Effect of vertically rotary sub-soiling tillage and saline water irrigation on water and salt movement in soil

【Objective】 Vertically rotary sub-soiling tillage is a new cultivation method to improve soil water storage. In this study, the effect of its combination with saline water irrigation on water and salt movement in soil were studied. 【Method】 The experiment was conducted in a laboratory. It consisted of three salinity treatments with salt concentration of the irrigation water being 0 g/L (S1), 3 g/L (S2), and 5 g/L (S3) respectively, and two tillage treatments: conventional tillage (FG) and vertically rotary sub-soiling tillage (FL). For each treatment, we measured the movement of water and salt in the soil. 【Result】 With the increase in irrigation water salinity, regardless of tillage, irrigation water infiltration rate and advancing rate of the wetting front in the vertical direction both increased first followed by a decline, while the advancing rate in the horizontal wetting front increased steadily. Compared to FG, FL reduced the infiltration time by 8.70, 15.27 and 14.89%, and the advancing time of the horizontal wetting front by 10.00, 17.39 and 20.95%, respectively, for salinity treatment S1, S2 and S3. The Kostiakov model accurately described the relationship between the cumulative infiltration and infiltration time for the two tillage treatments with R2>0.99. After 20 days since irrigation, the soil moisture content in FL was lower than that in FG when irrigation water salinity was the same, while under the same tillage, the soil moisture content increased with irrigation water salinity, despite at insignificant levels. After 20 days since irrigation, soil desalination rate in FL was 42.95%-55.98%, compared to 32.34%-43.29% in FL. It was also found that for salinity treatment S1, S2 and S3, the average soil salinity in FL decreased by 22.38%, 18.54% and 15.68%, respectively, compared to those in FG. 【Conclusion】 Saline water irrigation combined with vertically rotary sub-soiling tillage improves irrigation water infiltration, advancing of wetting fronts, as well as soil desalination. For all treatments we compared, vertically rotary sub-soiling tillage combined with an irrigation water salinity of 3 g/L is optimal.