Calibration of saline water quality assessment standard based on EC and CROSS considering soil water-salt transport and crack formation

Cation ratio of soil structural stability (CROSS) can replace sodium adsorption ratio (SAR) to evaluate the effects of base cations on soil structure. It is generally accepted that in saline water with the same electrical conductivity (EC), a higher CROSS reflected a greater reduction in soil infiltration rate. However, we hypothesized that once the CROSS reached a certain value, soil cracks developed, alleviating the decrease in infiltration rate. We set up an indoor one-dimensional soil column infiltration experiment, using saline water with the same EC (4.0 dS m⁻¹) but varying CROSS_opt (Optimal CROSS) values (100.8 (NM100), 67.3 (NKM67), 37.9 (NCM38), 27.8 (NC28), and 9.3 (mmol_c L^–1)^0.5) (KC9), and deionized water as the control (CK). The results demonstrated that Ksat decreased as CROSS_opt increased, but there was no significant difference between NC28, NCM38, and NKM67 (P > 0.05). NM had the lowest Ksat, around 50 % of CK's. There was a positive correlation between CROSS_opt and soil salination rate, with NM100 having about a 30 % higher salination rate than KC9. Only KC9 reduced the crack number compared with CK, and NKM67 had the most cracks. Compared with CK, NM100, NC28, and KC9 reduced the soil crack aspect ratio, with KC9 having the smallest ratio. The anisotropy of NKM67, NCM38 and KC9 was closer to 1.0 compared with CK, while NM100 was closer to 0. Based on EC and CROSS_opt, we propose categorizing water samples into three types: no permeability problem expected, severe permeability problem expected, and no severe permeability problem expected. This study provides valuable theoretical support for assessing saline water quality and protecting soil quality.