Mitigating the Impact of Irrigation With Effluent Water: Mixing With Freshwater and/or Adjusting Irrigation Management and Design

Abstract

The use of treated wastewater (WW) for irrigation is steadily increasing worldwide. However, irrigation with WW requires special attention as it may alter soil hydraulic properties and, eventually, affect crop yields. The main goal of this study was to investigate two approaches that could mitigate this adverse impact: (i) mixing WW with local freshwater (FW) and (ii) adjusting the irrigation management and design to the deteriorated soil hydraulic properties. Four water qualities resulting from mixing FW and WW at different ratios for irrigation of an avocado orchard planted on a clayey soil were considered: FW, M 1/3 (2/3 FW-1/3 WW), M 2/3 (1/3 FW-2/3 WW), and WW. Increasing the WW component in the irrigation water reduces the soil's saturated hydraulic conductivity and infiltrability, and this reduction is depth dependent. It also reduces the transpiration of trees and their trunk growth. This is supported by numerical simulations that showed that irrigation with WW produced the reduction in plant transpiration relative to irrigation with FW. Numerical simulations indicated that irrigation management and design could be adjusted to improve plant water uptake and reduce the differences due to water quality. The results indicate that decreasing the irrigation rate and increasing the wetted area per tree could increase the water uptake in WW-irrigated soils to almost equal that in FW-irrigated soils. This can be achieved by using drippers with lower discharge and by using more drippers per dripline, more driplines per tree, and more drippers per tree (concentric loops of driplines around each trunk).

Critical knowledge gaps and research priorities in global soil salinity

“…In addition to effects of marginal waters such as treated wastewaters on soil salinity, specific prevalent solution ions can interact with the soil matrix. Specifically, Na is affecting soil pore distribution, soil structure and thus the flow-controlling hydraulic properties such as soil water retention and permeability (Assouline et al, 2020;Assouline and Narkis, 2011). Such effects were simulated by Russo (2013), showing that exchangeable Na in treated wastewater may considerably reduce the soil's hydraulic conductivity, thus impacting infiltration rates of irrigated soils.…”

“…One way to promote the success of utilizing water resources of marginal quality is to adopt irrigation methods appropriate to local soil and climate conditions and to develop appropriate site-specific irrigation methods and fertigation management protocols (Assouline et al, 2020). Pressurized irrigation methods, and especially drip irrigation, currently globally under-utilized, are more efficient than traditional surface irrigation and can minimize environmental impacts and health risks.…”

“…The turn to desalination as a strategy for water security is a positive opportunity to reverse the maybe dangerous and apparently non-sustainable trends consequential to irrigation with water containing high concentrations of salts (Assouline et al, 2015(Assouline et al, , 2020Raveh and Ben-Gal, 2018;Tal, 2016). Treatment of brackish groundwater and of water specifically destined for irrigation may in the future benefit from technologies that, contrary to the current popular reverse osmosis based desalination, will selectively remove problematic monovalent ions while leaving agricultural desirable bivalent ions like calcium and magnesium (Cohen et al, 2018).…”

Review: Modeling the Effects of Salinity and Sodicity in Agricultural Systems

“…An adapted version of the SOTE model has also been used to examine plant responses to salinity and sodicity (Yin et al, 2021) and how variations in plant tolerance to salinity levels effect overall water dynamics in agroecosystems (Yin et al, 2023). The Russo framework has been used to study how alternating between irrigation with treated wastewater and desalinated water can improve water uptake in orchards, as compared to irrigation with freshwater alone (Assouline et al, 2020;Russo, 2016;Russo et al, 2015Russo et al, , 2020.…”

Modelling Salinity and Sodicity Risks of Long-Term Use of Recycled Water for Irrigation of Horticultural Crops

“…We used the UNSATCHEM module of HYDRUS-1D [53] to evaluate the long-term dynamics of coupled water flow, solute transport, and major ion geochemistry in the predominant soils in the NAP region under different applications of irrigation water quality and soil amendments [10]. Few studies have evaluated the impact of the long-term use of RW on soil properties and crop yield [12,54]. This study mainly focuses on managing the long-term use of RW, utilizing scarce GW, and their various alternate and blending combinations.…”