A diffusive model of maize root growth in MAIZSIM and its applications in Ridge-Furrow Rainfall Harvesting

The ability to accurately simulate root density and its spatial distribution can enhance our understanding of plant adaption to the soil environment and agricultural water management. “Ridge-Furrow Rainfall Harvest (RFRH)” is a recently proposed management practice, which utilizes a mulched ridge and furrowed soil to increase infiltration and conserve water within soil profiles. However, this management technique has not been extensively assessed for its effects on yield and water use. Two-dimensional (2D) root models are useful tools to assess crop yield and water use in RFRH systems as they can simulate root growth and water uptake. MAIZSIM is a comprehensive mechanistic model of maize (Zea mays L.) growth and yield, which uses a 2D finite element representation for soil physical/chemical processes and root growth. However, MAIZSIM utilizes a simple recursive model based on carbon (C) allocation to simulate root distribution. Therefore, the objectives of this study are to (I) develop and implement a finite element based diffusive root growth model in MAIZSIM with evaluations on model performance; and (II) study the effects of RFRH management on maize yield, water use and root development using MAIZSIM with the new root model. The root model was written into three modules, which (I) allocates total C from plant photosynthesis for root growth based on soil water availability and transpiration demand; (II) assigns new allocated C for root growth to selected spatial locations in soil; and (III) calculates the spatial root distribution as C diffusion. The root model was validated using observed root data from published studies, under the influences of soil bulk density, penetration resistance, and soil water conditions (normal, irrigation and drought). Numerical simulations for RFRH management, compared to a flat soil, demonstrated that, although soil evaporation was decreased, the differences for yields, shoot and root dry mass were small. In conclusion, (I) the newly develop diffusive root model provided an accurate way to simulate maize root growth; (II) despite the positive effects of RFRH management on soil water conservation, its influence on maize yield is relatively small. The diffusive model can be used to evaluate the root growth in response to climate changes or management practices and support integrated agricultural simulators that included soil, crop and environmental components.