Study On The Impacts Of Physiochemical Regulation On Soil Water Movement

The vast arid and semi-arid regions in China accounts for 52.5% of the nation's total area.The semi-arid zone, with the Loess Plateau as the most important part, is the main area ofrain-fed agriculture. Low rate of rainwater use, high soil surface evaporation and soil erosionand water runoff are main problems in the Loess Plateau regions, which restrict thesustainable development of agriculture. To reduce surface runoff and evaporation, and toincrease rainwater use efficiency are of great importance to reduce drought disasters, alleviateshortage in water resources and soil and water loss, and to promote agricultural productivity. The physical regulation method suggested in the paper i.e. the runoff-runon method isindeed a micro-scaled water harvesting method, which uses part of the slope for rainwater torunoff into a runon part of the slope for water infiltration. The purposes are to increaselocalized soil storage of rainwater to increase rainwater utilization efficiency, promote thecapability of crop to sustain draught damage, and to increase crop production. Soilinfiltrability is an important parameter for efficient use of rainwater. Its rational determinationis of great significance. The chemical regulation method studied in the paper applied soil conditioners to the soil.Polyacrylamide (PAM) and phosphor-gypsum (PG) are known to be good soil conditionersfor maintaining soil structure and increasing infiltration. Mixture of them could increaserainwater infiltration and also could improve the functioning of PAM. It is determined thatphysicochemical regulation methods on sloped land is an important approach to developrain-fed agriculture. However, the effects of soil conditioners on soil water hydrodynamicparameters, soil evaporation and water infiltration still need further research. In this study,both PAM and PG were used as soil conditioner to investigate the interactive effects of thesoil conditioners on soil water hydrodynamic parameters and soil water evaporation with soilcolumn experiments. A runoff/runon method was advanced to measure soil water infiltrationcapability and the related algorithm and computational models were developed. Experimentswere conducted to verify the method and the models. The study on physiochemical regulationapproach will supply a foundation for rain-fed agriculture in the Loess Regions. The mainresults of the study are as the following. (1) Soil conditioner increased the water holding capability of soil. The bigger the suctionwas, the more obvious the effect. Application position and depth of soil conditioner had theiraffects on soil water availability and soil water regime. Surface application of the conditionersresulted in lower soil water holding capability. The higher the suction, the lower the waterholding capability, in some cases it was even lower than that of control. Soil conditionerswhen mixed in the soil profile, soil water holding capability improved. Soil conditioners alsoinfluenced the horizontal diffusion of soil water. The horizontal diffusion distance wasquadratically correlated with time. At short distance, the horizontal diffusion of soil water wasirrelevant with the dosage of soil conditioner. When the distance increased (> 6 cm), thedifferences among treatments seemed to be obvious progressively. The saturated hydraulicconductivity of soil treated with conditioners at the surface was significantly higher than thatof control. When soil was mixed with conditioners, with the same PG dosage, the saturatedhydraulic conductivity decreased with PAM. With the same PAM dosage, the higher thehydraulic conductivity increased with PG application. This phenomenon verified thealleviation of PG on PAM. (2) Evaporation experiments with soil columns showed that soil conditioners couldsignificantly reduce evaporation from soil surface. Considered all the influencing factors, thebest combination of PAM and PG for evaporation control was found to be P2P2 (PAM: 2g/m2,PG: 200g...