Estimating Soil Water Content and Evapotranspiration of Winter Wheat under Deficit Irrigation Based on SWAP Model

Abstract

Deficit irrigation strategy is essential for sustainable agricultural development in arid regions. A two−year deficit irrigation field experiment was conducted to study the water dynamics of winter wheat under deficit irrigation in Guanzhong Plain in Northwest China. Three irrigation levels were implemented during four growth stages of winter wheat: 100%, 80% and 60% of actual evapotranspiration (ET) measured by the lysimeter with sufficient irrigation treatment (CK). The agro−hydrological model soil−water−atmosphere−plant (SWAP) was used to simulate the components of the farmland water budget. Sensitivity analysis for parameters of SWAP indicated that the saturated water content and water content shape factor n were more sensitive than the other parameters. The verification results showed that the SWAP model accurately simulated soil water content (average relative error (MRE) < 21.66%, root mean square error (RMSE) < 0.07 cm3 cm−3) and ET (R2 = 0.975, p < 0.01). Irrigation had an important impact on actual plant transpiration, but the actual soil evaporation had little change among different treatments. The average deep percolation was 14.54 mm and positively correlated with the total irrigation amount. The model established using path analysis and regression methods for estimating ET performed well (R2 = 0.727, p < 0.01). This study provided effective guidance for SWAP model parameter calibration and a convenient way to accurately estimate ET with fewer variables.

Sustainability of a Rainfed Wheat Production System in Relation to Water and Nitrogen Dynamics in the Soil in the Eyre Peninsula, South Australia

“…Several studies [10,11] assumed a fixed value of the seasonal evaporation loss (110 mm) when determining water availability for rainfed wheat, which seems unreasonable. However, inter-and intra-season variabilities in the evaporation losses are common and are highly correlated with the diurnal and seasonal changes in the climate parameters and ground cover [61]. In the current study, seasonal E s losses were 5-30% lower than a fixed value (110 mm) suggested by French and Schultz [10].…”

“…During the validation period (2019), the error values varied from −0.04 to 0.07 cm 3 cm −3 . Wang et al [61] reported RMSE and mean relative error (MRE) values of 0.07 cm 3 cm −3 and 21.6%, respectively, as accurate estimation of water content dynamics in the soil by SWAP model under wheat irrigated with varied levels of deficit irrigations. Error estimates reported in other studies [37,62] also corroborate well with the values estimated in the current study, which showed a good agreement between measured and simulated water content dynamics in the soil.…”

“…The water content retained in the 0-30 cm horizon is crucial for seed germination and subsequent growth of crops, as the bulk of the fibrous roots of cereal crops mine this region for water and nutrient needs [69]. Wang et al [61] reported that the root activity of winter wheat is concentrated within the 0-40 cm soil layer and reported small changes in water content dynamics at the deeper depths.…”