Salt dynamics, leaching requirements, and leaching fractions during irrigation of a halophyte with different saline waters

Mansoor Al-Tamimi; Steve Green; Wasel Abou Dahr; Ahmed Al-Muaini; Dionysia Lyra; Khalil Ammar; Mohamed Dawoud; Paul Kenyon; Peter Kemp; Lesley Kennedy; Brent Clothier

doi:10.1071/SR23173

RESEARCH ARTICLE (Open Access)

Salt dynamics, leaching requirements, and leaching fractions during irrigation of a halophyte with different saline waters

Mansoor Al-Tamimi ^A , Steve Green ^B , Wasel Abou Dahr ^A , Ahmed Al-Muaini ^A , Dionysia Lyra ^C , Khalil Ammar ^C , Mohamed Dawoud ^A , Paul Kenyon ^D , Peter Kemp ^D , Lesley Kennedy ^E and Brent Clothier

^B ^*

+ Author Affiliations

- Author Affiliations

^A Environment Agency - Abu Dhabi, Abu Dhabi, United Arab Emirates.

^B The New Zealand Institute for Plant and Food Research Limited, Palmerston North, New Zealand.

^C International Center for Biosaline Agriculture, Dubai, United Arab Emirates.

^D Massey University, Palmerston North, New Zealand.

^E OnlyFromNZ, Wellington, New Zealand.

^* Correspondence to: brent.clothier@plantandfood.co.nz

Handling Editor: Gavan McGrath

Soil Research 62, SR23173 https://doi.org/10.1071/SR23173

Submitted: 29 August 2023 Accepted: 21 November 2023 Published: 18 December 2023

© 2024 The Author(s) (or their employer(s)). Published by CSIRO Publishing. This is an open access article distributed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND)

Abstract

Context

More than 830 million ha of soils are salt affected, representing around 9% of the world’s land surface. Groundwater high in salt already covers some 16% of the land area. Saline water can be used effectively for irrigation by salt leaching to despatch the accumulated salts, but this can pose a risk of salinisation of groundwater. It is important that the efficacy of salt leaching is confirmed, and the impacts of salt loading below the rootzone can be assessed.

Aims

We examine the efficiency and impact of salt leaching to remove salt from the rootzone.

Methods

Our soil, a Typic Torripsamment, is the dominant soil across the Arabian Peninsula. We carried out detailed laboratory experiments of salt leaching dynamics via salt breakthrough curves, analytical modelling, and through the field monitoring of impacts.

Key results

Analytical solutions well predicted the salt breakthrough curves from repacked soil columns in the laboratory and we were able to confirm that all of the soil’s water was actively involved in transport, and that salt behaved as an inert tracer. The breakthrough curves were well predicted using a small solute dispersivity, so piston displacement was found to be a good assumption. Salt was easily flushed from the columns. To back this up in the field, soil sampling was carried out down to 1 m across 36 profiles after the harvest of a halophytic crop irrigated with saline water. Salt storage was only 1.8 kg m⁻², even though 80 kg m⁻² had been applied. This is a positive result for managing irrigation.

Conclusions

Salt leaching can maintain equable salinity in the rootzone. However, this leaching carried salt back to groundwater at 2–3 times the concentration of the applied water. We confirmed that the amount of salt leaching back to groundwater can be significant.

Implications

This salt dilemma will require careful management to achieve crop yields and protect the environment.

Keywords: convection-dispersion, leaching fraction, mobile–immobile pore-water, piston displacement, residual salts, saline irrigation, salt breakthrough analysis, salt-leaching requirements.

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