Modelling root water uptake under deficit irrigation and rewetting in Northwest China

Abstract

The spatial and temporal distribution of root water uptake (RWU) under deficit irrigation are critical factors for crop growth. The SWAP (soil–water–atmosphere–plant) model was applied to analyze the pattern of RWU for winter wheat (Triticum aestivum L.) under three irrigation levels: no water deficit (100% evapotranspiration [ET]), moderate water deficit (80% ET) and severe water deficit (60% ET). The 2–yr experiments indicated that SWAP was highly accurate (mean relative error [MRE] <21.7%, root mean square error [RMSE] <0.07 cm3 cm−3) in simulating the soil water content (SWC). Root water uptake was significantly (P < 0.01) different in the 0‐ to 60‐cm soil layer. The 0‐ to 60‐cm soil layer was the main source of RWU, and the average value accounted for 89.4% of the total root zone. Water stress had the greatest adverse effect on heading to grain filling, reducing RWU by 0.0026 cm3 cm−3 d−1. The critical SWC was 67.9% of the field capacity, when the RWU dropped to 95% of the control treatment. After rewetting, compensation and hysteresis effects on RWU were observed. The ranking of RWU recovery ability after rewetting was: emergence to jointing > jointing to heading > grain filling to maturity > heading to grain filling. Recovery time of RWU was 2 to 11 d and gradually increased with growth stage. The simplified RWU model established using path analysis and regression performed well (R2 = 0.836; P < 0.01) for RWU. This provided a more convenient way to accurately estimate RWU with fewer variables.

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

“…Three irrigation levels were impleme g each stage: 100% (no water deficit), 80% (moderate deficit) and 60% (severe deficit) of a easured by the large weighing lysimeter with sufficient irrigation treatment (CK, namely 1) (Figure 3). The range of the device was 0 to 6 t, and the measurement accuracy was less [35]. The size of the lysimeter is consistent with the plot.…”

“…This was because T a was closely related to root water uptake. Different irrigation amounts caused variations in soil water status, and these effects were reflected in the changes in root morphology (root length and density distribution) and physiological functions (root vitality and water uptake) [35,[65][66][67]. Under water stress, roots were vulnerable to drought and died.…”

“…Sensitivity analysis is a prerequisite for model calibration [33]. The calibration of the simple module in the SWAP model is the process of continuously adjusting the van Genuchten-Mualem model (VGM) parameters to minimize the deviation between the simulation SWC and the observed values [31,35,37]. Therefore, we mainly analyzed the sensitivity of VGM parameters.…”

“…where n is the number of measured values; P i is the i th predicted value; and O i is the i th observed value. We adjusted the corresponding VGM parameters in SWAP until MRE ≤ 20% and RMSE ≤ 0.05 cm 3 cm −3 [30,35,37,55]. The adjusted parameters were used for model verification for all other treatments.…”

Estimating the Effects of Deficit Irrigation on Water Absorption and Utilization of Tomatoes Grown in Greenhouse with Hydrus-1D Model

“…Clement et al [22] concluded that deep-rooted crops have the advantage of obtaining deep soil water under drought conditions by comparing the water absorption status of the roots of different types of perennial crops. Wang et al [23] defined the water content corresponding to the 95% RWU of the control treatment as the critical water content and concluded that the critical water content was different in different growth stages of winter wheat. In addition, the absolute RWU of different types of soil was affected by ET 0 [24].…”