Soil hydraulic properties as affected by Vetiver and Polyacrylamide

Suitable land management result in improving the soil hydro-physical properties and erosion control in arid and semi-arid regions. Application the cover crop as bioengineering tool is a good choice to improve soil hydro-physical properties and to protect the soil against erosive factors. Anionic polyacrylamide (PAM) has been widely used in this field, as well. In literature, the individual effect of Vetiver and PAM on Soil structural stability and erosion indices has been investigated. The objective of this study was to investigate and compare the effect of vetiver cultivation system, PAM and their combination on hydraulic properties and physical quality index of soil in experimental plots.
This study was performed in loamy soil plots of a loamy soil in Agriculture Campus, Ferdowsi University of Mashhad. The experimental treatments include vetiver cultivation (VP0), PAM (20 (P2) and 40 (P4) kg ha-1), simultaneous application of vetiver and PAM concentrations (VP2, and VP4). In addition, P0 (no PAM and vetiver) was regarded as control treatment. The soil moisture contents for different treatments were measured at 0, 5, 10, 50, 100, 300, 500, 1000, and 1500 kPa. According to this data the van Genuchten’s equation was fitted to the soil moisture characteristic curve using the RETC software, and the parameters of model were estimated by the least square error methods. Also, saturated hydraulic conductivity and soil physical quality index were determined. This study was designed based on randomized complete blocks in a factorial arrangement with 3 replications. Data of van Genuchten’s parameters, Sgi index, and Ks were analyzed using SPSS 23 software.
The results showed that vetiver and PAM through increasing the aggregation and stability of soil structure, and improving the structural properties increased θs, and ks. However, the effect of PAM on ks depends on its concentration and viscosity. Vetiver decreased θr, and the hydrophilic molecules of PAM polymer increased θr. Vetiver increased considerably the value of α parameter and decreased air entry value by increasing the soil macro-pores. Although, the value of α parameter was not affected by PAM. Vetiver increased the value of n parameter, while PAM decreased its value. Also, vetiver and PAM increased the Sgi through the aggregation and improving the soil structure and physical condition. In general, vetiver had more effect on parameters of van Genuchten model and improvement of soil hydraulic properties than the PAM and the combination of vetiver and PAM showed the greatest effect.
Generally, the results of this research indicated that the very low cost and long-term bioengineering technique based on vetiver system can be recommended to improve physical and structural properties of soil in semi-arid regions such as Iran.