Calculate Soil Water Potential

Soil Water Potential Equation:

\[ \Psi_{soil} = - \frac{RT}{V_w} \ln(h) \]

Temperature (T):

Relative Humidity (h):

(0-1)

Gas Constant (R):

J/mol·K

Molar Volume of Water (V_w):

m³/mol

Soil Water Potential (Ψ_soil):

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1. What is Soil Water Potential?

Soil water potential (Ψ_soil) is a measure of the energy status of water in soil. It represents the potential energy per unit volume of water in soil compared to pure water at reference conditions. It's crucial for understanding water movement in soil and plant water uptake.

2. How Does the Calculator Work?

The calculator uses the soil water potential equation:

\[ \Psi_{soil} = - \frac{RT}{V_w} \ln(h) \]

Where:

\( \Psi_{soil} \) — Soil water potential (Pa or MPa)
\( R \) — Universal gas constant (8.314 J/mol·K)
\( T \) — Absolute temperature (K)
\( V_w \) — Molar volume of water (0.000018 m³/mol)
\( h \) — Relative humidity (0-1)

Explanation: The equation relates the energy status of soil water to the relative humidity of soil air through thermodynamic principles.

3. Importance of Soil Water Potential

Details: Soil water potential determines the direction and rate of water movement in soil, affects plant water availability, and influences microbial activity. It's more meaningful than water content alone for understanding water status in soil.

4. Using the Calculator

Tips: Enter temperature in Kelvin, relative humidity (0-1), gas constant (typically 8.314 J/mol·K), and molar volume of water (typically 0.000018 m³/mol). All values must be positive.

5. Frequently Asked Questions (FAQ)

Q1: What are typical values for soil water potential?
A: Range from 0 MPa (saturated) to below -1.5 MPa (permanent wilting point). Most plants grow best between -0.01 to -0.03 MPa.

Q2: How does temperature affect soil water potential?
A: Higher temperatures increase the potential (makes it less negative) because thermal energy increases water molecule activity.

Q3: Why use relative humidity in the equation?
A: The humidity of soil air is in equilibrium with soil water, and this relationship allows calculation of the energy status.

Q4: What's the difference between water content and water potential?
A: Water content measures how much water is present, while water potential measures its energy state and availability to plants.

Q5: How is this used in agriculture?
A: Helps determine irrigation timing, predict plant water stress, and understand soil-plant-water relationships.