Modeling heat-water-salt transport, crop growth and water use in arid seasonally frozen regions with an improved coupled SPAC model

Abstract

The soil–plant-atmosphere continuum (SPAC) that is a dynamic, interactive and coupled system is particularly complicated in arid seasonally frozen regions (ASF regions) with the effects of soil freeze–thaw process and salinity. A quantitative understanding of heat-water-salt transport and crop growth in the SPAC over an entire agricultural year (agr-year) is an importance of promoting best practices for water use and crop production. In this paper, an improved coupled SPAC model (SHAW-SC) is presented and applied for continuously simulating the SPAC system of ASF regions over an agr-year. The model is developed based on modifying the SHAW model (version 3.0) and incorporating the EPIC crop growth module. The main new features of the SHAW-SC include extending the model capability for canopy growth and yield formation, improving the description of soil solute transport in the shallow groundwater systems, and providing functions to describe the effects of surface mulching on soil evaporation and salinity stress on crop growth and transpiration. Model testing and application were conducted with two agr-year data at the sunflower experimental field in irrigated areas of the upper Yellow River basin, northwest China (with an arid and cold climate). Simulations of soil water content, temperature, and crop growth indicators fitted well with the observations both in calibration and validation (with NSE > 0.64 and sufficiently small RMSE); meanwhile, simulation of salinity concentration was also satisfactory (NSE: 0.32 and 0.83; RMSE: 1.09 and 2.44 g L−1), despite the complexity of salt transport and the measurement difficulty. In addition, the comparison with previous experimental results also showed the reasonability of modeling results. Then, a comprehensive and quantitative analysis of the SPAC dynamics was conducted over an agr-year, with identifying five characteristic periods (i.e. pre-freezing, soil-freezing, soil-thawing, pre-planting and crop growth periods). Results provided a fuller understanding of the characteristics of water-salt dynamics and balance components, and the related issues of crop stress, water use and salinity control on an entire agr-year scale. Model testing and application proved that the proposed SHAW-SC was an efficient tool to simulate coupled processes of heat-water-salt transport and crop growth for ASF regions, and as well an enhancement of current SPAC models for practical field applications.