101 Questions answered
Diagnosing Lentil and Faba Bean Struggles
Lentils and faba beans are highly sensitive to low soil pH. If they used to grow well but are now regularly struggling (and you can’t blame seasonal conditions), soil acid ification could be the problem. While many soils in SA have an inherent neutral to alkaline pH, acidity can still develop.
Lentil roots like soil pH to be above 6.0 (pHCa). Acidic soils delay and limit no dulation, and hence reduce yields.
A soil test will diagnose the problem. If the pH in the 0–10 cm soil test appears fine, the problem could be sub-surface acidity, sub soil acidity or acidic soil stratification (sometimes called an acid choke).
Sub-surface acidity is when soil pH is 5.0 or less from 10cm or deeper.
Acidic soil stratification or an acid choke is a small band of acidic soil that is ‘hidden’ by a standard 10 cm soil test. When the 10 cm soil sample is collected, it mixes in higher pH soil with the acidic layer,masking the pH of the problem area.
Subsoil acidity is when pH is <5.0 in the subsoil, usually around 25cm or deeper. This is not normally an issue in South Australian cropping soils.
If you suspect acidity, collect and test soil samples in 5 cm increments down to 20 cm depth in a poorly performing area or use a field pH kit and spray indicator dye down the surface to see if anacidic layer is visible. Note that a field kit measures pH in water not in calcium chloride, so readings tend to be about 0.8 pH units higher. A 0-10 cm sample may not detect acidity in this stratified situation.
