Principles and experimental verification of capillary suction method for fast measurement of field capacity

Field capacity (FC), as the upper limit of water content in the soil profile available to plant use, is a crucial characteristic of soil water content, and is of great importance to irrigation and soil water management. A new method was advanced for fast determination of FC using soil capillary suction, based on the matric potential of soil water and the concept of FC. The foundation of the new method is based on the fact that the FC is the maximum sustained moisture content of the soil without groundwater impacts. The experimental method, device and procedures were designed to conduct a serial of laboratory experiments for FCs of five actual soils. The results show that: 1) the newly suggested method is feasible in terms of both the principles and the experimental methods; 2) the measured FC values with the new method were a little lower than those with Welcox method by about 9%, which is mainly due to the hysteresis of soil moisture in the sorption and desorption processes; 3) the measured values with the two methods were very well linearly correlated as y=1.09x. Compared with the conventional methods, the new method needs much shorter time to make a measurement. The new method for FC with soil capillary suction will find its wide applications.