Toward Mechanistic Modeling of Root Growth and Nutrient Uptake in CROPGRO.

The CROPGRO model currently has one-dimensional (1-D) rooting with depth, but there is a need for two-dimensional (2-D) rooting for use in mulch-bed vegetable production, as well as value in more mechanistic root growth and uptake of P and N.  Nutrient uptake and water uptake share many important linkages with root growth; thus the modeled root growth pattern, both seasonally and vertically with depth, determines the potential ability to take up water and nutrients.  A 2-D rooting pattern is needed for plastic-covered mulch beds and banded fertilizer application.  Root growth is linked to plant carbon balance, crop life cycle, and stresses from water deficit, N deficit, or P deficit which cause shift in partitioning of assimilate to root growth.  Root growth is affected by static and dynamic soil factors (e.g., Al, Ca, soil temperature, soil strength and aeration from the interaction of soil water status and soil texture).  We implemented a dynamic 1-D approach based on soil static and dynamic properties, following the approach of Jones et al. (1991), and compared this to the current 1-D rooting in CROPGRO.  We also developed a 2-D rooting method for use in plastic-mulch bed production of vegetables under drip irrigation.  Root P uptake and plant response to P are new features in the DSSAT models that may benefit from 2-D rooting and new formulations for nutrient uptake.  Alternative formulations of root function relative to water and nutrient uptake will be compared over a range of root length densities, concentrations of N and P in solution, and plant growth demand for nutrients.  More dynamic root growth dependent on soil properties, new uptake functions, along with species and cultivar coefficients for root growth will improve on the current root hospitality function with soil depth which is not universal, but both crop and soil-specific.