Modeling root growth and the soil–plant–atmosphere continuum of cotton crops

A simple and functional model to simulate cotton root growth is coupled to models of water balance and leaf water potential to predict the behavior of the soil–plant–atmosphere continuum (SPAC) of cotton crops. The root-growth model takes into account the dry matter partitioning to roots, root depth increase as a function of thermal time, soil mechanical resistance and soil water stress, and allows the inclusion of spatial variability of soil physical properties. The water balance model uses a cascade approach to simulate drainage while soil and plant evaporation are calculated separately following the model of Ritchie. The leaf water potential model (LWPM) is based on Ohm’s Law analogy, where water flow resistance to the roots is calculated using an empirical equation and the resistance within the plant is calculated as a function of a threshold leaf water potential. The model simulated correctly the soil resistance and the temporal and spatial distribution of roots in the soil profile. The model simulated total soil water content and midday leaf water potential well, even when a compacted soil layer was present, but the agreement to observed data was poor for the vertical distribution of soil water content, mainly in the zone of greatest root concentration