Agricultural Water Management 243 (2021) 106446

Contents lists available at ScienceDirect

Agricultural Water Management
journal homepage: www.elsevier.com/locate/agwat

Evaluation of a Sprayable Biodegradable Polymer Membrane (SBPM)
Technology for soil water conservation in tomato and watermelon
production systems

T

Michael V. Braunacka, Vilim Filipovićb,*, Raju Adhikaric, George Freischmidtc,
Priscilla Johnstonc, Phil S. Caseyc, Yusong Wangd, Jiří Šimůneke, Lana Filipovićb,
Keith L. Bristowda

CSIRO Agriculture & Food, LB 59 Narrabri, NSW, 2390, Australia
University of Zagreb, Faculty of Agriculture, Department of Soil Amelioration, Svetošimunska 25, 10000, Zagreb, Croatia
CSIRO Manufacturing, Private Bag 33, Clayton, Victoria, 3169, Australiad
CSIRO Agriculture & Food, PMB Aitkenvale, Townsville, Qld, 4814, AustraliaeDepartment of Environmental Sciences, University of California Riverside, Riverside, California, 92521, USAbc

A R T I C LE I N FO

A B S T R A C T

Keywords:
Water use eﬃciency
Soil evaporation
Soil water content
Soil temperature
Biodegradation

Reducing soil evaporation, especially in temperate climate zones, increases crop production. Plastic mulch ﬁlms
(PMFs) are very eﬃcient in conserving soil water conservation; however, plastic pollution is raising environmental and human health concerns. Therefore, a newly developed Sprayable Biodegradable Polymer Membrane(SBPM) Technology was tested for its ability to conserve soil water, suppress weeds, modify soil temperature,and improve crop yields. Two-year ﬁeld experiments were performed in tomato and watermelon cropping
systems, where SBPM was compared to no mulch and PMF controls. SBPM loadings were 3.0, 1.0, 0.5, and0.25 kg m−2, with fumigation (F) and without fumigation (NF) in tomato, and 1.5, 1.0, 0.5, and 0.25 kg m−2 inwatermelon. In tomato, the soil volumetric water content (VWC) in the topsoil was signiﬁcantly higher for all
treatments compared to the control, in the following order: 1 kg m−2 F > 0.5 kg m−2 NF > 1 kg m−2
NF > 0.5 kg m−2 F > Control in 2016/17; and 3 kg m-2 NF > Control > 0.5 kg m−2 F > 3 kg m−2
F > 0.5 kg m−2 NF in 2018. With watermelon in 2017, VWC was lower in the topsoil of the SBPM treatments
than with PMF, but higher during the 2018 trial when no crop was grown. The amount of conserved soil water
appeared to be determined by the physical integrity (unevenness/holes/tears) of the SBPM and PMFs. Soilsalinity increase/decrease was associated with the volume of inﬁltrating water in the diﬀerent treatments. Soil
temperature increased signiﬁcantly under the highest SBPM loading of 3 kg m−2 NF, using a 55 cm width ofpolymer coverage. The yield responses across treatments were not signiﬁcant. Field experiments proved theeﬀectiveness of the SBPM technology, but also highlighted some limitations of it when compared with conventional PMFs. The SBPM technology needs ongoing reﬁnement to improve its sprayability, durability, biodegradability, and cost-eﬀectiveness.

1. Introduction

surface/subsurface drip irrigation) with plastic mulch ﬁlms (PMFs).
PMFs are now a common cropping practice due to a variety of beneﬁts
to the crop, mostly regarding increased biomass production. PMFs canbe used to (i) modify soil temperature, which promotes earlier sowing,
faster growth, and earlier harvests, (ii) suppress weeds (farmers use
fewer pesticides), (iii) reduce nutrient losses by leaching, (iv) prevent
fruit contact with soil, and (v) reduce soil water loss by minimizing soil
evaporation (Fritz, 2012; Filipović et al., 2016; Kader et al., 2017).
PMFs, while providing beneﬁts to crop growth, still have disadvantages

With a rapidly growing global population, improvements in cropping systems management to overcome challenges related to future
food security are required (FAO, 2017). Eﬃcient use of water andagricultural inputs (e.g., nutrients, pesticides) must support agronomic
practices to increase crop yields. Since the late 1950s, one of the mosteﬀective technologies used in agricultural production for improving
water use eﬃciency is to combine eﬃcient irrigation strategies (e.g.,⁎

Corresponding author.
E-mail address: vﬁlipovic@agr.hr (V. Filipović).

https://doi.org/10.1016/j.agwat.2020.106446
Received 17 March 2020; Received in revised form 12 August 2020; Accepted 13 August 20200378-3774/ © 2020 Elsevier B.V. All rights reserved.

Agricultural Water Management 243 (2021) 106446

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mulch ﬁlms. A greenhouse study was carried out using seedling test
plots to investigate the performance of spray coatings and their eﬀect
on crop and soil properties. The biodegradable coatings showed that theagronomic performances were comparable with the ones of a commercial low-density polyethylene mulch ﬁlm, which produced a similarrate of plant growth and dry matter accumulation.
In a recently reported glasshouse study (Braunack et al., 2020a,
2020b), the agronomic potential of the SBPM technology was identiﬁed. The aims were to (i) evaluate the eﬀectiveness of the SBPM in
reducing soil evaporation and its eﬀect on seedling emergence and (ii)to determine an eﬀective SBPM bandwidth (100 vs. 150 mm) and SBPM
application rate to conserve seedbed water. The study demonstrated
that the high application rate (1 kg m−2) is eﬀective in reducing soil
evaporation, but it also reduced crop emergence if applied after sowing.
The SBPM suppressed weed growth similar to the conventional mulch
ﬁlm and was the most eﬀective at 0.5 kg m−2 with a 150 mm application width. There is still only a limited number of studies regarding
the use of the SBPM Technology in ﬁeld trials, with most research
performed under controlled conditions in greenhouse/glasshouse experiments. The reason for this small-scale testing is that the majority of
published studies focussed on the properties of the polymer itself,
which is appropriate for an early-stage product.
The current study aims to identify the potential of the SBPM technology to conserve soil water and increase soil temperature, as well as
to observe its eﬀect on soil salinity and crop yield, during a 2-year ﬁeld
trial with tomatoes and watermelons. The SBPM, applied at various
rates, was compared to controls of standard practice, i.e., no mulch(tomato) and PMF (watermelon/bare soil). The novel sprayable biodegradable polymer, tested on a ﬁeld scale, is designed to improve thegermination and establishment of crops in conditions where surface soil
dries quickly by providing a protective barrier that reduces soil evaporation, suppresses weeds and moderates soil surface temperatures.

due to disposal problems and environmental pollution. As reported in
Sander (2019), the global agricultural mulch ﬁlm market will reach
7.5 million tons by 2021, with China applying an estimated 1.4 million
tons of applied plastic mulch per year (Gao et al., 2019). Recovery of
PMFs from the soil surface is costly, labor-intensive, time-consuming,and can aﬀect successive crop yields and cause environmental pollution
with microplastics. Due to the increasingly stringent regulations regarding the use of non-degradable plastic in agriculture, plastic mulches
are likely to be phased out in the near future. To minimize environmental plastic pollution, various biodegradable and oxo-degradable
mulches and also spray-on mulch ﬁlms have been developed in the last
decade (Kairajan and Ngouajio, 2012; Vox et al., 2013; Adhikari et al.,2016; Sintim et al., 2019; Chen et al., 2019).
The number of publications regarding the development of preformed biodegradable mulch ﬁlms is in an uprising trend (e.g., Sintim
and Flury, 2017; Gao et al., 2019; Chen et al., 2020; Filipović et al.,2020). Sprayable mulch coatings are now also receiving increasing attention globally as a next-generation alternative because of their environmental beneﬁts and ease of application (Adhikari et al., 2019;
Sartore et al., 2013, 2018; Braunack et al., 2020a, 2020b).
Many of the management practices (e.g., costs, labor, disposal) andenvironmental concerns (e.g., persistent chemicals, toxicity) can beeliminated by using a SBPM technology. Ideally, the formulation ofsprayable biodegradable polymers used in agriculture will enable water
to inﬁltrate into the soil while simultaneously forming a barrier toprevent soil water evaporation from the soil surface (Johnston et al.,2017). For now, the goal is to develop and use a polymer formulationthat is biodegradable, sprayable, and nontoxic while providing thesame beneﬁcial eﬀects of preformed PMFs.
A ﬁeld trial conducted by Al-Kalbani et al. (2003) using polysiloxane polymer aqueous spray showed water savings of 25–50% andincreased yields by 10–80%. It also reduced wind-dispersed weeds because of the polymer membrane. Adhikari et al. (2016) reported a newwater dispersible sprayable biodegradable polymer, which forms amembrane on the soil surface to minimize soil evaporation. These authors also demonstrated on small ﬁeld plots that, compared with baresoil, 28 % less irrigation water was able to sustain melon yields. Under
controlled laboratory conditions, the biodegradable spray-on polymer
also reduced soil evaporation by more than 60 % compared with thebare soil control. To increase the versatility of the polymer membrane,
the addition of black pigment was used to help suppress weeds.
Sartore et al. (2018), in their research, used polymeric protein-based
biocomposites as water dispersions to generate in situ bio-based mulch
coatings by spraying, as an alternative to low-density polyethylene

2. Materials and methods
2.1. SBPM ﬁeld experiment with tomatoes
Field experiments were conducted on two sites owned by CSIRO cooperators located near Echuca, Victoria; Australia (-36.229533S,
144.79575E) during the 2016/17 (Experiment 1: E1), and 2017/18(Experiment 2: E2) seasons. The soil at both sites was classiﬁed as a
Chromosol (Isbell, 2016). The ﬁeld experiments at E1 had a random
strip layout, consisting of raised soil beds, with a single row of processing tomatoes planted on top of the bed. Plots were 50 m long with a

Fig. 1. Scheme of a ﬁeld SBPM application for (a) a 2-year ﬁeld trial with tomatoes (2016/2017, 2017/2018), (b) watermelon (2017), and no crop (2018). Figures on
the right show an inﬁeld SBPM application with (c) tomato and (d) watermelon at the Echuca and Finely sites in Australia.
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M.V. Braunack, et al.

2.2. SBPM ﬁeld experiment with watermelon

5 m buﬀer between the plots. There were three (x 3) replicates for eachtreatment. A similar layout was employed in E2, using three beds with
two rows of tomatoes planted 30 cm apart, centrally on the beds
(Fig. 1a).
During 2016/17, treatments of a banded (20 cm) surface applicationof the SBPM at loadings of 1 and 0.5 kg m−2, either fumigated (F) with
Metham (from Nufarm Australia) or non-fumigated (NF), were compared with no mulch control. The top of the beds was sprayed with thepolymer (Adhikari et al., 2015) on 19th December 2016, with two
nozzles (T-jet OC-08, pressure 50 kPa), on either side of the plant line,
giving a narrow bandwidth of 20 cm on the top of each bed. The
polymer loadings were 1 and 0.5 kg m−2, respectively.
During 2017/18, bed tops were sprayed with polymer (Adhikari
et al., 2015) on 22nd November 2017, using six nozzles (T-jet OC-08,
OC-06, OC-04 & OC-02, pressure 200 kPa), with pairs of nozzles spaced
at 30 cm and 50 cm apart to apply a 55 cm wide band of polymer on thesurface of the bed. The polymer loadings were 3 and 0.5 kg m−2 onfumigated (F) or non-fumigated (NF) plots.
The polymer cured membrane are transparent and non-transparent
in pigmented formulation. The membrane showed phase mixed morphology with a low temperature glass transition temperature -50 °C andbroad melting endotherms above 200 °C associated with the ordering ofhard segments. The non-pigmented membrane showed a contact angleof 101.66˚ with 8% water absorption in 17 h’ time at room temperaturecompared to pigmented membrane showing 25 % water absorption.
The non-pigmented membrane showed a tensile strength 14.29 MPa
and Young’s modulus 2.52 MPa. The polymer ester and amide linkages
are susceptible to degradation by hydrolysis, enzymatic, light andthermal degradation processes and acidity of soil (Adhikari et al.,2015).
Processing tomato seeds (Solanum Lycopersicum, cv. H2401 &H1175, both from Heinz Seed Company) were planted on 9th December
2016 (a single row) and 10th November 2017 (twin rows) with aplanter. Before planting, 30 and 66 units of nitrogen (N) and phosphorus (P), respectively, were applied to the beds. During the season, N,
P, Ca (calcium), and Zn (Zinc) were applied as a liquid fertilizer forseason’s totals of 313, 95, 44, and 1.2 units, respectively, on a sevenday fertigation program. The experiment was irrigated with a drip tapelocated centrally in each bed at a depth of 25 cm, as per the farmschedule with 448 and 614 mm applied in 2016 and 2017, respectively.
Treatments were unable to be irrigated independently as the standard
on-farm practice used this holistic irrigation system layout. However,each plot received the same amount of irrigation.
Soil capacitance probes (EnviroPro from MEA, Australia) were installed on the 15th and 16th December 2016, and on the 22nd
November 2017, to monitor volumetric soil water content, soil temperature, and soil electrical conductivity at 10 cm intervals from the soil
surface down to 80 cm depth (e.g., 10 cm, 20 cm, 30 cm, 40 cm, 50 cm,
60 cm, 70 cm, and 80 cm depth). One probe was installed in each plot,
positioned 10 cm from the drip line and between two emitters. The
position was constrained by tomato plants, so a probe may not havebeen placed exactly between emitters. Data were collected by ﬁeld
station and transmitted through a ﬁeld hub to a web site for real-timedata acquisition every 30 min (MEA, Australia). Data reported is theaverage of three plots. A weather station was also installed to monitor
rainfall, air temperature, solar radiation, and wind speed and direction,with data recorded at 15 min intervals and transmitted to the web site
at MEA, Australia.
The processing tomatoes were machine harvested on 8th May 2017
and 13th March 2018, from E1 and E2, respectively, from the single or
double rows of tomato for the full 50 m plot length. The sensor network
was removed from the ﬁeld before machine harvesting of tomatoes toprevent damage to sensors and connecting cables. No irrigations took
place between sensors removal and harvest.

A ﬁeld experiment with watermelon was conducted in 2017 and ano crop ﬁeld experiment in 2018 on a CSIRO co-operators property
located near Finley, New South Wales, Australia (-35.567131S,
145.415676E). Both experiments were conducted on the same siteusing SBPM loadings of 1.5, 1, 0.5, and 0.25 kg m−2. The soil at theﬁeld site was classiﬁed as a red Kandosol (Isbell, 2016). The ﬁeld experiment had a random strip layout, consisting of raised soil beds withplots 25 m long for the SBPM treatments and the plastic mulch ﬁlm
control (Control_PMF), with a 5 m buﬀer between the plots, and withthree replicates for each treatment (Fig. 1b). The drip tape was locatedcentrally in the beds 15 cm below the soil surface.
The surface of the beds was sprayed with SBPM (Adhikari et al.,2015) on 10th January 2017 and 22nd February 2018, with six nozzles(pressure 310 kPa) conﬁgured in three pairs 0.6 m apart (T-jet brown
05, 30 cm between pairs), giving a bandwidth of 80 cm on the surface ofeach bed. The polymer loadings were 1, 0.5, and 0.25 kg m−2 in 2017
and 1.5, 0.5, and 0.25 kg m−2 in 2018. A ﬁne mesh ﬁlter (50 μm) was
initially used in the spray line, but continued blockages necessitatedreplacement with a courser mesh ﬁlter (150 μm), which was cleaned at
the end of each 100 m run. The standard practice of the black PFM wasmechanically applied over the bed, with the edges buried at the base of
the bed covering completely raised soil. In contrast, the sprayable
polymer was only applied to the top of the bed.
Watermelon seedlings (Citrullus Lanatus, cv. Nightshade) wereplanted on 10th January 2017. Before planting, Rustica Plus1 (12 % N,
5% P, 14 % K, 9% S, 3.1 % Ca, 1.2 % Mg, 0.1 % Zn, and 0.02 % B) wasapplied at 500 kg ha−1. Supplemental N, P, and K were applied as aliquid fertilizer (Calcium nitrate, Nitro P1, and Thio K1, for a season
total of 400, 150, and 50 l ha−1) on a seven-day fertigation program
during the crop growth. No crop was planted during the 2018 season.
Soil capacitance probes (EnviroPro) were installed 10 cm from one
side of the drip tape and between emitters on 10th - 12th January 2017and 20th - 21st February 2018 to monitor volumetric soil water content, soil temperature, and soil electrical conductivity, in 10 cm increments from the 10 cm depth down to the 80 cm depth. Data were collected by ﬁeld stations and transmitted through a ﬁeld hub to a web site
for a real-time data acquisition every 30 min (MEA, Australia). A
weather station was also installed to monitor rainfall, air temperature,solar radiation, and wind speed and direction, with data recorded at
15 min intervals and transmitted to the web site (MEA, Australia).
Failure of the ﬁeld hub resulted in no data being collected until 17th
January 2017, and another failure delayed data acquisition in 2018 till
2nd March 2018, when replacements were installed. Other data outages
occurred due to the native animals chewing sensor wiring. The sensor
network was removed from the ﬁeld before the hand-harvesting ofwatermelon to prevent damage to connecting cables. Watermelons were
hand-harvested on 5th April 2017, with all watermelons collected. No
crop was planted in 2018, providing an opportunity to monitor soil
water, temperature, and salinity under the black plastic and the SBPM
treatments, which excluded the eﬀects of a watermelon crop, allowing
assessment of the SBPM eﬀectiveness in conserving initial soil proﬁlewater over time.

2.3. Statistical analysis
Statistical analysis of experimental ﬁeld data (soil water content,
soil temperature, soil electrical conductivity, and crop yield) was performed using the Statistical Analysis Software (SAS; SAS Institute,2001). Analysis of variance was performed using one-way ANOVA. The
signiﬁcance of diﬀerences between the means was determined using
Tukey’s Honestly Signiﬁcant Diﬀerence test at P < 0.05.

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M.V. Braunack, et al.

Table 1Long-term monthly averages (1881/2018): temperature (oC), rainfall (mm),wind speed (m/s), and relative humidity (%) for Echuca (Victoria) and Finley(NSW) for the period from planting (Dec) to harvest (May). (http://www.bom.
gov.au/climate/averages/tables/cw_074106.shtml).
Echuca location
Month

Temperature (°C)

Rainfall (cm)Wind
speed (ms−1)

Relative
humidity (%)

DecemberJanuary
February
March
April
May

21.3
23.0
22.9
20.1
15.9
12.1

29.1
27.7
26.6
30.7
32.9
40.5

4.2
4.0
3.4
3.3
3.0
2.8

30
29
31
37
44
56

Finley location
DecemberJanuary
February
March
April
May

21.9
24.0
23.8
20.9
16.4
12.6

34.5
33.0
29.1
34.5
32.3
41.0

3.4
3.2
2.8
2.8
2.7
2.4

33
33
35
38
46
57

3. Results
3.1. Climatic parameters measured at the experimental sites
Long-term monthly average climate data for both sites are shown in
Table 1. They closely reﬂect the conditions experienced during the ﬁeld
experiments at Echuca (Fig. 2a, b). For example, the long-term rainfall
total for December to May is 136 mm, while the actual amount during
the experiment was 140 mm. Average daily climatic conditions at
Finley for the period from planting through to harvest of melons also
reﬂect the long-term data (Fig. 2c, d). The long-term average temperature for January is 21 °C, rainfall 33 mm, relative humidity 46 %,and the prevailing wind being from a southerly direction at an averagewind speed 3.1 m s−1. The measured parameters for January 2017 are
all within the long-term average for the area (Table 1).
3.2. SBPM ﬁeld experiments with tomatoes: soil water, soil temperature, soil
salinity, and yield
During both tomato growing seasons (2016/17, 2017/18), the soil
proﬁle water increased with depth (Fig. 3a, d), with some variations
between treatments observed. Soil proﬁle water at 10 cm was signiﬁcantly diﬀerent across treatment plots compared to the control (nomulch), with the 1 kg m−2 fumigated treatment having the highest
average water content (39.5 %), and the control showing the lowest
average water content (28.5 %) in the 2016/17 growing season(Table 2). Similar trends occurred in the 2017/18 season, where the
3 kg m−2 non-fumigated treatment was signiﬁcantly wetter than thecontrol (34.8 % vs. 28.5 %). In the 2016/17 season, all treatments
showed higher water contents compared to the control plot (1 kg m−2
F > 0.5 kg m−2 NF > 1 kg m−2 NF > 0.5 kg m−2 F > Control). In
the 2017/18 season, only the plot with the highest application of SBPM
(3 kg m−2 NF) had a higher average water content at the 10 cm depth
compared to the control plot (3 kg m−2 NF > Control > 0.5 kg m−2
F > 3 kg m−2 F > 0.5 kg m−2 NF). This was reﬂected in the soil watercontent at diﬀerent depths in the soil proﬁle (10–80 cm), where at each
depth in plots treated with 1 and 3 kg m−2 of polymer, the soil was
consistently wetter than at the corresponding depths in the othertreatments and control plots.
Soil temperatures were variable during the 2016/17 season. The soil
in all treated plots tended to be cooler than in the control plot, except
for the 0.5 kg fumigated treatment, which was warmer than the control
treatments at depths of 30 and 40 cm, and again 70 and 80 cm, as theFig. 2. Climatic parameters (rainfall, average air temperature, relative humidity, and solar radiation) recorded on two experimental locations: Echucawith tomato in 2016/17 (a) and 2017/18 (b), Finley with watermelon 2017 (c)and bare soil 2018 (d).

season progressed (Fig. 3b). Soil temperature changes corresponded tothe changes in the soil water content: as the soil water content increased, soil temperature decreased (Fig. 3a, b). However, during the2017/18 season, soil in all treated plots was warmer than in the control
plot (Fig. 3e). Soil temperature also decreased with depth, but not to thesame extent as during the previous season (Fig. 3e). The only polymer
treatment, which showed a signiﬁcant diﬀerence in soil temperature atthe 10 cm depth compared to the control, was the 3 kg m2 non fumigated treatment, likely due to better membrane thickness and integrity(surface layer without any major cracks).
Soil proﬁle salinity (electrical conductivity) varied between thetreatments and also with the soil depth during both seasons (Fig. 3c, f).
Salinity was signiﬁcantly higher in the soil in all treated plots during
the 2016/17 season (Table 2), while during 2017/18, only the 3 kg non4

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M.V. Braunack, et al.

Fig. 3. The eﬀect of the Sprayable Biodegradable Polymer Membrane on seasonal averages of the soil water content (%, v/v), soil temperature (oC), and salinity/
electrical conductivity (dS m−1), obtained from two experiments with tomatoes during the 2016/17 (LSD P < 0.05 1.4, 0.1, and 0.02 for water content (v/v),
temperature (Co), and electrical conductivity (dS m−1), respectively) and 2017/18 (LSD P < 0.05 0.1, 0.07, and 0.01 for water content (v/v), temperature (Co), andelectrical conductivity (dS m−1), respectively) growing seasons. The results are averages of three plots at multiple soil depths (10-80 cm) in each treatment with
diﬀerent amounts of applied SBPM (3, 1, and 0.5 kg m-2), either fumigated (F) or non-fumigated (NF). Control plots did not have a mulch application.

proﬁle water (mm; calculated from VWC data), soil temperature (°C),
and electrical conductivity (dS m−1) is presented in Fig. 4. Average airtemperatures were 20.4 and 22.9 °C in seasons 2016/17 and 2017/18,
respectively, which also inﬂuenced evapotranspiration.
During the 2016/17 season, the soil in all treated plots (1 kg m−2
NF, 1 kg m−2 F, 0.5 kg m−2 NF, and 0.5 kg m−2 F) was wetter than in
the control plot, resulting in lower soil temperatures in the majority oftreated plots than that in the control plot (Fig. 4a, b). In contrast,
salinity was higher in the SBPM treated plots than in the control plot. As
already stated, this is possibly due to a lack of rainfall inﬁltration inplots with SBPM (Fig. 4c). In the 2017/18 season, the results were notas straightforward, although the 3 kg m−2 NF treatment showed thelargest diﬀerence in the soil water content at the ﬁrst two measurement
depths, with increased soil temperature through the entire soil proﬁle(Fig. 4d, e). Furthermore, soil salinity was variable in all experimental
plots, with no clear indication of a trend (Fig. 4f).

fumigated treatment showed a signiﬁcant increase in soil salinity
compared to the control plot. This eﬀect is probably due to the absenceof rainfall and the lack of water inﬁltration into the soil. However,average salinity levels in the soil proﬁle ranged from 0.44 dS m−1 at
10 cm to 0.92 dS m−1 at 60 cm during 2016/17, and from 0.2 to
0.4 dS m−1 at 10 cm to from 0.9 to 1.2 dS m−1 at 80 cm during 2017/18, which could not inﬂuence tomato yield signiﬁcantly (NSW DPI,
2016). During both seasons, there was no signiﬁcant eﬀect of thepolymer treatments on tomato yields, possibly because of a very variable yield among the treatment repetitions (ranging from 55 to 151 t
ha−1 in 2016/17 and from 42 to 151 t ha−1 in 2017/18). During bothexperimental years, the highest tomato yield was obtained from theplots that were treated with SBPM (129 t ha−1 in the 0.5 kg m-2 fumigated plot and 117 t ha−1 in the 3 kg m-2 fumigated plot), indicatingthat the eﬀect of the SBPM treatments on tomato yield should be further
investigated.
To further illustrate the diﬀerence between the SBPM technology
and no mulch control, comparison between average values of the soil
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M.V. Braunack, et al.

Table 2The eﬀects of the Sprayable Biodegradable Polymer Membrane (SBPM) on the volumetric soil water content (%), soil temperature (oC), and soil salinity/electricalconductivity (EC; dS m−1) at the 10 cm depth, and tomato yield (t ha−1) during 2016/17 and 2017/18 growing seasons. Averages were calculated from three
replicate plots, with diﬀerent SBPM treatments (3, 1, and 0.5 kg m-2), either fumigated (F) or non-fumigated (NF). Control plots did not have a mulch application.
Volumetric water content (VWC) (%)

Temperature (°C)

Salinity/EC (dS m−1)

Yield (t ha−1)

2016/17

Control
1 kg m−2, NF
0.5 kg m−2, NF
1 kg m−2, F
0.5 kg m−2, F
Statistical signiﬁcance28.5 c36.2 ba
37.1 ba
39.5 a33.6 b
P < 0.01

21.7 a21.2 a21.4 a21.5 a21.6 an.s.

0.32 b
0.39 a0.40 a0.44 a0.39 a
P < 0.01

119 a
117 a
99 a
107 a
129 a
n.s.

2017/18

Control
3 kg m−2, NF
0.5 kg m−2, NF
3 kg m−2, F
0.5 kg m−2, F
Statistical signiﬁcance28.3 b34.8 a24.1 c26.8 cb
27.3 cb
P < 0.01

21.3 b
22.5 a21.3 b
21.3 b
21.3 b
P < 0.01

0.34 b
0.41 a0.22 c0.34 b0.32 b
P < 0.01

105 a
76 a
103 a
117 a
97 a
n.s.

Means with the same letter are not signiﬁcantly diﬀerent at P < 0.05; n.s.: non-signiﬁcant interaction; EC electrical conductivity.

Fig. 4. Observed diﬀerences in proﬁle soil water (mm), soil temperature (oC), and electrical conductivity (dS m−1) between treatments (trt) and no mulch control in
the SBPM experiments with tomatoes during the 2016/17 ((mm) LSD P < 0.05, trt*depth = 1.4, (Co) LSD P < 0.05, trt*depth = 0.1, (dS m−1) LSD P < 0.05,
trt*depth = 0.02) and 2017/18 ((Co) LSD P < 0.05 trt*depth = 0.07, (dS m−1) LSD P < 0.05 = 0.01) seasons. Positive: the treatment is wetter, warmer, and has ahigher electrical conductivity than the control (no mulch). The results are average values from three replicate plots, collected using sensors at multiple soil depths(10-80 cm) with treatments using diﬀerent amounts of applied SBPM (3, 1, and 0.5 kg m-2) in soil either fumigated (F) or non-fumigated (NF).

6

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soil proﬁle under the 1.5 kg m−2 SBPM loading contained signiﬁcantly(LSD P < 0.05) more water than the other treatments down to the 60
cm depth, while there was no signiﬁcant diﬀerence between the 1.5 and0.25 kg m−2 loadings below this depth (Fig. 5d).
Soil temperature was lower in all SBPM treatments compared to the
PMF control at all depths during the 2017 season (Fig. 5b, Table 3). A
similar trend was observed in the 2018 season, except at the 70 cm
depth, where soil temperature in all SBPM plots was warmer than in the
PMF control plot (Fig. 5e). It is clear that the SBPM cannot competewith the conventional PMF in terms of increasing soil temperature.
However, in the absence of crop, this diﬀerence was insigniﬁcant(Fig. 5b vs. e).
With a few exceptions, soil salinity/electrical conductivity was
lower in the SBPM treated plots than in the PMF control plot during the2017 watermelon season (Fig. 5c, Table 3). During the 2017 season, soil
salinity increased with depth throughout the soil proﬁle in all SBPM
treatment plots (Fig. 5c). Proﬁle electrical conductivity was variable
during 2018 and also signiﬁcantly increased with the treatment anddepth (LSD P < 0.05) over the period of measurements (Fig. 5f). The
1.5 kg m−2 SBPM treatment plot had higher electrical conductivity than
all other treatments throughout the season and at all depths except for
80 cm (Fig. 5f).
The comparison between the average values of soil proﬁle water(mm; calculated from VMC data), soil temperature (°C), and electricalconductivity (dS m−1), measured in the control PMF plot and the SBPM
treated plots is presented in Fig. 6 to illustrate the diﬀerences between
the SBPM technology and a conventional PMF. It further shows that the
VWC in the topsoil under treatment was lower in 2017 under watermelon, while it was higher in 2018 under the SBPM treatments (Fig. 6aand d). Soil temperature was lower in both years under the SBPM
treatments (Fig. 6b, e), while electrical conductivity showed variable
results, mostly associated with the amount of inﬁltration (Fig. 6c and f).
Electrical conductivity was generally lower in the SBPM plots than in
the control PMF plot during the year 2018 when no crop was grown.
Larger variability in electrical conductivity was observed: the 1.5 kg m-2
SBPM treatment consistently had higher electrical conductivity than thecontrol plot, while the 0.5 and 0.25 kg m-2 treatments had lower electrical conductivity in the surface soil than the control PMF plot, buthigher electrical conductivity deeper throughout the soil proﬁle(Fig. 6f). The soil VWC showed signiﬁcant treatment, depth, and time
diﬀerences (Fig. 6d, LSD P < 0.05).

Table 3The eﬀects of the Sprayable Biodegradable Polymer Membrane (SBPM) on thevolumetric soil water content (%), soil temperature (oC), and salinity/electricalconductivity (EC; dS m−1) at the 10 cm depth, and watermelon yield (t ha−1) inthe 2017 growing season (no crop was grown in 2018). Averages were calculated from three replicate plots for diﬀerent SBPM treatments (1.5, 1, 0.5, and0.25 kg m-2). Note that the control treatment here used PMF (Control_PMF).
Volumetricwater content(VWC) (%)

Temperature (°C)

Salinity/EC (dS
m−1)

Yield
(t
ha−1)

2017

Control_PMF
1 kg m−2
0.5 kg m−20.25 kg m−2
Statisticalsigniﬁcance42.3 a38.4 b36.1 c32.9 d
P < 0.01

25.6 a22.8 b
22.7 b
22.7 b
P < 0.01

0.32 a0.20 c0.27 b
0.23 cb
P < 0.01

53.5 a43.3 a34.6 a36.6 an.s.

2018

Control_PMF

20.0 b

16.9 a0.14 cNo
crop

1.5 kg m−2
0.5 kg m−20.25 kg m−2
Statisticalsigniﬁcance23.5 a22.9 a23.2 a
P < 0.01

16.7 a16.1 a16.1 an.s.

0.27 a0.16 c0.21 b
P < 0.01

Means with the same letter are not signiﬁcantly diﬀerent at P < 0.05; n.s.: nonsigniﬁcant interaction; EC: electrical conductivity.

3.3. SBPM ﬁeld experiments with watermelon and no crop: soil water, soil
temperature, electrical conductivity, and yieldIn the second experiment at Finley, watermelons were grown during
the ﬁrst season in 2017, while no crop was grown during the 2018season. In contrast to the ﬁrst set of experiments with tomatoes, thecontrol plot was covered with PMF to estimate if the SBPM Technology
could compete with conventional mulching practices. Treatments using
lesser amounts of SBPM were chosen to ascertain whether their performance was competitive with relatively low-cost PMFs. The resultspresented in Table 3 show that the PMF plot was signiﬁcantly wetterand cooler at the 10 cm soil depth, indicating that the PMF outperformed the SBPM, at least in the case of growing watermelon during
the 2016/17 season. Although the highest watermelon yield of 53.5 t
ha−1 was recorded in the PMF plot, there was no signiﬁcant diﬀerencein watermelon yield between the PFM plot and the SBPM plots (due tohigh variations among replicates of each treatment).
The soil in all treated plots was drier than in the Control PMF plot,measured in the top 20 cm of the soil proﬁle after planting watermelon.
As the season progressed, the soil in the plot with the 1 kg m−2 SBPM
treatment became signiﬁcantly wetter at soil depths of 30, 40, 50, 60,
70, and 80 cm and remained wetter than in the Control PMF plot
(Fig. 5a). The volumetric soil water content at 10 cm showed a decreasing trend with the amount of polymer applied: Control_PMF > 1
kg m−2 > 0.5 kg m−2 > 0.25 kg m−2. This trend also occurred in thewatermelon yield, where the highest yield was recorded in the Control_PMF plot, although it was not signiﬁcant (53.5 t ha-1 in the PMF
plot, followed by 43.2 t ha-1 obtained in the 3 kg m−2 SBPM treatmentplot).
During the 2018 season, when no crop was grown, a diﬀerent trend
in the soil water content (10 cm; Table 3) was recorded. A signiﬁcantly
higher soil water content was found at all SBPM treated plots comparedto the Control PMF as follows: 1.5 kg m−2 > 0.25 kg m−2 > 0.5 kg
m−2 > Control_PMF. However, the diﬀerences among the SBPM
treatments were not signiﬁcant. An interesting observation was thatwithout any crop grown, SBPM retained a higher soil water content
than the PMF. As shown in Fig. 5d, the soil proﬁle water content increased with depth, with all SBPM treatments wetter than the PMF
control (LSD P < 0.05), except for the 0.5 kg m−2 SBPM treatment,
which was drier than the PMF control, but only at 80 cm (Fig. 5d). The

3.4. Seasonal water dynamics under the SBPM
The VWC recorded at the 10 cm depth during each growing season
at the Echuca and Finley sites in relation to rainfall (mm) and irrigation
is presented in Fig. 7. In experiments with tomatoes during the 2016/17
season, the VWC at the control plot was lower than for all SBPM
treatments, while during the 2017/18 season, only the highest level ofthe SBPM application (3 kg m−2 NF) had a larger volumetric watercontent than the bare soil (control). For the second set of experimentswith watermelon and the PMF used as a control, it seems that the SBPM
did not perform at the same level as the PMF. However, it can also beseen that the 1 kg m−2 SBPM plots had a higher VWC than the control
PMF plot during the mid-season in 2017. This was also the case in the2018 season when no crop was grown when the VWC did not respondso rapidly to rainfall patterns and displayed a smoother line throughout
the experiment.
4. Discussion
As reported in Kader et al. (2017), in addition to reducing soil
evaporation, conserving soil moisture, and eﬀecting soil temperatureand soil structure, soil mulching also suppresses weed growth by limiting photosynthetically active radiation (PAR), all of which aﬀect thesoil microbiology and soil health. The main challenge facing current
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M.V. Braunack, et al.

Fig. 5. The eﬀect of Sprayable Biodegradable Polymer Membrane (SBPM) on seasonal averages of the soil proﬁle water content (%, v/v), soil temperature (oC), andelectrical conductivity (dS m−1), obtained from two experiments with the SBPM and plastic mulch ﬁlm (Control_PMF), one with watermelon during the 2017 season(LSD P < 0.05 1.0, 0.1, and 0.04 for soil water (v/v), temperature (Co), and electrical conductivity (dS m−1), respectively), and another with no crop during the2018 season (LSD P < 0.05 0.6, 0.05, and 0.02 for soil water (v/v), temperature (Co), and electrical conductivity (dS m−1), respectively). The results are averagevalues from measurements in three plots, collected using sensors at multiple soil depths (10-80 cm), from plots with diﬀerent amounts of applied SBPM (1.5, 1, 0.5,
and 0.25 kg m-2).

similar trend, where the highest average soil water content was observed in treatments with high polymer loadings: 1 kg m−2 F in thetomato experiment in 2016/17 (39.5 %); 3 kg m−2 NF in the tomato
experiment in 2017/18 (34.8 %), 1.5 kg m−2 in the experiment with nocrop and the PMF in 2018 (23.5 %). The exception was the 2017 watermelon experiment where a 1 kg m−2 loading resulted in the highest
soil water content (38.4 %) of all SBPM treatments, but lower than in
the PMF control (42.3 %).
Improvements in the soil water conservation aspect of the SBPM
technology were demonstrated in the presented ﬁeld trials. One experiment (no crop in 2018) showed greater water conservation in thesoil proﬁle than the conventional PMF. The latter result is likely attributable to the presence cracks/breakages in the PMF (which can occur
quite commonly) that allow increased water evaporation. In contrast,
the SBPM does not lay over the soil but adheres to the soil surface andbiodegrades rather than breaking into small fragments like plastic
mulch ﬁlms do, resulting in environmental pollution with microplastics

plastic-based soil mulching practices is to replace these materials that
can avoid the potential to pollute the environment while being nontoxic
and biodegradable (Sintim and Flury, 2017; Filipović et al., 2020). The
SBPM used in our ﬁeld experiments was developed as an environmentally sustainable product because it is biodegradable andbreaks down into non-harmful by-products, such as carbon dioxide,water, and soil microbial biomass (Adhikari et al., 2015). Biodegradability of the product can have a large impact on reducing the expenses
needed for mulch disposal, while the use of nontoxic compounds iseliminating the possibility of environmental pollution.
The largest positive eﬀect on soil water content was observed for the
SBPM treatments with higher loadings (1 and 3 kg m−2) that formed athicker, more uniform membrane that reduced soil water evaporation.
In a previous SBPM glasshouse study (Braunack et al., 2020a), the water
conservation trend was similar, with soil water content decreasing withdecreasing loading (1 kg m−2 > 0.5 kg m−2 > 0.25 kg m−2 > nomulch control). In the ﬁeld experiments presented here, we observed a8Agricultural Water Management 243 (2021) 106446

M.V. Braunack, et al.

Fig. 6. Observed diﬀerences in proﬁle soil water (mm), soil temperature (oC), and electrical conductivity (dS m−1) between SBPM treatments (trt), one withwatermelon during the 2016/2017 season (mm), LSD P < 0.05 trt * depth = 1, (Co), LSD P < 0.05 trt*depth = 0.1, (dS m−1), LSD P < 0.05 trt*depth = 0.04) andanother with no crop during the 2017/2018 season ((mm), LSD P < 0.05 trt*depth = 0.6, (Co) LSD P < 0.05 trt*depth = 0.05, (dS m−1), LSD
P < 0.05 trt*depth = 0.02). Positive: the treatment is wetter, warmer, and has a higher salinity than the control (PMF). The results are average values from three
replicate plots, collected using sensors at multiple soil depths (10-80 cm) with treatments using diﬀerent amounts of applied SBPM (1.5, 0.5, and 0.25 kg m-2).

and biodegradable plastic mulch ﬁlms (Bilck et al., 2010; Kairajan and
Ngouajio, 2012). The higher polymer loadings appear to perform similarly to PMFs by maintaining more water in the soil proﬁle compared
to bare soil. In both tomato seasons, the soil proﬁle water was variable,with the 1 kg m−2 F and 3 kg m−2 NF treatments resulting in wetter soil
proﬁles than the other polymer treatments and the no mulch control.
The fact that the average soil proﬁle water content was higher under
the polymer treatment was not expected because only a 20 cm wide
strip was applied, with no side application (2016/17). However, this isconsistent with studies using the PMF, where the soil VWC was higher
under the ﬁlm compared to bare soil (Kairajan and Ngouajio, 2012).
Soil proﬁle moisture decreased as the season progressed and the crop
matured, with the mid-season peaks corresponding to the frequency ofirrigation and rainfall events. Similarly, Chen et al. (2019) compared
the PMF with a biodegradable ﬁlm in a 2-year ﬁeld trial. They showedthat during early and middle crop growth periods, the soil water content was similar in the biodegradable and PMF scenarios. Signiﬁcantdiﬀerences in the soil VWC were observed only after the average(Kairajan and Ngouajio, 2012). Similar results were presented by
Adhikari et al. (2015, 2016), who reported a reduction in soil water
evaporation of up to 28 % and 60 % in ﬁeld trials and under controlledlaboratory conditions, respectively. The ﬁeld-scale results with the
SBPM conﬁrm that the SBPM should be further tested and ﬁne-tuned toreplace PMFs, which are currently causing signiﬁcant pollution of soils
and water systems (Gao et al., 2019; Braunack et al., 2020b).
Vaicekauskaite et al. (2019) presented a biodegradable spray-on mulch
based on sodium alginate, which was developed as an alternative tothin plastic ﬁlms for potential use in horticulture. Similarly, Sartore
et al. (2018) tested polymeric protein-based biodegradable spraycoatings in greenhouse trials, which showed agronomic performances
comparable to the commercial low-density polyethylene mulch ﬁlm.
During the 2016/17 tomato season, the average VWC in the soil
proﬁle increased with soil depth in all SBPM treated plots. Although the
SBPM treatments maintained more water in the soil proﬁle than thebare soil, crop yield was not signiﬁcantly aﬀected (Table 2), contrary topreviously observed yield increases with the application of preformed
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M.V. Braunack, et al.

suggesting that the current SBPM polymer cannot compete with PMFs
(Table 3). However, the results showed that compared to the no mulch
control plot, the SBPM applied at higher rates (i.e., 3 kg m−2) increased
soil temperature. Similar results were presented by Sun et al. (2015),
who studied whether the biodegradable ﬁlm could accommodatechanging soil conditions during diﬀerent crop seasons. Sun et al. (2018)used six diﬀerent treatments, which included four diﬀerent ratios of
starch/polybutyrate adipate terephthalate (PBAT) biodegradable
mulching ﬁlms. In their experiment, it was found that the soil temperature under the biodegradable ﬁlms was 0.4–2.9 °C, 0.8–2.8 °C,
0.6–2.0 °C, and 0.1–1.3 °C lower than under PMFs at soil depths of 5,
10, 15, and 20 cm, respectively.
When applying the SBPM to surface soil, the practice is to incorporate a carbon black pigment into it to absorb solar radiation(creating a light barrier) to inhibit/prevent photosynthetic weed
growth and convert it to heat to promote growth kinetics (Sartore et al.,2018). Braunack et al. (2020a) used the same pigmented SBPM formulation, as in this study. They observed that when they used a wider
application band of the SBPM on the soil surface (150 mm wide strips),
soil water evaporation was reduced, and the soil VWC and temperature
increased compared to the control. This agrees with our study, in whichhigher soil temperatures were observed on plots with wider and higher
SBPM applications (e.g., 3 kg m−2 SBPM and 55 cm wide strips), presumably because a thicker membrane covered a larger surface area.
Uniform coverage of the SBPM on the soil’s surface during application is critical to forming a uniform membrane to provide eﬀective
water barrier properties. Diﬀerential wicking (adsorption to soil) of thepolymer into the soil can result in inconsistencies in membrane thickness leading to inferior water barrier performance. Adhikari et al.
(2019) proposed that increasing the viscosity of the sprayable polymer
was a way to reduce wicking and control the amount of polymer delivered to form an eﬀective water barrier membrane, providing that theincreased viscosity did not compromise polymer’s sprayability and ﬁlm
formation ability.
The highest levels of salinity/electrical conductivity were recorded
in soil with the highest topsoil water content (tomato 2016/17: 1 kg
m−2 F; tomato 2017/18: 3 kg m−2 NF; watermelon 2017/2018:
Control_PMF; no crop 2018: 1.5 kg m−2). Generally, increased soil VWC
was a result of lower soil evaporation under the most eﬀective mulch
covers. The amount of non-irrigated water (rainfall) inﬁltrating the soil
was reduced, in turn inhibiting salt leaching into the deeper soil. Under
the conditions of increased VWC, salt transport eﬀects from non-irrigation water (rainfall) entering the system appeared to be lower. Under
these conditions, non-irrigation water mostly ran oﬀ raised beds,
causing minimal salt leaching into deeper soils. Consequently, transverse salt transport at the surface would be expected to predominate asvertical resistance to mass transport and diﬀusion is greater thantransverse resistances, eﬀectively resulting in desalination of the surface proﬁle. Similar ﬁndings were also obtained by Qi et al. (2018),
who investigated the combined eﬀects of tillage and mulching on soil
water contents and salt transfers under drip irrigation. Qi et al. (2018)
tested the following mulch management practices: ridge tillage withpartial or full ﬁlm mulching, and ﬂat tillage with partial or full ﬁlm
mulching. In all of these treatments, salts were pushed to the edge ofthe soil wetting front. Simulations also conﬁrmed that increasing theamount of irrigation water induces soil desalination.
Electrical conductivity in our study did not reach levels that would
signiﬁcantly compromise crop yield. This is in contrast to previously
reported results: 1.5, 2.4, and 3.8 dS m−1 for no yield loss, 19, and 25 %yield loss, respectively (NSW, DPI, 2016). Also, it was observed thatsalinity increased with soil depth, with the highest values recorded
deeper in the soil proﬁle in experiments with crops, which may indicatethat roots were extracting applied fertilizer down to the 50 cm depth,
thus lowering the overall electrical conductivity values. As reported in
Chen et al. (2018), the spatial distribution of roots is aﬀected by mulchand salinity (electrical conductivity), with irrigation management also

Fig. 7. The eﬀect of the Sprayable Biodegradable Polymer Membrane (SBPM)
on the soil VWC (%) measured at the 10 cm soil depth during the experiments
with: a, b) tomato (2016/17 and 2017/18, respectively), where no mulch was
the control; c) watermelon (2017) where the PMF was used as the control; andd) the no crop scenario in the 2018 season when the PMF was used as thecontrol. The results are presented as averages from the three plots having different amounts of applied SBPM (3.0, 1.0, and 0.5 kg m−2) with fumigant (F) or(1.5, 1, and 0.5 kg m−2) no fumigant (NF). Note: the daily irrigation values
were not recorded for all experimental sites.

fraction of the disintegrated area of the SBPM was larger than about 40% (which occurred late in the season). This emphasizes the importanceof SBPM biodegradation properties, which should be adjusted to thecultivated crop. In both tomato seasons, yields were not the highest forplants grown on the SBPM treated plots with the highest average VWC(1 kg m−2 F, 3 kg m−2 NF). Surprisingly, they were highest for plants
grown on other SBPM treated plots (0.5 kg m−2 NF and 3 kg m−2 F),
which is likely attributable to waterlogging deeper in the soil proﬁle. As
reported in a previous study that evaluated drip irrigation scenarioswith PMF, straw mulch, and bare soil, tomato yield, and water use efﬁciency were higher under mulched treatments when less water wasapplied (e.g., Biswas et al., 2015).
The eﬀects of SBPM on soil temperature are not clearly apparent,
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M.V. Braunack, et al.

keeping the application rate as low as possible (to reduce costs), toincrease the SBPM performance to a level comparable with plastic
mulch ﬁlms, as a prerequisite for the common use of the SBPM technology in various crop production systems.

having a measurable eﬀect. Our results show that the electrical conductivity level in the topsoil was primarily aﬀected by the amount ofinﬁltration. This ﬁnding is supported by Abd El-Wahed et al. (2017),
who recorded the lowest soil salinity value at the plot receiving thehighest amount of irrigation.
The SBPM technology tested here is the ﬁrst of its kind tested at theﬁeld scale. Most other sprayable products have predominantly beentested using hand sprayers in greenhouses/controlled environments
where conditions are less variable (e.g., Vox et al., 2013; Sartore et al.,2013, 2018; Braunack et al., 2020a, 2020b). Future perspective needs
to be focused on ﬁne-tuning the polymer formulation to balance mechanical properties that maintain a ﬁrm elastic binding with soil anddurability throughout the crop growing season. The SBPM researchshould focus on increasing its performance while, at the same time,
limiting the cost of production to a minimum. The researchers will needto test various biodegradable polymer formulations in long-term ﬁeld
trials under diﬀerent climatic conditions to deﬁne to what extent the
SBPM technology can compete with conventional plastic mulch ﬁlms.

Declaration of Competing Interest
The authors report no declarations of interest.
Acknowledgments
This research was supported by CSIRO and the Science and Industry
Endowment Fund (SIEF). We also acknowledge and thank Darin
Hodgson for technical support; co-operating growers for provision of
the experimental sites, fabrication of experimental spray rigs, andagronomic support in conducting the ﬁeld experiments. We also acknowledge and thank the UKF visiting grant, which was assigned toProfessor Vilim Filipović for the bilateral research project EnviroSBPM(https://sites.google.com/view/envirosbpm/) between the Universityof Zagreb, Croatia, and CSIRO Agriculture & Food, and Academic
Mobility Grant awarded from the University of Zagreb to Dr. Lana
Filipović.

5. Conclusions
The newly developed Sprayable Biodegradable Polymer Membrane(SBPM) technology was tested for its ability to conserve soil water,
suppress weeds, modify soil temperature, change salinity (i.e., electricalconductivity), and improve crop yields. Two-year ﬁeld scale experiments were performed in tomato and watermelon production systems
where the SBPM was compared to no mulch and plastic mulch ﬁlm(PMF) treatments. Systematically varied SBPM application loadings
were investigated across two crops: 3, 1 and 0.5, kg m−2, with orwithout fumigation in experiments with tomato and 1.5, 1, 0.5, and0.25 kg m-2 in experiments with watermelon with no fumigation during
two-year ﬁeld experiments.
In the tomato experiment, the soil proﬁle water content at the 10 cm
depth was signiﬁcantly diﬀerent in all SBPM treated plots compared tothe control plot (no mulch), with the trend being: 1 kg m−2 F > 0.5 kg
m−2 NF > 1 kg m−2 NF > 0.5 kg m−2 F > Control in 2016/17; and3 kg m−2 NF > Control > 0.5 kg m−2 F > 3 kg m−2 F > 0.5 kg m−2
NF in 2018. This was also reﬂected in the soil water content measured
using sensors at other depths in the soil proﬁle (10–80 cm), where ateach depth, the soil under 1 and 3 kg m−2 of SBPM polymer was consistently wetter than the soil at the corresponding depth at the other
SBPM treated plots and the control. As expected, ﬁeld results were morevariable compared to previous glasshouse experiments due to the seasonal climatic variations and less homogeneous soil conditions.
When compared with the PMF as the control used in the experiments with watermelon, the topsoil water content was lower in all
SBPM treated plots during the 2017 season. However, when no crop
was present in the experimental plots (2018), the topsoil water content
was higher in all SBPM treated plots, which was explained by theconsistency in the formation of a thick SBPM membrane at the soil
surface in contrast to the breakages, which regularly appear in plastic
mulch ﬁlms.
In examining inﬂuencing parameters, soil temperature signiﬁcantly
increased only in treatments receiving the highest SBPM application
rate (3 kg m−2 NF and a coverage width of 55 cm). Yield response was
not signiﬁcant, although the highest recorded average yields were fromplants grown on plots under the SBPM treatments. Increased soil watercontents were a response to lower evaporation rates under the mosteﬃcient mulch cover, which also reduced the amount of water (rainfall) passing through the soil, thus decreasing soil desalinization. Earlier
ﬁeld experiments proved that the SBPM indeed resulted in better soil
water conservation while indicating that there are still some performance restrictions when compared to conventional plastic mulch ﬁlms.
SBPM Technology should be further improved and tested while
ensuring its sprayability, biodegradability, and non-toxicity. The research should focus on the uniformity of the SBPM management, while

Appendix A. Supplementary data
Supplementary material related to this article can be found, in the
online version, at doi:https://doi.org/10.1016/j.agwat.2020.106446.
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