Water And Salt Transport Characteristics Of Water-Repellent Soil Under Trickle Irrigation

As an essential natural resource in our life, water yields a fundamental role in economicdevelopment and ecological balance. Especially in recent years, how to lead a preferablyrational and effective utilization of water resources has been put on agenda accompanyingwith the increasingly enormous progress in social economy. Agricultural soil degradation isalways caused by the existence of water repellent soils and saline-alkaline soils. Dripirrigation, as an advanced irrigation method, can not only conserve irrigating water and energy,but can effectively reform the land. In this study, a set of three-dimensional experiments onsoil water movement and salt transportation were launched by simulating the drip sourceinfiltration in field. Water movement and salt transport characteristics of hydrophilic andhydrophobic soils under conditions of single or double point source infiltration were analyzed.The conclusions are stated as follows:Under single source point infiltration, three typical hydrophilic soils with varioustextures were selected as the tested soils. Influences of three different dripper discharges onevery single soil texture were analyzed and compared systematically, including variation ofwetting front along with time, three-dimensional distribution characteristics of soil watercontent and distribution features of soil salt content and chloride concentration. The resultsshowed that the horizontal or vertical wetting front and infiltration time followed a favorablepower function relationship under different dripper discharges. A second-order polynomialrelationship was obeyed by soil salt content at a certain point under soil surface and distanceof this point to dripper. This method can wash out soil salts around below relevant dripper todecrease chloride concentration and further provide an ideal environment for crop rootsystem.Out of3typical hydrophilic soils,2soils derived from the west of China were madehydrophobic with different repellent degrees. Under single source point infiltration withidentical dripper discharge, water movement and salt transport characteristics of different soilsof various repellent degrees were analyzed. Additionally, changes of wetting front anddistribution features of soil water content, salt content and chloride concentration of3degreessoils (hydrophobicity of degree0,1and3) with time were studied. The results showed that:(1) Horizontal and vertical wetting front of2degrees soils abided by a power functionrelationship with time under a dripper discharge of0.07ml/min;(2) soil salt content at a certain point under soil surface and distance of this point to dripper followed a goodsecond-order polynomial relationship;(3) Slightly hydrophobic soil had similar distributionfeatures of water and salt content, though the existence of discrepancy in quantitativeness.Therefore, drip irrigation can also provide a favorable environment for crop growth in somefield influenced by slightly hydrophobicity.In double source point infiltration experiment,3hydrophilic soils were put up ashydrophobicity with degree3. Except research contents mentioned at section (Ⅱ), changes ofwetting front of interference section and distribution features of water content, salt contentand chloride concentration of interference section with time were also analyzed. The resultsshowed that:(1) interference time of hydrophobic soils is shorter than that of hydrophilic soilsunder the same dripper distance and discharge. The worse the infiltration performance, theshorter the interference time;(2) Horizontal and vertical wetting front of saline-alkaline soiland time followed a logarithmic and polynomial relationship, respectively; Vertical wettingfront of Lou soil of degree3hydrophobicity obeyed a logarithmic relationship with time;Vertical wetting front of the other kinds of soils followed a relationship of power functionwith time; Wetting front of interference section of3hydrophilic soils matched a goodpolynomial relationship with time;(3) Soil water content is the highest at the point underdripper, then began to decrease with the increase of distance of dripper to the point; The initialcontact point at interference section had the highest water point. The longer the distance tothis point, the smaller soil water content;(4) Soil salt content and chloride concentration werethe lowest under the dripper, then increased along with increase of distance to the dripper;(5)In interference section, salt content at the center is the lowest. It began to increase withincrease of distance to the center;(6) Distribution characteristics of degree3hydrophobic soilsalt content, water content and chloride concentration were irregular and unclear. But watercontent of the upper layer of soil was always higher than that of the subsoil. The distributionof soil salt content and chloride concentration were the direct opposite of that of soil watercontent. Double source point interference infiltration technique can also restrain salt contentand supply a fairly good environment of water and salty ions for degree3hydrophobic soils.