Effects of Four Organic Soil Conditioners on Some Hydraulic and Solute Transport Parameters in a Sandy Loam Soil

In coarse-textured soils, because of possessing higher macropores, in general, water and nutrient holding capacity is low. The objective of this study was to investigate the effects of polyacrylamide (PAM), cattle manure (MR), vermicompost (VC) and biological sludge (BS) as soil conditioners on hydraulic and solute transport paramerers of a sandy loam soil. PAM (0.25 and 0.5 gkg-1 of air dry soil), MR (12.5 and 25 gkg-1 of air dry soil), VC (2.5 and 5 gkg-1 of air dry soil) and BS (1.7 and 3.4 gkg-1 of air dry soil) were mixed with soil and uniformly packed in to plastic pans (50 cm diameter and 25 cm height) and PVC tubes (15 cm diameter and 25 cm height) and then incubated in greenhouse at (0.7-0.8) FC moisture content and temperature of 22±4 ºC for 6 months. Plastic pans were used for soil sampling to construct soil moisture curves (SMCs) at 7, 30, 60, 120 and 180 days after start of incubation. Saturated hydraulic conductivity (Ks) and breakthrough curves (BTCs) were determined at the same times in PVC tubes. Van Genuchten-α parameter was obtained from fitting SMCs to van Genuchten (VG) model. Dispersivity (λ) parameter was obtained from fitting BTCs data to convection-dispersion equation (CDE). Van Genuchten-α parameter at both levels of PAM and second level of MR and VC was significantly (P<0.05) reduced. At both levels of PAM, compared with the control and other conditioners, Ks remained unchanged after 60 days of incubation relative to former times. All of soil conditioners decreased dispersivity (λ) parameter of CDE model. The findings of this study showed that PAM and MR were more effective than other conditioners at the used levels, in improving soil physical conditions.