Improving aggregate stability and hydraulic properties of Sandy loam soil by applying polyacrylamide polymer

Abstract

Improving soil properties, especially in arid and semiarid regions, is an urgent need for sustainable food production. This study aims to evaluate the effect of applying two types of anionic polyacrylamide polymers (PAMs) with different molecular weights on: (1) soil aggregate stability, (2) infiltration rate and (3) saturated hydraulic conductivity of sandy loam soil and introduce a novel modelling approach to predict the effect of PAM addition on the mentioned soil properties. Polymers were applied at five different concentrations; 0, 100, 250, 500 and 1000 mg L−1. Direct positive relations between the concentrations of PAM (low and high molecular weight) and saturated hydraulic conductivity and infiltration rate were observed. Nevertheless, the relations were more pronounced in case of low molecular weight PAM. The difference between the effect of the two PAMs on infiltration rate was statistically significant at α = 0.05. On the other hand, the differences were not significant except for the 1000 mg L−1 concentration in case of saturated hydraulic conductivity. Meanwhile, concentration has an effect on increasing soil aggregate stability only in case of low molecular weight PAM. At the concentration 1000 mg L-1 of low molecular weight PAM, aggregate stability and saturated hydraulic conductivity increased 3-fold while infiltration rate increased by more than 7-fold compared to the control. It is hypothesized that the change in the mentioned properties is correlated to the amount of PAM adsorbed by the soil and hence they can be used as surrogate parameters of adsorption. Modified versions of the Langmuir and Freundlich isotherm equations were used to model the change in aggregate stability and saturated hydraulic conductivity in response to the PAM concentration. The pseudo-first and second kinetics models were applied to predict the change in infiltration rate. The models showed excellent fit to the experimental data, thus supporting our hypothesis. The results suggest that low molecular weight PAM is more efficient in improving the physical properties of sandy loam soil. The modelling approach presented in this work may be extended to other types of soil. Other isotherm models may be used to predict the response of soil to PAM concentration where the Langmuir or Freundlich isotherms do not apply. This modelling approach provides land managers with a decision support tool to optimize PAM application.