Evaluating the saline water irrigation schemes using a distributed agro-hydrological model

Abstract

Quantitatively assessing the practicality and sustainability of saline groundwater for irrigation at the regional level could provide a valuable reference for macro decision-making and management in terms of alleviating the severe contradiction between freshwater shortages and food production. In this study, the distributed agro-hydrological SWAP-WOFOST (Soil-Water-Atmosphere-Plant-WOrld FOod STudy) model was applied in the east-central North China Plain (NCP). The model was used to simulate the five saline water irrigation scenarios for a 20-year period, and the effects on the spatiotemporal variations in crop yield, water productivity (WP), and soil water and salt balances were analyzed. Furthermore, appropriate saline water irrigation schemes were solved considering crop yield reduction and soil salt accumulation. Finally, spatial matching between the appropriate irrigation schemes and saline groundwater resources from the perspectives of “water quality” and “water quantity” was evaluated. The main results were as follows. (1) The average yield and WP of winter wheat during the simulation period remained stable or increased slightly under saline water (2–6 g L−1) irrigation for winter wheat compared with that under freshwater irrigation, whereas the average yield and WP of the following summer maize decreased to varying degrees. (2) When the sum of seasonal precipitation and irrigation of summer maize was >450 mm, 401–450 mm, 351–400 mm, 200–350 mm and <200 mm, the average soil salt leaching depth was approximately 120 cm, 100 cm, 80 cm, 60 cm and 40 cm, respectively. (3) On the premise that the average salt content of the 2-m soil profile at summer maize harvest during the simulation period was less than 3 g kg−1, if the average crop yield reduction of the rotation system in the range of ≤500 kg hm−2, ≤1000 kg hm−2, ≤1500 kg hm−2 and ≤2000 kg hm−2 was permitted, the dominant maximum irrigation water salinity in the study area was 3 g L−1, 4 g L−1, 6 g L−1 and 6 g L−1, respectively. (4) The average saline water amount needed for winter wheat irrigation during the simulation period was approximately 22.78 × 108 m3, which was approximately 9% more than the exploitable amount of saline groundwater. The results could support decision-making related to developing and using shallow saline groundwater for irrigation.