Effect of High temperature and Heat damage on Rice production in Fanchang County and its Prevention and remedial measures

In the process of rice production, the most influential and difficult climatic factors are temperature and moisture. Reasonable irrigation can replenish and regulate water, but the temperature is difficult to control. It has a significant impact on the life of rice.

Rice is the main crop in grain production in Fanchang County, which ranks first in terms of planting area and total yield. At present, the rice planting area in Fanchang County is about 16360 hectares (including multiple cropping index), of which medium indica rice is about 13191 hectares (mainly hybrid rice), early rice is about 1514 hectares, and double late rice is about 1655 hectares. Therefore, planting rice well and obtaining high yield plays a very important role in developing the county's rural economy, "two high and one excellent" agriculture, increasing farmers' income, increasing agricultural efficiency and stabilizing market supply.

1 the relationship between temperature and rice production

1.1 the effect of temperature on the vegetative growth of rice although rice originated in the tropics, through continuous cultivation and continuous improvement of varieties, rice planting areas have been widely used in tropical and temperate regions. Rice can also be grown in some alpine marginal areas of northern China. This shows that rice has strong adaptability to different climates. However, the production and development of rice has its most suitable temperature range, and too high or too low temperature is disadvantageous to its growth.

1.1.1 germination temperature of rice seeds. Generally, the lower limit of germination temperature of rice seeds is 8 ℃ (cold-tolerant varieties can also germinate at about 0 ℃). If it is too low, it will germinate slowly and may rot, and the upper temperature is 43 ℃. Therefore, the temperature range of rice seed germination is 0: 43 ℃, and the optimum temperature is about 18: 33 ℃, but the germination ability decreases at 15: 30 ℃. Therefore, in a sense, 15 ℃ and 33 ℃ are not in the physiologically suitable temperature range.

1.1.2 the growth temperature at seedling stage. The optimum temperature for wet seedling raising was 25: 30 ℃. In the early stage, the temperature increased with the increase of temperature when the temperature reached 20 ℃, and the seedling exposed water layer was the fastest at 30 ℃. The optimum temperature for radicle elongation and rooting in soil is 25-30 ℃. When it reaches 35 ℃, the root mainly grows in the water layer, which is easy to cause seedling floating and rooting instability, so the root at seedling stage is more sensitive to high temperature.

The growth of single and double night seedlings in Fanchang county is basically in a suitable water temperature, but the seedling field of early rice early sowing has weak resistance to the outside world, slow growth, especially difficult to take root, in case of bad weather, such as cold wave in spring, low temperature (below 12 ℃), and improper management, it is easy to cause rotten seedlings, so some protective measures should be taken.

1.1.3 Seedling temperature after transplanting. In general, the critical temperature needed for rice transplanting is 15 ℃, and the most suitable root temperature is 25-28 ℃. After transplanting, the average temperature of aboveground growth increases linearly in the range of 18-33 ℃, while the growth decreases significantly at or below this temperature range. The temperature of rice at tillering stage is 15-33 ℃, which is disadvantageous to tillering beyond its range, but the suitable temperature is 25 ℃ in daytime and 20 ℃ at night.

1.2 effects of temperature on reproductive growth and maturity of rice the reproductive period of rice is longer, which lasts about 60 days from panicle differentiation to grain maturity. The formation of effective panicle before heading, grain filling and plumpness after heading are the three key processes that determine the yield of rice, so special attention should be paid to the climatic conditions in the reproductive period.

1.2.1 the temperature produced by the number of ears. Without considering the factors such as water, temperature, sunshine and soil, the optimum temperature for the formation of rice spikelet was 20-23 ℃. The results showed that the number of tillers of rice was the most dead at the temperature of 2530 ℃ 15 ~ 20 days before heading. 20 ℃ was the most suitable for panicle formation, and 35 ℃ was the most suitable for tiller formation.

1.2.2 the temperature at heading and ripening stage. The suitable average temperature from heading to maturity is about 23 ℃. The harm to maturity in the low temperature range is more serious than that in the short-term high temperature range. The late double cropping rice in Fanchang County has a cold current at the late heading stage, which will greatly reduce the seed setting rate, so it is required that the double late rice should have full heading before September 23. The seed setting rate of rice is higher when the water temperature is 25 ℃ in the day and 20 ℃ at night. When the water temperature rises to 35 ℃, the seed setting rate of rice is about 50% lower than that at normal temperature. When the day temperature is 35 ℃ and the night temperature is 30 ℃, the seed setting rate of rice is seriously affected, which is due to the increase of sterility probability due to low pollen quantity and non-cracking pollen caused by high temperature during the day and night.

2 production of high temperature heat damage and its harm to rice growth

Fanchang County encountered rare low rain and high temperature during the growth of single cropping hybrid rice for several years in a row, especially the continuous high temperature from mid-July to early August, which caused serious disasters to medium indica rice that was heading and flowering. The average seed setting rate of perennial rice was more than 80%, while in 2003 it was only 50% 60%, moderate 25% and 35%, and the serious ones were less than 10%. It caused a substantial decline in grain production.

2.1The heat damage caused by continuous high temperature made rice flowering without fruit bearing rice was the most sensitive to temperature 10 days before and after booting to heading and flowering stage, and the most suitable temperature was 25: 30 ℃. When the temperature was higher than 30 ℃, it was obviously harmful to flowering and fruiting. In production, the daily average temperature and the daily maximum temperature higher than 35 ℃ are usually regarded as the heat damage index of rice at heading and flowering stage. If the continuous high temperature was more than 35 ℃ at booting stage, the floral organ development was not complete, the pollen was poor, and the vigor decreased. In the heading and flowering stage, heat damage will occur in the event of continuous high temperature, resulting in rapid water loss, affecting flowering and pollen tube elongation, resulting in failure of normal pollination, or the formation of empty shell grains when the pollen dies before it blooms, that is, "flowers but not fruit". The rice heading at a constant temperature of 38 ℃ is sterile, and high temperature can directly kill pollen.

2.2 the harm and loss degree of heat damage to medium indica rice in Fanchang county for several consecutive years, the seed setting rate of medium indica rice in Fanchang county decreased and the yield failed, especially the varieties with early sowing date and early mid-maturity. According to the survey and statistics, according to the average unit yield of 8250kg/ hectares, the per capita income of farmers affected by the disaster has been reduced by 900 yuan to 1200 yuan per hectare.

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