Effects of infiltration and evaporation with treated wastewater and salt solutions on soil moisture and salinize-alkalization

Abstract: In order to study the special effects of treated wastewater irrigation on soil salinize-alkalization, we built 5 large soil bins with length of 1.2 m, width of 1.2 m and height of 1.5 m, and filled with loam and sandy soil in 0～80 and 80-120 cm, respectively. Three infrared lamps and one electric fan were placed above the soil bin. After that, indoor large soil bins infiltration and evaporation experiments were conducted to research the effects of infiltration and evaporation with clear water, treated wastewater and salt solutions with SAR=3, 10 and 20 (mmolc/L)0.5 on soil, and soil solution salt and ions migration and accumulation, and soil alkalization. During the 10 times of infiltration and evaporation experiments (simulation field irrigation for 2 years), the electrical conductivity (EC), sodium adsorption ratio (SAR), pH, K+, Ca2+, Na+, Mg2+, Cl-, SO42-, and HCO3- in soil and soil solution were measured. The results showed that compared with the clear water irrigation, soil moisture in 0～40 cm loam were larger and the increasing of sandy soil moisture in 80-120 cm led to lagged effect. The reason was that the dissolved organic matter (DOM) and suspended solids in treated wastewater caused clay dispersion and blocked the soil pores, respectively，and Na+ in treated wastewater and salt solutions with SAR=20 (mmolc/L)0.5 caused clay swelling and dispersion, during the infiltration and evaporation with treated wastewater and salt solution with SAR=20 (mmolc/L)0.5. The soil salt accumulated in treated wastewater and salt solutions treatments after 10 times of infiltration and evaporation, and the cumulant was between 9.54% and 51.83%, and the salt in leacheate was most in treated wastewater treatment, which was 1.09-1.42 times of other treatments. All treatments had similar effects on soil solution SAR value and soil pH, which were less than 3 (mmolc/L)0.5 and 8.5, respectively. The results showed a low possibility of soil alkalization during infiltration and evaporation with treated wastewater and salt solutions. As a coexistence system with variety of materials like salinity, nutrients, suspended solids and DOM, the mass concentrations of K+ and Ca2+ in soil solution showed a different distribution in various depths during infiltration and evaporation with treated wastewater. The mass concentration of Cl- in treated wastewater was about 0.3 times of salt solutions, but the mass concentration of Cl- in soil solution in treated wastewater treatment was 0.95-1.29 times of salt solutions treatments. The mass ratio of Cl- in soil also varied in different soil depths. The treated wastewater treatment had a stronger leaching ability on soil Cl-, and it may attribute to the particularity of treated wastewater and the results of soil maintain charge balance. According to the results, it was concluded that compared with clear water and salt solutions, soil salinity and some salt ions indicated a different migration and distribution in the soil profile after infiltration and evaporation with treated wastewater, and more attention should be paid to the migration and leaching of K+, Ca2+ and Cl-. The results of this research provide references for the long-term secure and rational irrigation with treated wastewater in agriculture.