Evaluating Soil Water–Salt Dynamics under Brackish Water Drip Irrigation in Greenhouses Subjected to Localized Topsoil Compaction

Abstract

Localized soil compaction in greenhouses resulting from less frequent tillage operations and frequent trampling by farmers inevitably disturbs the continuity and homogeneity of soil’s hydraulic properties, which impacts the precision of greenhouse cultivation regarding water supply and salinity control. However, predicting water–salt dynamics under partly compacted topsoil is difficult because of the interactions between many factors related to soil properties, including irrigation method and water quality, which are especially subjected to varied compaction sizes and positions. Here, two field treatments were conducted in brackish water (3 g L−1) drip-irrigated plots, with the designed soil compaction region (40 cm width and 30 cm depth) adjacent to (T1) and below (T2) the drip lines. The calibrated and validated HYDRUS-2D model was applied to analyze salt exchanges across the vertical and horizontal interfaces between the compacted and non-compacted zones and the associated solute concentration variations within these two zones. The results indicated that the limited horizontal solute flux under T1 enhanced the subsequent downward flux below the drip lines, whereas, under T2, the restricted downward flux with relatively limited improved horizontal salt spreading resulted in more salt retention in the soil profile. Additional scenario simulations considering the vertical and horizontal extension of soil compaction sizes (ranging from 10 × 10 cm to 40 × 40 cm) were also conducted and revealed that, with the same increment in compaction size, the vertical extension of the compacted zone aggravated salt accumulation compared with that of horizontal extension, while the simulated cumulative water and salt downward fluxes were positive in relation to the compaction sizes in both vertical and horizontal directions under T1, but negative under T2. The findings of this study explore the effect of relative positions between drip lines and the soil compaction zone on salt transports under brackish water irrigation and reveal the potential soil salinization trend as extending compaction regions in the vertical or horizontal direction.