Аннотация:An inverse proportional relationship between soil water potential and the differential water capacity of elementary soil particles 1.3–40 μm in diameter in loamy brown forest soil has been identified for the first time. An inverse linear relationship has also been identified between differential water capacity and the logarithm of elementary soil particle size within the range of hygroscopic moisture. A decrease in the diameter of elementary soil particles by more than 10 times (from >20 μm to <2 μm) increases their differential water capacity by almost 10 times. The knowledge of the exponential relationship between the soil water content and the soil water potential within the range of hygroscopic moisture significantly facilitates the determination of differential soil water capacity.