How to Find Total Plant Available Water

One of the most important factors in determining plant growth and yield is soil moisture, and the most critical aspect in this regard is the amount of plant available water in the soil. Plant available water is defined as the fraction of water that can be taken up by a plant’s roots from the soil. In this article, we will discuss how to find the total plant available water in the soil.

Soil Texture and Available Water Capacity

The first step to finding total plant available water is to determine the soil texture. This refers to the relative proportions of sand, silt, and clay particles in the soil. The soil texture has a significant impact on the amount of plant available water that can be stored in the soil. Soils with high sand content have a lower available water capacity (AWC) than soils with higher proportions of silt and clay. AWC is defined as the amount of water that can be stored in the soil between field capacity (the maximum amount of water the soil can hold) and wilting point (the minimum amount of water required for the plant to survive).

Measuring Soil Moisture Content

Once the soil texture has been determined, the next step is to measure the soil moisture content. There are several methods for doing this, including gravimetric soil moisture measurement, time domain reflectometry, and capacitance probes. Gravimetric soil moisture measurement involves weighing a sample of soil before and after drying it in an oven to determine the moisture content. Time domain reflectometry and capacitance probes use electronic methods to measure the soil’s electrical properties, which are related to the soil moisture content.

Calculating Total Plant Available Water

Once the soil texture and moisture content have been determined, the total plant available water can be calculated. This is done by multiplying the AWC by the depth of soil in the root zone. The root zone is defined as the depth of soil that the plant’s roots can penetrate and extract water from. The depth of the root zone varies depending on the type of plant and the soil conditions.

Example Calculation

For example, let’s say we have a soil with a sandy loam texture, and we have determined that the AWC is 0.15 inches of water per inch of soil. We also know that the root zone for our crop is 18 inches deep. To calculate the total plant available water, we simply multiply 0.15 by 18, which gives us 2.7 inches of water. This means that for every inch of soil in the root zone, there is 0.15 inches of plant available water, and for the entire root zone, there is 2.7 inches of plant available water.

Conclusion

Finding the total plant available water in the soil is critical for determining the soil water status for plant growth and yield. By knowing the soil texture, soil moisture content, and root zone depth, we can calculate the total plant available water in the soil. This knowledge can help farmers and gardeners optimize irrigation practices and improve crop productivity.