Variation Of Soil Water Content And Coupling Of Soil Water And Nutrients In Typical Red Soil Region Environment

There are large area,enough water and heat resources in red soil,which distributed in many provinces in China.The red soil has great potential for agriculture development,but seasonal drought is the main factor to hinder agriculture production. Many researchers had given their suggestions to fight drought,there still have many problems.Meanwhile,acidification and pollution also led to the deterioration of ecological environment.Exploiting water resource and developing land recourse reasonably should be essential measures of agricultural sustainable development. Experimental district and simulation in laboratory were taken to study the variation of soil water content,soil nutrient and the transportation of major anions in acid rain. Results were as follows:(1) The saturated hydraulic conductivity was an influential factor of the infiltration property.The undisturbed and disturbed soil saturated hydraulic conductivities of a typical red soil from upland and paddy land respectively were studied.In addition,influencing factors of the soil saturated hydraulic conductivities also had been studied,including soil bulk density,soil texture and the organic matter content.The results showed that the range of the undisturbed soil saturated hydraulic conductivity was between 44.8×10^-4～1.94×10^-4 and the disturbed soil saturated hydraulic conductivity was between 2.59×10^-4～1.09×10^-4.The surface layer's saturated hydraulic conductivity was the largest one.According to the results of SPSS, it can be concluded that bulk density was the main influencing factor,soil texture and the organic matter content also influence the soil saturated hydraulic conductivity.(2) Hydraulic characteristics and soil reservoir of red soil were studied to find out the reason of seasonal water shortage.The results were as follows:in upland red soil, there were no obvious differences of available water content between different layers in soil profile,which variation range was from 82.17-99.59×10^-3 cm³Â·cm^-3.In paddy field,variations of available water content,from 112.89-230.2×10^-3 cm³Â·cm^-3.Between different layers were remarkable.Soil saturated water content was mainly influenced by soil bulk density.The soil water content was determined by soil clay content in the high suction situation in paddy field.The total soil reservoir and the unavailable soil reservoir were relatively high in upland red soil,but the available soil reservoir was only 17.71 mm.In paddy field,the unavailable soil reservoir was lower.The available soil reservoir was about 30.74 mm,higher than that in upland red soil.The result had shown that the lower available soil reservoir caused by soil physical and chemical properties.This should be a very important factor to seasonal water shortage in red soil region.(3) Seasonal drought and the low available soil moisture,which are restrictive factors of agricultural production.Soil moisture and physic-chemical properties of red soil were determined to analyze the soil moisture dynamic variation in different periods and to find out the profit and loss of soil moisture and their impact factors. The results showed that the variation of red soil moisture in a year can be divided into four phases:filling period(from March to June);deficit period(from June to August); recovery period(from August to October);stable period(from October to March). The weather factors have different influences in different experiment plots.Effect of evaporation in N plot,NP plot and NPK plot shows a degressive trend.On contrast, effect of rainfall shows an ascending trend.(4) Variation of nitrate and ammonium with seasons in soil profiles was studied. The results indicated that nitrate and ammonium contents were high in surface soil layer in every treatment and low in bottom layer.Nitrate and ammonium in upland soil layer reached the highest contents of 248.34 mg·kg^-1 and 127.24 mg·kg^-1 in May in N treatment,due to winter wheat required more nutrients in jointing-flowering stage in April and May,fertilization was applied in large amounts to crops.The nitrate and ammonium had significant relation in straight line between NPK and NP plots.There were diverse relations in different months in N and blank plots.Influenced by Vegetation,nitrate and ammonium contents had a sharp positive relation with soil organic matter in every treatment and changed with exponential function.(5) Acid rain is a problem which increases agricultural,environmental and ecological concerns worldwide.SO₄^2- and NO₃^- are major anions in acid rain,which can speed up soil acidification and lead to leaching loss of base cations.In this study, some soil columns were used to describe the break through curves(BTCs) of infiltration of SO₄^2- and NO₃^- in typical red soils.The results were as follows:the penetrative velocity of NO₃^- was faster than SO₄^2-.BTCs of NO₃^- have remarkable differences in different layers.The peak value of BTCs in plough layer,which C/C₀ value was 0.39,was the highest in soil profiles.The order of the peak value of BTCs was plough layer＞parent material layer＞leached layer＞plow pan layer.The trail of BTCs of SO₄^2- was prolonged obviously in each layer.The order of the peak value of BTCs was plough layer＞leached layer＞parent material layer＞plow pan layer.The peak value of BTCs in plough layer was 0.22,and higher than other layers. Hydrus-1D model was used to simulate the penetrative process.Correlative coefficients of BTCs and its simulation value were more than 0.9 generally.It shows that Hydrus-1D model is a useful tool to estimate the penetrative process of SO₄^2- and NO₃^- in red soil region.The infiltration of SO₄^2- and NO₃^- was predicted by this model after an acid rain fall in rainy season.It can be concluded that a sustained infiltration of SO₄^2- will result in leaching loss of base cations.