Combining Field and Laboratory methods to calculate Soil Water Content at Field Capacity and Permanent Wilting Point

摘要

Field Capacity (FC) and Permanent Wilting Point (PWP) are typical terms that are used to define soil water content and its availability to plants. Related concepts such as Total Available Water (TAW) capacity and the Readily Available Water (RAW) capacity are also used in many agronomic applications where soil water balance calculations are done, such us, irrigation scheduling, soil conservation, etc. Therefore, obtaining realistic values of the volumetric water content at FC and PWP is crucial. It is a general practice to determine the water content at FC and PWP using pressure plates at -33kPa and -1500kPa, respectively. Recently, the soils scientific community has been questioning this approach. One of the problems is associated with sample equilibration at low potentials (-1000 and -1500 kPa), (Cresswell et al., 2008; Gee et al, 2002) and the effect of the osmotic potential in saline soils (also, PWP related). As remarked by Ratliff et al. (1983) and Gebregiorgis and Savage (2006), another important aspect is that Field Capacity should be determined in the field, since there are many errors associated with laboratory determinations done with pressure plate apparatus. The objective of this study is to compare pressure plate laboratory determinations of water content at FC and PWP with combined field and laboratory techniques.