Effects of soil conditioners on physical quality and bromide transport properties in a sandy loam soil

In coarse-textured soils, water and nutrients are lost from the root zone through deep percolation and preferential flow, resulting in poor soil quality. The objective of this study was to investigate the influences of polyacrylamide, cattle manure, vermicompost and biological sludge as soil conditioners on moisture retention and bromide transport parameters in a sandy loam soil. Polyacrylamide (0.25 and 0.5 g kg−1 of air-dried soil), cattle manure (12.5 and 25 g kg−1 of air-dried soil), vermicompost (2.5 and 5 g kg−1 of air-dried soil) and biological sludge (1.7 and 3.4 g kg−1 of air-dried soil) were mixed with the soil and uniformly packed into plastic pans and PVC columns, and incubated in a greenhouse at 0.7 to 0.8 field capacity moisture content (0.143–0.163 g g−1) and at 22 ± 4 °C for 6 months. Pans were used to take core samples to determine soil moisture curve parameters at 7, 30, 60, 120, and 180 days. Bromide breakthrough curves were measured at the same time in the PVC columns. Polyacrylamide significantly increased slope of soil moisture curve at its inflection point as compared to the control and other soil conditioners. Polyacrylamide also prevented early breakthrough of bromide at 7 days by decreasing saturated hydraulic conductivity, compared to the control and biological sludge. All soil conditioners reduced dispersivity parameter in convection–dispersion model. Significant (P ≤ 0.01) positive correlation (r = 0.81) was found between dispersivity parameter in convection–dispersion and mobile–immobile models at the five incubation times. The results showed that polyacrylamide was more effective than other soil conditioners in improving physical quality of sandy loam soils.

► Polyacrylamide increased slope of soil moisture retention curve.
► Polyacrylamide prevented early breakthrough of bromide by decreasing Ks.
► Soil conditioners reduced dispersivity in convection-dispersion equation model.
► Polyacrylamide improved physical quality of the sandy loam soil.