| Jianghan Plain is an important commodity grain production base in China.Its rice cultivation has a long history.In recent years,under the influence of economic interests,the area of paddy fields has been increasing.Due to the different farming patterns of dryland and paddy fields,there is a significant difference in soil macroporosity between different years of hydroponic cultivation.This difference will significantly affect the water flow characteristics and the process of water loss.In this paper,the author uses computed tomography(CT)and field-stained tracer methods to quantitatively analyze soil macropore morphological parameters and profile flow characteristics in 2-year paddy fields,18-year paddy fields,and 100-year paddy fields in Jianghan Plain.It is expected to provide scientific basis for the formulation of reasonable water management measures in rice fields.The main conclusions of this paper are as follows:(1)Due to different years of hydroponic cultivation,there are obvious differences in the three-dimensional image features of large pores in rice fields in 2,18 and 100 years.The distribution of macropores decreases dramatically with increasing soil depth.And its distribution is not uniform.The distribution of macropores is as follows:100 years of paddy fields<18 years of paddy fields<2 years of paddy fields.The distribution of large soil pores of straw soil is richer than that of non-straw soil.The distribution of macropores in the tillage layer is much larger than that of the plow pan.The soil with straw shows more obvious.In the 2-year paddy field,large-scale pores are mainly distributed in strips.In the 18-year paddy field,the large pores of rice fields showed coexistence of points and strips.In 100-years paddy field,the large pores of paddy fields are mainly points.(2)The soil macroporosity,macropore area,macropore quantity,and the law of perimeter variation were similar in the three paddy fields,and they gradually decreased with increasing soil depth.The macroporosity,macropore area,macropore quantity,and perimeter of the tillage layer are larger than the plough bottom layer and subsoil layer.The plough bottom layer and the subsoil layers all showed a sharp decrease.The performance was as follows:100 years of paddy fields<18 years of paddy fields<2 years of paddy fields.The circle rate increases with the increase of soil depth,and finally approaches 1.There are significant differences in macroporosity,macropore quantity,macropore area,perimeter,and circle rate between straw and no straw soils.In addition,straw soil fluctuates more than no straw soil.The roots under the straw mainly affect the characteristics of macropores in the soil of the tillage layer.It has little effect on the deep soil.(3)The ratio of soil macroporosity increases first and then decreases with the increase of pore diameter.The pore diameters of the three paddy fields are mainly 1-2 mm,accounting for about 30%-40%of the total,and there are more in 100 years than the other two rice fields.It shows that:>2 mm diameter macropores with 2 years of paddy fields>18 years with rice fields>100 years with rice fields.Macropores with a diameter of>2 mm all showed a decreasing trend.The most significant reduction in paddy fields in 100 years.There is a significant difference in the distribution of pore diameters between straw soil and no straw soil.In the 2-year rice field,the soil pore diameters of the straw were distributed in the range of 0.6-3 mm,and the amount was more than that of the no straw soil.The pore diameter of 0-20 cm soil layer is 100 years of paddy field>18 years of paddy field>2 years of paddy field,while the soil below 20 cm is 100 years of paddy field<18 years of paddy field<2 years of paddy field.(4)The soil staining characteristics of the three types of paddy fields showed significant differences.The stained area ratio in the tillage layers of the three types of farmland is the highest.With the increase of soil depth,the area ratio of dyeing decreased sharply.However,the area ratio of the subsoil dyeing area increased significantly.In 2 years and 18 years of the paddy field was significantly more than that in 100 years.Affected by long-term different cultivation and irrigation measures,the soil properties of the three types of paddy fields are different,which causes various vertical and lateral flow characteristics.In the process of vertical infiltration,the water flow is the most obvious in 2 years of in the rice field,followed by 18 years,and the water flow is the weakest in 100 years.With the increase of the distance from the dye spraying area,the dyeing area decreases gradually.In addition to the ploughing layer,the colored area of other soil layers in the 100 years of paddy field was less than 2 years and 18 years of rice field.The lateral flow of paddy field in 100 years is more obvious than that of the other two paddy fields.(5)Variation of the stained path count and the stained path width were similar,and their fluctuation decreased with the increase of soil depth.Stained path count and stained path width were significantly increased in the soil layers of rice fields in 2 and 18 years,and more than 100 years.<10 mm,10-100 mm,and>100 mm dye path widths showed significant differences in connectivity.In addition to the width of<10 mm,the dyeing path can extend continuously from the soil surface to the bottom of the soil profile.The other two grades of the dyeing path show discontinuities.The dyeing path with the width>100 mm is the most obvious.The width of the 10-100 mm dyeing path was the dominant in the tillage layer.In the 100-year paddy field,it is far more than in the 18-year and 2-year paddy fields.However,the width of the dyeing path of each field plough was decreased sharply.In 2 and 18 years,the subsoil in paddy fields is mainly staining paths with<10 mm and 10-100 mm widths.It is obviously more than 100 years of paddy fields.The number of dyeing paths in the tillage layer is 100 years of paddy field>18 years of paddy field>2 years of paddy field.The soil below the tillage layer showed the most in 2-year paddy field,followed by 18-year paddy field and then is 100-year paddy field.(6)The types of soil water flow in three kinds of paddy fields are different.There are more than three types of soil water flow in each paddy field.Only 100 years of paddy fields and 18 years of paddy fields have a homogeneous flow.The water flow type of subsoil layer is obviously different.The 100-year paddy field is dominated by low-interaction macropores.The effect of pore and water exchange is not obvious.The 18-year paddy field is dominated by migmatization macropores.The 2-year paddy field is dominated by high-interaction macropores,and the exchange of pores and water was obvious.The phenomenon of preferential flow in paddy soil is the most significant in 2 years,followed by paddy field in 18 years,and then is the paddy field in 100 years. |
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