Time dependence of soil water hysteresis in a minesoil reclaimed by sewage sludge amendments

One of most important problems in soil thermodynamics is related to soil water hysteresis , which arises mainly from differences in the processes of emptying and filling individual pores during wetting and drying. In a minesoil coming from excavations, amended with six different types of sewage sludge (composted or thermally dried), it was observed that the critical point (c, wc) that separates the region dominated by complete pore filling/emptying from that dominated by partial pore filling/emptying could be found using the linear relationship between suction and time. Differences in temporal variation rates of soil gravimetric water content, before and after this critical point were more evident during the soil drying process. The selected minesoil required a mean of 1.6 min to change their water content from dryness to wilting point (Δttotal) under the wetting process, but under the drying process around 130 min was required for a similar water content change at the same temperature, verifying soil hysteretic conditions. It was observed, mainly at short term, that composted sludge increased soil water holding time (Δttotal) under both the drying and wetting processes. Changes in the temporal dependency of hysteresis could be explained partially by the relationship with soil organic carbon.