According to the principle of energy balance, the temperature difference between the blade and the air varies depending on the strength of the net solar radiation and the amount of crop evapotranspiration. When the crop receives sufficient water supply, the blades cool due to transpiration and the temperature drops below the temperature that can be achieved when transpiration is inhibited; when the water supply decreases, the latent heat of crop transpiration decreases, the sensible heat increases, and the temperature of the leaves increases. rise.
Tannner first discovered that the canopy temperature can reflect the water status of plants, and put forward the idea of ​​using plant temperature to indicate water deficit in plants. Idso and Jackson have successively put forward indicators such as the Japanese drought stress indicator and crop water deficit indicator based on the temperature difference between the crown and the air, which have been applied to various crops in different regions. Kang Shaozhong, Cai Huanjie, Shi Peihua, etc. generally believe that the difference in temperature between the crown and the water can better reflect the state of crop water, and believe that the best observation of the crown and air temperature difference is in the afternoon.
Transpiration is an important physiological activity of crops. It not only promotes water transport and material transport in crops, but also weakens the range of changes in temperature. It also ensures that crops need photosynthesis and is vital to the life activities of crops. The influence of the temperature difference of wheat leaf on transpiration rate can directly reflect the condition of soil moisture. Wu Haiqing et al. found that the transpiration rate of winter wheat increases with increasing soil moisture. Considering the relationship between transpiration rate, photosynthetic rate and water use efficiency, it can be concluded that there is extravagant transpiration and water consumption in winter wheat under high soil moisture conditions; Potted plants were used to study the relationship between transpiration and its influencing factors of winter wheat seedlings under different soil moisture conditions. It was found that transpiration rate and stomatal conductance both showed a decreasing trend with the decrease of soil moisture. Through gradual regression, different soil moisture was obtained. The regression model of transpiration rate and influencing factors of winter wheat seedlings under the conditions; Wan Changjian et al. analyzed the temporal and spatial changes of wheat transpiration rate based on actual observational data. The main meteorological factors affecting wheat transpiration were temperature, light intensity and humidity. Based on the analysis, a simplified model for calculating the transpiration rate of wheat using conventional meteorological data was established. The above research results provide different methods for studying the physiological and ecological environmental adaptability of wheat. The effect of light intensity on the temperature difference of wheat leaf temperature is different under different soil moisture conditions. At the same time, the temperature difference of wheat leaf also directly affects the transpiration rate of the leaf. This experiment used artificial control of soil moisture to study the effect of light intensity on the temperature difference of wheat leaf under different soil moisture and the effect of wheat leaf temperature difference on transpiration rate, in order to provide scientific basis for wheat water-saving irrigation and drought defense.
1 Materials and methods
This experiment was conducted in the experimental field of the Crop Irrigation Section of the Farmland Irrigation Research Institute of the Chinese Academy of Agricultural Sciences. The use of drip irrigation equipment to control the amount of irrigation does not require natural precipitation. The depth of the test pit is 2 m, the area of ​​each pit is 1. 5 m × 2.0 m, the cement covers and the back cover, the soil in the pit is fully mixed, and the field water capacity is 24. 0 %, withered humidity was 7.6 %. The test cultivar was Chengmai 9405, a semi-winter cultivar, and the sowing date was October 10, 2006. Different soil moisture was maintained from the turning of wheat to the wax ripening period. The test consists of five treatments, namely: A (about 40% of the soil water capacity in the field), B (about 50% of the soil capacity in the field), C (about 60% of the soil capacity in the field), and D (the amount of soil water in the field). About 80%) and E (greater than 90% of the soil field capacity). On April 30, 2007, wheat entered the flowering stage. On May 10, the soil moisture content was measured on five treatments using a neutron radon meter. They were: A: 9.04 %, B: 11. 01 %, C: 14. 89 % , D : 19. 62 % , E : 24. 00 % , and the leaf temperature, air temperature, and light intensity were measured every 8 hours at 8:00 - 18:00 using the LI-6200 portable crop physiometer. , transpiration rate and so on. Recommended instruments: light box, smart light incubator.
2 Results and Analysis
2.1 Change in temperature difference of wheat leaf under different soil moisture
The observation results showed that when the soil moisture was 14.89 %, the temperature of wheat leaves was lower than that of soil moisture when the soil moisture was 9. 04 % was 1. 77 °C, and the soil moisture was 24. 0 % when the soil moisture was lower than 0.62 °C. It can be seen that under conditions of low soil moisture, the temperature of the leaf is higher, and the temperature of the leaf gradually decreases with the increase of soil moisture. Under the suitable soil moisture, the temperature of the leaf reaches the lowest value. According to the analysis, suitable soil moisture is conducive to the increase of transpiration rate of wheat, and the increase of transpiration rate accelerates the self-circulation of crops. Acceleration of water dispersion rate can effectively reduce the temperature of wheat leaves. Low soil moisture is prone to drought stress, soil moisture is more likely to cause waterlogging and then affect the smooth cycle of wheat. At the same time, the decrease of leaf temperature can prolong the function of the leaf and prolong the grouting time, which is very favorable for the accumulation and transfer of nutrients.
The change trend of temperature difference and light intensity of wheat leaf were analyzed. It was found that when the soil moisture was less than 15.0%, the leaf temperature difference of wheat had the same trend as the light intensity (Fig. 1). The maximum temperature difference between wheat leaf temperature appears at 12: 00 -13:00, which is the strongest light intensity, indicating that when the soil moisture is relatively small, the temperature difference of wheat leaf temperature is basically determined by the intensity of light intensity. The intensity of light increases gradually before noon, the latent heat of the leaves for transpiration decreases, the sensible heat increases, and the temperature of the leaves rises accordingly. As a result, the temperature difference between the leaves of wheat increases gradually and reaches its maximum at 12:00 - 13:00. At the same time, it was found that with the increase of soil moisture, the time when the maximum temperature difference of wheat leaf temperature appears is gradually out of sync with the light intensity. The analysis found that with the increase of soil moisture, the temperature of wheat leaf temperature difference occurs gradually. The higher the soil moisture, the earlier the temperature difference of wheat leaf temperature appears. That is to say when the crop gets sufficient water supply, the blades cool due to transpiration and the temperature drops below the temperature that can be reached when transpiration is inhibited. The intensity of light intensity control of wheat leaf temperature difference gradually weakens with increasing soil moisture.
2. 2 Response of temperature difference of wheat leaf to light intensity under different soil moisture
According to the correlation analysis of temperature difference and light intensity of wheat leaf under different soil moisture, it was found that when the soil moisture content was less than 15%, the linear relationship between temperature difference and light intensity of wheat leaf was significant (r > 0.9). With the gradual increase of soil moisture, the linear correlation between the two gradually decreases. This shows that when the soil moisture is more than 15%, the adequate supply of water increases the total transpiration of winter wheat and reduces the temperature of the leaves. The light intensity will effectively increase the photosynthetic accumulation under the condition of high soil moisture, and no longer be the temperature of wheat leaves. Poor determinants. In other words, when the soil moisture reaches more than 80% of field capacity, the effect of light intensity on the leaf temperature difference in wheat is no longer a major factor (Fig. 2-6).
2. 3 Effect of leaf temperature difference on leaf transpiration rate in wheat
It can be seen from Fig. 7 - 11 that when the soil moisture is less than 15%, the transpiration rate increases with the temperature difference of the wheat leaf temperature before 11:00 in the morning, and after 12:00, the transpiration rate does not follow the wheat leaf. The temperature difference increased and did not show regularity. When the soil moisture exceeds 15%, the full supply of water not only ensures a higher transpiration rate, but also effectively reduces the temperature of the leaf, and reduces the temperature difference of wheat leaf temperature. From the morning, the temperature difference between the leaf temperature and the transpiration rate of wheat On the contrary.
3 Conclusion
1) The results of this study indicate that when the soil moisture is low, the temperature difference between the wheat leaf temperature is basically determined by the intensity of light intensity. With the increase of soil moisture, the extreme temperature difference of wheat leaf temperature gradually advances. The higher the soil moisture, the earlier the wheat leaf temperature difference occurs, which indicates that the light intensity controls the leaf temperature difference of wheat along with the soil. The humidity gradually decreases.
2) When the soil moisture is less than 15%, the linear relationship between the leaf air temperature difference and the light intensity of wheat is significant (r > 0.9). With the gradual increase of the soil moisture, the linear correlation between the two gradually decreases. When the soil moisture reaches more than 80% of field capacity, the light intensity is no longer the main factor affecting the temperature difference of wheat leaf.
3) When the soil moisture is less than 15%, the transpiration rate in the morning increases with the increase in the temperature difference between the leaves of wheat. After 12:00, the transpiration rate does not increase with the increase in the temperature difference between the leaves of wheat, and does not show regularity. When the soil moisture exceeds 15%, from the morning, the temperature difference between the leaf temperature and the transpiration rate of wheat is opposite.
4) Comprehensive analysis can be seen that the response of the temperature difference of wheat leaf to light intensity and the impact on leaf transpiration rate of soil moisture threshold is about 15% (about 60% of field water capacity).
5) The difference in wheat leaf temperature can better reflect the soil moisture status, which provides a strong theoretical support for the use of the crown temperature difference in the retrieval of soil moisture, and will be further applied and verified in future studies.
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