A new procedure for simulating minimum and maximum daily leaf water potential (LWP) has been introduced in the new version of the CALGOS cotton model. Simulations using this procedure have been validated using data from a cotton irrigation experiment (conducted in 1991 at the west San Joaquin Valley of California, with cultivar 'GC510', subsurface drip irrigation, and rows spaced 76 cm). Reasonable simulations for various irrigation treatments have been obtained.

Sensitivity tests of the model indicated that LWP is strongly affected by the average soil water potential, which is computed from the distribution of active roots in relation to the distribution of water in the soil profile. A good simulation of LWP therefore depends on the use of a reasonable model for cotton root growth and activity.