MODELING AGRO-ECOSYSTEMS IN ARID SEASONALLY FROZEN REGIONS WITH AN ENHANCED SOIL-PLANT-ATMOSPHERE CONTINUUM MODEL

Agro-ecosystems are inherently dynamic and interactive, and are particularly complex in arid, seasonally frozen regions due to the impacts of soil freeze-thaw and salinity effects. Accurate and continuous modeling of the soil-plant-atmosphere continuum (SPAC) across both the plant growing season and the frost period is vital for understanding and managing water utilization and salinity control and for promoting agricultural production. We developed an improved SPAC model through an extensive modification and extension of the SHAW model. The model enables simultaneous solutions for the transport of heat (with freeze-thaw), water, and salt, along with chemical equilibrium and plant development. Key enhancements include: 1) extending the model's capability for canopy growth and yield formation; 2) refining the description of soil solute transport in shallow groundwater systems; 3) providing descriptions of surface mulching effects on soil evaporation and salinity stress on crop growth and transpiration; and 4) introducing functions to describe salt precipitation-dissolution and its effects. The model was applied and tested with data from a sunflower field and a highly salt-affected natural field. The simulated results for soil water and salt contents, efflorescence mass, temperatures, and crop growth indicators agreed well with observations. Notably, the modifications for solute transport and salt precipitation-dissolution significantly improved the simulation accuracy. Results provided a comprehensive understanding of water-salt dynamics and salt precipitation-dissolution, and the related issues of crop stress, water use, and salinity control on an annual scale. Model testing and applications demonstrate that the model could be a valuable tool for simulating agro-ecosystems in cold regions with saline soils.