Soil Is Never Without Water

Abstract

Regardless of the circumstances, it is undeniable that some amount of water resides within all soil pores across the natural landscape. The amount can be easily determined by merely weighing a small soil sample, drying it at temperature 105 °C for about 6 h, and weighing it again. The difference of the two weights – those before and after drying – is the weight of all water initially present in the soil. When we divide this value by the weight of the oven-dried soil and multiply by 100, we obtain the weight percentage of the soil water content. This value lacks the information needed to ascertain which portion of the soil pores or what fraction of the total porosity was filled by water. To obtain this important information, we have to divide the volume of water expelled from the soil as a result of drying it at 105 °C by the initial volume of the soil sample before it was dried. Inasmuch as the density of soil water is nearly identical to 1, i.e., its weight in grams is numerically equal to its volume in cm³, we obtain the volumetric fraction of soil water content by dividing the weight of water initially present in the soil by the initial volume of the soil sample. Multiplying this fraction by 100, we obtain the volumetric percentage of soil water content. And from this calculated value, we recognize immediately which portion of the soil pores or what fraction of the total porosity was filled by water.