content of the meadow core soil layer decreased by 9.20%,while the total organic carbon content of the meadow black soil layer and all soil layers of the gley slurry soil increased by1.53%-56.11%.The contents of carbohydrate carbon in all soil layers of meadow surface soil,meadow black core soil and gley slurry soil decreased by 9.18%-18.52%.The humus carbon content of meadow soil and meadow black soil decreased by 5.24%-14.00%,while the humus carbon content of all soil layers increased by 5.76%-18.77%.The content of mineralized carbon decreased by 25.64%-26.83% in all soil layers of meadow soil,and increased by 18.91%-27.09%in plow bottom and gley white clay core of meadow soil.(3)With the increase of hydrotillage years,the bulk density of meadow soil surface and plough bottom,meadow black soil surface and gley slurry soil increased by 40.41% at most,and decreased by 12.94% at most in other soil layers.The proportion of gas phase in each soil layer decreased significantly,up to 90.98%,while the proportion of liquid phase increased,up to32.60%.The total porosity of meadow soil surface and plow bottom,meadow black soil surface,gley clay surface and plow bottom decreased by 34.29% at most,while that of other soil layers increased by 20.90% at most.The saturated water conductivity of meadow plow bottom and core soil,meadow black soil plow bottom and gley white clay plow bottom increased by 29.86% at most,and decreased by 15.48% at most in other soil layers.The particle composition of less than2μm in meadow soil and meadow black soil,and that of 20-200μm in meadow black soil increased in the heart soil layer,but decreased in the other soil layers.The change law of 2-20μm particle composition was opposite.The particle composition of 20-200μm in meadow soil decreased in the plow bottom,but increased in the other soil layers.The particle composition of20-200μm in gley alba soil decreased in all soil layers,while the other particles increased.The composition of small microaggregates under 10μm in surface layer increased significantly,while that of other large microaggregates decreased significantly.The composition of large microaggregates above 10μm in plough bottom and heart layer increased significantly,while that of other small microaggregates decreased significantly.(4)With the increase of hydrotillage years,the total organic carbon in all soil layers of meadow soil,gley white clay soil and the surface layer of meadow black soil increased by58.19%,while the total organic carbon in other soil layers of meadow black soil decreased by10.83%.The contents of carbohydrate carbon in the bottom layer of meadow core soil,meadow black soil and gley white clay soil increased by 16.67%,while the contents of carbohydrate carbon in other soil layers decreased by 45.00%.The content of humus carbon in each soil core decreased by 26.34%,and that in other soil layers increased by 57.76%.The content of mineralized carbon in all soil layers decreased by 64.62% at most. |
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