Modeling Root Growth and Water and Nutrient Uptake In MaizSim.

Crop root models range in complexity from simple multivariate equations of root density to complex mechanistic models that describe architecture and function in detail. The amount of complexity is often a function of the objective of the root model or the underlying hypothesis. Calculation of below ground processes like water and nutrient uptake in support of a plant model can be solved with a pragmatic approach of simulating root density distributions in the soil. To study plant physiological processes like water and nutrient transport inside the root system, more detailed architectural models may be useful. The applicability of complex architectural models may be limited when used with a simple crop model where the complexity of the root model does not match the complexity of the plant model. The objective of this study was to evaluate the use of a diffusive quasi architectural root model (Dupuy et al. 2010) in the corn model MaizSim, a new mechanistic simulation model of maize growth and development. The current version of MaizSim consists of a crop growth model, a root model based on the soybean model GLYCIM and a finite element soil water and solute transport model based on 2DSOIL. Root growth was modeled according to a diffusion scheme, where new roots can grow into a neighboring element when enough carbon was available. The preference into which element roots grow was determined by gravitropism, water content, nitrogen availability and bulk density of the soil. This root density distribution model was modified according to the approach of Dupuy by modeling three distributions simultaneously: (1) root length density, (2) the root apical meristem density and (3) branching frequency density. Young roots can only grow out of apical meristems, which resemble the maximal distance of root branches from the stem at a given time. The branching frequency describes the number of newly grown roots from a single meristem. With these three parameters a more realistic distribution of root density with soil depth can be simulated, yielding to an improved root growth over time. The quasi-architectural model was validated by comparing field observations and crop development data with model observations. Nitrogen and water uptake was more realistic for the improved root model. Root growth strategies beneficial for certain climate scenarios could be determined. The validated model can be used to predict crop growth under different combinations of changing seasonal precipitation patterns and increasing temperature.