How to Calculate Plant Available Water

Plant available water is a crucial factor in determining the growth and health of your plants. It is the amount of water in the soil that can be absorbed and used by plant roots. Calculating plant available water is important in helping you determine how much water your plants need and when they need it. Here are some methods you can use to calculate plant available water.

Field Capacity Method

The field capacity method is one of the most common ways of calculating plant available water. It involves taking soil samples to determine the amount of water that the soil can hold after being fully saturated with water. To determine plant available water using the field capacity method, follow these steps:

Take a soil sample and weigh it.

Add water to the sample until it reaches its field capacity, which is the point where the soil is fully saturated but not waterlogged.

Weigh the sample again to determine the amount of water that was added.

Subtract the weight of the dry soil from the weight of the wet soil to determine the amount of water held in the soil at field capacity.

Use this number to calculate the plant available water by subtracting the permanent wilting point (the point at which plants can no longer extract water from the soil) from the field capacity.

Texture Triangle Method

The texture triangle method is used to calculate the plant available water based on the soil texture. It involves plotting the percentage of sand, silt, and clay on a texture triangle to determine the water-holding capacity of the soil. To use the texture triangle method, follow these steps:

Determine the percentage of sand, silt, and clay in your soil.

Plot the percentages of sand, silt, and clay on the texture triangle.

Draw a line from the sand percentage to the silt percentage, then from the silt percentage to the clay percentage.

The intersection of these lines will indicate the water-holding capacity of your soil.

Use this number to calculate the plant available water by subtracting the permanent wilting point from the water-holding capacity.

Tensiometer Method

The tensiometer method is used to measure the soil moisture tension, which is the energy required by plant roots to extract water from the soil. A tensiometer is a device that consists of a porous ceramic tip connected to a vacuum gauge. To use the tensiometer method, follow these steps:

Insert the porous ceramic tip of the tensiometer into the soil at the root zone of your plants.

Fill the tensiometer with water to create a vacuum in the gauge.

Monitor the vacuum gauge to determine the soil moisture tension.

Use this number to determine the plant available water by subtracting the permanent wilting point from the soil moisture tension.

In Conclusion

Calculating plant available water is essential for growing healthy plants. There are different methods you can use to determine the plant available water, including the field capacity method, the texture triangle method, and the tensiometer method. Knowing the plant available water in your soil can help you determine how much water your plants need and when they need it. Using the right method to calculate the plant available water can help you grow healthy and thriving plants in your garden or farm.