1. Department of Agricultural and Biosystems Engineering 4/11/17
Low Cost Method of Determining Maize Moisture Content for Small Holder Farmers in Uganda
Noelle Hinrichs
Department of Agricultural and Biosystems Engineering 4/11/17

2. Farmers in Uganda drying maize in the sun.
Introduction
Maize (corn) is an important food for many people in developing countries, and critical to many small holder farmers in Uganda.
Maize is harvested wet (>20% moisture) and must be dried to <13% moisture for safe storage.
Insufficiently dried maize will mold if put into storage.
Aflatoxin, a carcinogen, is a result of the aspergillus fungus that grows on moist corn in storage.
Maize moisture cannot be reliably determined by observation – it must be measured.
Electronic meters used in the developed countries are too expensive for small holder farmers in developing countries.
A low-cost method of determining maize moisture content is needed.
Farmers in Uganda drying maize in the sun.

3. How do we measure maize moisture?
Oven dry method.
Measure the change in weight after 72h at 103C
The official standard, but impractical in the field.
Electronic moisture testers.
Moisture content is proportional to the dielectric properties of maize.
Hand-held meters cost $250 or more.
Equilibrium moisture content.
Maize in a sealed container will come to moisture equilibrium with the air.
The relationship between moisture content, temperature and relative humidity is known (Chung-Pfost equation, ASABE Standard D324.2)
Relationship between temperature, relative humidity and moisture content.

4. A Low-cost Method?
Could a low cost hygrometer be used to measure the equilibrium temperature and relative humidity?
Previous research at Purdue University determined that relatively low-cost hygrometers (<$5) were accurate enough for small holder farmers to use.

5. Objectives Replicate and verify the previous research.
Determine if low-cost hygrometers are accurate and simple enough for small holder farmers in Uganda to use in order to determine maize moisture content.
If the low-cost hygrometers are accurate and simple enough, these farmers can use the to know whether or not the maize is dry enough to store safely.

6. Experiment #1 - Hygrometers
20 hygrometers were purchased on Amazon.
Manufactured in China, two different suppliers.
Cost was $2 to $6, although they appear to be the same.
There was no documentation on performance.
Hygrometers were placed in an environment of known temperature and relative humidity.
Saturated salt solutions (NaBr, NaCl, and KCl) in a sealed container result in known a relative humidity.
Hygrometer temperature and relative humidity readings were compared to known conditions to determine accuracy.

7. Hygrometer Testing: Trial 1 (jars)
Average error
At 58% RH: ± 9.5 percentage points
At 75% RH: ± 8.1 percentage points
At 83% RH: ± 8.25 percentage points

8. Hygrometer Testing: Trial 2 (bags)
Average error
At 58% RH: ± 7.1 percentage points
At 75% RH: ± 25.9 percentage points
At 83% RH: ± 16.7 percentage points

9. Hygrometer Testing: Trial 3 (bags)
Average error
At 58% RH: ± 3.5 percentage points
At 75% RH: ± 13.6 percentage points
At 83% RH: ± 20.3 percentage points

10. Sources of Error
Too much water could have been added to the salt solution.
Water could have spilled out of the weighing tins.
Leakage could have occurred due to the bags used.

11. Experiment #2 - Maize
Hygrometers shown to be “accurate” were selected for further testing.
Maize of four levels of moisture content (MC) were created by adding calculated amounts of water and allowing them to come to equilibrium.
10.8% (initial, no water addition), 12%, 15% and 18%
MC verified with an electronic meter.
Maize placed in a small plastic bag with the hygrometer (triplicates) and allowed to come to equilibrium, then RH and temperature recorded.
Predicted MC compared to known MC.

12. Boerner Divider used to get unbiased samples of corn
Hygrometer at equilibrium with air, showing relative humidity percentage

13. Maize Testing: In progress
Preliminary results at 21C
Actual MC (%)
Predicted MC (%)
Error
10.8
10.7
-0.1
13.0
13.5
0.5
14.9
16.3
1.4
19.8
19.3
-0.5

14. Conclusions So Far The hygrometers accurately measured temperature.
Some hygrometers did not accurately predict relative humidity.
More of a problem than what was stated by the original research.
Hygrometers must be individually tested before use to determine if they are “accurate enough.”
Accurate enough = ± 5 percentage points RH
It appears that hygrometers that pass initial tests will be accurate enough to be used by small holder farmers in Uganda.

15. Acknowledgements Sukup Manufacturing Company
Iowa State University – Honors Research Grant
Dr. Thomas Brumm
Sam Cook

16. Department of Agricultural and Biosystems Engineering 4/11/17
Low Cost Method of Determining Maize Moisture Content for Small Holder Farmers in Uganda
Noelle Hinrichs
Department of Agricultural and Biosystems Engineering 4/11/17