Work out soil moisture content instantly with clear inputs, formula shown and shareable results.
Gravimetric moisture is water mass over oven-dry mass: 45 g of water in 195 g of dry soil is 23.1%. Multiplying by bulk density converts it to volumetric moisture, 31.2% here, which is the figure irrigation scheduling needs because it reads directly as millimetres of water per 100 mm of soil depth.
Gravimetric moisture
theta(g) = (wet - dry) / dry x 100
Volumetric moisture
theta(v) = theta(g) x bulk density
Because it converts straight into an equivalent rainfall depth, which is what crops and irrigation systems are measured in.
The volumetric moisture retained after free drainage, typically 15% in sand and 35-40% in clay. Water beyond it drains away.