1. Relationship between rice water consumption and meteorological conditions
There are many factors affecting rice water consumption, mainly transpiration, evaporation and leakage (including lateral leakage and vertical leakage). The water required for photosynthesis of rice itself is relatively small and can be ignored. The water consumption of transpiration and evaporation is mainly restricted by meteorological conditions, in which temperature and light play a decisive role in rice transpiration and evaporation.
(1) Relationship between water consumption and temperature in rice growing period
A mathematical formula is established by using the water consumption of rice during its growth period and its accumulated temperature (expressed by ∑T) greater than 0℃:
The higher the temperature, the greater the water consumption of rice. This is because with the increase of temperature, the water surface evaporation increases; At the same time, in a certain temperature range, with the increase of temperature, the activities of various enzymes in crops also increase, and the more water is consumed by metabolism, photosynthesis and transpiration.
(2) The quantitative relationship between water consumption and sunshine in rice growing period.
There is a good one-to-one correspondence between water consumption and sunshine (expressed by ∑S) in rice growth period.
Rice from jointing stage to filling stage is a transitional period from vegetative growth to reproductive growth. The plants are getting bigger and bigger, and the population is increasing. It needs enough sunlight to enhance photosynthesis, transpiration and evaporation, so it consumes more water.
2. Determination method of rice irrigation quantity
(1) comprehensive model of water consumption in rice growth period
The water consumption of rice is caused by many factors, which are primary and secondary. If other conditions are relatively stable, the water consumption of rice (represented by E) is basically a function of (∑T) and (∑S). Therefore, the mathematical relationship of rice water consumption is obtained by using the correlation integral synthesis method:
(2) Determination method of water consumption in a certain period of time.
Due to the influence of external conditions and physiological ecology, the water consumption in different stages is obviously different and has certain rules. To know the water consumption of rice in a certain period of time, we only need to calculate the difference of water consumption before and after a certain period of time.
(3) The relationship between water consumption and leakage of rice and groundwater level.
According to the experimental data, during the growth of rice, the change of groundwater level in rice field is not significant. The amount of leakage varies with soil properties. The leakage of high sandy soil field is large, but that of clay loam soil is small. For the same soil quality, the leakage is basically a fixed number, which can be expressed by g = dn. Where g is the leakage, d is the daily leakage and n is the number of days.
(4) Determination of irrigation quantity
The first is to calculate the amount of irrigation.
The irrigation amount of rice is mainly used for transpiration, evaporation and leakage; How much is also affected by precipitation. Therefore, the irrigation quantity is expressed by the following functional relationship:
Where: g is the leakage and r is the precipitation. When the precipitation on that day is greater than 50mm, only 50mm is calculated, and the excess precipitation is deemed to be excluded.
The second is to determine the actual irrigation amount.
The irrigation amount can be calculated in a certain period, but the precipitation trend and soil properties in the next 3-4 days must be considered to determine the irrigation amount. At present, the decision-making classification table of irrigation amount (table 1) can basically consider the above three factors, and then adopt the corresponding irrigation amount.
Table 1 Classification Table of Irrigation Decision-making
Calculate the irrigation amount (mm), high sandy soil precipitation level, sandy loam precipitation level and loam precipitation level.
No small, no big, no big, no small, no big.
10~20 Ⅰ Ⅰ Ⅱ Ⅳ Ⅰ Ⅰ Ⅱ Ⅳ Ⅰ Ⅱ Ⅱ Ⅳ
20~40 Ⅰ Ⅰ Ⅱ Ⅳ Ⅰ Ⅰ Ⅱ Ⅳ Ⅰ Ⅱ Ⅱ Ⅳ
≥40 Ⅰ Ⅰ Ⅲ Ⅳ Ⅰ Ⅱ Ⅲ Ⅳ Ⅰ Ⅱ Ⅲ Ⅳ
Table 1 Forecast the future precipitation and soil properties according to the calculated irrigation amount, clearly divide the irrigation amount into four grades, and adopt four corresponding decisions respectively.
I: irrigation quantity is calculated irrigation quantity;
Ⅱ: Irrigation amount is 80% of the calculated irrigation amount;
Ⅲ: Irrigation amount is 50% of the calculated irrigation amount;
Ⅳ: No irrigation for the time being.
When the calculated irrigation amount is less than 10mm, no irrigation will be carried out regardless of soil properties and whether it will rain in the future.
The table 1 is used to predict the rice irrigation amount in Rugao city in 2006, and the prediction conclusion is basically consistent with the actual situation.
(5) Irrigation methods
In practice, the labor force and work arrangement of the electric irrigation station should be considered. Generally, irrigation is started every 4 ~ 5 days, and the irrigation amount is the water consumption calculated after various elements are input into the model in the first 4 ~ 5 days plus the leakage and the difference with precipitation in these 4 ~ 5 days. Therefore, the paddy field has formed a combination of shallow water and wetting, with wetting as the main irrigation technology. At the same time, according to the growth characteristics of rice, at the end of tillering, when the number of seedlings reaches about 80% of the effective panicle number, in order to inhibit ineffective tillering, air drying is carried out in the field until people can walk in the paddy field without sinking their feet.
summary
At (1)200 1, compared with the conventional irrigation method as the control, the irrigation experimental field saved an average of 5476.5m3/hm2, an average of 87kw h/hm2 and an average of 906kg/hm2. According to rice 1.40 yuan/kg, the average income per hectare is increased.
(2) This water-saving irrigation technology is characterized by adopting shallow, wet and dry regulation in time according to the water consumption law of rice in each growth period and combining with pest control, and making rational use of natural precipitation. Breaking through the irrigation mode of long-term flooding of rice, the water consumption in rice field is diversified, and the combination of promotion and control not only meets the water demand of rice, but also improves the microclimate of farmland, increases the air flow in soil and promotes the development of roots. Therefore, in the experimental field, the rice stalks are thick, the stalks are yellow when mature, and the Huang Liang of the grains are full, and no sheath blight and lodging phenomenon are found.
(3) Because the water consumption of rice is the result of many meteorological factors, this paper considers the main factor, and some uncertain factors play a secondary role, such as the influence of wind on evaporation, which needs further study.
References:
1 Major in Agrometeorology, Beijing Agricultural University. Agrometeorology. Science Press, 1982.
2 Yang Yongqi. Statistical methods in agrometeorology. Meteorological Press, 1983.
3 Wang Futang et al., Introduction to Agrometeorological Forecast. Agricultural press, 199 1.
4 Peng Shizhang, Yu Shuangen. Water-saving irrigation technology for rice. China Water Resources and Hydropower Press, 1997.
(Author: Rugao Agricultural Water Conservancy Experimental Station, Jiangsu Province) (Reporter anonymous)