Salts dynamics in maize irrigation in the Hetao plateau using static watertable lysimeters and HYDRUS-1D with focus on the autumn leachingirrigation
Tiago B. Ramosa, Meihan Liub,c, Paula Paredesd, Haibin Shic, Zhuangzhuang Fengc, Huimin Leib, Luis S. Pereirada Instituto Superior Técnico, University of Lisbon, Portugal.
b Tsinghua University, Beijing, China.
c Inner Mongolia Agricultural University, Hohhot, China.
d LEAF—Linking Landscape, Environment, Agriculture and Food Research Center, Instituto Superior de Agronomia, University of Lisbon, Portugal.

HYDRUS Conference, Prague, 2023The Hetao plain• 570,000 ha• Arid climate (annual precipitation averages 137 mm)• Silty soils• Main crops (maize, sunflower, vegetables)• Irrigation method (flooding)• ECgw 1.75 – 1.90 dS m-1

Nachshon (2018)
Xiong et al. (2021)

The Hetao plain

Author: Long GuoImages from the photos’ context of FAO’s International Network of Salt affected Soils meeting, 2021

Author: Jingrou Xiao

Set of lysimetersSet of lysimeters

Objectives

1. to calibrate/validate the HYDRUS-1D model for simulating soil water contents, boundary fluxes in the interface
between the saturated and unsaturated zones, the electrical conductivity of the saturation paste extract (ECe),and the actual crop evapotranspiration (ETc act) using the static water table lysimeters data.
WTD = 1.25, 1.5, 2.0, and 2.25 m
Seasons = 2018 (calibration) and 2017 (validation)
2. to compute the soil water and salt balances in the various lysimeters over the 2017 and 2018 maize growing
seasons.
3. to evaluate the effectiveness of autumn irrigation for salt leaching when different application depths are used.

Model setup

Atmospheric BC dual-Kc approach

Variable pressure
head - WTD

Model setup• Richards equation for water flow

Atmospheric BC dual-Kc approach• MvG functions for SHP• Feddes model for water stress• Mass model for salinity stress• Compensation mechanism• ECsw as nonreactive tracer using the CDEequation• Verhulst-Pearl logistic growth function for root
growthVariable pressure
head - WTD

Results of model calibration/validation
Soil water contents• Inverse modeling of SWC data
• Calibrated parameters: θs, α, η, Ks• Noted variability between lysimeters• Calibration of SHP for each lysimeter• Example for lysimeter with WTD=1.25m

R2: 0.752–0.940
RMSE: 0.021–0.033 cm3 cm-3
NSE: 0.742–0.938

Results of model calibration/validation
Upward fluxes• Manual calibration• Tunning of root growth function and Ks (second layer)

R2: 0.479–0.859
RMSE: 0.259–0.480 mm
NSE: 0.157–0.817

Results of model calibration/validation
Soil salinity• Manual calibration• Calibrated parameter: soil dispersivity

R2: 0.328–0.635
RMSE: 0.609–1.182 dS m-1
NSE: 0.127–0.378

Results of model calibration/validation
Actual ET

10.0

ETc act (mm)8.0

• Calibrated parameter: critical value of the water stress index ωc6.0

6.0

4.0

4.0

2.0

2.0
21/06/17

31/07/17

2017; WTD=1.5m

8.0

6.0

6.0

4.0

4.0

2.0

2.0

ETc act (mm)

0.0
10.0
06/08/18
28/04/18
17/06/18
2018; WTD=2.0m

09/09/17

8.0

8.0

6.0

6.0

4.0

4.0

2.0

2.0

0.0
10.0
12/05/17
31/07/17
2017;21/06/17
WTD=2.25m

ETc act (mm)0.028/04/18
17/06/18
06/08/18
10.02018; WTD=1.5m

09/09/17

8.0

0.0
10.0
12/05/17
2017;21/06/17
WTD=2.0m31/07/17

R2: 0.794–0.933
RMSE: 0.754–1.544 mm
NSE: 0.617–0.823

2018; WTD=1.25m

8.0

0.0
10.0
12/05/17

ETc act (mm)• Manual calibration

10.0

2017; WTD=1.25m

0.0
10.0
28/04/18
17/06/18
06/08/18
2018; WTD=2.25m

09/09/17

8.0

8.0

6.0

6.0

4.0

4.0

2.0

2.0

0.0
12/05/17

21/06/17

31/07/17

0.0
28/04/18

09/09/17

Time (days)

17/06/18

06/08/18

25/09/18

25/09/18

25/09/18

25/09/18

Time (days)
ETc

Simulated ETc act

Measured ETc act

Water and salt balance
Autumn irrigation: 200 mm• Upward fluxes and salt transport were higher atshallower WTD• Percolation decreased with deeper WTD• Higher measured ECe at shallower WTD• Leaching efficiency: Salt leaching / Salt inputs• Best condition for WTD=1.5 m

100Leaching efficiency (%)• The WTD had minor impact on Tc act (RWUreductions of 24-27%)

8060
40
200

77.7
1.25

83.5
1.5

66.9
2.0WTD (m)

51.3
2.25

The autumn irrigation leaching
Lysimeters with WTD ≤ 1.5 m:• Increasing AI = Less LE• Highest LE with AI = 200 mm
Lysimeter with WTD = 2.0 m:• Highest LE with AI = 250 mm
Lysimeter with WTD = 2.25 m:• Highest LE with AI = 220-350 mm
All lysimeters:• Reducing AI = Higher salinity

Conclusions• The relationships between the controlling factors of soil salinity are complex.
• For deeper WTD, soil salinization in Hetao can be controlled with autumn irrigation depths of 220-250 mm.
• For shallower WTD, the effectiveness of autumn irrigation is to be known in the long-term, and new solutions
are required.