EJERS, European Journal of Engineering Research and Science
Vol. 4, No. 12, December 2019
DOI: http://dx.doi.org/10.24018/ejers.2019.4.12.1641 16

Abstract—Using chemicals as a weed control method is the
most preferred method in weed control because they are easily
accessible, easily applicable and inexpensive. But, with the new
environment-friendly regulations, the importance of non-
chemical methods has increased all over the world. In addition,
organic farm and non-chemical agricultural methods are
gaining importance with increasing social environment and
health awareness. Non-chemical methods, called, "alternative
methods” have been one of the most popular research subjects
in recent years. The physical removal or killing of weeds is
usually done by hand or by means designed tools for this task,
which varies from country to country. The most known
modern non-chemical weed control methods are; electric
current, microwave heating, superheated steam, infrared
using, pneumatic system, freeze-drying, laser cutting, and
fresnel lens systems. The most popular of these methods are;
electric current method and microwave heating. In electric
current and microwave heating methods, there are no
chemical residues in soil and plants after application. It has
been shown in the studies that, the microwave weed control
method can destroy weeds and seeds when appropriate
frequency, sufficient time and required power level are
selected. Therefore, in the selection of non-chemical weed
control methods, some important parameters of plant and soil
should be known. The electrical and dielectric properties of
plants and soil such as, electrical resistance (R), impedance (Z),
dielectric constant (ε’), loss factor (ε’’), the permittivity (ε),
permeability (µ) and conductivity (σ) should be known
especially in microwave and electric current methods. The
other parameters like the age, height, and density of the plant
is an issue to be considered in all control methods. But, the
moisture content of soil and plant may not be taken into
consideration in hot water and steam applications. For the
freeze-drying method, the moisture and water content of the
plant and soil must also be taken into account.
Index Terms—Weed Control, Parameters, Microwave, Non-
Chemical, Electric Current.
I. INTRODUCTION
In the past years, herbicides (chemicals) have been
accepted as the main tool in weed control, but with the new
regulations made especially in the European Union, the
importance of non-chemical methods has increased all over
the world. The most known non-chemical weed control
methods are; fire-fighting, superheated steam, infrared
using, pneumatic system, freeze-drying, laser, electric
current, microwave heating, and fresnel lens systems.
From a detailed survey of the application of models to
weed control, it is concluded that modeling has
fundamentally been concerned with answering issues that
Published on December 4, 2019.
H. Sahin is an Assist. Prof. Dr. at Harran University Department of
Agricultural Machinery at Vocational School of Technical Sciences
Sanliurfa-TURKEY (e-mail: hsahin@harran.edu.tr).
contribute comparatively little to our understanding of
‘sustainable’ systems of crop protection [1]. Chemical used
in weed control has led to an increase in the number of
herbicide-resistant weed populations [2].
On the other hand, organic production and non-chemical
agricultural methods are gaining importance with increasing
social environment and health awareness. Especially in
weed control management, non-chemical methods, called,
"alternative methods” have been one of the most researched
subjects in recent years. The physical removal or killing of
weeds is usually done by hand or by means designed tools
for this task, which varies between cultures. Pre and post-
sowing, pre and post-emergence with chemicals applied
methods, provides a sustainable and long-term strategy to
minimize weeds and maximize crop yields [3]. The
widespread use of herbicides in agricultural fields has led to
the development of anti-herbicide resistance in weeds. The
resulting herbicide activity has increased the demand for
alternative weed control technologies. Alternative control
methods, which determine the most appropriate method for
commercial development, have not yet reached the desired
technological level due to the lack of an accurate and fair
comparison [4]. Management in large-scale agricultural
production, the SSWM (site-specific weed management),
provides a fair and accurate comparison of non-chemical
weed control methods [5].
Chemicals used as a weed control method effect the
development of weeds and aim to minimize or completely
eliminate economic loss. Control methods using chemicals
are used in the control of weeds in agricultural areas as well
as in non-agricultural areas. However, in scientific studies,
it was determined that the herbicides detected in drinking
water can only be separated from the water by ozone
purification method. In a study, the herbicides used in the
vineyards such as; orflurazon and oxadiazone, at the end of
a month in the grape grains and soil residue was found to be
a serious danger in consumption [6], [7]. As the damages of
chemical drugs used in weed control are understood and
environmental sensitivity increases, it is observed that there
is a rise in the tendency towards non-chemical control
methods especially in organic farming applications [8]. The
abandonment of chemical control methods and moving
towards organic agriculture emerges as a highly desirable
situation in society. However, many manufacturers accept
the use of chemicals very quickly because of their ease of
application [9].
Although the only method of combating any weed is
sometimes sufficient, it may not be sufficient for some weed
species. Therefore, it may sometimes be necessary to apply
several methods simultaneously or in a certain order. The
recent expansion of organic farming has increased interest
A Review on Parameters Affecting the Choice of
Alternative (Non-Chemical) Weed Control Methods
Hasan Sahin

EJERS, European Journal of Engineering Research and Science
Vol. 4, No. 12, December 2019
DOI: http://dx.doi.org/10.24018/ejers.2019.4.12.1641 17
in non-chemical weed control methods. Some of the non-
chemical methods used in weed control are;
• Electric current
• Microwave heating
• Superheated steam
• Freeze drying
• Hot water application
• Pneumatic system
• Infrared using
• Laser cutting
• Fresnel Lens heating
Fresnel lens weed control method is to concentrate solar
radiation on a plant or region. The experiment results show
that to calculate the effect of Fresnel lens concentrated solar
radiation at different exposure times, stages of plant growth,
and moisture of soil surface conditions. On a dry soil
surface, exposure times of 1 to 10 s reaches 290º C [10].
Weed control with electric current is not a new technic.
Electric current control method has experimented since
1970 for restriction of germination of weed seeds. The using
electrical energy to inhibition weed was developed in 1800,
and a few patents have been registered in the USA [11]. As
the disinfection of soil with electric current or microwave
method does not leave any chemical residue [12], [13], [14]
it seems to be an alternative to the chemical weed control
method.
Weed cut with a laser is another alternative weed control
method. It delays the re-growth of weed, weakens and killed
weeds. It’s also a low-cost and ecological weed control
method [15].
In another study, the applicability of the microwave
method of destroying weeds, which causes significant losses
in agricultural production. Mustard, oats, and cress were
used as an experimental plant in this study. After
microwave application to the plants, most plants lost their
viability [16]. Reference [17], in his study investigated to
determine the level of restriction of germination of the weed
seeds instead of plants. In the study, weed seeds were sown
at equal depths (8-10 mm) to the soil, to investigate the
effects of microwave energy on the germination of plant
seeds. The results show that a restriction of 100 % was
observed in the germination of seeds exposed to microwave
for 2.8 kW and 126 seconds.
Reference [18], emphasized the necessity of knowing the
dielectric properties of agricultural products in thermal
processes using the microwave and radiofrequency. When
the dielectric properties of agricultural products are
examined, it is stated that their reactions as a function of
temperature and moisture content at different microwave
frequencies.
Site-specific weed management (SSWM) techniques have
gained interest in the precision farming community over the
last years. Because the SSWM, application technology can
save the large amounts of herbicides. On the other hand, the
mechanical weed management technologies adapting to the
weed location in the field can be applied to a large spectrum
of crops [19].
Weed management systems should be re-studied in light
of new, developing weed control technologies. The science
of weed management needs to refocus on the foundation's
ecology to enable an ecological promote agricultural
sustainability [20].
II. PARAMETERS AFFECTING THE METHOD SELECTION
In this study, selection parameters only for the non-
chemical (alternative) methods will be discussed as shown
in Table I. In the selection of non-chemical weed control
methods, the parameters listed below are decisive.
• Soil properties
• Weed length
• Weed age
• Weed dielectric properties
• Weed electrical properties
• Weed density per unit area
• Root thickness and depth of weed
• Leaf width of weed
• The water content of weed
• Soil moisture content
Parameters such as plant age, height, root thickness, and
depth are the factors that determine the amount of energy to
be applied to the weed. The main problem in determining
the economic applicability of non-chemical weed control
methods is the complexity of many factors listed above.
Cost, yield, timelessness and the effect of alternative labor
use are factors to be considered when comparing non-
chemical weed control methods. It is an advantage to
chemical methods that mechanical methods are not
preferred because of their latency or time dependence.
Although the use of alternative labor is a common debate in
the choice of chemical or mechanical methods, it is a factor
that has little impact on cost [21].
Especially in electric current method and microwave
method, electrical resistance (R), impedance (Z), dielectric
constant (ε'), loss factor (ε'') of the weed species and soil in
order to calculate the energy exposure time and the resulting
energy losses. and distribution factor (tan δ). However, the
moisture contained in the soil and the plant, the properties
of the soil, the root and the leaf structure of the plant are
important factors affecting the heat treatment efficiency.
The behavior of the soil and the plant under the influence of
microwave radiation is determined by the percentage of the
radiation absorbed, transmitted or reflected. The dielectric
constant (ε’) and the loss factor (ε'') of the applied material
is also the basic parameters in the design of microwave
applicators.
Dielectric properties of agricultural products are
important in terms of measuring moisture content in cereals,
accurately determining the behavior of agricultural products
exposed to RF and microwave in dielectric heating
applications [22].
When electric current applied to the body of the plant
according to Eqn. (1) and (2) the amount of energy (𝐸)
transferred to one plant depends on the electrical resistance
(𝑅𝑃) of the plant the contact time of the electrodes to the
plant (𝑇𝑐) and the applied voltage (𝑉) has to be known [23].
The effective contact time of the plants contacted by the
electrodes at any time (𝑛𝑐) is equal to the product of
electrode length (𝐿), effective electrode width (𝑊𝑒𝑓𝑓) and
plant density is (𝐷), [23].
𝐸 =
𝑉2 𝑇𝑐
𝑅𝑃
(1)

EJERS, European Journal of Engineering Research and Science
Vol. 4, No. 12, December 2019
DOI: http://dx.doi.org/10.24018/ejers.2019.4.12.1641 18
𝑛𝑐 = 𝐿 𝑊𝑒𝑓𝑓 𝐷 (2)
Similarly, it can be seen at Eqn. (3), the total resistance
load (𝑅𝐿) is equal to the sum of the resistance of each plant
(𝑅𝑝) touching to the electrodes simultaneously and plus the
resistance of the (𝑅𝑠) soil.
𝑅𝐿=[∑
1
𝑅𝑝
𝑁
𝑖=1 ]
−1
+𝑅𝑠 (3)
The required power generator will increase as the
numbers of touching electrodes increase.
If we want to use microwaves efficiently in weed control,
we need to know about the dielectric properties of the
plants. The dielectric properties of materials are usually
expressed by relative complex permittivity, where the real
part (ϵ’) is the dielectric constant and the imaginary part (ϵ”)
is the loss factor The interaction of electromagnetic waves
with the material is closely related to the dielectric
properties of the material. Electromagnetic properties such
as permittivity, conduction, reflection, scattering, and
refraction are expressed depending on the dielectric
properties of the materials. The small amount of water or
moisture contained in the material significantly affects the
dielectric properties of the material [18].
𝑡𝑎𝑛 𝛿 =
𝜀′′
𝜀′ =
𝑒𝑛𝑒𝑔𝑦 𝑙𝑜𝑠𝑠 𝑝𝑒𝑟 𝑐𝑦𝑐𝑙𝑒
𝑒𝑛𝑒𝑟𝑔𝑦 𝑠𝑡𝑜𝑟𝑒𝑑 𝑝𝑒𝑟 𝑐𝑦𝑐𝑙𝑒
(4)
The dielectric properties of agricultural products and
plants have great importance because of their direct relation
with moisture and water content. Dielectric properties of
different fruits and nectars have been reported in the
literature such as apples, cherries, grapefruits, and oranges
[24].
In the study conducted to understand the effect of water
stress on the dielectric properties of plant leaves, the
significant effect of water stress on the resonance frequency
of individual leaves was statistically shown [25].
The effects of frequency, electric field strength, seed
moisture content, seed temperature, variant change, and
other factors were discussed and practical application
aspects in the seed industry were discussed in the study on
RF exposure to germination increase and alfalfa seed
improvement [26].
In all non-chemical methods, the parameters affecting the
control efficiency are also directly affecting the energy
efficiency and the cost itself. Therefore, plant and soil
properties are of great importance in non-chemical control
methods.
Any material is electromagnetically characterized by
three parameters; the permittivity (ε), permeability (µ) and
conductivity (σ) of a material. The greater the tan δ
(dielectric loss tangent) value of a material, the greater it's
capacity to absorb microwave energy, Eqn. (4), [27].
III. CONCLUSION
As can be seen in Table I, the age, height and density of
the plant is an issue to be considered in all control methods.
The electrical properties like electrical resistance (R),
impedance (Z) of weed species and the soil is important for
the electric current method. However, the energy losses
occurring in both electric current and microwave methods
and the lack of knowledge of the electrical-dielectric
properties of the plants make the applicability of the
methods economically difficult.
Therefore, electrical and microwave applications of weed
and soil electrical resistance (R), impedance (Z), dielectric
constant (ε’), loss factor (ε’’) and distribution factor (tan δ)
needs to be known.
The moisture content of soil and plant may not be taken
into consideration in hot water and steam applications.
However, if the freeze-drying method is to be used, the
moisture and water content of the plant and soil must be
taken into account.
It is superior to alternative (non-chemical) methods
because the chemicals used in weed control are easily
accessible, easily applicable and inexpensive.
The use of microwave energy in the weed control has
gained popularity today. High energy-based microwaves are
used very efficiently in weed control [28]. The use of
microwaves that do not produce chemical residues in the
environment as a weed control method seems to be a good
alternative [29]. Therefore, alternative production methods
have not yet reached an economic advantage in terms of
technological production and application costs.
In addition, the electroporation method, which is one of
the newly applied methods, also aims to damage the cell
membrane by a pulsed high voltage electric field. It causes a
dielectric breakdown that damages the cell membrane and
results in the cell membrane collapsing and cell death. The
electroporation technique applied to weed seeds is
becoming a non-chemical method for weed control [30].
Similarly, in an experimental study, it was stated that
(pulse) pulsed electric current is more effective than the
sinusoidal current in creating depth of damage in tissues of
different plants [31]. In a study, a voltage multiplier of
Cockroft-Walton type was used which can produce variable
voltage for variable load. This voltage multiplier provides
the required voltage according to the changing plant density
without the need for any additional circuit, processor or
controller [32]. It is also important to note that low DC
voltages such as 8-16 volts increase plant viability and
quality [33].
Inadequate stresses to kill weeds can cause adverse
effects on the strengthening and proliferation of weeds.
All these studies show that non-chemical weed control
methods are strengthened with new studies day by day. In a
short period of time, these methods, which are environment-
friendly, energy-saving, fast and economical, will contribute
to agricultural life through field applications.
Especially in microwave and electric weed control
methods, the electrical and dielectric properties of the plant
must be determined before the selection of parameters such
as microwave power and electric current. In addition, in the
weed control method of electricity, it is necessary to know
the electrical and dielectric properties of the plant as well as
its soil. It is also important to know the dielectric properties
in measuring the amount of water that agricultural products
and weeds contain during and after drying/destroying
processes.

EJERS, European Journal of Engineering Research and Science
Vol. 4, No. 12, December 2019
DOI: http://dx.doi.org/10.24018/ejers.2019.4.12.1641 19
TABLE I. PARAMETERS AFFECTING THE EFFICIENCY OF NON-CHEMICAL WEED CONTROL METHODS
Parameters
Non-Chemical Weed Control Methods
Microwave
Heating
Electric
Current
Lazer
Cutting
Freeze
Drying
Hot
Water
Fresnel
Lens
Infrared
Using
Pneumatic
Cutting
Steam
Heating
Soil properties   
Plant length         
Plant age         
Dielectric properties of plant   
Electric properties of the plant 
Plant density/unit area         
Root thickness and depth        
Leaf width of the plant      
The water content of plant     
Soil moisture content  
REFERENCES
[1] Doyle, C. J. (1997). A review of the use of models of weed control in
integrated crop protection. Agriculture, ecosystems &
environment, 64(2), 165-172.
[2] Westwood, J. H., Charudattan, R., Duke, S. O., Fennimore, S. A.,
Marrone, P., Slaughter, D. C., & Zollinger, R. (2018). Weed
management in 2050: Perspectives on the future of weed
science. Weed science, 66(3), 275-285.
[3] Brand, J., Yaduraju, N. T., Shivakumar, B. G., & Murray, L. (2007).
Weed management. Lentil, 159-172.
[4] Coleman, G. R., Stead, A., Rigter, M. P., Xu, Z., Johnson, D.,
Brooker, G. M., ... & Walsh, M. J. (2019). Using energy requirements
to compare the suitability of alternative methods for broadcast and
site-specific weed control. Weed Technology, 1-18.
[5] Bakker, T., Bontsema, J., & Müller, J. (2010). Systematic design of
an autonomous platform for robotic weeding. Journal of
Terramechanics, 47(2), 63-73.
[6] Hua, W, Bennett E, And Letcher R, 2006. Ozone Treatment and The
Depletion of Detectable Pharmaceuticals and Atrazine Herbicide İn
Drinking Water Sorced from the Upper Detroit River Ontario Canada.
Water Research 40 (2006) 2259-2266.
[7] Ying, G, And Williams B, 2000. Dissipation of Herbicides İn Soil and
Grapesin a South Australian Vineyard. Agriculture, Ecosystem and
Environment 78 (2000) 283-289.
[8] Sahin, H., 2012. A Research on Determination the Applicability of
Microwave as a Weed Control Method in Agricultural Production,
PhD Thesis, Harran University, Graduate School of Natural and
Applied Science.
[9] Ascard, J. 1990. Weed Control in Ecological Vegetable Farming. In
A. Granstedt (Ed). Proceedings of The Ecological Agriculture,
Nordiske Jordbrugsforskeres Forening, Seminar, 166, 178-184.
[10] Johnson, D. W., Krall, J. M., Delaney, R. H., & Pochop, L. O. (1989).
Response of monocot and dicot weed species to Fresnel lens
concentrated solar radiation. Weed Science, 37(6), 797-801.
[11] Nelson, S., O., 1996. A Review and Assessment of Microwave
Energy for Soil Treatment to Control Pests. Transactions of The Asae,
39(1), 281–289.
[12] Bigu-Del-Blanco, J., Bristow, J.M., and Romero-Sierra, C., 1977.
Effects of Low-Level Microwave Radiation on Germination and
Growth Rate in Corn Seeds. Proceedings of IEEE, Volume:65,
Issue:7, P:1086-1088.
[13] Ascard, J., Hatcher, P.E., Melander, B., and Upadhyaya, M.K., 2007.
Thermal Weed Control. Pp. 155-176.
[14] Aladjadjiyan, A., 2010. Effect of Microwave Irradiation on Seeds of
Lentils. Romanian Biophys., Vol.20, No:3, P:213-221, Bucharest,
2010.
[15] Fogelberg, F., 2004. Water-Jet Cutting of Potato Tops: Some
Experiences from. Sweden. P.111.
[16] Sahin H., Saglam R, 2015 “A Research about Microwaves Effects
on.Germination of Weed Plants”, Arpn Journal of Agricultural and
Biological. Science. Vol.10, No:3
[17] Sahin, H., 2014, Effects of Microwaves on Germination of Weed
Seeds, Journal of Biosystem Engineering 39(4):304-309. (2014. 12).
[18] Taheri, S., Brodie, G., Jacob, M. V., & Antunes, E. (2018). Dielectric
properties of chickpea, red and green lentil in the microwave
frequency range as a function of temperature and moisture
content. Journal of Microwave Power and Electromagnetic
Energy, 52(3), 198-214.
[19] Weis, M., Gutjahr, C., Ayala, V. R., Gerhards, R., Ritter, C., &
Schölderle, F. (2008). Precision farming for weed management:
techniques. Gesunde Pflanzen, 60(4), 171-181.
[20] Gage, K. L., & Schwartz-Lazaro, L. M. (2019). Shifting the
Paradigm: An Ecological Systems Approach to Weed Management.
Agriculture, 9(8), 179.
[21] Armstrong, D. L., Leasure, J. K., & Corbin, M. R. (1968). Economic
comparison of mechanical and chemical weed control. Weed
Science, 16(3), 369-371.
[22] Nelson, S. O. (2008). Dielectric properties of agricultural products
and some applications. Research in Agricultural Engineering, 54(2),
104-112.
[23] Vincent, Charles, Bernhard Panneton, and Francis Fleurat-Lessard,
Eds. Physical Control Methods in Plant Protection. (Page 174-179).
Springer Inra Editions, 2001.
[24] Khaled, D. E., Novas, N., Gazquez, J. A., Garcia, R. M., & Manzano-
Agugliaro, F. (2015). Fruit and vegetable quality assessment via
dielectric sensing. Sensors, 15(7), 15363-15397.
[25] Van Emmerik, T., Steele-Dunne, S. C., Judge, J., & Van De Giesen,
N. (2016). Dielectric response of corn leaves to water stress. IEEE
Geoscience and Remote Sensing Letters, 14(1), 8-12.
[26] Nelson, S. O. (2018). RF Electrical Seed Treatment to Improve
Germination. In 2018 ASABE Annual International Meeting (p. 1).
American Society of Agricultural and Biological Engineers.
[27] Jacob, J., Khadar, M. A., Lonappan, A., & Mathew, K. T. (2008).
Microwave dielectric properties of nanostructured nickel
ferrite. Bulletin of Materials Science, 31(6), 847.
[28] Bajwa, A. A., Mahajan, G., & Chauhan, B. S. (2015).
Nonconventional weed management strategies for modern
agriculture. Weed science, 63(4), 723-747.
[29] Rana, A., & Derr, J. F. (2018). Responses of Ten Weed Species to
Microwave Radiation Exposure as Affected by Plant Size. Journal of
Environmental Horticulture, 36(1), 14-20.
[30] Lundensia, A. S., & Persson, B. (2015). Destruction of seeds from
Sinapsis Alba, var. Emergo with 50 mM Ca2+ and high voltage
pulses. Acta Scientiarum Lundensia, 2, 1-14.
[31] Ivanovich, B. V., & Viktorovich, Y. I. (2018). Efficiency Estimation
of Type of the Electrical Exposure On Plants at Theır Processing. Ad
Alta: Journal of Interdisciplinary Research, 8(1).
[32] Rona, S. A., Valverde, B., De Souza, D. T. M., & de Andrade
Coutinho Filho, S. (2019). Weed inactivation device.
[33] Gogo, E. O., Huyskens-Keil, S., Krimlowski, A., Ulrichs, C.,
Schmidt, U., Opiyo, A., & Dannehl, D. (2016). Impact of direct-
electric-current on growth and bioactive compounds of African
nightshade (Solanum scabrum Mill.) plants. Journal of Applied
Botany and Food Quality, 89.
H. SAHIN was born in Turkey. He is an Assist. Prof.
Dr. at Harran University in Turkey. He received his
B. Sc. Eng. and M. Sc. Eng. degrees in Mechanical
Engineering from Engineering Faculty of Harran
University. He received Ph. D. degree in Agricultural
Machinery Engineering from same University in
2012. His main research interests are non-chemical
weed technologies, agricultural solar applications,
heating-cooling systems and microwave weed
management. He is currently a lecturer at the
Department of Agricultural Machinery Engineering at Harran University.
He is a member of UCTEA Chamber of Mechanical Engineers in Turkey.
He supervises M. Sc. students from Department of Agricultural Machinery
Engineering.