The changes in the growth period of rice varieties are determined by the combined effects of three factors: photosensitivity, temperature sensitivity, and basic nutritional growth period (one gender phase). Sensitivity reflects the response characteristics of the growth period of rice varieties to different day lengths, and the growth period of varieties with strong photosensitivity is significantly shortened in short days; temperature sensitivity is the response characteristics of the growth period of rice varieties to temperature. For varieties with strong temperature sensitivity, when the temperature is high, the growth period is shortened significantly; the basic vegetative growth period reflects the length of the growth period of rice varieties under high temperature and short days.
Rice is a thermophilic crop. Biological zero degree japonica rice is 10℃, and indica rice is 12℃. Early japonica is sown at a stable temperature above 10°C (plastic film seedlings at about 8°C) and seedlings are planted at 15°C or higher; early indica is sown at 12°C or higher and seedlings are planted at 17°C, otherwise rotten or dead seedlings will appear. Northern Early Japonica and Southern Early Indica should avoid low temperature damage during the booting stage (minimum temperature of japonica rice is not lower than 15℃, indica rice is not lower than 17℃), otherwise it will cause spikelet degradation, increase of false grains and delayed heading. The safe heading period of japonica rice requires the daily average temperature to be stable above 20℃, and there is no low temperature below 20℃ for more than 3 consecutive days. Indica rice (including hybrid rice) requires above 22～23℃, and no continuous 2～3 days below 22～ The low temperature of 23℃, otherwise it is easy to form empty husks and shriveled grains. However, the temperature above 35～37℃ (above 32℃ for hybrid rice) will cause the seed setting rate to decrease. During the filling stage, the daily average temperature should be between 23～28℃. When the temperature is low, the movement of matter slows down, and when the temperature is high, the respiratory consumption increases. Grouting is quite slow when the temperature is below 13～15℃. Japonica rice is more adaptable to low temperature than indica rice. It is necessary to keep the rice heading and grain filling period in light, temperature and moisture more suitable, and try to avoid the period of large diseases and insect pests to obtain higher photosynthetic yield and grain yield.
The water requirement of rice during the whole growth period is generally between 700 and 1200 mm, and the field transpiration coefficient is between 250 and 600. The total amount of rice transpiration varies with light, temperature, moisture, wind, fertilization status, photosynthetic efficiency of varieties, length of growth period and maturity. Changes over time. Transpiration is highest in single-season mid- and late rice at booting stage, double-season early rice at flowering stage, and double-season late rice at jointing and booting stage. Rice needs water layer irrigation to increase root vitality and transpiration intensity, and promote the accumulation of sucrose and starch and the movement of substances in the leaves. The appropriate depth of submerged irrigation is 5-10 cm, but in order to remove the toxic reducing substances in the soil and improve the permeability and root vitality of the soil, different degrees of open and sunning fields should be carried out. The rice seedling stage should be irrigated with shallow water frequently, which is good for rooting; the tillering stage is to promote the branching, adjust the temperature with water, and keep the water layer at about 2 to 3 cm. The drainage at the later stage of the tillering promotes root development; the jointing and booting stage is the most water-required period of rice , It is suitable to irrigate deep water (6-10 cm); according to the weather and soil conditions, the heading and flowering period can be lightly dehydrated or maintain a certain water layer. The relative humidity of the air is 70-80% favorable for fertilization; Wet and dry, beneficial to improve root vitality and material allocation and operation. Rice is the most severely affected by drought during the greening stage, meiosis stage, and early flowering and filling stages. The lack of water during the greening stage affects the live seedlings and tillers; the lack of water during the meiosis stage causes a large number of spikelets to degenerate, delayed ear emergence, and seed setting rate. Decrease; drought at the heading stage affects ear production and severe yield reduction; drought at the irrigation stage will reduce the grain weight and affect yield. Rice is most sensitive to flooding in the green, meiotic, and flowering stages. Long-term flooding will cause dead seedlings, young ears to rot and lower seed setting rates.
Rice is a sun-friendly crop, which requires high light conditions. The saturated light intensity of a single leaf of rice is generally about 30,000 to 50,000 lux, and the light saturation point of the population increases with the increase of the leaf area index. Generally, the highest tillering stage is About 60,000 lux, the booting stage can reach more than 80,000 lux, but its photosynthesis is not as obvious as corn with the increase in illumination. Rice is a short-day crop, and different types of varieties respond differently to the length of light. Early rice and middle rice do not have a certain critical light length for ear emergence. They can emerge normally under short-day or long-day conditions. They are short-day insensitive. Late rice varieties promote ear emergence in short days and delay ear emergence in long days. The critical light length of earing is short-day sensitive.
(4) Basic nutritional growth period
Indica rice in the southern region requires a cumulative temperature greater than 10°C for different maturity and the number of growth days (seeding-maturity) as follows.
Early rice: early-maturing species>10°C accumulated temperature of 2400°C, and growing days 110 days; middle-maturing species>10°C accumulated temperature of 2400-2600°C, growing days 110-120 days; late-maturing species>10°C accumulated temperature above 2600°C, growing days more than 120 days .
Mid-season rice (one-season rice): Early-maturing species>10°C accumulated temperature <3000°C, and the number of growing days is less than 130 days; mid-maturing species>10°C accumulated temperature is 3000-3200°C, and the number of growing days 130-140 days: late-maturing species>10°C accumulated temperature is above 3200°C , The number of birth days is more than 140 days.
Late rice: early-maturing species> 10 ℃ accumulated temperature of 3000 ℃, growing period of 120 days; mid-maturity species> 10 ℃ accumulated temperature of 3100-3300 ℃, growing period of 120-130 days; late-maturing species> 10 ℃ accumulated temperature of 3300 ℃, growing period of more than 130 days .
(5) Safety period
Safety period refers to the smooth progress of rice planting, full ears, and maturity within the boundary period, without causing serious low temperature hazards, and avoiding losses caused by rotten seedlings, empty husks, and grains. Especially for double-cropping rice, the important growth stages-from safe seeding of early rice to safe heading and flowering and safe maturity of late rice-should be in the best period of meteorological conditions, namely, safe seeding period, safe heading period and safe mature period. The low temperature and cold damage of early rice, high temperature and heat damage and the low temperature and cold damage of late rice and other unfavorable conditions.
① Safe sowing period of rice. The agro-climatic resources of rice are different in different regions, and the safe sowing period also varies accordingly. The earliest safe planting date of rice in China is postponed as the latitude increases. For indica rice in southern China and southern Yunnan, it is from late February to early to mid-March; for indica and japonica rice in the Yangtze River Basin from late March to mid-April and late March to late April, respectively ; North China japonica rice is around mid-April, southern japonica rice is late April, and northeastern rice regions are from the end of April to mid-May; Northwest China is 10-15 days later than North China at the same latitude; the central and northern Yunnan-Guizhou Plateau is longer than eastern China at the same latitude More than 10 days late; the Sichuan Basin is about 10 days earlier than the middle and lower reaches of the Yangtze River at the same latitude.
②The rice is safe at the full heading stage. The safe heading period is gradually postponed from high latitudes to low latitudes and from north to south. In Northeast China, from the end of July to the beginning of August, the japonica rice in North China and Huanghuai (including northern Jiangsu and Anhui) is from late August to early September; the southern indica rice is in August. Before the end of the month, indica rice in the Yangtze River Basin will be in early and mid-September, and japonica rice will be in mid- and late September; indica rice in South China will be in late September to mid-October; the western inland and the Yunnan-Guizhou Plateau will be 10-30 days earlier than the eastern regions of the same latitude.
③The safe maturity period of rice. Rice heading to maturity requires a daily average temperature of more than 15 ℃, 35 days for indica rice and 40 days for japonica rice. If the air temperature remains above 15°C in the next 40 days after safe heading, the heat resources can ensure safe heading. Early and mid-September in Northeast China; mid-September to early October in Northwest China; early and mid-October in North China; mid-October to late October in Chengdu Plain; end of October to late October in the middle and lower reaches of the Yangtze River Early; the central and northern Yunnan-Guizhou Plateau is in late September to early October, and the low mountain and Pingba area is in late October; South China and southern Yunnan are in early and late November.