Analysis of Factors Affecting Seed Moisture Determination

Analysis of Factors Affecting Seed Moisture Determination

Mr. Zhan Genyin, Senior Agronomist, Wheat, Maize Seed Quality Supervision, Inspection and Testing Center, Ministry of Agriculture

According to the “Seed Inspection Regulations for Crops,” the four quality indicators of seed purity, cleanliness, germination, and moisture are mandatory inspection items for seed inspection. The quality indicators are implemented by the national mandatory standards, and any one batch of seeds. If the index fails to meet the national standards, it will be judged as a substandard seed. As one of the indicators of seed quality, if it fails to meet the national standards, it will bring serious economic losses to a seed production or business enterprise. This must not be taken lightly. For example: Originally a batch of qualified seeds, just because of the inaccurate detection data of water, making it a "non-conformity" seed, resulting in enterprises spending a lot of manpower and material resources to carry over, drying, or even economic punishment and suffering unnecessary economic losses. . On the contrary, it was originally a group of seeds with excessive moisture. However, due to the inaccuracy of the measurement data, it became a “qualified” seed. This would allow seed companies to relax their vigilance and generate paralysis and ultimately cause a batch of seeds to be scrapped.
For a long time, some people have always thought unilaterally that as long as the quality of seeds is up to the other three standards, as for moisture, that is insignificant. Practice has proved that this understanding is wrong. The level of seed moisture directly affects the transportation of seeds, safe storage and the life of seeds. Because some seed companies do not pay enough attention to the determination of seed moisture, the seeds suffer frost damage and mildew, and eventually the accidents of severe loss of seed viability occur frequently. The lesson is extremely profound. We are not prepared to discuss the significance of moisture measurement. We will only talk about the individual's superficial understanding of the problems that should be noted in the moisture measurement process. The wrong places are also expected to be given advice from experts and peers.
The Crop Seed Inspection Regulations stipulates two methods for determining moisture, one is a low-temperature drying method, and the other is a high-temperature drying method. The differences between these two methods are mainly as follows: 1 The time for sample drying is different. . The low constant temperature drying method requires a drying time of 8 hours; the high temperature drying method requires a drying time of 1 hour. 2 different temperatures. The low constant temperature drying method requires that the preheating temperature of the oven is 110°C-115°C, the temperature used for drying the sample is 103°C±2°C; the high temperature method requires the preheating temperature of the oven is 140°C-145°C, and the drying sample is used The temperature is 130-133°C. 3Required different environmental conditions. Low-temperature drying requires indoor relative humidity to be less than 70%; high-temperature drying does not require this. 4 The crop types to which the two methods apply differ. The two can not be confused.
In order to avoid or reduce operational errors, the following points must not be ignored except that they are carefully handled in accordance with the "Regulations":
1. Seed and environment Seed moisture has a close relationship with the environment temperature and humidity. When the external environment humidity is high, the seeds easily absorb moisture, thus increasing the moisture content of the seeds. When the outside air is dry, the moisture in the seeds is easily distributed outwards, making the seeds moisture. decline. Therefore, when opening the moisture sample sealed container to extract the sample for crushing, when using the balance to weigh the sample, every effort should be made and the operation process may be shortened to minimize the exposure time of the sample in the air to prevent the seed from absorbing moisture or Dissipate moisture, causing distortion of the measurement result.
Second, instruments and equipment used in equipment, shall comply with the requirements of the regulations, and qualified by the qualified measurement department. This can not be ignored, especially for testing organizations that issue notary data to the society.
It is worthy of special attention that the rotational speed of the grinding mill has a great influence on the moisture measurement results. The difference in rotational speed between different types of sample grinding mills often results in large differences in the measurement results. The results of the author's experiments show that the use of a crushed mill crushed sample with a rotational speed of 1400 revolutions per minute results in a measured result that is higher than that measured with a 10,000-pound cyclone crusher crushed specimen with a rotational speed of 10,000 revolutions per minute. 5 percentage points or even higher, and the higher the sample moisture content, the greater the difference. In other words, the result of a sample that was crushed with a low-speed crushing mill was unsatisfactory in the same sample, and the sample that was crushed using a high-speed crusher (such as a cyclone mill) might pass the test; that is, regardless of the measurement. Whether the results are acceptable or not, the test results of the low-speed crusher grinding and crushing are always higher than those of the samples crushed by the high-speed crusher. At present, most of the sample grinding mills used in the seed laboratories in China are grinding mills with a rotational speed of 1400 rpm.
At present, there are various types of electronic moisture measuring instruments on the market, which are mainly divided into three categories: capacitive, resistive and microwave. It is fast and convenient, but a large number of rapid moisture analyzers are inaccurate and reproducible. Poor. In particular, the plug-in quick moisture meter is very different. Vertical insertion, oblique insertion, flat insertion, and inserting speed are different. In addition, there are pressure rods and clamp-type quick moisture meters, which often result in different measurement results depending on the size of each person. Better is the computer moisture meter. The data is more reliable, but it is often expensive. It also requires standard calibration. And only when the time is tight, the task is heavy, and the large-scale centralized acquisition of seeds, the test results of the rapid moisture meter can be used as a rough reference for understanding the seed moisture, but it is not feasible to issue notarized data to the society, even if the data is reliable. No, because there is no regulation in the inspection protocol for the determination of seed moisture using a quick moisture meter. This can't be violated, it can't be arbitrary.
When using a balance to weigh the weight of a sample before or after baking, a balance of 0.001 g, that is, a balance of 1/1000, must be used. This leaves no room for choice. The calculation process must strictly follow the rules of digital rounding and must not be continuously revised. The tolerance between repetitions is 0.2%. In the event of an out-of-tolerance, the cause should be carefully searched. If it is a calculation error, it should be corrected. Otherwise one sample must be remeasured.
Third, the operation should pay attention to the problem:
(1) The time and temperature required for drying the sample must be strictly in accordance with the requirements of the "Regulations" and cannot be delayed or advanced at will, and the temperature cannot be arbitrarily set. In particular, the high-temperature drying method at 130°C for 1 h may cause the seed sample to become carbonized (eruption) if it is dried over a long period of time, and the combined water in the seed is baked out, which makes it more unreasonable to bias the determination result of the seed sample. high.
(2) Samples spilled on the weighing pan during the weighing process must be completely removed before the weighing result is recorded, and cannot be cleared after recording. The result of the recording should be the weighing data after the spilled sample is removed. If you clear after recording, the weight of the sample spilled on the weighing pan will be counted in the lost weight data, and the measurement result must be high. Some careless examiners tend to ignore these seemingly tiny yet extremely important details. This is also one of the important reasons for the distortion of the samples and the distortion of the detection results. There are also some inconveniences that the inspector easily guilty of is that the pre-baking sample (box weight + sample weight) has been weighed and recorded, but the sample is leveled with a finger or a horn spoon. As a result, the finger and the horn spoon will be Removing some trace samples will also result in inaccurate measurement results. If it is necessary to flatten the sample in the baking box, it should be done before the weighing data is recorded. The recorded data should be the data after the flattening.
(3) When the sample is taken out of the oven, the oven should be covered in a box and then placed in a desiccator to cool it. However, in this process, sometimes the thread on the glove or glove is caught by the lid. In the case of break-up, when the baking box is hot, either accidentally spills the sample or breaks the thread on the box, so that the result of the weighing after cooling will certainly be inaccurate; during the lid adding process, sometimes Inadvertently inadvertently inserting a gloved finger into the sample cartridge causes the sample to become detached, which distort the measurement result.
(D) In ​​the process of smashing the sample, do not touch the seed directly. The smashed sample should be quickly capped after being loaded into the sample bottle. When the sample is weighed, gloves should be worn. Do not directly take the baking box by hand. The hand sweat on the baking box, affect the measurement accuracy. (Don't forget that we are using a balance that measures up to 0.001g!)
According to reliable information, the Seed Quality Inspection Department of the National Agro-tech Extension Center of the Ministry of Agriculture is organizing some provincial-level seed inspection agencies and relevant experts to revise some of the current “Seed Inspection Regulations for Crops,” and at the same time “Standards for Crop Seed Quality”. The quality indicators of some of the crop seeds will also be revised. I hope that everyone will pay attention to the new changes in the above standards.
The above points are purely empirical in nature. Comrades who only test the quality of seed for beginners should refer to them in practice. Please be critical of the mistakes.