Effects of Dual‐Layer Subsurface Drainage and Fenlong Tillage on Soil Water and Salt Transport in Soils With Low‐Permeability Layers

ABSTRACT To elucidate the effects of engineering and agronomic measures on soil water and salt transport in soils with low‐permeability layers, a field experiment was conducted using a dual‐layer subsurface drainage system. Soil water–salt distribution and desalination performance were evaluated under drainage‐only and combined drainage–Fenlong tillage treatments. Under the drainage‐only treatment, four leaching events reduced salinity in the 0–40‐cm layer from 12.44 to 7.25 g kg −1 (42%), with reductions of 41% and 40% in deeper layers. Desalination decreased as pre‐irrigation salinity declined, and the effect was weaker at 5–7.5 m from the drain. Under the combined drainage–Fenlong tillage treatment, a single leaching event achieved a desalination rate of 35% in the 0–40‐cm layer with only a 15% increase in irrigation water. Relative weight analysis (RWA) showed that Fenlong tillage independently contributed 16% to surface soil desalination—ranking third after pre‐irrigation salinity (47%) and irrigation amount (23%)—confirmed by residual analysis ( p = 0.0015). Over 2 years, natural conditions alone failed to remove salts, whereas dual‐layer drainage reduced 0–40‐cm salinity from 12.44 to 5.43 g kg −1 (56%). These findings provide a scientific basis for the reclamation of severely saline–alkali land with low‐permeability layers.