Journal of Hydrology 587 (2020) 125000

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Journal of Hydrology
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Research papers

Assessing the role of rainfall redirection techniques for arresting the landdegradation under drip irrigated grapevines

TV. Phogata,b,c, , T. Pitta,b, R.M. Stevensd, J.W. Coxa,b, J. Šimůneke, P.R. Petriea,b,f⁎aSouth Australian Research and Development Institute, GPO Box 397, Adelaide SA 5001, Australia
The University of Adelaide, PMB1, Glen Osmond, SA 5064, Australiac
CCS Haryana Agricultural University, Hisar 125004, IndiadFormerly South Australian Research and Development Institute Staff, AustraliaeDepartment of Environmental Sciences, University of California, Riverside, CA 92521, United Statesf
The University of New South Wales, Sydney, NSW 2052, Australiab

ARTICLE INFOABSTRACTThis manuscript was handled by Corrado
Corradini, Editor-in-Chief, with the assistanceof Weiping Chen, Associate Editor

Altering the soil surface features can potentially regulate water and solute movement processes in the soils, andreduce the accumulation of salts in the plant root zone. In this study, HYDRUS-2D was used consecutively forthree years (2011–2014) to evaluate the potential impact of different rainfall redirection and water harvesting
techniques such as no mounding or control (A), mid-row mounding (B), mid-row mounding covered with plastic(C), and plastic buried in the soil in mid-row (D) on water balance, root zone salinity dynamics, and salt balancein the soil in three grapevine producing regions (Loxton, McLaren Vale, and Padthaway) in South Australia.
Simulations covered varied soil, climate, irrigation quality (0.3, 1.2, and 2.2 dS/m), and vine management
conditions typical of each region. Seasonal transpiration (Tp), evaporation (Es), and drainage (Dr) accounted for
39–49, 26–44, and 17–25%, respectively, of the total drip irrigation applied to the vineyards across the threelocations. Relative to the control, mounding mid-row soils (B) did not significantly alter the water balance at any
site; adding an impermeable plastic layer to that mound (C) reduced Es (48–54%), and increased Dr (by two
thirds) and Tp (1–16%). A tremendous ameliorative impact of mid-row mounding with plastic (C) was observedin the spatiotemporal salinity dynamics in the soils at all three locations (salt removal efficiency LEs > 1). An
increased leaching fraction under the mid-row mounding with plastic (C) led to considerable (up to 14.6 t/ha)
salts leaching from the crop root zone, which was double the other treatments. Buried plastic (D) showed slightly
better outcomes than the control or mid-row mounding, particularly for seasonal salt leaching in heavy textured
soils. Salt removal efficiency (LEs) > 1 in light- and medium-textured soils as compared to heavy-textured soils
indicates better salt removal in the former soils. The results demonstrated that the mid-row mounding withplastic is an effective technique to reduce root zone salinity in the drip-irrigated horticultural crops.

Keywords:
Rainfall redirection
Mulching
Leaching
Salinity
Grapevine
HYDRUS-2D

1. Introduction
Irrigation induced soil salinization is a worldwide phenomenon,
especially in arid and semiarid regions where poor quality water is used
for crop production. It is not only impacting soil quality and reducing
crop productivity but also curtailing the cultivated area and rendering
the soil unfit for sustainable crop production (e.g., Cao et al., 2018).
Poor quality water includes untreated or recycled municipal sewage
water, partially treated or untreated effluents/spent wash from industries, groundwater and drainage water, which are often used for
irrigating the crops as a supplement to the rainfall or a good quality
source. Food and Agriculture Organization (FAO, 2016) reported⁎

that > 19 percent of the total irrigated land (about 62 m ha) in theworld suffers from salinization. Every day for > 20 years, an average of
2,000 ha of irrigated land in arid and semi-arid areas across 75 countries have been degraded by salt-related degradation (Qadir et al.,2014). It is anticipated that increased temperature and reduced rainfall
projections by IPCC (2014) may intensify the risks of soil salinizationand endanger sustainable crop production, including high-value horticultural crops such as grapevine.
Irrigated grapevines are grown across every continent and arehighly managed growing systems where water availability and its
quality are often the most limiting factors (Flexas, 2016; da Silva et al.,2018). In Australia, > 90% of grapevines are grown under highly

Corresponding author at: South Australian Research and Development Institute, GPO Box 397, Adelaide SA 5001, Australia.
E-mail address: vinod.phogat@sa.gov.au (V. Phogat).

https://doi.org/10.1016/j.jhydrol.2020.125000
Received 2 February 2020; Received in revised form 20 April 2020; Accepted 21 April 2020
Available online 23 April 20200022-1694/ Crown Copyright © 2020 Published by Elsevier B.V. All rights reserved.

Journal of Hydrology 587 (2020) 125000

V. Phogat, et al.

efficient micro-irrigation systems (ABS, 2015). South Australia is amajor grape and wine-producing region in Australia, contributing 48%of the total wine grape crush, and 93% of vineyards use supplementary
drip irrigation (ABS, 2015). But, the quality of irrigation water used forgrapevine cultivation is highly variable across different vine-growing
regions. For example, in McLaren Vale, recycled water (ECw = 1.0–1.7
dS/m) is commonly used to supplement rainfall. In contrast, in theSouth East region, groundwater (ECw = 1.9–2.4 dS/m) is the dominantsource for irrigating grapevines (Stevens et al., 2012; Pitt et al., 2015).
Increased use of these waters (recycled and groundwater) for irrigation,
frequent droughts, and climate change projections of diminishing precipitation are putting enormous pressure on growers to maintain andsustain viticulture production around the world (e.g., DeGaris et al.,2015; van Leeuwen and Darriet, 2016). Besides, increased use of saline
water for irrigating grapevines is posing a potential danger of soil salinization, inflicting a serious impact on the long-term sustainability ofthese vineyards (Stevens et al., 2012).
Irrigated agriculture has managed the use of saline waters byleaching of salts from the rootzone depending on crop salt tolerance(Ayers and Westcot, 1985). The traditional irrigation management
strategy under conditions where the supply of water is not limited is toprovide extra water such that the ratio of the actual depth of drainage
to the depth of irrigation, i.e., the leaching fraction (LF), satisfies theleaching requirement (LR) (FAO, 1994). Due to the complexities ofinteractions between water, soil, and plant uptake, matching of LF with
LR is not straightforward (Dudley et al., 2008). In addition, the unavailability of good quality water and the complexity of implementation of LR for salinity control under drip irrigation systems may lead toenormous amounts of salt deposition laterally in the soils (e.g., Hanson
et al., 2008). Complex soil heterogeneity and widespread stratificationin Australian grapevine growing areas) and poor drainage conditions
may also confound efforts to tackle soil salinization (Singh, 2019;
Wichelns and Qadir, 2015).
Under such situations, on-farm water harvesting techniques such as
mulching and rainfall redirection play a key role in regulating waterand solute movement processes in the soil (Wang et al., 2009). For
example, drip irrigation coupled with plastic mulch has been introduced over a large area in China to reduce evaporation and to optimize the efficiency of available water resources (Liu et al., 2013).
Several studies have reported benefits of mulching in term of water use
efficiency (Adhikari et al., 2016; Zhao et al., 2014; Yu et al., 2018), seed
emergence (e.g., Dong et al., 2010), crop yield (Qin et al., 2014; Yu
et al., 2018), salinity control (Bezborodov et al., 2010; Abd El-Mageed
et al., 2016), soil temperature management (e.g., Li et al., 2017; Zhang
et al., 2018), and weed control (e.g., Ramakrishna et al., 2006). Field
experiments on rainfall redirection techniques (removing under vine
mound and mounding in mid-row with rainfall harvesting) have established a reduction of the soil salinity and Na+ and Cl- content inwine grapes (Stevens et al., 2013; Pitt et al., 2015). However, it is notclear whether these techniques apply beyond the particular combinations of water quality, climate, and soils at the experimental sites. Indeed, it is worth examining the impact of these techniques on waterbalance, root zone salinity dynamics, and salt leaching in soils.
Conducting long-term experiments involving numerous variables
under varied soil, water, and climate conditions are costly, and laborand time-intensive. On the other hand, numerical models are excellent
cost-effective tools to study the impact of climate, soil, water, and crop
variables on water and solute transport in the soil (Phogat et al.,2018a). Among the available agro-hydrological models, HYDRUS (2D/3D) (Šimůnek et al., 2016) has been widely used to simulate water
movement and salinity dynamics under drip irrigation (Ramos et al.,2012; Selim et al., 2013; Chen et al., 2015; Phogat et al., 2014, 2019)because of its flexibility to accommodate different types of complex
boundary conditions, to consider root water and nutrients uptake, andits ease of use due to a user-friendly graphical interface. However, few
modelling studies have included a mulched boundary for drip irrigation(e.g., Liu et al., 2013; Wang et al., 2014; Li et al., 2015; Zhao et al.,2018). These studies were only confined to evaluating the dynamics ofwater distribution in soils, and the reduction of evaporation due tomulched conditions on the flat surface by considering a no-flow
boundary over the mulched surface. Simulations of water and salinity
dynamics under different mid-row rainwater harvesting techniques(e.g., mounding with and without plastic, and sub-surface plastic)
coupled with drip irrigation of grapevines could potentially serve as a
new concept for implementing the surface boundary in modelling studies. Furthermore, to our knowledge, no modelling study has been focussed on evaluating the ameliorative effect of rainfall directed fromthe mid-row of horticultural crops.
Therefore, in this investigation, HYDRUS-2D was used to evaluate
the impact of different rainfall redirection and water harvesting techniques (A - no mounding or control, B - mid-row mounding, C - mid-row
mounding covered with plastic, and D - plastic buried in the soil in midrow) on water balance, root zone salinity dynamics, and salt balance indifferent grapevine growing regions (Loxton, McLaren Vale, andPadthaway) over multiple seasons (2011–2014) involving varied soil,
climate, irrigation quantity and quality, and crop conditions. The outcome of this investigation would be helpful in evaluating these innovative practices for controlling soil salinization and salt leaching forsustainable grape production.
2. Materials and methods
2.1. Description of the study sites
The present investigation was carried out in three grapevine
growing regions in South Australia (SA), i.e., McLaren Vale (McLaren
Vale region), Padthaway (South East), and Loxton (Riverland) (Fig. 1).
These sites have different climate, soil, irrigation water quality, andgrowing practices, representing diverse and varied conditions forgrapevine cultivation. The water and salt balance modeling study was
conducted for three consecutive seasons (2011–12 to 2013–14) at thethree locations. All experimental details including soil characterization,
irrigation scheduling, water quality, crop performance and yield forthese trials can be found in Pitt et al. (2015), Stevens et al. (2012,2013), and Phogat et al. (2017, 2018b) for the McLaren Vale (McL),
Padthaway (Pad), and Loxton (Lox) sites, respectively. However, briefsite-specific information about data acquisition relevant to the current
study is given below.
2.1.1. McLaren Vale
McLaren Vale (McL) is a premium wine grape region in South
Adelaide, which is characterized by a Mediterranean climate. The climate data for the study site were obtained by running a data drill forthe study site (Jeffrey et al., 2001). The average maximum temperature,potential evapotranspiration, and rainfall for the last 100 years at theexperimental site were 20.9 °C, 1568.5 mm, and 555 mm, respectively.
Other data for simulations were obtained from an experimental study
conducted at a commercial Cabernet Sauvignon vineyard (35°14́S and
138°31́E) located within the region (Pitt et al., 2015). The vineyard wasplanted in 1998 with a vine spacing of 2.75 m by 1.8 m. The vines were
irrigated with a drip system with 1.2 L/h drippers spaced at 0.6 m andaligned along the length of vine rows. Treated wastewater for irrigation
was obtained from the Christies Beach Wastewater Treatment Plant anddistributed through a pipeline scheme managed by Willunga Basin
Water (WBW). Water samples were collected from irrigation emittersthroughout the growing season and assessed for salinity (Pitt et al.,2015). The average irrigation water salinity (ECw) during the study
period (2011–14) was 1.2 dS/m (range 1.0–1.3 dS/m). The amounts ofseasonal supplementary irrigation applied to grapevine at McLaren Vale
ranged from 86.6 to 135.3 mm during 2011–14 (Table 1).
A comprehensive soil testing program was carried out at the
McLaren Vale study site due to the existence of a complex
2

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SimpsonDesertN

Great Victoria
DesertLake Eyre
Lake Maurice
Lake
Lake Frome
T orrens
Lake
Gairdner

Port Augusta

Adelaide

LoxtonMurrayRiver

McLaren Vale
Padthaway

M t GambierFig. 1. Locations of study sites (Loxton, McLaren Vale and Padthaway) in different grapevine regions in South Australia.

are quite variable and are influenced by rainfall patterns and the typesof irrigation practices. Surface drippers spaced at 60 cm were used toapply supplementary groundwater irrigation to vines with a salinity
varied from 1.9 to 2.3 dS/m. The average salinity of irrigation water(ECiw) over the three seasons (2011–14) was 2.2 dS/m. The pressurecompensated drippers had a discharge of 2.1 L/h. In the absence ofgood quality surface water resources at Padthaway, irrigated vines weresolely dependent on groundwater for supplemental irrigation. Seasonal
water applications during the simulation period amount to 242.5 mm(Table 1).
The soils at the Padthaway study site varied from sandy clay loam at
the surface to clay at lower depth (Stevens et al. (2012). The soil hydraulic parameters (Table 2) used in the modelling study were estimated from measured values of the water content-pressure head relationship in undisturbed cores taken from 0 to 30 and 30–100 cm.
Other soil parameters (the saturated hydraulic conductivity and bulk
density) for both layers were also measured on undisturbed soil cores.
Similar hydraulic parameters were assumed at different locations acrossthe vine lines (UV, UT, and MR). While measured initial soil salinity(ECe) at UV down to the 80 cm depth varied from 4 to 4.5 dS/m at thestart of the simulation, the ECe at MR and UT (1.2 to 2.0 dS/m, respectively) were less than half of that (Stevens et al., 2012).

Table 1
Annual rainfall (P) and seasonal irrigation (I) in vineyards during 2011–2014 atdifferent locations in South Australia.
Location

2012–13PI

2013–14P
I

AverageP
I

McLaren Vale

2011–12P
I(mm)
614.3 86.6

437.1

129.5

524.0

135.3

525.1

117.1

Padthaway
Loxton

466.4
298.2

446.4
198.7

242.5
435.0

576.9
348.3

242.5
377.0

496.6
281.7

242.5
378.2

242.5
322.5

heterogeneous soil formation in this region (Pitt et al., 2015). Undisturbed core samples were collected from 0 to 15, 30–60, and
60–100 cm soil depths under vine (UV), under the track (UT), and in
mid-row (MR) regions to examine the variability in soil characteristics(Pitt et al., 2015). The soil hydraulic parameters (Table 2) were estimated following van Genuchten-Mualem constitutive relationship (vanGenuchten, 1980), utilizing measured soil water retention data on undisturbed soil core samples collected from UV, UT, and MR regions. The
saturated hydraulic conductivity (Ks) and the bulk density (Db) werealso measured on undisturbed soil cores following standard procedures(Klute, 1986). Hence, input parameters represent a complex variability
existing at different soil depths and laterally across the vine rows.

2.1.3. Loxton
Loxton (34°27́S and 140°34́E) is a part of the Riverland vineyard
region, which is located along the River Murray corridor and utilizes
the good quality river water for grapevine irrigation. It has a warmer
Mediterranean climate and receives less rainfall compared to the othertwo regions. The average maximum temperature, potential evapotranspiration, and rainfall for the last 100 years were 23.8 °C, 1823 mm,
and 265 mm, respectively (Phogat et al., 2017).
The Chardonnay vineyard at Loxton (Lox) was irrigated with asurface drip system. The water was applied through pressure compensated drippers with a discharge of 1.6L/h. The plant spacing is similar
to the vineyards at the other two locations. The vineyard was irrigatedwith water from the River Murray, which has salinity varying from 0.2
to 0.4 dS/m, with a mean value of 0.3 dS/m during the study period(Phogat et al., 2018b). Seasonal irrigation applications were much

2.1.2. Padthaway
Padthaway (36°37́S and 140°32́E), in the South East of South
Australia, is characterized by the presence of medium-textured soils
underlain with limestone rocks, popularly known as Terra rossa.
Padthaway (Pad) has a warm Mediterranean climate with good rainfall.
The average rainfall and potential evapotranspiration over the last
100 years amount to 523.3 and 1553.4 mm, respectively. Climateparameters for modelling were taken from a nearby Bureau of
Meteorology observatory.
Relevant crop data for modelling was obtained from a field experiment in a commercial own-rooted Chardonnay vineyard, locatedapproximately 12 km south of Padthaway (Stevens et al., 2012, 2013).
The vineyard was planted in 1996 with Chardonnay clone I10V1.
Salinity trends in the shallow unconfined aquifer on the Padthaway Flat
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Table 2Estimated soil hydraulic parameters at different sites (McLaren Vale, Padthaway, and Loxton) used in simulations.
Soil texture
McLaren Vale
Sandy clay loam (UV)
Sandy clay loam (UT)
Sandy clay loam (MR)Clay (UV)Clay (UT)
Clay (MR)Clay (UV)Clay (UT)
Clay (MR)
Padthaway
Sandy clay loam
Clay loam
LoxtonLoamy sandLoamy sand
Loam

Soil depth (cm)θr(cm3cm−3)

θs(cm3cm−3)α(cm−1)n

Ks(cm d-1)lDb(g cm−3)

0–30
0–30
0–30
30–65
30–65
30–65
65–10065–10065–100

0.23
0.23
0.19
0.26
0.31
0.27
0.26
0.27
0.25

0.50
0.46
0.47
0.49
0.49
0.50
0.49
0.46
0.43

0.014
0.013
0.01
0.014
0.03
0.01
0.114
0.1
0.014

1.5
1.5
1.4
1.4
1.4
1.4
1.2
1.2
1.4

137.8
57.4
153.9
20.7
33.2
87.7
58.7
13.8
35.1

0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5

1.50
1.55
1.44
1.55
1.55
1.40
1.49
1.49
1.32

0–30
30–100

0.07
0.17

0.48
0.44

0.020
0.058

1.25
1.3

26.0
11.0

0.5
0.5

1.3
1.44

0–30
30–60
60–100

0.04
0.05
0.05

0.4
0.38
0.37

0.027
0.04
0.04

2.2
1.7
1.62

388.8
259.2
172.8

0.5
0.5
0.5

1.53
1.41
1.44

θr is the residual water content, θs is the saturated water content, Ks is the saturated hydraulic conductivity, Db is the bulk density, and α, n, and l are the van
Genuchten shape parameters.

higher at Loxton as compared to the other two locations due to lessrainfall and low water retention capacity of light-textured soils. The
average seasonal irrigation over the three seasons at Loxton was
378 mm (Table 1).
The soils at the Loxton site are predominately sandy in texture. The
soil hydraulic parameters for this modelling study were taken from
Phogat et al. (2017) and are shown in Table 2. The saturated hydraulicconductivity (Ks) and the bulk density (Db) were measured on undisturbed core samples using standard procedures. Similar soil hydraulic parameters were assumed at different locations across the vine
lines [under vine (UV), under the track (UT) and in the mid-row (MR)regions]. Furthermore, HYDRUS-2D was calibrated and validated for
spatial and temporal distributions of the soil water content over multiple seasons (Phogat et al., 2017).

heads at the flux boundary could make the numerical code unstable(Šimůnek et al., 2016). During irrigation, the drip line boundary washeld at a constant water flux, q, equal to the dripper discharge rates atdifferent locations. The atmospheric boundary condition was assumed
for the remainder of the soil surface. A no-flow boundary condition was
specified on the left and right edges of the soil profile to account forflow and transport symmetry. A free drainage boundary condition was
assumed at the bottom of the soil profile.
To implement a plastic cover over the mound (treatment C), arcs
were constructed 3–5 cm below the surface boundary, and a no-flow
boundary condition was imposed in the domain over the plastic sheet
on both sides at the desired locations (see Fig. 3). The extent of evaporation from the soil over the no flow mulched surface was assumed
equal to the losses due to wear and tear of the mulch. Liu et al. (2013)
reported that plastic mulch reduced the soil evaporation by 90% under
optimum conditions. However, year-old mulch can deteriorate and be
torn apart at some places, leading to significant evaporation losses.
Essentially, placing the plastic mulch below a thin soil layer helped toprotect it from the hot weather and other mid-row operations (Pittet al., 2015). Another advantage of adopting this approach was to facilitate rainwater movement along the ridge/mound to the lower
reaches of the furrow/soil. This approach, further, allowed simulating
the variable impact of dynamic pressure heads due to rainfall on flow
conditions in the soils. Similarly, for treatment D, a no-flow boundary
was embedded into the domain at the location (10 cm below the soil
surface) where the plastic sheet was placed in the field studies. Finemesh size was adapted below the time-variable flux boundary (below
the dripper) in all treatments to facilitate dynamic flow conditions in
response to frequent irrigations. All specified boundary conditions areillustrated in Fig. 3. Simulations were conducted separately for eachtreatment for three years (July 1, 2011- June 30, 2014) using daily time
steps for boundary conditions.

2.2. Modelling domain and boundary conditions for different treatments
Field experiments at Padthaway and McLaren Vale consisted of four
rainfall harvesting and redirection treatments, i.e., control (A), a midrow mound (B), a mid-row mound covered with plastic (C), and buriedplastic in the mid-row region (D). The establishment of these treatments
at field sites is discussed in Stevens et al. (2012) and Pitt et al. (2015),
respectively, and is shown in Fig. 2 for the McLaren Vale site. Similar
modelling scenarios were conducted at Loxton to match the treatments
at the other two sites. In the control treatment, actual mid-row conditions show depressions in the wheel ruts due to heavy traffic associatedwith mechanical pruning (or pre-pruning), fungicide/herbicide spray
program, and mechanical harvest operations. In the other treatments(B, C, and D), a shallow ripping operation and/or removing the undervine mounding soil facilitated the mid-row mounding operations. These
modifications on the soil surface are also illustrated in the modellingdomains (Fig. 3).
The modelling domains for different treatments were constructed in
HYDRUS-2D (Šimůnek et al., 2016) based on the vine spacing, drip
design parameters, and mid-row treatments (Fig. 3). The vine row ispresent in the centre of the domain, which was extended equally on
both sides across the vine row. The vertical depth was equal to 100 cm,
which relates to the rooting depth of grapevines in the field experiments(Stevens et al., 2012; Pitt et al., 2015; Phogat et al., 2017). A timevariable flux boundary condition was applied to a 20 cm long boundary
directly below the dripper, centred on 137.5 cm from the top left cornerof the soil domain (Fig. 3). The length of this boundary was selected toensure that all irrigation water could infiltrate into the soil without
producing positive surface pressure heads, because positive pressure

2.3. Estimation of potential transpiration (Tp) and potential evaporation(Es)
HYDRUS-2D requires daily values of potential Tp and Es under thefield conditions as inputs and then calculates modelled values depending on soil moisture dynamics. In this study, the FAO-56 dual-crop
coefficient approach was employed to estimate the daily values of potential Tp and Es for grapevine at three locations (Allen et al., 1998).
This method has been used previously in many studies for input data
generation (e.g., Phogat et al., 2014, 2017). It combines two coefficients, i.e., a basal crop coefficient (Kcb) responsible for transpiration
4

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V. Phogat, et al.

Fig. 2. Field view of the rainfall redirection treatments (A-control, B-Mid-row mound, C-Mid-row mound with plastic, and D-Buried plastic) imposed at the McLaren
Vale experimental site.

Fig. 3. Schematic view of the HYDRUS-2D spatial modelling domain for A) control, B) mid-row mound, C) mid-row mound with plastic mulch, and D) buried plastic
treatments based on vine and drip spacing and mid-row dynamics. Applied boundary conditions are also shown.

and a soil evaporation coefficient (Ke) (i.e., Kc = Kcb + Ke), with dailyreference crop evapotranspiration (ET0) to estimate daily crop evapotranspiration (ETC) as follows:

ETC = (K cb + K e ) ET0

fertigation management. The longitudinal dispersivity was assumed as
one/tenth of the modelling domain (with the transverse dispersivity
being one-tenth of the longitudinal dispersivity) (Beven et al., 1993;
Cote et al., 2003) and the molecular diffusion coefficient of salts inwater was considered as 1.656 cm2/day (Phogat et al., 2017). The data
for EC of irrigation water (ECiw) was based on the water quality analysis. However, average values of ECiw were considered for modellingfor all locations (McLaren Vale = 1.2, Padthaway = 2.2, andLoxton = 0.3 dS/m) as there was only a small variation in the irrigationwater quality over the study period. The rainfall chemistry analyzed by
Cresswell et al. (2010) in the Adelaide region estimated the salinity(ECrw) of 0.12 dS/m, and this value was used in simulations as acommon value for all locations. To facilitate the prediction of theleaching of salts from the soil profile, all input ECiw and ECrw values
were converted into mass units using a common approximation (1 EC(dS/m) = 640 mg salts/L). The salt leaching efficiency was estimated tocompare the effectiveness of various rainfall redirection techniques. It
was estimated for all locations annually as the amount of salts leached
below a 1 m depth per volume of water drained.
The initial water content distribution was set to either measured
values (McLaren Vale and Padthaway) or to field capacity (Loxton).
Measured values of ECe in the soil were converted to salinity at actual soil
water content following a linear relationship by Pitt et al. (2015) and tosalt mass as per the approximation 1 EC (dS/m) = 640 mg salts/L.

(1)

Standard Kcb values for grapevine were adjusted for the local climate, taking into consideration crop height, wind speed, and minimum
relative humidity averages for the period under consideration(2011–2014) at all locations (Allen et al., 1998). Location-specificparameters used to estimate daily Es, and Tp for grapevine following the
FAO-56 dual-crop coefficient approach for three locations are given in
Table 3. Values of daily potential transpiration (Tp) and soil evaporation(Es) obtained in this way were used as time-variable boundary conditions (see Fig. 3) in the HYDRUS-2D model, along with precipitation
received at the site during the study period. More details about the
FAO-56 dual-crop coefficient can be found in Allen et al. (1998) andAllen and Pereira (2009).
2.4. Solute parameters for salinity dynamics in the soil
Soil solution salinity (ECsw) distribution was modelled as a non-reactive solute (e.g., Ramos et al., 2011; Wang et al., 2014; Phogat et al.,2014, 2019). These studies demonstrated that this approach could be
successfully used in environments under intensive irrigation and5

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for buried plastic (D) relative to the control. The mid-row
mound + plastic (C) maximised vine water uptake followed by theburied plastic treatment. The average increase in grapevine Tp in the
mid-row mound + plastic treatment was 16% higher than the control.
Normally, transpiration/root water uptake are expected to increase forsites with plastic mulch as compared to no mulch sites (Allen et al.,1998), because temperatures are higher under mulch, and root growthis promoted (Gao et al., 2014; Saglam et al., 2017). At the same time,
there was a drastic reduction (54%) in Es in the mid-row
mound + plastic treatment, which may have produced higher Dr,
especially during the 2012–13 and 2013–14 seasons. Therefore, theaverage seasonal Dr in mid-row mound + plastic treatment increased
three times compared to the other treatments. Moreover, the averagesoil water storage (ΔS) also increased about four times under mid-row
mound + plastic as compared to the control. The water conservation
effect of plastic mulch has been documented in many previous studies
for drip irrigation (e.g., Saglam et al., 2017).
The average water balance components at Padthaway were comparable to the McLaren Vale site. Nonetheless, the average soil water
storage (ΔS) at the end of the grapevine season was 5% higher, and theaverage Es component was 7% lower than at the McLaren Vale site
(Table S-1, supplementary material). Similarly, Tp and Dr also increasedby 7.5% and 19% (almost three times), respectively, when the control
treatments were compared. On the other hand, at Loxton, rainfall redirection techniques had a little impact on vine water uptake as Tp
remained similar in all treatments (Table S-2, supplementary material).
However, average Tp accounted for 49% of the applied water, while
26% of irrigation and rainfall contributed towards Es, with the remaining 25% of water draining out of the soil profile (1 m). Drainage(Dr) almost doubled in the mid-row mound + plastic treatment (C)compared to the control (A), showing the impact of surface mulching on
direct water loss from the soil surface.
Leaching fractions (LF) estimated for the range of treatments at thethree locations are shown in Fig. 4. The average LF for the mounding
only (B) and buried plastic (D) treatments were similar to the control(A). However, annual LFs were influenced by the site-specific soil texture and climate conditions (rainfall), being higher at Loxton(0.15–0.25). Notably, LFs were considerably lower at Padthaway
during 2011–12 due to a relatively dry soil profile at the start of thesimulation compared to the other sites. Later on, the LF at Padthaway
matched corresponding values at McLaren Vale. On the other hand, the
LF in the mid-row mound + plastic (C) treatment increased on average
three times at McLaren Vale (0.26–0.39) and Padthaway (0.16–0.4) andtwo times at Loxton (0.31–0.4) compared to the corresponding averagevalues for other treatments. Hanson et al. (2008) reported similarleaching fractions (0.07–0.31) under drip irrigation, which encourages
rapid localized leaching, especially in light-textured soils.
Indeed, treatment mid-row mound + plastic has emerged as the

Table 3
Values of important parameters used to estimate daily transpiration (Tp) anddaily evaporation (Es) for vineyards at different locations.
Parameters

McLaren Vale

Padthaway

LoxtonKcb ini
Kcb mid
Kcb endKcb mid adj (2011–12)
Kcb mid adj (2012–13)
Kcb mid adj (2013–14)
Kcb end adj (2011–12)
Kcb end adj (2012–13)
Kcb end adj (2013–14)
fw, surface drip
fw, rain
RAW (mm)
TAW (mm)
TEW (mm)
REW (mm)
Plant height h (m)Rooting depth Zr (m)Vineyard density (Fc eff)
Evaporable depth Ze (m)Mid-season Min RH (%) (2011–12)
Mid-season Min RH (%) (2012–13)
Mid-season Min RH (%) (2013–14)
Av. Wind speed (m/s) (2011–12)
Av. Wind speed (m/s) (2012–13)
Av. Wind speed (m/s) (2013–14)

0.20
0.65
0.5
0.66
0.67
0.69
0.51
0.52
0.54
0.29
1
74
150
20
10
1.5
1.0
0.5
0.15
40
36
37
1.77
1.41
2.43

0.20
0.65
0.5
0.72
0.71
0.72
0.57
0.56
0.57
0.39
1
46
85
20
10
1.5
1.0
0.5
0.15
36
33
34
3.06
2.37
2.83

0.20
0.65
0.5
0.71
0.73
0.72
0.56
0.58
0.57
0.22
1
34
60
12
8
1.5
1.0
0.5
0.15
30
26
27
2.16
2.24
2.17

Kcb are the basal crop coefficients for initial (ini), mid (mid), and late (end) seasons
adjusted (adj) to local climate, fw is the wetted soil surface fraction, RAW isreadily available water, TAW is total available water, TEW is total evaporable
water, and REW is readily evaporable water.

3. Results and discussion
3.1. Seasonal water balance
Seasonal water balance components for grapevine under different
rainfall redirection treatments at the McLaren Vale site are shown in
Table 4. The average water balance, irrespective of seasons and treatments, divided the transpiration (Tp), evaporation (Es), and drainage(Dr) as 39, 44, and 17% of the total water application, respectively.
Among the treatments, the results were similar for the mid-row
mounding treatment (B) and the control (A), while Tp increased slightly
Table 4
Simulated components of the annual water balance for vineyards under different rainfall redirection treatments for three consecutive seasons(2011–2014) at McLaren Vale.
P

Tp

Es

Dr

ΔS

82.16

614.3

245.14340.90

65.91

51.21

437.1
524.0

196.37261.66317.20309.28

85.53
93.96

−25.00−14.40

614.3
437.1
524.0

245.94195.04259.14341.79318.78310.05

63.96
86.31
94.73

52.21
−26.47−13.43

614.3
437.1
524.0

289.89231.11295.07155.31147.53142.07183.98219.92219.5579.97−25.89
−6.98

614.3
437.1
524.0

264.68207.57277.11343.43319.17307.34

28.57
65.69
90.17

58.14
−14.41−18.47

McL

0.3

Pad

Lox

0.2

A

B

C

2013-142012-132011-122013-142012-132011-122013-142012-132011-120.0

2013-140.1

2012-13

2012–13129.442013–14135.20B) Mid-row mound2011–1282.16
2012–13129.442013–14135.20C) Mid-row mound + plastic
2011–1282.16
2012–13129.442013–14135.20D) Buried plastic
2011–1282.16
2012–13129.442013–14135.200.4

2011-12A) Control
2011–12I
mm

Leaching fraction

Year/ Treatment

D

Fig. 4. Annual leaching fractions under grapevine for different treatments (Acontrol, B- Mid-row mound, C- Mid-row mound with a plastic cover, D- Buriedplastic) at McLaren Vale (McL), Padthaway (Pad), and Loxton (Lox).

Tp is seasonal transpiration; Es is seasonal evaporation; Dr is seasonal drainage;
ΔS is soil storage/depletion
6

Journal of Hydrology 587 (2020) 125000

V. Phogat, et al.

Soil depth (cm)i) McLaren Vale
2011-122013-142012-13

A

A

A

B

B

B

C

C

C

D

D

D

ii) Padthaway
A

A

B

B

B

C

C

C

D

D

D

A

A

A

B

B

B

C

C

C

D

D

D

Soil depth (cm)A

Soil depth (cm)iii) Loxton

Lateral distance from the vine (cm)Fig. 5. Electrical conductivity (ECe) distributions in the soil at i) McLaren Vale, ii) Padthaway, and iii) Loxton in different treatments (A - control, B - Mid-row mound,C - Mid-row mound + plastic, D - Buried plastic) at the end of 2011–12, 2012–13, and 2013–14 grapevine seasons.

most favourable treatment with increased plant water uptake, a higher
fraction of the evaporative flux diverted towards leaching, a substantial
increase in the LF, which altogether can help in maintaining a favourable environment by transporting salts out of the root zone. These results further confirm that plastic mulching, compared to the mid-row
mounding, was an effective on-farm water management strategy that
can improve the rhizosphere environment for a long-term sustainablegrapevine production.

3.2. Soil salinity dynamics
3.2.1. Spatiotemporal salinity distribution in the soil
The impact of the rainfall redirection techniques on spatial salinity(ECe) dynamics in the soil at the end of 2011–12, 2012–13, and 2013–14
growing seasons at the three locations is shown in Fig. 5. Generally, theECe distribution at the McLaren Vale and Padthaway sites in the undervine (UV) was higher than in the mid-row irrespective of the treatment
because drip irrigation applies water close to the vines. Rapid water
7

Journal of Hydrology 587 (2020) 125000

V. Phogat, et al.

8

ECe (dS/m)

6

UV_M

MR_M

UV_P

MR_P

8

6

4

4

2

2

0
8

ECe (dS/m)A) ControlC) MR mound+plastic

0
8

6

6

4

4

2

2

0

0

B) MR moundFig. 6. Temporal changes in the average
profile ECe (dS/m) in the soil as influenced
by different treatments (A - control, B - Midrow (MR) mound, C - MR mound + plastic,
D - Buried plastic) under the vine (UV) andin the mid-row (MR) region at the McLaren
Vale (UV_M; MR_M) and Padthaway (UV_P
and MR_P) sites during July 2011- June
2014.

D) Buried plastic

extraction due to the high root density in this region results in the deposition of salts. On the other hand, in the mid-row, reduced water uptake and little salt addition via irrigation coupled with adequate rainfallinduced salt flushing produced lower ECe. However, at McLaren Vale, atrend towards increasing ECe occurred, especially in the under-vine at theend of successive seasons, which is correlated with proportionally higher
additions of salts through irrigation coupled with less localized leaching.
Among the treatments, the bigger ECe “bulge” was present in the undervine in the control (A) and the mid-row mound (B) treatments as compared to the mid-row mound + plastic(C). At the end of the 2013–14
season, the maximum ECe in the under vine region was 4.2, 3.5, 3.0, and3.5 dS/m, respectively, in the control (A), a mid-row mound (B), a midrow mound + plastic (C), and buried plastic (D) treatments at McLaren
Vale. However, salinity remained below 0.5 dS/m in a mid-row
mound + plastic (C), whereas it was < 0.9 dS/m in the control (A) andmid-row mound (B) treatments and much higher in the buried plastic (D)(0.9–1.5 dS/m). The results showed that at McLaren Vale, the predominance of heavy-textured heterogeneous soils and high irrigationwater salinity encouraged salt deposition in the vicinity of the vine. Thissituation is similar to the poorly drained soils, which potentially encourage salinization and waterlogging problems in irrigated agro-systems(Wichelns and Qadir, 2015; Singh, 2019).
At Padthaway, the extent of ECe distribution in the soil was muchgreater than at McLaren Vale, irrespective of regions and treatments,
because the initial salinity in the under-vine (4–4.5 dS/m) and mid-row(1.2–1.8 dS/m) regions was very high compared to the other two sites.
Apparently, the high ECiw of the irrigation water (2.0–2.35 dS/m), coupled with medium to heavy-textured soils with low hydraulic conductivity (11–26 cm/day), is conducive to salt deposition within the soil
profile in the immediate vicinity of the vine (under-vine region), where
irrigation is applied through drippers. Therefore, pockets of high ECe(5.5–7.0 dS/m) at Padthaway still existed under the vine below the 50 cm
depth in all treatments except mid-row mound + plastic at the end of the
2011–12 vine growing season (Fig. 5ii). The maximum salinity zone had
an average ECe from 3.5 to 4.0 dS/m at the end of 2013–14. However,this zone spreads over a large area in the control (A) and mod-row mound(B) treatments as compared to buried plastic (D), where it was restrictedwithin a small region, mostly in the deeper zone of the profile. In midrow mound + plastic (C), a significant volume of water passed throughthe zone of high salinity, pushing the salts out of the profile. Consequently, salinity was greatly reduced during the first season. During thefollowing seasons (2012–13; 2013–14), the soil profile salinity was reduced below threshold (2.2 dS/m) in almost the entire mid-row, whereas
pockets of higher salinity existed in the under-vine below 30 cm. Hence,treatment mid-row mound + plastic (C) continued to be by far the mosteffective at salt removal compared to the other treatments.
Interestingly, at Loxton, ECe remained lower in the UV region ascompared to MR, irrespective of the rainfall redirection treatments(Fig. 5iii). At the end of the 3rd season (2013–14), a low ECe zone(< 0.5 dS/m) increased laterally in all treatments. The presence ofsandy soils and a three times higher amount of irrigation water of ECiwof 0.3 dS/m applied within a localized region facilitated rapid leachingof the salts. In contrast, ECiw at McLaren Vale and Padthaway was 4 and7 times higher, respectively, than at Loxton, which potentially added anenormous quantity of salts in the soil in the under-vine area in these
drip-irrigated vineyards. ECe in the soil profile always remained below
the grapevine threshold (2.2 dS/m) in all treatments. The buried plastic
treatment allowed a small amount of salt deposition just below theplastic; this is due to the plastic membrane blocking vertical drainage ofwater and promoting lateral salt migration to the area underneath theplastic. In mid-row mound + plastic (C), the low salinity zone (< 0.5dS/m) extended further under the vine compared to the other treatments. It is also evident that most of the irrigation-induced salts wereleached out of the 1 m soil profile. Hence, the current irrigation amountand quality of water did not pose any salinity threat in the root zone ofthe vine, irrespective of treatments. Christen et al. (2007) showed asimilar impact on the salinity distribution when using good quality irrigation water in a loamy soil.
Daily profile-averaged ECe in the under-vine and mid-row regions at
the McLaren Vale and Padthaway sites are shown in Fig. 6. Data for the
Loxton site is not shown as the salinity levels were much lower than thegrapevine threshold ECe of 2.2 dS/m (Zhang et al., 2002). A progressive
increase in ECe was found at McLaren Vale in all treatments over thethree seasons except in mid-row mound + plastic (C) where ECe remained almost constant (< 0.5 dS/m). ECe (0.9 dS/m) in buried plastic(D) was maximum in the mid-row region at the end of the simulation.
Despite increasing trends, ECe remained below the crop threshold in the
mid-row region in all treatments. On the other hand, it increased above
the threshold in the under-vine during the latter half of 2013–14, irrespective of treatments. It seems that heavy-textured soils with enormous profile heterogeneity and anisotropic flow conditions (Pittet al., 2015) have played a crucial role in nullifying the treatment impact at McLaren Vale compared to the other Padthaway.
At the Padthaway site, the average ECe in the MR region remained
below the threshold in all treatments except buried plastic (D).
Interestingly, in this treatment, ECe under the mid-row increased above
the threshold during the 2013–14 growing season. Buried plastic possibly harboured more salts directly below the plastic layer due to the8Journal of Hydrology 587 (2020) 125000

V. Phogat, et al.

blockage of vertical drainage, as was also seen at Loxton also (Fig. 5).
However, the average ECe in the under-vine reduced drastically in alltreatments after an initial increase during the 2011–12 summers. Although it remained higher than the grapevine threshold (2.2 dS/m), theimpact of the rainfall redirection was very dramatic in the mid-row
mound + plastic (C) treatment where ECe fell below the threshold
during the post-winter season of 2013–14. The mean ECe in the buriedplastic (D) treatment falls between values obtained in the control (A)and mid-row mound + plastic (C) treatments in the under-vine area. In
other studies also mulching has been found to be a better field-management option to reduce the upward movement of salts and evaporative water losses (Zhao et al., 2014; Chen et al., 2016) and thatmulching with different materials is a promising technique for salinity
control in agriculture (Bezborodov et al., 2010; Abd El-Mageed et al.,2016).
The mid-row mound + plastic treatment (C) maintained relatively
lower salinity within the vine root zone as compared to the othertreatments, especially for recycled water and groundwater irrigatedgrapevines with heavier-textured soils, providing a better growing environment for vine and a superior salt leaching approach as comparedto other techniques. The results of the modelling suggest that thetreatments behaved differently at different locations, and the impact on
the ECe distribution under grapevine due to rainfall redirection techniques depends on combined effects of the soil type, water quality, andweather conditions.

ha), and Loxton (136 to 247 kg/ha) were much lower as compared tosalts added through irrigation during the same period.
Although salt additions in the soil in different treatments were similar, salt storage (ΔS_S) and leaching (Dr_S) altered due to different
rainfall redirection techniques (Table 5). Interestingly, all treatments
showed an increased amount of salt remaining in the profile at McLaren
Vale and Padthaway (except mid-row mound + plastic) during all
seasons where recycled water and groundwater were used for irrigation, respectively. On the other hand, at Loxton, salt leaching was very
rapid, and a high amount of leaching occurred compared to the amountadded through irrigation and rainfall (Table 5). Therefore, there was a
net depletion of salts from the soil at the end of the 2013–14 season in
all treatments. Similarly, the average salts storage at Padthaway in the
mid-row mound + plastic (C) treatment was reduced by half as compared to the other treatments due to a rapid increase in the drainage
flux, which, however, was not sufficient to flush all salts out of the soil
profile. This suggests that soil texture and heterogeneity play an important role in the transient salt storage in the soil.
The average annual amount of salts leaching (Dr_S) in the control
treatment (A) at each of the study sites remained almost similar to the
mid-row mounding (B) over the three seasons (Table 5). Similarly, thedynamics of daily salts leaching in these treatments (A and B) almost
overlapped over the entire simulation period (2011–2014) at all locations except for slight deviations at Loxton (Fig. 6). This suggests that
mid-row mounding (B) had a small impact on salts leaching from theroot zone, irrespective of soil, water, and climate conditions. However,
the mid-row mound + plastic (C) treatment resulted in more than twice
the average salt mass removed (884 kg/ha) as compared to the control(406 kg/ha) at McLaren Vale. Similarly, the buried plastic (D) treatment also showed higher average salts leaching (563 kg/ha) than thecontrol (A) at Loxton. Although the average amount (4860 kg/ha) ofsalts leached (Dr_S) at Padthaway in the mid-row mound + plastic
treatment (C) was more than one and half times of the control (A), it
was about five times the corresponding amount at McLaren Vale. It isestimated that about 14.6 t/ha salts were leached during 2011–14 atPadthaway in the mid-row mound + plastic treatment (C), which was
57% higher than for the control. Total salt leaching in other treatments
ranged from 9.3 to 9.7 t/ha. The drastic increase in the salt leaching in
the mid-row mound + plastic (C) treatment occurred due to the twopronged strategy of the redirection of rainfall and the reduction of
evaporation losses due to the surface cover. It can be seen that the3.3. Seasonal salt balance
Salt balance dynamics in the soil under different rainfall redirection
techniques is shown in Table 5. There were different initial amounts ofsalts in the soils at different sites due to textural differences, and thequantity and quality of water used for grape production. At Padthaway,
initial salt contents (8298 kg/ha) in the soil profile were 3.5 and 5 times
higher than at McLaren Vale and Loxton, respectively. The annual
amount of salts added through irrigation (I_S) during the simulation
period (2011 to 2014) varied from 631 to 1038 and from 900 to
1200 kg/ha at the McLaren Vale and Loxton sites, respectively. However, almost similar amounts of I_S (3352.8 kg/ha) were added annuallyat Padthaway during different years due to less variation in the seasonal
irrigation volumes. Additionally, the amount of salts added through therain (P_S) at McLaren Vale (302–434 kg/ha), Padthaway (308–408 kg/

Table 5
Seasonal salt additions by irrigation (I_S), precipitation (P_S), salt leaching (Dr_S), and soil storage/ depletion (ΔS_S) in the soils (kg/ha) for grapevine at different
locations under different treatments during 2011–2014.
Treatments

Year

A

Initial salts
2011–122012–132013–14
Average
Initial salts
2011–122012–132013–14
Average
Initial salts
2011–122012–132013–14
Average
Initial salts
2011–122012–132013–14
Average

B

C

D

McLaren Vale
I_S
P_S

Dr_S

631.0
994.1
1038.4
887.8

433.9
302.3
373.7
370.0

292.7
377.6
548.0
406.1

631.0
994.1
1038.4
887.8

433.9
302.3
373.7
370.0

287.9
408.9
591.1
429.3

631.0
994.1
1038.4
887.8

433.9
302.3
373.7
370.0

840.2
839.7
971.6
883.8

631.0
994.1
1038.4
887.8

433.9
302.3
373.7
370.0

246.6
495.1
948.1
563.2

ΔS_S
2394.43166.64085.34949.44067.12454.13231.14118.54939.54096.42440.92665.63122.33562.83116.92375.13193.43994.74458.73882.3

Padthaway
I_S
P_S

Dr_S

3352.93352.93352.73352.8

330.4
308.0
408.3
348.9

427.3
3158.05671.33085.63352.93352.93353.13353.0

330.4
308.0
408.3
348.9

465.0
3012.85848.43108.73352.93352.93352.73352.8

330.4
308.1
408.2
348.9

3828.06648.04104.74860.23352.93352.93353.13353.0

330.4
308.1
408.2
348.9

440.3
4999.74306.93249.0A is control, B is Mid-row mound, C is Mid-row mound + plastic, D is Buried plastic
9

ΔS_S
8297.511553.4
12056.4
10146.011251.98702.511920.912569.010482.011657.3
8816.58671.85684.75341.06565.88122.511365.510026.8
9481.210291.1

Loxton
I_S

P_S

Dr_S

901.5
1201.61069.91057.6

209.6
132.7
248.0
196.8

1396.61315.8
1857.41523.3901.5
1201.61069.91057.6

208.4
132.7
248.0
196.4

1381.91366.51763.21503.9901.5
1201.61069.91057.6

209.6
132.7
248.0
196.8

1957.31370.21441.6
1589.7901.5
1201.51069.91057.6

209.6
132.7
248.0
196.8

1208.81146.31558.01304.4

ΔS_S
1618.51333.11351.5812.0
1165.51635.01362.91330.7885.41193.01618.0
771.8
735.9
612.2
706.6
1605.21507.61695.51455.41552.8

Journal of Hydrology 587 (2020) 125000

V. Phogat, et al.

drainage flux (6.7 ML/ha) in this treatment was more than double ascompared to the other treatments (2.6–2.7 ML/ha) (Table 4). Differences in daily salt leaching in different treatments and at different locations are also distinctly visible during the entire simulation period(Fig. 6). High episodic salts leaching peaks occurred especially at the
McLaren Vale and Padthaway sites, whereas leaching was a continuous
process in the sandy soil at Loxton. Typically, large peaks at all locations were preceded by high rainfall events and were also influenced by
the amount of salts present in the soil. Notably, at Padthaway, hugeamounts of salts (3.35 t/ha/yr) are added in the soils (see Table 5)through high salinity (2.2–2.35 dS/m) groundwater irrigation, which
are deposited in the soil and ready to be transported following large
rainfall events generating large leaching fractions.
Indeed, the huge amount of salt leaching at Padthaway, irrespectiveof treatments, may raise salinity concerns for shallow groundwateraquifers. A groundwater monitoring study observed an increase in thesalt contents by about 600 mg/L in shallow aquifers from around
800 mg/L to 1400 mg/L in parts of Padthaway during the last 25 years(Cleugh, 2006). Apparently, excessive transport of irrigation-induced
root zone salts under grapevine may pose a potential danger for the
groundwater quality. Hence, a trade-off exists between the extent ofleaching and the imminent threat of groundwater degradation and,judicious decisions are required for sustainable salinity management
and controlling the pollution of groundwater.

2.4
2.0

LE s

1.6

Leaching efficiency

2012-132013-14

A

B

C

McL

D

A

B

C

Pad

D

A

B

C

0.8

Lox

y (Mcl) = 1.195 x0.56
0.10

0.20

LF

0.30

0.40

0.50

treatments and seasons, indicating a strong depletion pattern. However,
the mid-row mound + plastic (C) treatment had a maximum LEs valueof 1.74 kg salts/kg salts applied during 2011–12. Hence, the occurrenceof LEs larger than one at Loxton is attributed to the prevalence of highly
permeable sandy soils, low salinity of irrigation water (0.3 dS/m), andalmost double amount of irrigation application than at the other sites,
which facilitated the rapid flushing of salts from the root zone.
In drip-irrigated systems, it is hard to determine the leaching requirement (LR) due to spatially-variable soil wetting patterns that leadto localized leaching below the drip line (Hanson et al., 2008). Historically, LR is the LF, which when passed through the root zone, reduces the root zone salts below the crop threshold. Hence, in drip irrigation systems, a LF that corresponds to LEs ≥ 1 can potentially leachannually added salts from the root zone. It can serve as a good estimate
for leaching of irrigation induced salts from the root zone. Hence, a sitespecific relationship was developed between a seasonal LF and corresponding LEs at different locations, irrespective of treatments (Fig. 8).
At Lox (sandy soils), a very low LF (0.1) was found to rapidly attainLEs > 1, while at Padthaway (medium-textured soils), the threshold LF
was 0.18. The threshold LF for the McLaren Vale site (heavy textured,heterogeneous soils) was exceptionally high (0.74), which seems impractical. However, in the mid-row mound + plastic treatment (C), an
average LF of 0.33 was able to flush 70% of added salts at McLarenVale, thus showing promising results. On the other hand, this soil has
restricted drainage conditions (Singh, 2019), especially in the subsoils,
which may require different management options for salinity control.
Overall the mid-row mound covered with plastic (C) was the most efficient technique for leaching salt from the root zone and attaining
LEs > 1, especially at Padthaway. Salt leaching results were extremely
variable as influenced by soil texture and heterogeneity. These techniques should be adopted cautiously depending on the soil, climate, andirrigation water quality at a particular location.
The main drawback of the plastic mulch is its cost, its labour-intensive application, and environmental risk of plastic residues in thesoil (Silin and Xujian, 2008; Changrong et al., 2014). These issues needdue consideration before implementing the mounding with plastic
strategy although biodegradable plastic mulching (Adhikari et al.,2016; Saglam et al., 2017; Chen et al., 2019, 2020) or sprayable biodegradable polymer membrane (Filipović et al., 2020) are viable options for addressing the environmental issues. Other options of environmentally friendly mulching, such as compost, wood chips, andplant residues, are also available. The application of organic mulches isequally labour intensive, but they have numerous other beneficial impacts such as increasing soil water retention (Granatstein and Mullinix,
2008; Yu et al., 2018), and enhancing soil organic matter, nutrient
cycling, and N availability (Neilsen et al., 2003; Sanchez et al., 2003;
Hoagland et al., 2008; TerAvest et al., 2010). On the other hand, theyalso have adverse impacts, such as causing tree root diseases, rodent
infestation (Merwin and Stiles, 1994), and weed seed distribution

0.5
0.0

Pad

Fig. 8. Relationship between the salt leaching efficiency (LEs) (kg salts leached/
kg salts added) and a leaching fraction (LF) in different soils at McLaren Vale
(McL), Padthaway (Pad), and Loxton (Lox).

2011-12

1.0

McL

1.2

0.0
0.00

Salt removal (leaching) efficiency (LEs) is defined as the ratio of theamount of salts leached from the soil profile and the corresponding
amount added during a given time (e.g., an annual or crop cycle),which offers a more quantitative measure of the salt balance to compare
different treatments (Lu et al., 2019). At McLaren Vale, the LEs remained less than one irrespective of treatments and seasons, indicating
an overall tendency of salt deposition in the root zone (Fig. 7). However, LEs increased almost two-fold in the mid-row mound + plastic (C)treatment compared to the control and mid-row mounding, and varied
from 0.63 to 0.77 kg salts leached/kg added. Interestingly, at Padthaway, during 2011–12, LEs was very low (average 0.12–0.13 kg leached/kg salts added) in all of the treatments besides mid-row
mound + plastic (1.04 kg leached/kg added). In the later years of thesimulation, it reached a value larger than one (1.01) only under the
mid-row mounding during 2013–14 and the buried plastic (1.37)
during 2012–13. However, LEs remained above one in mid-row
mound + plastic (C) during all seasons and reached a maximum valueof 1.81 kg salts leached/kg added during 2012–13. Therefore, only the
mid-row mound + plastic (C) treatment showed continuous depletionof salts from the soil at Padthaway.
The LEs remained larger than one at Loxton irrespective of

1.5

y (Pad) = 5.599 x0.988

0.4

3.4. Leaching efficiency and leaching requirement

2.0

y (Lox) = -5.835 x2 + 3.18 x+ 0.79

D

Lox

Fig. 7. Average salt leaching efficiency in terms of percent of annual salts
leached from the total added (kg/kg salts added) and percent of salts leachedper m3 of drainage (Dr) (kg/m3 of drainage) at McLaren Vale (McL), Padthaway(Pad), and Loxton (Lox) under different treatments (A - control, B - Mid-row(MR) mound, C - MR mound + plastic, D - Buried plastic).
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Journal of Hydrology 587 (2020) 125000

V. Phogat, et al.

(Rowley et al., 2011). Moreover, their role in redirecting rainfall, salts
dynamics, and leaching seems limited and not yet fully explored.
Therefore, the use of plastic mulches still seems to be a relatively better
alternative if the overall goal is to reduce the soil salinization andleaching of soluble salts from the crop root zone.

Declaration of Competing Interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements

4. Conclusions

The authors are thankful to the Australian Water Recycling Centreof Excellence (Grant ID: AWRCOE 3145) and the Goyder Institute for
Water Research (Grant ID: I.1.3) for funding assistance.

Leaching of soluble salts from an irrigated soil root zone is necessary
for sustainable crop production since all water additions, and subsequent evaporation and transpiration, will increase salt concentrations. This investigation was carried out to understand the impact ofdifferent mid-row management techniques such as mounding andplastic mulching for directing rainfall for reducing salt accumulation in
the root zone of drip-irrigated grapevines. Four different treatments [nomounding or control (A), mid-row mounding (B), mid-row mounding
covered with plastic (C), and plastic buried in the soil in the mid-row(D)] were evaluated using a numerical model (HYDRUS-2D) for simulating the water balance, root zone salinity dynamics (ECe), and salt
dynamics in the soil for multiple seasons (2011–2014) in three grape
growing regions. These vines had been irrigated with varied water
qualities, ranging from river water (0.2–0.5 dS/m) at Loxton, recycledwater (1.0–1.3 dS/m) at McLaren Vale, and groundwater (1.9–2.3 dS/m) at Padthaway.
Results demonstrated that mid-row mounding with plastic mulching(C) was effective at controlling salinity under drip-irrigated grapevines.
It showed a threefold increase in drainage flux (Dr), a drastic reductionin evaporation (Es) (48–54%), and an increase in transpiration (Tp) of
grapevine (1–16%), as compared to the control (A). Despite such remarkable impacts of mid-row mounding coupled with plastic mulch,soil texture, and the quantity and quality of irrigation water haveplayed an important role in controlling salt transport in the soil.
Modelling simulations confirmed that in heavy textured highly heterogeneous soils (McLaren Vale site) in vineyards irrigated with recycled water (ECiw = 1.2 dS/m), this treatment, in spite of one and halftimes higher salts leaching than in the other treatments, could not
maintain a salt removal efficiency (LEs) > 1 over the simulation
period. Therefore, the final average profile ECe in the under-vine (UV)region increased from 1.1 to 2.4 dS/m, which is more than the salinity
tolerance threshold (2.2 dS/m) for grapevines. Groundwater-irrigated(ECiw = 2.2–2.35 dS/m) grapevines on medium-textured soils(Padthaway site) with double the irrigation amount compared to
McLaren Vale, and a similar annual rainfall maintained LEs > 1 during
all three seasons, reduced the average ECe in the UV region from 5.2 to
3.2 dS/m. A leaching fraction of 0.18 was found to leach all annually
added salts out of the root zone in the latter soils.
These results suggest that rainfall redirection techniques have thepotential to play an important role in reducing root zone salts. Still, theextent of the reduction will vary depending on the soil and agro-climatic zone. The requirement for salt removal from the soil is influenced
by soil texture, soil heterogeneity, irrigation quantity and quality,
rainfall volume, distribution and intensity, and the salinity tolerance
threshold of the cropland, thus requires site-specific modelling andmanagement.

Appendix A. Supplementary data
Supplementary data to this article can be found online at https://doi.org/10.1016/j.jhydrol.2020.125000.
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CRediT authorship contribution statement
V. Phogat: Methodology, Software, Data curation, Formal analysis,
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administration. R.M. Stevens: Conceptualization. J.W. Cox:
Supervision. J. Šimůnek: Writing - review & editing. P.R. Petrie:
Writing - review & editing.

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