Effects of Polyacrylamide, Manure, Vermicompost and Biological Sludge on Aggregate Stability, Penetration Resistance and Available Water Capacity in a Sandy Loam Soil

Seal formation increases penetration resistance and decreases infiltration rate and volume in soil during irrigation and rainfall. The objective of this study was to investigate the effects of four natural and synthetic organic conditioners on aggregate stability, penetration resistance and available water capacity in a sandy loam soil with weak structure under greenhouse conditions. Soil conditioners with two application rates including polyacrylamide (PAM) 0.25 and 0.5, cattle manure 12.5 and 25, vermicompost 2.5 and 5 and biological sludge 1.7 and 3.4 (all in g.kg-1 of air dry soil) were mixed with the soil and uniformly packed in plastic pans and PVC tubes with 25 cm height and 50 and 25 cm diameter, respectively. Both pans and PVC tubes were incubated at (0.7-0.8) FC moisture content and at temperature of 22±4 ºC for 6 months. Pans were used for undisturbed soil sampling in order to measure water aggregates stability (WAS) and available water capacity (AWC) at 7, 30, 60, 120 and 180 days. Penetration resistance (PR) was measured at the same times in the tubes. Both applied levels of PAM significantly (p<0.05) increased WAS compared to the control and other conditioners and the increase continued for 180 days. Both levels of PAM and manure significantly (p<0.05) decreased PR compared to the control. Conditioning effects of vermicompost and biological sludge on WAS and PR became insignificant. All of the conditioners at the second level of application significantly (p<0.10) increased AWC. According to our findings, application of 0.25 gkg-1 PAM because of its lower cost, and 25 gkg-1 manure for its availability would improve both structure and water holding capacity of the coarse-textured soils.