Differential water capacity of soil

In the pressure form of Richards' seepage equation, the differential wa-ter capacity function is used and calculation of its values is necessary to solve the equation. The course of function variability was determined basing on the soil moisture characteristic. To obtain simpler solutions, the water capacity was expressed as a function of moisture. Using van Genuchten and logistic functions, its course for six soils available in the relevant literature was determined. Two sandy soils were used to dis-cuss the water capacity hysteresis and simple formulae were proposed, enabling the coefficient for scanning runs to be determined.