September 28, 2010 by Dr. Gaylon Campbell
For the first few days after a heavy rain or irrigation the water drains from the soil profile untilits water content approaches a relatively stable value called the drained upper limit or field capacity. When plants have extracted all of the water available to them, the root zone water content approaches a lower limit of available water, or permanent wilting water content. The water held by the soil between these two limits is called plant available water. These two limits are often associated with water content values at specific soil water potentials. Field capacity is often taken as the water content of a soil at -33 kPa water potential. Permanent wilt is taken as the water content at -1500 kPa. Methods typically used for determining plant available water are slow and inaccurate. Join us as we present a method to measure field capacity using a tensiometer and an extrapolation technique, and a method to measure permanent wilting water content with a dew point potentiameter and an extrapolation method which are both much faster and more accurate then traditional methods.
Do you have more questions about methods for determining plant available water? Post your questions on one of our forums and receive answers from Decagon scientists and other user or you can find answers to some frequently asked questions. You can also speak directly with one of our researchers by calling 1-800-755-2751.
Or you can visit the water potential instruments product pages to learn more about determining plant available water in soils.