Current Water Deficit Stress Simulations in Selected Agricultural System Models

System models that adequately simulate plant water stress effects are valuable tools for developing management practices that help improve water-use efficiency in agriculture. Plants experience water stress when water supply in the soil fails to meet the demand. Although it is easy to define the concept, accurate quantification and representation of water stress in crop models have been a challenge in system modeling. A critical review of literature shows that the water deficit stress modulates: (i) phasic plant developmental rates, (ii) leaf initiation and expansion growth, (iii) photosynthesis, (iv) carbon allocation and partitioning, and (v) root length and density in soil layers. In this paper, we present reviews of current simulations of plant water stress and its integration with crop growth and development processes in the APSIM, CropSyst, DSSAT-CSM, GLYCIM, and RZWQM models. In general, these models use the ratio of actual to potential transpiration or evapotranspiration to represent water stress. Potential evapotranspiration in general is computed by Penman–Monteith or Priestley–Taylor equations treating plant canopy as a big-leaf. In plants, the processes of carbon assimilation, transpiration, energy balance, and stomatal behavior are coupled. In the above models, there are no explicit simulations of leaf energy balance and leaf temperature or stomatal conductance in quantifying transpiration and photosynthesis. For improved simulations of crop growth and development under water deficit conditions, accurate simulations of these coupled processes governing water movement through the soil-plant-atmosphere continuum is essential. In this article, we also reviewed and presented examples of models (those not included in the five models listed above) that address these coupled processes. Results of performance evaluations of the above models in specific water deficit experiments substantiate their potential in developing cost-effective and scientifically sound decision support tools in agricultural water management.