Soilwat module water balance doesn't simulate reliably when layer thicknesses exceed recommended bounds.
e.g. a top layer of 4 cm and a second layer of 50 cm can cause issues with simulation of water balance for Soilwat.
I'm not sure what the bounds should be. Recommended thicknesses for layers with depth are 10 to 15, 15 to 20, 30, 30, ... (cm).
Perhaps the bounds could be specified in the 'ini' file.
Suggested bounds (cm) with depth -
5 to 15, 10 to 25, 20 to 40, 20 to 50, 20 to 50, etc.
I note that DSSAT takes any set of layer thicknesses and internally re-maps them to a standard set similar to our recommended set. Don't know if this is a good or bad thing to do. However, at least simulations should warn (or enforce) limits on layer thicknesses to maintain simulation integrity.