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Slope farmland, as a product of contradictions between population and resources under backward production conditions, is an important agricultural production resource. Its nutrient enters rivers and lakes with soil erosion, making the water eutrophic. The problem of loss of nutrients on cultivated land in the early 1970s attracted attention. The serious pollution of lakes and the increase of fertilizer input are all caused by the migration of nutrients. According to statistics, agricultural non-point source pollution accounts for 1/3 of all pollution in China, and it continues to deteriorate. The study found that the real root cause of water pollution is Loss of soil nutrients. Former researchers used soil testers to do a lot of research on nutrient loss along with runoff from the surface, but there were fewer studies on the loss of soil nutrients with subsurface runoff, and studies on the effects of preferential flow, soil flow, and other water movement processes on nutrient loss were still under investigation. stage. Therefore, a comprehensive understanding of the impact of water movement on nutrient loss can effectively reduce soil nutrient loss and prevent non-point source pollution.
The characteristics, methods and influencing factors of nutrient loss on sloping farmland have been studied. Rainfall acts on topsoil, causing the loss of nutrients on slope farmland. It is closely related to the regional rainfall process and has a random nature. Nutrient loss is extensive with the runoff entering water bodies and spreading over vast areas. Loss of nutrients at a certain fixed point is indeterminate. It has a large spatial change with time and space and time. Because the loss of nutrients reaches a certain amount, it reflects the poor and degraded soil and is lagging and potentially threatening. Nutrients are distributed in runoff and sediment along with runoff, making the monitoring, control, and treatment more difficult and complex.
The loss of soil nutrients is a physical chemical process that is comprehensively affected by rainfall characteristics and underlying surface factors. Soil nutrient leaching, loss of soil nutrients, and entry into the atmosphere through gaseous volatilization or dust are the three main approaches. Li Junbo believes that soil nutrient loss pathways are carried by runoff sediment and runoff water. The predecessors learned about nutrient loss from different perspectives and obtained a lot of research results. In recent years, the study of nitrogen leaching has been widely concerned by many researchers. The use of isotope tracers and other technologies in foreign countries to study nitrogen leaching is a lot, nitrogen loss is less, and the combination of the two is less. The northern China mainly concentrates on the precipitation conditions and the effects of irrigation water on the loss of nitrogen and phosphorus in soils. The southern region mainly concentrates on the law of nutrient leaching in red soil and nitrogen loss in paddy soil.
The characteristics and ways of nutrient loss determine the multifaceted nature of its influence factors. Precipitation is the driving force of production and sand production, and runoff is also the medium that carries nutrients. Therefore, rainfall intensity is one of the main factors influencing the loss of nutrients on slope lands, and rainfall time, ground slope, slope length, soil physical and chemical properties, crop coverage Degrees, land use methods, land preparation methods and other underlying factors directly affect the slope runoff, it is also the main factor affecting the loss of nutrients. Previous studies on the leaching and loss of nutrients caused by surface runoff have been conducted under artificial rainfall or natural rainfall conditions on different influencing factors. However, leaching and loss are usually studied separately to make a comprehensive assessment of the effect of nutrient loss on non-point source pollution. Limited.
The impact of soil moisture movement on nutrient loss in sloping farmland The study of the influence of preferential soil flow on nutrient loss in sloping farmland The preferred stream is a term proposed for soil water movement in recent years and is a relatively common form of rapid non-equilibrium soil water movement. It quickly reached the deep soil and even the underground non-uniform flow. The test results of the soil moisture analyzer showed that the formation of surface runoff, the formation of underground runoff and the process of movement and loss of nutrients were greatly affected, and the formation of debris flows, landslides and collapses were induced. The transported solute can cause serious deterioration of groundwater quality. Preferential flow phenomenon, as a special movement form of soil moisture, has become one of the key and difficult problems in the study of world hydrology.
At present, the research on the effect of preferential flow on nutrient loss in slope farmland is rarely reported in China. Many scholars have studied the characteristics and influencing factors of preferential flow, and concluded that because infiltration water does not have sufficient time to maintain balance with other parts of the slow migration of soil matrix, Make the priority flow non-balanced in the flow path. The static factors affecting the preferential flow are mainly the soil physical and chemical properties, biological factors and initial soil moisture content. The dynamic factors are rainfall intensity, irrigation methods, farming methods, and dry and wet and freezing and thawing. Soil macropores, which are generally distributed as aggregates, are the preferential pathways in the soil. The number, connectivity, and distribution characteristics in a certain area influence the occurrence of preferential flow phenomena. The initial soil moisture content reflects the upper layer physical characteristics of the layered soil and has a preferential effect on the preferential flow. Important role; studies have shown that when the initial soil moisture content is high, the application of pesticides, short-term rainfall makes the migration path of pesticides deep. Rainfall intensity and irrigation methods influence the preferential flow movement process. Tillage methods, freeze-thaw cycles, and dry-wet alternation processes change the structure and porosity of the soil, leading to the formation of preferential flow.
No-tillage increases soil permeability and increases the amount of contaminants flowing into groundwater. Niu Jianzhi also believes that large spinal cord animals in the no-tillage field can drastically drive preferential flow generation. The study of the self-cleaning zone using a PVC cut-off soil column showed that the freeze-thaw and dry-wet alternating process resulted in large pores in the soil and the formation of preferential flow. Qin Yaodong made a detailed discussion on the research status and progress of large pore flow in soil. He Fan believes that the priority flow rate is mainly determined by the secondary flow of production and the amount of rainfall in the early stage. When the priority flow and the surface runoff flow line are unimodal, the linear relationship between the two flows depends on the amount of secondary rain and the amount of rainfall in the previous period. The difference. Niu Jianzhi’s research shows that soil is loose, porous and porous, low-intensity, low-rainfall, and long-term rainfall, and that there are thick layers of ground cover and abundant root layers, which are the preconditions for preferential flow. . Wang Wei used the bright blue staining method to divide the occurrence area of ​​preferential flow in the forest. The results showed that with the increase of soil depth, the macropores showed the distribution of aggregated states and the number gradually decreased. The “funnel†shaped pores are favorable for water preferential transport. Grasping the influencing factors of priority flow and combining the characteristics of nutrient loss, it is of great significance to study the influence of preferential flow on nutrient loss to fully understand the loss of nutrients on slope farmland.
The effect of soil currents on nutrient loss from sloping cultivated lands The formation of soil currents originates from the flow of soil water in the soil. Together with surface runoff and underground runoff, it constitutes the runoff process of the basin. It is also an important part of the runoff of the slopes, resulting in the generation of runoff. Loss of nutrients has an important impact. Researches on the flow of soils in foreign countries focus on the study of the medium-flow model. The domestic emphasis is on the formation of soil currents, influencing factors, runoff characteristics, and nutrient output characteristics of soils on the slopes of the purple and red soils.
Soil nutrient loss characteristics in sloping paddy soils in the purple soil area The presence of soil currents in the soil causes changes in the surface erosion status and affects the nutrient output characteristics. Xu Pei used simulated rainfall to study the runoff characteristics of soil in purple soil and sloping farmland. It showed that the dominant factor in the increase of soil flow was shallow soil layer. Tillage improved soil structure, increased water infiltration, and gentle slope conditions, while at the same time peak soil flow. The flow increases significantly with increasing rain intensity. Ding Wenfeng and Jia Haiyan used the artificial rainfall method to study the formation of midstream in the purple soil of the Three Gorges reservoir area, indicating that the midstream flow is active, and the more loose the soil is, the greater the flow is. The flow in the active soil in gravity erosion plays a very important role in promoting the development. Even the amount of erosion caused by this is much higher than the forms of slope erosion such as sheet erosion and gully erosion. This is related to the previous research on the slopes of the Yangtze River Basin. Erosion is mainly based on surface erosion. Zheng Zheng's application of coupled runoff model for slope-soil flow shows that the effect of slope on flow in soil is not obvious, which is different from that of Ding Wenfeng et al. Ding Wenfeng used a combination of 4 different slopes and 5 different rain strength experiments to study, indicating that although the total amount of midstream flow in the total runoff is not high, but its carrying nutrient content is 4.362 to 63 times the surface runoff nutrient content, which Contrary to the findings of Jia Haiyan. The loss of nutrients carried by the soil in the stream is still immature and further research is still needed.
Soil Nutrient Loss Characteristics in Sloping Soils in Red Soil Region Yin Zhongdong studied the interaction of surface vegetation cover, dead material cover, bare land slope surface and rain intensity on the gentle slope of red soil, indicating that the flow in bare soil is much less than After the water conservation measures, the flow and the total amount of soil in each layer of the covered land were greater than the coverage; the medium flow of the bottom layer of the covered area was less than the surface layer, while the other two areas were opposite. Wang Feng used different types of land use as the starting point, combined with different types of rainfall, indicating that the formation of subtropical streams in the red earth region varies with the type of rainfall. Yan Liping's research shows that the trends of total nitrogen and total phosphorus concentrations in different layers of soil on different slopes of flue-cured tobacco sloping fields are basically the same, but the variation of total phosphorus concentration in the midstream of different slope positions shows a fluctuating decreasing law with depth, and the coefficient of variation with depth increases. Become smaller.
The research on the nutrient loss from the formation of soils by the former is relatively small. When it comes to specific nutrient loss, most of them are combined with surface runoff. There are many studies on nitrogen and phosphorus nutrients, but lack of potassium. the study. Therefore, in practical production, it is not only necessary to control surface runoff, but more importantly, it is necessary to increase the water holding capacity of the soil and reduce the flow in the soil so that nutrient loss can be controlled.
Impacts of underground runoff on nutrient loss from sloping cultivated lands. Underground runoff is the part of the precipitation that seeps into the ground and becomes groundwater and leaks into the watercourse in the form of springs or percolating water. The domestic research on underground runoff has focused on the digital simulation method for forecasting the underground runoff process. Its relationship with surface runoff can be recorded using the soil moisture recorder, the application of surface-underground runoff coupling model in the watershed, and the retreat of underground runoff. There are few studies on the effects of subsurface runoff on soil nutrient loss, etc. Li Xinhu used a large-scale soil leakage device to study the loss of nutrient in underground runoff caused by three kinds of ecological measures: Baixi grass cover, Baixi grass cover and bare soil. It showed that under the three kinds of ecological measures, the loss of nutrients under cover was the largest, followed by coverage, and exposure. The minimum; the nutrient of underground runoff mainly comes from the leaching of nutrients in the upper soil. The stronger the leaching, the larger the underground runoff and the more nutrient loss. At present, the study of nutrient loss in subsurface runoff is seldom and still in an exploratory stage. To understand the effect of subsurface runoff on soil nutrient loss, further research is needed on the loss of nutrients with subsurface runoff.
From the current research, the study on the nutrient loss system of slope farmland is not perfect, and the research on the effects of surface runoff on nutrient loss tends to be mature, while neglecting the process research on the effects of preferential flow, subsurface flow and underground runoff on nutrient loss. Preferential flow affects the loss of soil nutrients has not yet been quantified; there are few studies on the impact of soil flow on nutrient loss, usually combined with surface runoff to study, and lack of integration with other processes such as underground runoff; little research on the effect of underground runoff on nutrient loss, There is also a large research space. The study focused on the mechanism of nutrient loss on slope farmland and carried out studies on the influence of multiple factors. It can gradually quantify the current qualitative research, solve the unresearched aspects one by one, and effectively control the loss of nutrients on slope farmland, reduce soil erosion, and improve soil quality. Control non-point source pollution and achieve sustainable development of slope farmland.
The characteristics, methods and influencing factors of nutrient loss on sloping farmland have been studied. Rainfall acts on topsoil, causing the loss of nutrients on slope farmland. It is closely related to the regional rainfall process and has a random nature. Nutrient loss is extensive with the runoff entering water bodies and spreading over vast areas. Loss of nutrients at a certain fixed point is indeterminate. It has a large spatial change with time and space and time. Because the loss of nutrients reaches a certain amount, it reflects the poor and degraded soil and is lagging and potentially threatening. Nutrients are distributed in runoff and sediment along with runoff, making the monitoring, control, and treatment more difficult and complex.
The loss of soil nutrients is a physical chemical process that is comprehensively affected by rainfall characteristics and underlying surface factors. Soil nutrient leaching, loss of soil nutrients, and entry into the atmosphere through gaseous volatilization or dust are the three main approaches. Li Junbo believes that soil nutrient loss pathways are carried by runoff sediment and runoff water. The predecessors learned about nutrient loss from different perspectives and obtained a lot of research results. In recent years, the study of nitrogen leaching has been widely concerned by many researchers. The use of isotope tracers and other technologies in foreign countries to study nitrogen leaching is a lot, nitrogen loss is less, and the combination of the two is less. The northern China mainly concentrates on the precipitation conditions and the effects of irrigation water on the loss of nitrogen and phosphorus in soils. The southern region mainly concentrates on the law of nutrient leaching in red soil and nitrogen loss in paddy soil.
The characteristics and ways of nutrient loss determine the multifaceted nature of its influence factors. Precipitation is the driving force of production and sand production, and runoff is also the medium that carries nutrients. Therefore, rainfall intensity is one of the main factors influencing the loss of nutrients on slope lands, and rainfall time, ground slope, slope length, soil physical and chemical properties, crop coverage Degrees, land use methods, land preparation methods and other underlying factors directly affect the slope runoff, it is also the main factor affecting the loss of nutrients. Previous studies on the leaching and loss of nutrients caused by surface runoff have been conducted under artificial rainfall or natural rainfall conditions on different influencing factors. However, leaching and loss are usually studied separately to make a comprehensive assessment of the effect of nutrient loss on non-point source pollution. Limited.
The impact of soil moisture movement on nutrient loss in sloping farmland The study of the influence of preferential soil flow on nutrient loss in sloping farmland The preferred stream is a term proposed for soil water movement in recent years and is a relatively common form of rapid non-equilibrium soil water movement. It quickly reached the deep soil and even the underground non-uniform flow. The test results of the soil moisture analyzer showed that the formation of surface runoff, the formation of underground runoff and the process of movement and loss of nutrients were greatly affected, and the formation of debris flows, landslides and collapses were induced. The transported solute can cause serious deterioration of groundwater quality. Preferential flow phenomenon, as a special movement form of soil moisture, has become one of the key and difficult problems in the study of world hydrology.
At present, the research on the effect of preferential flow on nutrient loss in slope farmland is rarely reported in China. Many scholars have studied the characteristics and influencing factors of preferential flow, and concluded that because infiltration water does not have sufficient time to maintain balance with other parts of the slow migration of soil matrix, Make the priority flow non-balanced in the flow path. The static factors affecting the preferential flow are mainly the soil physical and chemical properties, biological factors and initial soil moisture content. The dynamic factors are rainfall intensity, irrigation methods, farming methods, and dry and wet and freezing and thawing. Soil macropores, which are generally distributed as aggregates, are the preferential pathways in the soil. The number, connectivity, and distribution characteristics in a certain area influence the occurrence of preferential flow phenomena. The initial soil moisture content reflects the upper layer physical characteristics of the layered soil and has a preferential effect on the preferential flow. Important role; studies have shown that when the initial soil moisture content is high, the application of pesticides, short-term rainfall makes the migration path of pesticides deep. Rainfall intensity and irrigation methods influence the preferential flow movement process. Tillage methods, freeze-thaw cycles, and dry-wet alternation processes change the structure and porosity of the soil, leading to the formation of preferential flow.
No-tillage increases soil permeability and increases the amount of contaminants flowing into groundwater. Niu Jianzhi also believes that large spinal cord animals in the no-tillage field can drastically drive preferential flow generation. The study of the self-cleaning zone using a PVC cut-off soil column showed that the freeze-thaw and dry-wet alternating process resulted in large pores in the soil and the formation of preferential flow. Qin Yaodong made a detailed discussion on the research status and progress of large pore flow in soil. He Fan believes that the priority flow rate is mainly determined by the secondary flow of production and the amount of rainfall in the early stage. When the priority flow and the surface runoff flow line are unimodal, the linear relationship between the two flows depends on the amount of secondary rain and the amount of rainfall in the previous period. The difference. Niu Jianzhi’s research shows that soil is loose, porous and porous, low-intensity, low-rainfall, and long-term rainfall, and that there are thick layers of ground cover and abundant root layers, which are the preconditions for preferential flow. . Wang Wei used the bright blue staining method to divide the occurrence area of ​​preferential flow in the forest. The results showed that with the increase of soil depth, the macropores showed the distribution of aggregated states and the number gradually decreased. The “funnel†shaped pores are favorable for water preferential transport. Grasping the influencing factors of priority flow and combining the characteristics of nutrient loss, it is of great significance to study the influence of preferential flow on nutrient loss to fully understand the loss of nutrients on slope farmland.
The effect of soil currents on nutrient loss from sloping cultivated lands The formation of soil currents originates from the flow of soil water in the soil. Together with surface runoff and underground runoff, it constitutes the runoff process of the basin. It is also an important part of the runoff of the slopes, resulting in the generation of runoff. Loss of nutrients has an important impact. Researches on the flow of soils in foreign countries focus on the study of the medium-flow model. The domestic emphasis is on the formation of soil currents, influencing factors, runoff characteristics, and nutrient output characteristics of soils on the slopes of the purple and red soils.
Soil nutrient loss characteristics in sloping paddy soils in the purple soil area The presence of soil currents in the soil causes changes in the surface erosion status and affects the nutrient output characteristics. Xu Pei used simulated rainfall to study the runoff characteristics of soil in purple soil and sloping farmland. It showed that the dominant factor in the increase of soil flow was shallow soil layer. Tillage improved soil structure, increased water infiltration, and gentle slope conditions, while at the same time peak soil flow. The flow increases significantly with increasing rain intensity. Ding Wenfeng and Jia Haiyan used the artificial rainfall method to study the formation of midstream in the purple soil of the Three Gorges reservoir area, indicating that the midstream flow is active, and the more loose the soil is, the greater the flow is. The flow in the active soil in gravity erosion plays a very important role in promoting the development. Even the amount of erosion caused by this is much higher than the forms of slope erosion such as sheet erosion and gully erosion. This is related to the previous research on the slopes of the Yangtze River Basin. Erosion is mainly based on surface erosion. Zheng Zheng's application of coupled runoff model for slope-soil flow shows that the effect of slope on flow in soil is not obvious, which is different from that of Ding Wenfeng et al. Ding Wenfeng used a combination of 4 different slopes and 5 different rain strength experiments to study, indicating that although the total amount of midstream flow in the total runoff is not high, but its carrying nutrient content is 4.362 to 63 times the surface runoff nutrient content, which Contrary to the findings of Jia Haiyan. The loss of nutrients carried by the soil in the stream is still immature and further research is still needed.
Soil Nutrient Loss Characteristics in Sloping Soils in Red Soil Region Yin Zhongdong studied the interaction of surface vegetation cover, dead material cover, bare land slope surface and rain intensity on the gentle slope of red soil, indicating that the flow in bare soil is much less than After the water conservation measures, the flow and the total amount of soil in each layer of the covered land were greater than the coverage; the medium flow of the bottom layer of the covered area was less than the surface layer, while the other two areas were opposite. Wang Feng used different types of land use as the starting point, combined with different types of rainfall, indicating that the formation of subtropical streams in the red earth region varies with the type of rainfall. Yan Liping's research shows that the trends of total nitrogen and total phosphorus concentrations in different layers of soil on different slopes of flue-cured tobacco sloping fields are basically the same, but the variation of total phosphorus concentration in the midstream of different slope positions shows a fluctuating decreasing law with depth, and the coefficient of variation with depth increases. Become smaller.
The research on the nutrient loss from the formation of soils by the former is relatively small. When it comes to specific nutrient loss, most of them are combined with surface runoff. There are many studies on nitrogen and phosphorus nutrients, but lack of potassium. the study. Therefore, in practical production, it is not only necessary to control surface runoff, but more importantly, it is necessary to increase the water holding capacity of the soil and reduce the flow in the soil so that nutrient loss can be controlled.
Impacts of underground runoff on nutrient loss from sloping cultivated lands. Underground runoff is the part of the precipitation that seeps into the ground and becomes groundwater and leaks into the watercourse in the form of springs or percolating water. The domestic research on underground runoff has focused on the digital simulation method for forecasting the underground runoff process. Its relationship with surface runoff can be recorded using the soil moisture recorder, the application of surface-underground runoff coupling model in the watershed, and the retreat of underground runoff. There are few studies on the effects of subsurface runoff on soil nutrient loss, etc. Li Xinhu used a large-scale soil leakage device to study the loss of nutrient in underground runoff caused by three kinds of ecological measures: Baixi grass cover, Baixi grass cover and bare soil. It showed that under the three kinds of ecological measures, the loss of nutrients under cover was the largest, followed by coverage, and exposure. The minimum; the nutrient of underground runoff mainly comes from the leaching of nutrients in the upper soil. The stronger the leaching, the larger the underground runoff and the more nutrient loss. At present, the study of nutrient loss in subsurface runoff is seldom and still in an exploratory stage. To understand the effect of subsurface runoff on soil nutrient loss, further research is needed on the loss of nutrients with subsurface runoff.
From the current research, the study on the nutrient loss system of slope farmland is not perfect, and the research on the effects of surface runoff on nutrient loss tends to be mature, while neglecting the process research on the effects of preferential flow, subsurface flow and underground runoff on nutrient loss. Preferential flow affects the loss of soil nutrients has not yet been quantified; there are few studies on the impact of soil flow on nutrient loss, usually combined with surface runoff to study, and lack of integration with other processes such as underground runoff; little research on the effect of underground runoff on nutrient loss, There is also a large research space. The study focused on the mechanism of nutrient loss on slope farmland and carried out studies on the influence of multiple factors. It can gradually quantify the current qualitative research, solve the unresearched aspects one by one, and effectively control the loss of nutrients on slope farmland, reduce soil erosion, and improve soil quality. Control non-point source pollution and achieve sustainable development of slope farmland.
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