ARID ZONE JOURNAL OF ENGINEERING, TECHNOLOGY & ENVIRONMENT
AZOJETE - CIGR Section VI Special Issue:

Innovation & Technologies for Sustainable Agricultural Production & Food Sufficiency
AZOJETE, December, 2018. Vol. 14(SP.i4): 219-224

Published by the Faculty of Engineering, University of Maidiguri, Maidiguri, Nigeria.

Print ISSN: 1596-2490, Electronic ISSN: 2545-5818
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*Corresponding author Email address: mo.omobowale@ui.edu.ng

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ORIGINAL RESEARCH ARTICLE

COMPARATIVE EVALUATION OF NOVEL LOW-COST MOISTURE METERS SUITABLE
FOR GRAIN MOISTURE MEASUREMENT

S. K. Ajao1, M. O. Omobowale*2, K. O. Popoola1, A. A. Ala1, G. P. Opit3
1Department of Zoology, University of Ibadan, Nigeria;

2Agricultural and Environmental Engineering Department, University of Ibadan, Nigeria;
3Department of Entomology and Plant Pathology, Oklahoma State University, Stillwater, OK, USA.

ARTICLE INFORMATION

Received: October, 2018
Accepted: December, 2018

Keywords:
Moisture content
Maize
Moisture meter
Postharvest loss
Grain quality

ABSTRACT
Monitoring grain quality is an important postharvest activity which
starts at harvest, continuing during storage and up to the point of
sale. High moisture in stored maize can be detrimental to food
safety because of the likelihood of aflatoxin contamination and
other forms of deterioration. Moisture meters are devices which
provide real-time access to measuring moisture levels thereby
allowing farmers to meet grain quality requirements. A newly
developed low-cost moisture meter known as the Post-Harvest Loss
(PHL) moisture meter is a device with potentials for massive
deployment among smallholder farmers. This study was therefore
set up to compare the efficiencies of some existing moisture meters
compared with this newly developed device. Two commercially
available moisture meters — Dickey john GAC 2100 and John Deere
meters were compared with the PHL moisture meter and oven-
dried method (ASABE standards) used as control. Maize grains from
a bagged storage experiment were used as samples over a 12-
month period. Results showed that the moisture meters had a
positive difference of ˂3% MCwb relative to oven-dried method.
Average measurements showed variances of 2.34, 1.08 and 0.56%
MCwb for John Deere, PHL and GAC 2100 meters respectively, when
compared with the oven-dried method. Thus, it was concluded that
the low cost PHL moisture meter may serve as an effective
alternative to the more expensive types and may be relatively easy
to adopt for laboratory and field use among smallholder farmers in
sub-Saharan Africa.

©2018 Faculty of Engineering, University of Maiduguri, Nigeria. All rights reserved

1.0 Introduction
The quality of grain is influenced by its moisture content (MC) (Rai et al., 2005). It is one of the
important parameters considered when deciding price and quality at the stage of harvest,
storage, processing and marketing. High moisture can lead to quality reduction and even crop
loss during storage (Armitage et al., 2008). When storage environments are not properly
maintained, quality and economic losses can occur from such agents as mold growth and insect
damage, which are usually the two most troublesome problems in modern grain storage

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Ajao, et al. Comparative evaluation of novel low-cost moisture meters suitable for grain moisture measurement.
AZOJETE, 14(sp.i4):219-224. ISSN 1596-2490; e-ISSN 2545-5818, www.azojete.com.ng

220

structures. Appropriately low grain moisture contents and low grain temperatures are the
primary weapons for preventing mold and insect infestations (Casada and Armstrong, 2008).
There are two basic methods of determining the MC of biomaterials –the primary/direct and
secondary/indirect methods (Obi et al., 2016). A primary moisture measurement method involves
determining the mass of an undried and dried sample to determine the amount of water in the
sample (Armstrong et al., 2017). In secondary methods, the MC is determined indirectly from the
empirical relationship between physical and chemical features and the actual MC obtained from
primary methods such as standard oven drying methods (Chen, 2003). Some common
instruments used in secondary methods such as moisture meters and probes rely on the
electrical characteristics of the grain, such as capacitance and conductance (Armstrong et al.,
2017) and are calibrated against the oven-based moisture determinations.

Heating whole grain in a hot air oven is the most widely used method for moisture content
determination (ASAE, 2002), however the long drying time necessitated the development of
moisture meters and probes. The need for a low-cost moisture meter in developing countries
has been advocated for several years to help mitigate postharvest losses of grain (World Bank,
2011; Maier, 2015). Fast as well as field usable portable grain moisture meters and probes are a
necessity to meet the requirements of farmers, grain storage personnel and agricultural products
marketing corporations (Rai et al., 2005).
Commercially available moisture meters include two low cost meters by developed country
standards; the Post-Harvest Loss (PHL) meter which was developed under a USAID project to
reduce post-harvest loss (~US$100) and John Deere portable device (~US$260, 2018 price). The
GAC 2100 bench-top moisture meter is an approved moisture tester by the Grain Inspection,
Packers and Stockyards Administration (GIPSA) and has been a highly regarded and used
electronic meter (~US$3600, 2018 price).

The objective of this research was to demonstrate the accuracy of three moisture meters
compared to the oven-dried reference method. The meters are — Post-Harvest Loss (PHL) meter
developed by the USDA-ARS Center for Grain and Animal Health Research, Manhattan KS, John
Deere Moisture Chek PLUS, model SW08120 (AgraTronix Streetsboro, Ohio) and Grain Analysis
Computer GAC 2100 Agri (DICKEY-john Corp., Auburn, Ill.). Both laboratory and field tests of
these four moisture measurements were carried out to validate their performance and to
provide basic information on moisture levels of maize over a 12-month storage period.

2.0 Materials and methods
2.1 Maize
Maize used in this study was sourced from a single local farm in order to ensure uniformity of
maize used for the study. Moisture content measurements of maize samples were collected
during a study of insect infestation of bagged grains in a storehouse located in Arisekola market,
Bodija, Ibadan (7°25’59 N, 3°54’43 E) from February 2017 – January 2018. Batches of 50 kg of
maize were placed individually in bags according to the various treatments as follows: (1)
untreated polypropylene (PP) bags,(2) Insecto diatomaceous earth–treated PP bags, (3) PICS
bags, (4) PP bags with a single hermetic liner, (5) ZeroFly storage bags, (6) Insecto diatomaceous
earth-treated ZeroFly storage bags, (7) ZeroFly storage bags with two PICS bag hermetic inner
liners and (8) ZeroFly storage bags with a single hermetic liner. Each bag had three sub-
replicates and were measured for each treatment. Monthly moisture measurements were taken

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221

for non-hermetic treatments while moisture measurements were taken every four months for
the hermetic treatments.

2.2 Moisture content measurement and data collection
2.2.1 Post-Harvest Loss (PHL) meter
The PHL meter was used by inserting the probe deep into each storage bag of maize in the
storehouse, left initially to stabilize over a 6-minutes period and then the temperature (°C) and
relative humidity (%) of air surrounding the grain determined was used to calculate and display
the moisture content of the grain. Three measurements were taken from each bag — at the
center, and opposite sides of the bag and the average moisture content, weight basis (MCwb)
calculated for each bag. This procedure was performed in the storehouse.

Inaddition to the field moisture data, a 1.2m open-ended grain probe (Seedburo Equipment,
Chicago, IL) was used to sample maize from bags. Composite samples were taken from the
center and opposite sides near the inner surface of each bag and placed inside labelled Ziploc
bags. Samples collected were then transported to the laboratory for data collection. About 700 g
samples collected from each bag were mixed thoroughly in a tray to ensure homogeneity for
moisture readings with GAC 2100, John Deere moisture meters and Oven-dried method.

2.2.2 GAC 2100 moisture meter
Maize sample was poured into the top unit of the moisture meter; the load key was depressed
and the sample automatically loads the grain into the test cell and a strike-off arm levels and
removes the excess. After about 15 seconds, the moisture reading and grain temperature was
displayed on its LCD. Three sample measurements were taken and the average MCwb was
calculated for each bag. Moisture reading for the first month (February 2017) was however not
available at the beginning of the study.

2.2.3 John Deere moisture meter
Sampled grain was scooped with a hollow plastic spoon into the top chamber of the meter and
the cap screwed on to compress the grains around the electrodes. A uniform pressure was
maintained on the test sample by a plunger in the cap which contains a heavy spring, allowing
the plunger shaft to protrude through the cap as pressure on the grain increases. The plunger
shaft was set flush with the surface of the cap each time a sample was tested. The unit was
powered by two 9V batteries to run the backlight display and the microprocessor which then
reports the water content and temperature of grains digitally. Three sample measurements were
taken and the average MCwb was calculated for each bag.

2.2.4 Oven–dried method
100 g samples (replicated two times) were oven-dried at 103°C for 72 hours (ASABE, 2008) using
a Memmert UF 55 Model 30-750 oven (Memmert GmbH + Co. KG, Schwabach). After heating,
the samples were allowed to cool inside a dessicator and the MCwb was calculated for each bag.
Two sample measurements were recorded and the average MC was calculated for each bag.

2.3 Statistical analysis
Data were summarized using the SPSS version 20 software to evaluate means of each response
variables.

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Ajao, et al. Comparative evaluation of novel low-cost moisture meters suitable for grain moisture measurement.
AZOJETE, 14(sp.i4):219-224. ISSN 1596-2490; e-ISSN 2545-5818, www.azojete.com.ng

222

3.0 Results and Discussion
3.1 Grain moisture content
In the non-hermetic bags where monthly moisture measurements were taken, moisture levels
recorded by the four methods in the bagged maize were higher at the end of the study
compared with moisture levels at the beginning (Fig. 1). In the hermetic bags, slight increases in
moisture readings were observed in months when measurements were taken (Fig. 2). MCwb
readings using the oven-dried method were uniformly lower than all the 3 moisture meters used
(Figs. 1 and 2). Among the moisture meters, GAC 2100 meter readings were consistently lower
than the PHL and John Deere meters. There were variations in the monthly measurements of
moisture in the triplicate bags during storage period. Moisture readings progressively increased
during the rainy season (April to October) but fell during the dry season (November to January).
High humidity observed during the rainy season which allows moisture gain from the
surrounding air and low humidity during the dry season accounted for the initial gain and later,
loss of moisture from the grains during the study. This appears to show that bagged grains
respond readily to monthly variation in climatic conditions (Armstrong et al., 2017). Combined
moisture measurement for all bags (hermetic and non-hermetic) showed that the John Deere,
PHL and GAC meter readings had mean positive differences of 2.34 ± 0.34%, 1.64 ± 0.27% and
1.08 ± 0.31% MCwb respectively, relative to the oven-dried method. Comparing the moisture
meters, John Deere meter had a mean positive variance of 1.26 ± 0.38% MCwb relative to GAC
2100 and PHL meter had a mean positive variance of 0.56 ± 0.25% MCwb. This result was in
agreement with Armstrong et al., 2017 who showed that PHL meter readings were lower than
John Deere moisture meter stating average positive differences of 0.45% and 2.12% MCwb for
PHL and John Deere meters respectively, relative to the GAC 2100 meter. Overall, moisture levels
in the bagged maize over the 12–month storage period were within safe levels for maize storage;
an average of 12.82% MCwb was recorded in all the bags. The highest moisture level recorded
for any bag was 15.5% using John Deere meter.

4.0 Conclusion
The use of robust moisture meters is important for farmers and grain managers to constantly
monitor moisture levels of stock. The PHL meter, John Deere meter and GAC 2100 meter provide
simple and rapid prediction of moisture readings of stored grains in the field and laboratory,
thus enabling farmers to make quick decisions on the maintenance of quality of their grains.

5.0 Acknowledgement
We thank the USDA/USAID funded Nigeria Agriculture Capacity Strengthening Program for the
moisture meters used in this study. Special thanks to the Food and Nutrition Laboratory, IITA
Ibadan for providing bench space to conduct the oven dried test. This study was funded by the
Swiss Agency for Development and Cooperation. Mention of proprietary product does not
constitute a guarantee of the product by the authors, institutions and sponsor, and does not
imply its approval to the exclusion of other products that may also be suitable.

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Fig 1: Monthly moisture measurement in the non-hermetic bagged maize from February 2017
to January 2018.

Fig 2: Quarterly moisture measurement in the hermetic bagged maize from February 2017 to
January 2018.

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Ajao, et al. Comparative evaluation of novel low-cost moisture meters suitable for grain moisture measurement.
AZOJETE, 14(sp.i4):219-224. ISSN 1596-2490; e-ISSN 2545-5818, www.azojete.com.ng

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