Can the physical‐hydraulic properties of degraded soil be improved using polymers?

Abstract

For a degraded soil it is assumed that improvements in key physical-hydraulic properties occur at an optimum superabsorbent polymer (SAP) application rate, following repeated wetting and drying cycles. A column experiment was carried out in a shade house (Ceará State, Brazil), following a completely randomized design, in a 6 × 4 factorial scheme in which six SAP application rates (0—control, 0.15, 0.30, 0.60, 1.20, and 2.40 g kg−1) were incorporated into a sandy loam soil and subjected to four numbers of wetting and drying cycles (one, three, six, and nine cycles), with three replications. Soil bulk density, total porosity, macroporosity and microporosity, degree of flocculation, plant available water, and pore distribution by size were evaluated. After six wetting and drying cycles, the highest SAP rate reduced soil bulk density by 4%–9% compared to the control. At an SAP application rate of 1.2 g kg−1 the degree of flocculation increased by 25%, mainly after six wet and drying cycles. From the rate of 0.15 g kg−1 SAP onward, there was a 20% reduction in macroporosity and a 28% increase in microporosity, increasing total porosity, particularly after six cycles. SAP rates ranging from 0.15 to 0.6 g kg−1 increased available water by 12%–33%, while the highest polymer rate increased available water by 40%–50% compared to the control. This increase in soil available water is of strategic importance for water use efficiency, crop yields, and restoration activities in degraded dryland sandy soils.