Wheat uses root depth growth rates which vary based on crop stages. The routines from APSIM ‘Plant’, and specifically using wheat as an example, were used as a base to develop new cotton root development routines. The second phase has a peak growth rate of about 30 mm /day. The first phase equates to a growth rate of 6 mm / day.
OZCOT’s root growth has two phases, from sowing to about 39 DAS and then from this point on until harvest. Published ‘kl’ values specifically for cotton are scarce, if not non-existent.
‘kl’ values for cotton estimated by the APSIM-Soil module Crop The logic used in APSIM’s ‘Plant’ was used as the base of the routine in cotton ‘ozcot_swbal_removeEp()’ (Appendix 1). In order to implement the standardised APSIM approaches for soil water uptake and root development which utilise the ‘kl’ extraction factors and ‘xf’ soil constraint factors for each soil layer, the cotton model required modifications. This was a legacy of the OZCOT model and was not consistent with the approach used for other models in APSIM. Plant growth, environmental conditions and soil hospitality for root growth play no part in the root development.
The equations used were developed for the heavy clay soils at Myall Vale, NSW Australia and the only variables that are used to estimate rooting depth are the depth of the soil profile and the Days After Sowing (DAS). OZCOT was designed with a very empirical approach to root development. Enhancements to the Root Development routines and water extraction routine in APSIM-CottonĪPSIM-Cotton is extensively based on the OZCOT (Hearn, 1994) cotton model.