1. Philips Equation Recall Richard’s Equation Solution S – Sorptivity
Assume K and D are functions of q, not z
Solution
Two terms represent effects of
Suction head
Gravity head
S – Sorptivity
Function of soil suction potential
Found from experiment

2. Infiltration into a horizontal soil column
Θ = Θo for x = 0, t > 0
Boundary conditions
Θ = Θn for t = 0, x > 0 x
Equation:

3. Measurement of Diffusivity by Evaporation from Soil Cores
Air stream q
q = soil water flux = evaporation rate

4. Measurement of Diffusivity by Evaporation from Soil Cores