This is the presentation of my review paper published in Proceedings of 21st International Conference on Hydraulics, Water Resources and Coastal Engineering held at CWPRS, Pune

1. APPLICATION OF SOIL
MOISTURE SENSOR: A
REVIEW
A N C H I T G A R G , P R I Y A M I T R A M U N O T H , R O H I T G O Y A L
M A L A V I Y A N AT I O N A L I N S T I T U T E O F T E C H N O L O G Y, J A I P U R
E M A I L : 2 0 1 5 P C D 5 3 5 5 @ M N I T. A C . I N
2 1 s t I n t e r n a t i o n a l C o n f e r e n c e o n
H y d r a u l i c s , W a t e r R e s o u r c e s a n d C o a s t a l
E n g i n e e r i n g
C W P R S , P u n e

2. INTRODUCTION
• The world, at present is facing shortage of water which is hampering the development
of agriculture and hence the food production. Agriculture is by far the largest consumer
of the Earth’s available freshwater: 70% of water withdrawals from watercourses and
groundwater are for agricultural usage, three times more than 50 years ago. By 2050,
the global water demand of agriculture is estimated to increase by a further 19% due to
irrigational needs. Approximately 40% of the world’s food is currently cultivated in
artificially irrigated areas. In addition, in the coming years, climate change will bring
about enormous and partly unpredictable changes in the availability of
water. (http://www.globalagriculture.org)
Total water withdrawal in 2010 = 761km3
(Source: FAO, 2010)
Water use in different sectors of India
Fig 1: Water use in different sectors of

3. • Under-irrigation and over-irrigation are common phenomena in agriculture and
landscapes. Over-irrigation of plants leads to deficiency of oxygen in the root zone as
excess water in the pores decrease oxygen in the pores of the soil. Also, in this water-
deficient world, saving water is becoming necessary.
• The soil moisture parameter in such situations play a lead role in helping the growers
know the exact amount of watering to be done. The soil moisture can be measured in
two following methods:-
a) Direct methods – least expensive methods. Eg: Feel & inspection method, Hand
push probe and Gravimetric method
b) Meters and Sensors – All those which are based on tensiometric or dielectric
sensors. Eg: tensiometer, gypsum blocks, TDR, FDR etc.

4. Soil-Water Relationship:-
Water availability is illustrated in the figure by
different water levels. Excess or gravitational
water drains quickly from the soil after a heavy
rain because of gravitational forces (saturation
point to field capacity). Plants may use small
amounts of this water before it moves out of the
root zone. Available water is retained in the
soil after the excess has drained (field
capacity to wilting point). This water is the
most important for crop or forage production.
Plants can use approximately 50 percent of it
without exhibiting stress, but if less than 50
percent is available, drought stress can result.
Unavailable water is soil moisture that is held
so tightly by the soil that it cannot be extracted
by the plant. Water remains in the soil even
below plants' wilting point. (Jeff Ball, 2001)
(Yonts et al., undated)Fig 2: Soil-Water Relationship

5. DIFFERENT TYPES OF SOIL MOISTURE
SENSORS
Soil water tension based sensors:-
1. Tensiometer
2. Granular matrix sensor

6. TENSIOMETER
Fig 3:
Tensiometer
Rapid,
easy,
inexpensiv
e
Can be used
in freezing
and thawing
conditions
Ideal for
sandy loam
and light
textured
soils
Periodic
maintenance
Malfunctions when
soil water tension
> 80 cb
Measures tension
only in vicinity
Enciso-Medina et al., 2007
Schmugge et al., 1979
Alam et al., 1997
Hensley et al., 1999
Werner, 2002
Goodwin, 2009

7. Different response
to different soil
types
GRANULAR MATRIX SENSOR
Fig 4: Granular Matrix
Sensor
Less
maintenance
in
comparison
to
tensiometer
Cheaper
than
tensiometer
Less
changes to
varying
temperature
s
Not responsive to
rains < 0.5 in.
Less accurate in
sandy soils
Shock et al., 1998
Irmak et al., 1990
Enciso-Medina et al., 2007
Berrada et al., 2014
Zazueta et al., 1994

8. DIFFERENT TYPES OF SOIL MOISTURE
SENSORS
Soil water content based sensors:-
1. Time Domain Reflectrometry
2. Frequency Domain Reflectrometry

9. Need to be
calibrated carefully
TIME DOMAIN REFLECTROMETRY (TDR)
Fig 5: TDR
unit
Responds
quickly to
varying soil
moisture
Readings at
multiple
depths with
single probe
Very little
disturbance
at test site
Costly & Cannot
be used in highly
saline soils
Reads soil
moisture only in its
vicinity
Marenghi, 2013
Pitts, 2016
Skierucha et al., 2012
Paige et al., 2008
Blonquist et al., 2005
Wolpert et al., 2013

10. Requires soil
specific calibration
FREQUENCY DOMAIN REFLECTROMETRY
(FDR)
Fig 6: FDR
unit
Very
accurate
Can be used
in highly
saline soils
Measures
SM at
several
depths in
same
location
Formation of sir
gaps , if sensor &
soil don’t make
good contact
Reads soil
moisture only in its
vicinity
Abouatallaha et al., 2011
Muñoz-Carpena et al., 2004
Linmao et al., 2012
Muñoz-Carpena et al., 2004
Wolpert et al., 2013

11. VH400 SOIL MOISTURE SENSOR
• Capacitance-based, small and rugged (Salih et al., 2013)
• Low cost monitoring of soil moisture, waterproof
• Rapid response time, more sensitive at higher water content
• Low power consumption (< 7mA) (www.vegetronix.com)
• Insensitive to salinity of water, does not corrode over time (Zaier et al., 2013)
• Can be operated in wide range of temperature (-40 oC to 85 oC) (www.vegetronix.com)
• Data logger is means of communication between the sensor to the user.
• Data logger can store and relay readings through SMS, SD Cards and Bluetooth

12. • Increasing demand of water and food is creating stress on the water resources. The
use of soil moisture sensors helps growers with irrigation scheduling by providing
information about when to water the crops.
• The irrigation water applied to the soils can be controlled and automated using soil
moisture sensors which help in determining the available water of the soil. This leads
to judicious use of water.
• Since, there are variety of sensors available in the market, the growers must consider
various factors while selecting the appropriate sensor for their use.
• The advantages and disadvantages of sensors must be considered as criteria for
selection because the working principle behind each type of sensor varies with its
application and type of soil.
• The VH400 sms is rapid and small capacitance-based sensor and its output can be
relayed on data logger through SMS, bluetooth and SD cards
• The wireless sensors in agriculture increases efficiency, productivity, profitability of
farming operations and maximises crop yield with minimum use of irrigation water.
CONCLUSION

13. REFERENCES
1. Ball J (2001) “Soil and Water Relationships”, article published on The Samuel Roberts
Noble Foundation, http://www.noble.org/ag/soils/soilwaterrelationships/
2. Global Agriculture Report, http://www.globalagriculture.org/report-topics/water.html
3. Yonts D, Benham B (undated) Irrigation Chapter-3: Soil water. Plant & Soil Sciences e-
library,.
http://passel.unl.edu/pages/printinformatonmodule.php?idinformationmodule=113044713
9&idcollectionmodule=1130274164
4. www.globalagriculture.org
5. Food and Agriculture Organisation, 2010
6. Zaier R, Zekri S, Jayasuriya H, et al. (2015) Design and implementation of smart irrigation
system for groundwater use at farm scale. International Conference on Modelling,
Identification and Control (ICMIC 2015)
7. Zazueta SF, Xin J (1994) Soil moisture sensors. Bulletin 292, Florida Cooperative
Extension Service, Institute of Food and Agricultural Sciences, University of Florida
www.experimental-hydrology.net/wiki/index.php?title=Soil_moisture_-

14. 8. Enciso MJ, Porter D, Périès X (2007) Irrigation monitoring with soil water sensors.
Cooperative Extension, B-6194, The Texas A&M University System.
9. Schmugge TJ, Jackson TJ, McKim HL (1979) Survey of methods for soil moisture
determination. NASA Technical memorandum
10. Werner H (2002) Measuring soil moisture for irrigation water management. Cooperative
Extension Services, College of Agriculture and Biological Sciences, South Dakota State
University. http://agbiopubs.sdstate.edu/articles/FS876.pdf
11. Hensley D, Deputy J (1999) Using tensiometers for measuring soil water and scheduling
irrigation. Coopertive Extensive Service. Department of horticulture, College of tropical
agriculture & human resources, University of Hawaii at Manoa. Landscape L-10.
12. Goodwin I (2009) How to use tensiometers?. Department of environment and primary
industries, Agriculture Victoria: ISSN 1329-8062
13. Irmak S, Payero OJ, Eisenhauer ED, Kranz LW, Martin LD, et al., (2006) Watermark
Granular Matrix Sensor to Measure Soil Matric Potential for Irrigation Management.
Extension EC783, Institute of Agriculture and Natural Resources, University of
Nebraska-Lincoln
14. Berrada A, Hooten MT, Cardon EG, Broner I (2001) Assessment of irrigation water
management and demonstration of irrigation scheduling tools in the full service area of
the Dolores project: 1996-2000. Technical Report, TR01-7, Colorado State University

15. 15. Marenghi P (2013) Soil moisture sensor: Types and technology.
http://www.auroras.eu/soil- moisture-sensor-types-and-technology/
16. Pitts Larry (2016) Monitoring soil moisture for optimal crop growth.
https://observant.zendesk.com/hc/en-us
17. Skierucha W, Wilczek A, Szypłowska A, Sławiński C, Lamorski K (2012) A TDR-
based soil moisture monitoring system with simultaneous measurement of soil
temperature and electrical conductivity. Sensors 10: 13545-13566. DOI:
10.3390/s121013545
18. Paige BG, Keefer OT (2008) Comparison of field performance of multiple soil
moisture sensors in a semi-arid rangeland. Journal of the American Water
Resources Association (JAWRA) 44(1):121-135. DOI: 10.1111/j.1752-
1688.2007.00142.x
19. Blonquist JM, Jones SB, Robinson DA (2005) A time domain transmission sensor
with TDR characteristics. Journal of Hydrology, 314:235-245.
20. Wolpert J (2013) Soil moisture sensors. University of California, Extension,
articles.extension.org/pages/31515/soil-moisture-sensors
21. Salih Md. EJ, Adom HA, Shakaff Md. YA, Shuib AM (2013) Real time wireless
agricultural ecosystem monitoring for cucumus melon Cultivation in natural ventilated

16. E-mail:-
2015PCD5355@MNIT.AC.IN
ANCHIT141991@GMAIL.CO
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