The objective is to determine the moisture content of seeds using methods suitable for routine use.
Seed moisture content is the percentage of weight loss when a seed sample is dried and is expressed as a percentage of the original sample weight. It is a crucial factor in maintaining seed quality.
Weight of the Submitted Sample
Materials Required
Grinding Mill
It should be constructed of non-absorbent material. It should grind evenly and should be operated at such a speed that during grinding, it should not cause heating of the ground material. Air currents that might cause loss of moisture must be reduced to a minimum. The fineness of grinding should be adjustable.
Container
Glass or non-corrosive metal (e.g., stainless steel).
Oven
Grinding
For some seeds (e.g. Cereals and Cotton) fine grinding is essential before the moisture content is determined. In such cases, at least 50% of the ground material should pass through a wire sieve with meshes of 0.5 mm and not more than 10% remain on a wire sieve with a mesh of 1.0 mm. For leguminous seeds, coarse grinding is recommended; at least 50% of the ground material shall pass through a wire sieve with meshes of 4.0 mm.
Pre-Drying
If the species is one for which grinding is necessary and the moisture content is more than 17%. (or 10% in the case of soy bean and 13% in rice) pre drying before grinding is necessary. For this purpose, two 50 g portions are weighed and placed on open trays at 130°C for 5-10 min. If seed moisture content is about 25% or more it should be pre-dried at 70° C for 2-5 hours, depending on the initial water content. The pre dried seeds should be kept in a closed desiccator for cooling. Then each of the duplicate quantities is weighed separately and about 20 g is ground. The ground material is then subjected to moisture testing using a hot air-oven as described below.
Moisture Estimation
It should be carried out in duplicate on two independently drawn 5-10 g working samples, weighed with an accuracy of 1 mg. Most species are dried for 1 hr at 130° C, cereals for 2 hours (130°C) and maize for 4 hours (130°C). Seeds containing high percentage of oil should be dried at 103°C for 17 hours.
Steps:
Moisture meters work based on the principle that wet grains are better conductors of electricity, while dry grains are less conductive. Therefore, the moisture content of seeds is directly proportional to their electrical conductivity.
These meters include a compression unit to compress the sample to a predetermined thickness. The thickness setting can be easily read on a vertical and circular scale. The seed material to be tested is placed in a test cup and compressed. Then, a push-type switch is pressed until the reading appears on the display. There is no need for temperature readings and correlated dials. In the computer version of digital moisture meters, temperature corrections are automatically compensated for.
Seed standards for moisture content
1. What is moisture content? |
2. Why is the determination of moisture content important? |
3. How is moisture content determined? |
4. What are the factors that affect moisture content determination? |
5. What are the limitations of moisture content determination? |
|
Explore Courses for UPSC exam
|