Influence Of Reclaimed Water Infiltration On Soil Water Hydrodynamic Characteristic Parameters Of Typical Soil In Subtropical Zone

The utilization of reclaimed water for irrigation is not only an effective way to alleviate the shortage of water resources,but also an important measure to improve the ecological environment and realize the benign cycle of water ecology.Irrigation water quality is a key factor affecting water movement in soil.It is of great significance to study the influence of reclaimed water on soil hydrodynamic characteristic parameters for the scientific management and utilization of reclaimed water.In this study,four types of typical soils,including red soil,tidal soil,purple soil and paddy soil,were selected as research objects.Using different concentrations of reclaimed water（RW）,according to the ratio of1:1 ratio of distilled water and recycled water that is 2 times dilution of reclaimed water（RW-2）,4 times dilution of reclaimed water（RW-4）,the 6 times diluted reclaimed water（RW-6）,and using the distilled water treatment（CK）as the control group,the infiltration experiments were carried out.The saturated water conductivity,water diffusivity and infiltration rate of disturbed soil were measured by one-dimensional vertical and horizontal infiltration test with constant water head.The characteristic curve of soil moisture was determined by centrifuge method and the important parameters were extracted by van Genuchten model and Brooks-Corey model.The characteristics and parameters of soil infiltration after 1 year of reclaimed water irrigation were determined by Mini Disk infiltration meter.The main research results are as follows:（1）The reclaimed water of different concentrations had different effects on the soil moisture front movement.The water quality treatment showed a promoting effect on paddy soil,a promoting effect first and then inhibit on purple soil.The RW treatment provided a promoting effect on red soil and tidal soil,and an inhibiting effect on the rest.The fitting analysis showed that there was a power function relationship between soil water transport rate and time,and the water transport rate curves of red soil,tidal soil,purple soil and paddy soil under RW treatment were:v（t）=0.8877×t^-0.5167,v（t）=0.6159×t^-0.5132,v（t）=0.3778×t^-0.5754,v（t）=0.5766×t^-0.4993,respectively.（2）Compared with the CK treatment,The RW treatment first promoted and then inhibited the water diffusion process of red soil,purple soil and paddy soil.The turning point occurred when the soil moisture content was about 0.2 cm³/cm³,while the water diffusion process of tidal soil was always inhibited.Correlation analysis showed that parameter a of soil water diffusivity curve was positively correlated with clay content（<0.002 mm）and SAR value（P<0.01）,and negatively correlated with organic matter content and electrical conductivity（EC）value（P<0.01）.b had a highly significant positive correlation with organic matter content,pH value and sand content（P<0.01）,and a highly significant negative correlation with clay content and SAR value（P<0.01）.（3）The effects of different concentrations of reclaimed water treatment on the saturated water conductivity of the four kinds of soil were shown as follows:red soil>purple soil>tidal soil>paddy soil;under RW treatment,the relative saturated water conductivity of the four kinds of soil was 1.72,1.28,1.36 and 0.85 successively.The saturated water conductivity of red soil,purple soil and paddy soil increased with the decrease of the reclaimed water concentration,while the saturated water conductivity of wet soil first decreased and then increased with the decrease of the reclaimed water concentration.Correlation analysis showed that K value of soil saturated water conductivity was negatively correlated with soil CEC value,pH value and EC value（P<0.01）,negatively correlated with organic matter content（P<0.05）,and positively correlated with SAR value（P<0.05）.（4）The RW treatment reduced the effective moisture content of red soil,tidal soil,purple soil and paddy soil by-6.25%,10.42%,3.94%and 12.15%,respectively.The RW treatment changed the pore size distribution of each soil.Compared with the CK treatment,the effective pore proportion of red soil,tidal soil,purple soil and paddy soil increased by-3.85%,8.79%,1.35%and 0.57%,respectively.The correlation analysis showed that residual water contentθ_r was positively correlated with clay content（P<0.05）,and pore shape coefficient n was negatively correlated with soil EC value（P<0.05）.（5）Under reclaimed water irrigation,the cumulative infiltration（I）of red soil increased with the decrease of the concentration of reclaimed water(I_RW<I_RW-2<I_RW-4<I_RW-6<I_CK),and the cumulative infiltration of other soil was not obvious except that I_RW was the lowest.Compared with the CK treatment,reclaimed water of different concentrations increased the permeability coefficient S value of red soil by 10.16%（RW）,30.51%（RW-2）,84.75%（RW-4）,and 98.30%（RW-6）,respectively.S value under reclaimed water treatment of tidal soil was also significantly higher than that CK treatment,and S value under RW treatment of purple soil and paddy soil was the minimum.Correlation analysis showed that the red soil,tidal soil infiltration rate coefficient c value and reclaimed water concentration reached extremely significant positive correlation（P<0.01）,and silt content showed a significant negative correlation（P<0.01）,the purple soil,paddy soil infiltration parameters c and S value was extremely significant negative correlation with pH value（P<0.01）.