Water Exchange And Interaction Between Super Absorbent Polymer And Soil Following Different Wetting And Drying Cycles

Super absorbent polymers(SAPs)are one of the most widely used chemical water-saving materials.It is of great significance for the research and application of SAPs to systematically study the water exchange and interaction between SAPs and soil,to clarify the water exchange mechanism in the multiphase system of SAPs and soil,as well as the indirect effect of soil aggregates on soil water movement.In this study,the analytical tools as total reflection infrared spectroscopy and environmental scanning electron microscopy were used through a series of simulation experiments.The changes of molecular structure and morphology of SAPs,and their effects on soil physical parameters and soil aggregates distribution in continuous dewater-rehydration process were all studied.The effects of SAPs on root morphology,leaf stomatal properties and chlorophyll fluorescence parameters of cucumbers under different water conditions were observed by pot experiment.The water exchange function and mechanism between SAPs,soil and root system were comprehensively evaluated in order to provide theoretical and technical support for farmland water management.The main results and conclusions were listed as follows:1.When the SAPs were mixed with the soil,the Si-O-Si bond,-OH,montmorillonite minerals,amorphous silica and other mineral colloids in the soil would enter into the three-dimensional network structure of the SAPs,resulted in uneven fold and even fracture of the membrane structure of the SAPs.With the increase of the amount of SAPs and the extension of the action time,the chemical effect of mineral colloid in soil on the SAPs was gradually intensified.It was directly proved that the reaction between soil mineral colloid and SAPs in different degrees was one of the main reasons for the decrease of water holding capacity of SAPs with the extension of service time.2.SAPs could increase the ratio of soil liquid phase,improve soil water holding capacity effectively,increase soil field capacity,soil effective water content,permanent wilting point and other water constants.However,the ratio of soil air phase would decrease,which would affect the permeability of the soil.Therefore,it was concluded that the SAPs was more suitable for the soil with larger pores.3.The effect of SAPs on soil water supply capacity was related to its dosage,particle size and soil moisture status.In extreme drought,SAPs could not increase the specific water capacity of soil,but reduce the water supply capacity of soil.In light drought,SAPs could significantly improve the water supply capacity of soil.At the early stage of used SAPs,the smaller the particle size was,the more obvious the effect of water supply capacity of soil was.4.SAPs could enhance the water stability and the average particle size of soil aggregates.Under the influence of SAPs crosslinking,the water stable micro-aggregates in soil less than 0.053 mm would bond to form more water stable macro-aggregates,so as to reduce the damage effect of dry-wet alternation on the soil aggregates.When the dosage of SAPs was 0.3% and the particle size was 0.3-0.45 mm,the effect on promoting the stability of soil aggregate was the most significant.5.When the irrigation amount was maintained at 55% ~ 90% of the field water capacity,the SAPs could increase the free water content of cucumber leaves and reduce the bound water content of cucumber leaves.According to the changes of chlorophyll fluorescence parameters and stomatal characters,when the soil was in light drought,the SAPs could alleviate the drought degree of cucumbers.However,when the soil was in moderate or extreme drought,the SAPs would aggravate the drought stress of cucumbers.