Integral energy
Integral energy is the amount of energy required to remove water from soil with an initial water content θ i {\displaystyle \theta _{i}} to water content of θ f {\displaystyle \theta _{f}} (where θ i > θ f {\displaystyle \theta _{i}>\theta _{f}} ). It is calculated by integrating the water retention curve, soil water potential ψ ( θ ) {\displaystyle \psi (\theta )} with respect to θ {\displaystyle \theta } : E i = ∫ θ i θ f 1 θ i − θ f ψ ( θ ) d θ {\displaystyle E_{i}=\int _{\theta _{i}}^{\theta _{f}}{\frac {1}{\theta _{i}-\theta _{f}}}\psi (\theta )\,d\theta } It is proposed by Minasny and McBratney (2003) as alternative to available water capacity.