Improving Soil Water Holding Capacity By Subsurface Water Retaining Membranes.

The subsurface water retention technology (SWRT) is a relatively new long-term approach that  increases water retention capacities in highly permeable soils resulting in sustainable crop production. Layers of dual polymer membranes 30 cm wide and 15 cm deep installed parallel to each other at depths of 35 cm and 50 cm at a sandy soil site in Central Michigan have been shown to increase corn grain yields during the summer 2012 draught by 135% and 174% on 30-inch and 15-inch row spacings, respectively. The objective of this study was to evaluate the effect of installation depth and aspect ratios (width to depth) of the SWRT membranes on soil water holding capacity for soils and climate conditions of Michigan.
     HYDRUS-2D model, that describes two-dimensional water flow in unsaturated soil, was calibrated and validated on data in a large sand-filled lysimeter with SWRT membranes installed at different depths with different aspect ratios. The model adequately reproduced soil water content dynamics measured at 12 locations inside the sand profile. Then HYDRUS-2D simulations were repeated with different soil textural properties for different SWRT installation depths and aspect ratios. The installation depths in these simulations were 20 cm, 40 cm, and 60 cm, while the aspect ratios were 2:1, 3:1, 5:1 and 10:1. Soil texture was sand, loamy sand, sandy loam and sandy clay loam with saturated hydraulic conductivity values of 7.1, 3.5, 1.1 and 0.3 m/day, respectively.  The results of simulations showed that water holding capacity of the soil can be differentially controlled by aspect ratios and installation depth of SWRT membranes. The SWRT membranes with aspect ratio 2x1 substantially increased soil water content at depths of membrane installation for all soil texture classes. This effect was diminishing with increasing aspect ratio of the membrane. The effect of the installation depth on the infiltration losses from the soil profile was not did significant. Overall best results were achieved in sand with 2:1 aspect ratio and installation depth of 40 cm. The HYDRUS-2D simulations showed that SWRT is an efficient management technology in improvement of soil water retention and water-use efficiency in highly water permeable soils.