| Cultivated land in Guizhou Province is an important prerequisite and guarantee for food production,and an important agricultural resource to ensure food supply and food safety.Yellow soil and calcareous soil,as typical soils in Guizhou Province,are also the main soil types for agricultural land in Guizhou with strong phosphorus fixation.Zhijin County of Bijie City in the province is rich in phosphate mineral resources,and the soil phosphorus content is relatively high.In addition,the effect of fertilization and rainfall makes the leaching pattern of phosphorus more special.In the past,it was generally believed that the main way of phosphorus loss was surface runoff,but more and more studies have confirmed that leaching loss is also an important way of phosphorus loss when soil phosphorus content is high,and sufficient rainfall will also further accelerate the process.Therefore,this study took the yellow soil and calcareous soil in the cultivated land of Zhijin County,Guizhou Province as the research object,and explored the vertical distribution of soil moisture and phosphorus in the two cultivated land types of paddy field and dry land through indoor soil column leaching experiments.Use the Hydrus-1D model to simulate the vertical migration process of soil moisture,and by changing the corresponding conditions to explore the effect of different rainfall conditions on the infiltration of soil moisture in the cultivated land in the study area,in order to provide a basis for the prevention and control of agricultural irrigation and agricultural non-point source phosphorus pollution in the study area.The main conclusions of the study are as follows:(1)The basic properties of yellow soil and calcareous soil under the background of different farming methods in the study area were obtained through laboratory experiments,which provided the basis for building the Hydrus-1D model.The average soil bulk density of yellow soil in the study area is 1.24g/cm~3,which is less than that of calcareous soil,which is 1.45g/cm~3.The average soil bulk density of dry land is1.43g/cm~3,which is larger than that of paddy field,which is 1.25g/cm~3.The average soil porosity of yellow soil is 0.49,which is larger than that of calcareous soil by 0.45.The average soil porosity of dry land is 0.44,which is less than that of paddy field by0.50,the deeper the soil depth,the larger the bulk density and the smaller the porosity.The soil texture of the study area is all silt loam,and the overall is alkaline.The soil moisture characteristic curve of the study area shows that the surface soil is more likely to lose water in the low suction range,and the water retention of the deep soil is better in the high suction range.The saturated hydraulic conductivity of the same soil type is generally higher than that of the lower soil,and the overall yellow soil infiltration rate is generally higher than that of calcareous soil,and the infiltration rate of paddy field is generally faster than that of dry land.The soil organic matter,nitrogen and phosphorus contents in the study area are relatively rich,and the average soil available phosphorus content is 8 mg/kg,which is less than 50 mg/kg.(2)The characteristics of water infiltration and phosphorus leaching in yellow soil and calcareous soil were analyzed through indoor soil column leaching experiments.The experimental results showed that the overall soil water content showed a rapid increase trend in the early infiltration stage,and after the soil reached a saturated state,the soil water content will fluctuate greatly,but the overall will be stable near the soil saturated water content,or slightly lower than the soil saturated water content.Among them,the water infiltration rate of yellow soil is generally faster than that of calcareous soil,and the water content of paddy fields after soil saturation is generally higher than dry land.The content of total phosphorus and soluble phosphorus in soil leachate also showed a trend of increasing first and then decreasing with time.Under normal fertilization,the content of soluble phosphorus in soil leachate was very low and mainly concentrated in the surface layer,and the soil leaching loss is very small.(3)Through the indoor soil column leaching experiment,combined with the measured data,the Hydrus-1D model was used to simulate the movement and change process of the vertical migration of four types of soil moisture in yellow soil dryland,yellow soil paddy field,calcareous soil dry land,and calcareous soil paddy field.Determine the final model-related parameters,in which the saturated water content of paddy field is generally higher than that of dry land,the soil saturated hydraulic conductivity of yellow soil paddy field topsoil is the highest(2.55cm/day),the calcareous soil dry subsoil is the lowest(0.22cm/day).Finally yellow soil dryland,yellow soil paddy field,calcareous soil dry land,calcareous soil paddy field,between four soil moisture infiltration Hydrus-1D model simulation value and the soil moisture measured value,the coefficient of determination R~2 are close to 1,the root mean square error RMSE and relative error RE both are small and close to 0,indicating that the overall simulation effect of the model is good and the accuracy is high,and it can be used to simulate the soil moisture infiltration process in the study area.(4)Using the Hydrus-1D soil moisture infiltration model with parameters calibrated,different scenarios were set up to simulate the influence of different rainfall conditions on soil moisture infiltration in yellow soil dryland,yellow soil paddy field,calcareous soil dry land,and calcareous soil paddy field.The greater the rainfall intensity,the faster the soil water infiltration rate,the more the soil water content increases,and the higher the peak value.With the increase of rainfall duration,soil water infiltration ability changed from strong to weak,and the increase of soil water content gradually slowed down from large.The rainfall type mainly affects the rainfall intensity and capacity in the early and later stages of rainfall,and the speed and magnitude of soil water content changes are related to it.Soil water content increased faster and more in the early stage of declining rainfall.The changes of soil water content are relatively more obvious in the later period of cumulative rainfall.Among different soil types,the change trend of water content of yellow soil dryland and paddy field is more similar,and the change trend of water content of calcareous soil dryland and paddy field is more similar,and the soil water content of yellow soil cultivated land surface and lower layer is more obviously affected by different rainfall conditions than calcareous soil cultivated land,the changes of soil water content in yellow soil cultivated land are faster and larger.In this study,the hydraulic parameters of yellow soil,calcareous soil,dry land and paddy field were determined,and the Hydrus-1D model of soil water infiltration in cultivated land in phosphorus-rich areas was established,and the dynamic simulation of soil water movement in yellow soil and calcareous soil in cultivated land in Guizhou was realized.It provides a basis for studying the characteristics of soil water infiltration in yellow soil and calcareous soil in Guizhou province. |
