(1) storage resistance. Rice seeds are caryopsis, which are wrapped by inner and outer lemmas, and the outer surface of the lemma shell is covered with fluff, which has low hygroscopicity and relatively stable water content, and is relatively stable under the conditions of air drying and washing. Because the outer surface of rice husk is covered with fluff, the seed pile is loose, and the porosity is generally 50% ~ 65%. Therefore, the air permeability of seed pile during storage is better than that of other seeds. At the same time, due to the rough surface of seeds, their dispersibility is worse than other cereal crops. Therefore, the lateral pressure on the warehouse wall is small, which is suitable for high stacking to improve the utilization rate of the warehouse.
The newly harvested rice seeds have high physiological metabolism intensity, and are often unstable at the initial stage of storage, which is easy to cause fever and even germination and mildew. Early and middle rice seeds are harvested in high temperature season. During the first half of the month, due to respiratory accumulation, the upper seed temperature often rises obviously, sometimes exceeding the warehouse temperature 10 ~ 15℃. Even rice with normal moisture content will have this phenomenon. If it is not treated in time, the humidity of the upper layer of the seed pile will become higher and higher, and water vapor will accumulate on the surface of the grain to form tiny water droplets, which is called "sweating". Rice seeds need less water to germinate, and usually only need 23% ~ 25% water content to germinate. Therefore, in rainy weather, you can't harvest, thresh and sow in the sun in time, but you can only germinate in the field or yard. After storage, it is easy to germinate if it is wet.
(2) Vulnerable to freezing injury. Due to the early frost period in Northeast China, especially the late-maturing varieties, they are often not fully mature at harvest, which affects the storage of seeds. According to experiments, the germination rate of seeds matured before frost is higher. When harvesting, as long as the wax ripens before frost, the germination rate should reach 92.4%, but the germination rate of seeds harvested after frost is only 57.3%.
Rice seeds with high water content are prone to freezing injury at low temperature in winter. The results showed that the germination rate of rice seeds with water content of 65438 08% decreased obviously at -20℃. After freezing at 1 day at -25℃, the germination rate of seeds with water content of 18% decreased to 71%. After freezing for 7 days, the germination rate of seeds with water content of 16.2% decreased to 84%. With the extension of freezing time, the germination rate decreased. In order to prevent freezing injury, the water content of rice seeds should be reduced to about 13% before the arrival of low temperature in winter.
(3) Poor heat resistance. Rice seeds have poor heat tolerance. If the temperature is not properly controlled in the process of artificial drying or solarization, it will increase the bursting rate, cause discoloration and damage the germination rate. Schmidt( 1956) showed that the seed germination rate began to decrease at 45℃ and decreased by half at 60℃. The study of Iwasaki (1976) showed that the activities of catalase and amylase were affected after rice seeds with water content of 14.3% were treated at 60℃ 1 hour, and the activities of the two enzymes were seriously damaged after being treated at 70℃ 1 hour.