Brief introduction of standard moisture determination method of seed moisture index

In the standard method, the seed moisture index is a required item. This article introduces the methods, procedures and precautions for the determination of seed moisture, which provides a reference for the standardized and standardized determination of seed moisture.

According to the "Crop Seed Inspection Regulations", the four quality indicators of seed purity, purity, germination rate, and moisture are mandatory items for seed inspection. The quality indicators implement the national mandatory standards. If an index fails to meet the standards stipulated by the state, it will be judged as unqualified seed. As a water reflecting one of the seed quality indicators, if it fails to meet the standards stipulated by the state, it will cause a considerable economic loss to a seed production or business enterprise, which must not be taken lightly [1]. For example: Originally a batch of qualified seeds, but because of the inaccurate water detection data, making it "unqualified" seeds, so that the company spent a lot of manpower and material resources to turn warehouses, dry, and even received financial penalties and suffered unnecessary economic losses . On the contrary, it was originally a batch of seeds with excessive moisture, but the inaccurate measurement data made it a "qualified" seed, which would make seed companies relax their vigilance, flow into the market, harm farmers' interests, and cause greater economic losses.

For a long time, it has been one-sidedly believed that as long as the other three items meet the standard, as for the moisture, it is a matter of insignificance. Practice has proved that this understanding is wrong. The level of seed moisture directly affects seed transportation, safe storage and seed life. Because some seed companies do not pay enough attention to the determination of seed moisture, the seeds suffer frost damage and mildew rot, and finally the accidents that cause serious loss of seed vigor occur frequently. The lesson is extremely profound. Therefore, correctly grasping the procedures and methods of moisture determination and issuing scientific and accurate moisture detection data [2, 3] are crucial for both seed companies and seed inspection agencies.

1 Moisture determination method and equipment

1.1 Method of moisture determination

Seed moisture refers to the percentage of the weight of free water and bound water in the seed to the original weight of the seed. At present, the commonly used methods for measuring the moisture of seeds are drying weight loss method (including drying method, infrared drying method) and electronic electronic moisture meter rapid measurement method (including resistance type, capacitive type and microwave type moisture analyzer), and the general formal report The standard method of oven is used for the determination of seed moisture. This article also takes the standard method as an example for specific explanation.

1.2 Moisture determination equipment

(1) Drying box. The drying oven has electric heating constant temperature drying oven and vacuum drying oven. At present, the electric heating constant temperature drying box is commonly used, which is mainly composed of a box body (heat preservation part), a heating part and a constant temperature part.

(2) Electric grinder. For grinding samples, there are two types of hob type and grinding disc type.

(3) Analyze the balance. Weighing is fast, and the sensed amount reaches 0.001g.

(4) Sample box. Commonly used is the aluminum box, the box and the lid are marked with the same number, compact and suitable, the specifications are 4.6cm in diameter, 2.0 ~ 2.5cm in height, the sample is 4.5 ~ 5.0g, can reach the thickness of the sample in the box 1cm2 does not exceed 0.3g Requirements.

(5) Dryer. Used to cool dried samples or sample boxes.

(6) Others. Need to mark cleaned grinding bottle, weighing spoon, coarse yarn gloves, writing brush, crucible tongs, etc.

2 Procedure for moisture determination

2.1 Inspection of samples for inspection

After a sample is delivered to the inspection room, according to the characteristics of moisture determination, it must first be inspected in three aspects [4]:

(1) Label inspection. Check whether the sample number, variety name and inspection item marked on the label on the container are consistent with those registered on the corresponding delivery card.

(2) Container inspection. Check whether the sample to be submitted is in a moisture-proof container and the seal is intact.

(3) Weight check. According to the requirements of moisture determination, the weight of the type to be ground should be no less than 100g, and the weight of the type not to be ground should be no less than 50g. Check whether the weight of the sample for inspection meets the requirements.

All of the above three aspects meet the requirements, and the relevant inspector must sign the transfer card before proceeding to the next procedure, otherwise the sample will be returned to the business room.

2.2 Make preparations for moisture determination

(1) Constant weight of aluminum box. After washing the to-be-used aluminum box (including the box lid), it is dried at 130 ° C for 1 hour. After taking out, it is cooled and weighed. After continuing to dry for 0.5 hours, it is cooled and weighed after taking out. When ≤0.002g, take the average weight twice; otherwise, continue to dry to constant weight.

(2) Dry the grinding bottle. After washing the grinding bottle (including stopper) to be used, it is dried at 130 ℃ for 0.5h, taken out and cooled down for use.

(3) Pre-adjust the balance. Turn on the rough balance and the balance with a sense of 0.001g in advance and level it to make it in a normal working state.

(4) Check the crusher. The sample to be ground should be checked in advance, clean the electric grinder, and choose the appropriate size sieve.

(5) Dryer inspection. Check the moisture absorption performance and sealing condition of the dryer before the measurement. If the silica gel is pink, it should be dried to blue in advance, and apply vaseline to the edge of the cover and base in time to enhance the tightness.

2.3 Sample preparation

Before sampling, fully mix the samples in the closed container, and then take out two independent test samples 15-25g from them and put them into the grinding bottle. The samples that need to be ground are in accordance with the requirements of GB / T 3543.6-1995 grinding fineness.

2.4 Sample drying

(1) Repeat the mixing of the treated samples in the grinding bottle, weigh 2 parts of 4.500 ~ 5.000g samples with a balance of 0.001g, put them into aluminum boxes of constant weight, and cover the box under the box , Write down the box number, box weight and actual weight of the sample.

(2) Flatten the sample, immediately put it into the drying oven with pre-adjusted temperature, and then close the door, when the temperature inside the oven rises to the specified temperature (low temperature drying method requires temperature 103 ± 2 ℃, high temperature drying) The method requires a temperature of 130 ~ 133 ℃) to start timing.

(3) After reaching the prescribed drying time (low temperature drying method requires 8h, high temperature drying method requires 1h), wear yarn gloves, open the box door, quickly close the box cover in the box, and remove the aluminum box , Cooled to room temperature in a desiccator, and weighed after about 0.5h.

2.5 Calculation and presentation of results

Calculate the percentage of seed moisture based on the weight of water lost after baking, and the result retains 1 decimal place. If the difference between two measurements of a sample does not exceed 0.2%, the result can be expressed by the arithmetic average of the two measurements, otherwise, the two measurements need to be repeated.

3 Precautions for moisture measurement

(1) When the moisture of seeds of cereal crops to be ground exceeds 18% and the moisture of seeds of legumes and oil crops exceeds 16%, the pre-baking method must be adopted.

(2) The oven temperature must be strictly controlled during the drying process. In order to shorten the temperature recovery time after the sample is placed in the oven, the preset temperature can be appropriately increased before the sample is placed (generally preheated to 110 ~ 115 ℃ by low temperature drying method, (High temperature drying method preheated to 140 ~ 145 ℃).

(3) After the drying time is over, the aluminum box cover should be immediately taken out and put into the desiccator to cool, instead of leaving the sample in the drying oven to prevent the sample from absorbing moisture in the oven and causing the test results Inaccurate.

(4) During the measurement process, sampling, weighing, grinding and other operating steps are required to be rapid to minimize the contact time between the sample and the air. If the low temperature drying method is used to determine the seed moisture, the relative humidity of the air in the laboratory must also be less than 70%.

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