High efficient irrigation method of Xinjiang cotton area based on crown air temperature difference

Abstract

The application discloses a Xinjiang cotton area efficient irrigation method based on crown air temperature difference, aims to solve the problems of low irrigation water use efficiency of Xinjiang cotton area under the background of water resource shortage and difficulty in realizing stable yield and quality of cotton production. The key technical means of the application is to control irrigation during the cotton flowering and bolling period, and to formulate corresponding irrigation schemes based on the crown air temperature difference TDCA of cotton field of-1.0 DEG C to-6.0 DEG C. The application can objectively and accurately reflect the gain and loss of cotton field water based on the objective cognition of the crown air temperature difference, and can realize on-demand irrigation according to the cotton field irrigation measures formulated according to the crown air temperature difference index, so that the cotton yield can be ensured and the water use efficiency can be improved. The application can provide a feasible way for the accurate water management of Xinjiang cotton area and realization of water saving and efficiency improvement, and has important significance for guaranteeing the sustainable development of the cotton industry in the area.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of agricultural production, in particular to a high-efficiency irrigation method for Xinjiang cotton area based on crown-air temperature difference. BACKGROUND

[0002] Cotton (Gossypium hirsutum L.) is an important economic and fiber crop in China. Xinjiang has a long history of cotton planting, but water resources are insufficient in most areas of Xinjiang, especially in southern Xinjiang, which is one of the main limiting factors for sustainable cotton production. With the application of mulched drip irrigation technology, water use efficiency (WUE) has been greatly improved, but WUE is only about 0.43. In Xinjiang cotton area, there is still a lack of effective irrigation guidance measures, resulting in waste of water resources and difficulty in achieving stable yield, let alone improving yield and efficiency.

[0003] In summary, in the face of increasingly scarce water resources today, how to efficiently use limited water resources to ensure the sustainable development of cotton planting in arid and semiarid areas (such as Xinjiang) is a problem to be solved. SUMMARY

[0004] The inventors found that in Xinjiang cotton area, crown-air temperature difference (TDCA) has a close relationship with water deficit and can be used as an indicator for drought stress and irrigation scheduling; the temperature of the cotton canopy layer reaches the lowest value in a day at about 7:00 am in the morning and reaches the highest peak in a day at about 16:00, which can be used to evaluate soil water characteristics. Irrigation amount and frequency affect the size of Tc peak value and have a negative correlation, and the Tc peak value decreases and is significantly lower than Ta after irrigation.

[0005] In view of at least one of the above technical problems, the present disclosure provides a high-efficiency irrigation method for Xinjiang cotton area based on crown-air temperature difference, aiming to solve the problem of low irrigation water use efficiency in Xinjiang cotton area under the background of water shortage and the difficulty of achieving stable yield and quality in cotton production.

[0006] According to one aspect of the present disclosure, a high-efficiency irrigation method for Xinjiang cotton area based on crown-air temperature difference is provided, irrigation control is performed during the flower and boll stage of cotton, and corresponding irrigation schemes are formulated based on the crown-air temperature difference TDCA of cotton field at -1.0℃ to -6.0℃ to meet the demand-based irrigation, thereby ensuring cotton yield while improving water use efficiency.

[0007] In some embodiments of the present disclosure, the crown-air temperature difference is monitored every day during the flower and boll stage of cotton, and irrigation is performed according to the following standards: when -2℃ < TDCA ≤ -1℃, irrigate 370-520 m 3 / hm 2 ; when -3℃ < TDCA ≤ -2℃, irrigate 250-340 m3 / hm 2 ; when -4℃ < TDCA≤ -3℃, irrigate 120-180 m 3 / hm 2 ; when -5℃≤ TDCA≤ -4℃, irrigate 60-90 m 3 / hm 2 ; when TDCA < -5℃, do not irrigate.

[0008] In some embodiments of the present disclosure, the daily crown-air temperature difference is obtained as follows:

[0009] In the cotton field to be monitored, at least three representative monitoring points are selected, and an infrared temperature sensor is arranged to continuously monitor the cotton canopy temperature Tc and the ambient temperature Ta in real time. A group of data is recorded every 10 minutes at each monitoring point from 14:00 to 18:00 in the afternoon, and the crown-air temperature difference TDCA = Tc-Ta is calculated. The average value is the daily crown-air temperature difference.

[0010] In some embodiments of the present disclosure, the cotton canopy temperature is monitored. The infrared temperature sensor is erected 20 cm above the cotton canopy, with an angle of 45° downward to the north direction to prevent interference of sunlight.

[0011] In some other embodiments of the present disclosure, the daily crown-air temperature difference is obtained as follows:

[0012] The infrared thermal imaging lens is carried on the unmanned aerial vehicle platform to collect the cotton canopy infrared thermal image of the cotton field to be monitored from 15:00 to 17:00 in the day. The FLIR Tools software is used to export the thermal imaging picture of the leaf and the corresponding temperature information. The canopy temperature is obtained by averaging the temperature of each pixel point in the region, and then the ambient temperature at that time is subtracted, which is the daily crown-air temperature difference.

[0013] In some embodiments of the present disclosure, for the cotton area in southern Xinjiang, winter irrigation and spring irrigation are respectively implemented in the winter and spring seasons before cotton planting. (The winter irrigation time is from November 10 to November 25, and the irrigation amount is 1500-2500 m 3 / hm 2 ; the spring irrigation time is from February 15 to February 20 of the next year, and the irrigation amount is 800-1200 m 3 / hm 2 ), to press salt and create bottom increment.

[0014] The one or more technical solutions provided in the embodiments of the present application have at least any of the following technical effects or advantages:

[0015] 1. Based on the objective cognition that the crown-air temperature difference can objectively and accurately reflect the gain and loss of water in cotton field, the technical measures for guiding cotton field irrigation are developed according to the crown-air temperature difference index, the irrigation on demand can be realized, the yield of cotton can be ensured and the water use efficiency can be improved, thereby providing a feasible way for the precise management of water in Xinjiang cotton area, realizing water saving and efficiency increasing, and having important significance for guaranteeing the sustainable development of cotton industry in the area.

[0016] 2. The canopy temperature can reflect the comprehensive influence of soil moisture and environmental factors on cotton, and can be used as a monitoring index for reflecting the water state of crops, and the unmanned aerial vehicle thermal imaging has the characteristics of convenient acquisition and large range, and it is feasible to use it for rapid inversion of the water state of cotton field in the future. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 It is a schematic diagram of cotton planting and drip irrigation tape laying in the test field in an embodiment of the present application.

[0018] Figure 2 It is an irrigation automatic control system based on Internet of Things in an embodiment of the present application.

[0019] Figure 3 It is a cotton canopy temperature field monitoring diagram in an embodiment of the present application.

[0020] Figure 4 It is a schematic diagram of monitoring area of infrared temperature sensor and calculation results in an embodiment of the present application.

[0021] Figure 5 It is a shooting and thermal imaging acquisition standard of thermal imaging unmanned aerial vehicle test area in an embodiment of the present application.

[0022] Figure 6 It is a curve of canopy temperature changing with air temperature per day before and after irrigation in 2020-2021 in an embodiment of the present application.

[0023] Figure 7 It is a curve of average canopy temperature from 12:00 to 20:00 in the whole growth period in 2020-2021 in an embodiment of the present application.

[0024] Figure 8 It is a box plot of air-canopy temperature difference (TDAC) in different growth periods in 2020-2021 in an embodiment of the present application.

[0025] Figure 9 It is a canopy temperature extracted from the thermal imaging diagram of unmanned aerial vehicle in an embodiment of the present application. DETAILED DESCRIPTION

[0026] The specific embodiments of the present application will be described below in conjunction with the embodiments, but the following embodiments are only used to illustrate the present application in detail, and do not limit the scope of the present application in any way.

[0027] Example 1: Study on the effects of different irrigation quotas and frequencies on cotton yield, quality, and canopy microenvironment.

[0028] 1. Experimental Setup

[0029] The experiment was conducted at the Alar Experimental Station of the Cotton Research Institute of the Chinese Academy of Agricultural Sciences, using a randomized block design, including a combination of three irrigation quotas and three irrigation frequencies, with the standard quota being 4200 m³. 3 / hm 2 Therefore, adhering to the principle of water conservation, the three irrigation quotas set in this example are the regular quota, which is the non-deficit quota of 4200m³. 3 / hm 2 (Non-deficit: ND), a slight deficit quota of 3700 m³ with a water reduction of 11.9%. 3 / hm 2 (Low deficit: LD), a moderate deficit quota of 3200 m³ with a water reduction of 23.8%. 3 / hm 2 (Moderate deficit: MD) The irrigation intervals for the three irrigation frequencies were 4 days, 8 days (normal), and 12 days, for a total of 9 treatments. Each treatment was set up with 3 replicates, for a total of 27 plots (see Table 1).

[0030] The planting method involves planting one film in six rows, with a row spacing of 66 cm + 10 cm (e.g., ...). Figure 1 The drip irrigation tape is laid in the middle of the narrow rows, with each plot consisting of 4 meters of film width (2.28 m per film) and 7 meters of length, covering an area of ​​63.84 m². 2 The variety used in 2020 was Zhongmian Institute 619, and the variety used in 2021 was Xinluzhong 40. Sowing dates for 2020 and 2021 were April 20th and April 21st, respectively. Sowing methods included mechanical mulching, manual sowing, and manual soil covering. The seedling density was 195,000 plants / hm². 2 .

[0031] Irrigation quotas and frequencies are controlled through an IoT-based automatic control system (e.g., Figure 2 Each irrigation pipeline is equipped with a smart water meter, which can be remotely controlled and its real-time water consumption read via a data acquisition device. When rainfall occurs, the subsequent irrigation volume is reduced by the rainfall during that period to ensure the water inflow to the experimental site remains at the set level. Actual irrigation details are shown in Tables 2 and 3.

[0032] .

[0033] .

[0034] .

[0035] 2. Field Management

[0036] The tillage method involves tractor tillage followed by combined tillage machine preparation. 375 kg / hm² of superphosphate is applied as base fertilizer before tillage. 2 225 kg / hm of urea 2 .

[0037] The sowing method involved mechanical mulching and hole punching, followed by manual sowing and covering with soil. The experimental station conducted annual winter and spring irrigation to suppress salt deposits and build up soil moisture. The winter irrigation period for the two years was from November 10th to November 15th, with an irrigation volume of approximately 2000 m³. 3 / hm 2 Spring irrigation takes place from February 15th to February 18th each year, with an irrigation volume of 1000 m³. 3 / hm 2 The amount of fertilizer applied and the plant protection and field management practices at the experimental station were consistent.

[0038] During the growing season, integrated irrigation and fertilization were carried out 10 times, with a total irrigation volume of 4200 m³. 3 / hm 2 Apply 375 kg / hm of urea. 2 300 kg / hm² of diammonium phosphate 2 Potassium dihydrogen phosphate 180 kg / hm 2 The treatment was repeated 8 times, with a total dosage of 345 g / hm. 2 Weeding and cultivation were carried out 8 times throughout the entire growth period. Pest and disease control was carried out 7 times in 2020 and 6 times in 2021. Weeding was mainly carried out by mechanical spraying of "dimethoate". In the early stage of pest control, thrips were the main pest, aphids were the main pest in the middle stage, and aphids and spider mites were the main pests in the later stage.

[0039] 3. Data Metrics and Acquisition Methods

[0040] (1) Cotton yield, fiber quality and IWUE acquisition

[0041] Cotton yield is calculated based on actual harvest. Since there are four films in the plot, in order to eliminate the interference of moisture between the rows, the middle two films are harvested at the time of actual harvest. Harvesting begins when the boll opening rate reaches more than 90%. After harvest, the number of unopened bolls is investigated and converted according to the weight of a single boll. At the same time, the actual harvest density is investigated.

[0042] The cotton fiber quality was commissioned to the Cotton Quality Supervision and Testing Center of the Ministry of Agriculture and Rural Affairs to conduct cotton fiber testing according to standard or conventional methods, measuring 10 indicators including fiber length, strength, micronaire value, maturity, uniformity, and uniformity index.

[0043] Irrigation water use efficiency (IWUE) (kg / m³) 3 The calculation formula is:

[0044] ;

[0045] In the formula, Y represents the cotton yield (kg / hm). 2 I represents the irrigation quota (m³). 3 / hm 2 ).

[0046] (2) Cotton canopy temperature

[0047] ① Canopy temperature acquisition based on infrared temperature sensor

[0048] Cotton canopy temperature was continuously monitored throughout its growth period using an SMCT infrared temperature sensor (22° half-angle, 0.1°C resolution, 0.2°C accuracy). Two sensors were used in each plot to take the average value. A single data logger was used for both data acquisition and soil moisture monitoring. The sensor position was adjusted every 3 days to ensure it remained 20 cm above the canopy at a 45° angle downwards and slightly north (da Silva and Rao 2005) (Figure 3). This prevented sunlight reflection from interfering with the measurement results, ensured consistent distance between the sensor and the canopy, and avoided including soil in the monitoring area. The measurement area size for this installation method was calculated using the target area calculation program and method for the SI-111 infrared temperature sensor of the same specifications (Instruments 2022). Figure 4 As shown, the calculation results indicate that the monitoring area of ​​each infrared temperature sensor in this experiment is 0.03m². 2 .

[0049] ② Canopy temperature acquisition based on thermal imaging UAVs

[0050] Infrared thermal images of cotton canopies were acquired using a DJI M600 Pro drone platform equipped with an infrared thermal imaging lens (FLIR Duo pro R, FLIRsystems, Inc, Wilsonville, USA). The drone flew at an altitude of 50m (Figure 5a), with an external optical temperature of 22°C, a relative humidity of 30%, and an emissivity of 0.94. Thermal images of each experimental plot were taken before and after each irrigation, ensuring that the plot boundaries were included in the frame (Figure 5b). The acquired canopy temperature images had a resolution of 640 pixels × 512 pixels. After acquisition, thermal images of the leaves were exported using FLIR Tools software to obtain the temperature information corresponding to each treatment. To eliminate interference from neighboring plots and field paths, the central area of ​​each experimental plot was selected for canopy temperature extraction, and the average temperature of each pixel within the selected area was used to represent the canopy temperature of that treatment.

[0051] 4. Analysis of the impact of deficit irrigation on cotton yield

[0052] The changes in cotton yield and its components were consistent between 2020 and 2021, as shown in Table 4. Table 4 shows that there were no significant differences in planting density among the irrigation treatments. Differences existed in the number of bolls per plant among the different irrigation treatments. Overall, with the same irrigation frequency, the LD treatment had the highest number of bolls per plant, followed by the ND treatment, and the MD treatment had the lowest. With a fixed irrigation frequency, the high and medium irrigation frequency treatments had a higher number of bolls per plant than the low irrigation frequency treatment at the same frequency. In 2020, there were no significant differences in the number of bolls per plant among the different irrigation frequency treatments for both LD and ND, but all were significantly higher than the high-frequency treatment MD4 of the MD standard. Similarly, in 2021, there were no significant differences in the number of bolls per plant among the different irrigation frequency treatments for both LD and ND, but all were significantly higher than the high and medium-frequency treatments MD4 and MD8 of the MD standard. Irrigation treatment has a certain impact on single boll weight. Data from the two years shows that single boll weight is mainly affected by irrigation quota. Under the same irrigation frequency, within a certain range, irrigation quota is directly proportional to single boll weight. Beyond this range, the impact of irrigation quota on single boll weight becomes insignificant. Specifically, single boll weight under LD and ND quotas is significantly higher than the corresponding treatment under MD quota at the same frequency, but there are no significant differences between the LD and ND treatments. The impact of irrigation frequency on single boll weight mainly occurs under MD quota, where single boll weight decreases as irrigation frequency decreases. However, under LD and ND quotas, irrigation frequency has no significant impact on single boll weight. Irrigation treatment has a certain impact on lint percentage, but the results are inconsistent between the two years. In 2020, it had a certain impact on LD8. The highest lint percentage was 48.06% in the low-frequency treatment MD12 with a moderate deficit quota, while the lowest lint percentage was 46.84% in the medium-frequency treatment LD8 with a slight deficit quota. In 2021, irrigation treatment had no significant impact on lint percentage.

[0053] Irrigation treatments significantly impacted seed cotton and lint yields. Overall, the LD4 treatment yielded the highest seed cotton and lint yields, followed by the LD8 treatment, while the MD4 treatment (with MD quota) yielded the lowest. There were no significant differences in seed cotton and lint yields among different irrigation frequencies under both LD and ND quotas. However, the seed cotton yields of the LD4 and LD8 treatments (with LD quota) were significantly higher than those of the three MD treatments. Under the MD quota, the medium-frequency MD8 treatment yielded higher yields than the high-frequency and low-frequency MD8 and MD12 treatments. Under both LD and ND quotas, seed cotton and lint yields tended to increase with increasing irrigation frequency, particularly under the LD quota. Due to the combined effects of irrigation quota and irrigation frequency, the high-frequency LD4 treatment under the LD quota yielded the highest seed cotton yields in both years, at 4709.12 kg / hm² and 6349.52 kg / hm², respectively. 2 Under the MD quota, the low-frequency irrigation MD12 treatment had the lowest yield for both years, at 3717.63 kg / hm². 2 and 5560.75 kg / hm2 .

[0054] .

[0055] 5. Analysis of the impact of deficit irrigation on cotton fiber quality

[0056] Table 5 shows the test results of the main fiber quality indicators under different irrigation treatments in 2020-2021. Irrigation quotas and frequencies had no significant impact on cotton fiber length and strength over the two years.

[0057] In 2020, irrigation treatment had a certain impact on the uniformity of cotton under the MD quota. Under this irrigation quota, the uniformity increased with the increase of irrigation frequency, and the uniformity of the high-frequency treatment MD4 was significantly higher than that of the low-frequency treatment MD12. There was no significant difference in uniformity under other irrigation quotas. However, in 2021, there was no significant difference in uniformity among the irrigation treatments.

[0058] Irrigation treatments in 2020 had a certain impact on micronaire values, with the three treatments with MD quotas showing the most significant impact. These treatments exhibited a trend of increasing micronaire values ​​with decreasing irrigation frequency, and the micronaire value of the low-frequency treatment MD12 was significantly higher than that of the low-frequency treatment MD4. No significant differences were found among the other eight treatments. In 2021, there were no significant differences among irrigation frequencies.

[0059] .

[0060] 6. Analysis of the impact of deficit irrigation on cotton irrigation water use efficiency

[0061] Table 6 shows the impact of deficit irrigation quota and frequency on irrigation water use efficiency (IWUE). Overall, when irrigation frequency is the same, irrigation quota and IWUE are negatively correlated; when irrigation quota is the same, IWUE tends to increase with increasing irrigation frequency, and there are also significant differences between high-frequency and low-frequency treatments under the LD quota. In 2020, the variation range of IWUE for each irrigation treatment was relatively small, with the highest IWUE of 0.82 kg / m³ under the MD quota in the MD8 treatment. 3 However, there was no significant difference compared to the other two treatments; the highest IWUE for the high-frequency LD4 treatment with LD rating was 0.81 kg / m³. 3 The IWUE of the three treatments under the ND standard was significantly lower than that of the corresponding frequency treatments under the other two standards, but there was no significant difference among the three treatments under this standard. In 2021, the IWUE varied considerably among different irrigation standards, and the differences in IWUE among treatments were significant. The IWUE of the high-frequency MD4 treatment under the MD standard was the highest at 1.46 kg / m³. 3Slightly higher than mid-frequency MD8 processing, and significantly higher than low-frequency MD12 processing; the highest IWUE for high-frequency LD4 processing under LD rating is 1.25 kg / m³. 3 It is slightly higher than the mid-frequency LD8 processing and significantly higher than the low-frequency LD12 processing; there is no significant difference among the three processing methods under the ND quota, but it is significantly lower than the other two quota processing methods at the same frequency.

[0062] .

[0063] 7. The impact of deficit irrigation on cotton canopy temperature

[0064] (1) Trend of canopy temperature over time

[0065] Cotton canopy temperature (Tc) is influenced by both air temperature (Ta) and irrigation. To clarify the relationship between Tc, Ta, and irrigation, diurnal variation curves of cotton canopy temperature versus air temperature were constructed for each treatment before irrigation (July 24, 2020, and July 28, 2021) and after irrigation (July 26, 2020, and July 30, 2021) for two years (e.g., [image of diurnal variation curves]). Figure 6 As shown), according to Figure 6 The analysis results were further used to plot the variation curves of the average Tc during the entire growth period for each irrigation treatment from 12:00 to 20:00. Figure 7 ).

[0066] As can be seen from the diurnal variation curves in Figure 6, the diurnal variation trends of canopy temperature and air temperature are highly consistent across irrigation treatments. Except for Figure 6(b), where air temperature shows an upward trend starting at 0:00, Ta and Tc for all treatments show a downward trend from 0:00, reaching their lowest values ​​around 7:00 AM. Subsequently, Tc rises along with Ta, reaching its highest peak around 4:00 PM, after which Tc and Ta decrease synchronously. The Tc curves also show differences due to the influence of irrigation quota and frequency. Looking at the distribution range of the diurnal variation curves for each treatment, regardless of whether irrigation is before or after, the Tc variation curves for all treatments are relatively loose between 12:00 PM and 8:00 PM, while they are more concentrated at other times, indicating that irrigation quota and frequency affect the magnitude of the Tc peak. Furthermore, before irrigation, the peak values ​​of Tc in each treatment were close, and some treatments were even higher than Ta. However, after irrigation, the peak values ​​of Tc were significantly lower than Ta. Comparing the pre- and post-irrigation values ​​in 2021, although the peak values ​​of Ta were similar two days before and after irrigation, the peak value of Tc showed a significant decrease after irrigation. Looking at the irrigation treatments, in 2020, the peak value of Tc in the MD12 treatment was significantly higher than Ta, while the peak values ​​of Tc in the LD12 and MD12 treatments were close to Ta. In 2021, the peak values ​​of Tc in the MD8, MD12, and LD12 treatments were significantly higher than Ta, indicating that irrigation quota and irrigation frequency have a significant impact on cotton canopy temperature.

[0067] from Figure 7The Tc variation curves throughout the entire growth period show that, overall, the trends of the Tc variation curves for each irrigation treatment can be roughly divided into three stages: Before July 1st, the main factor affecting the Tc trend of each treatment was ambient temperature. During this stage, there was no regular difference between the irrigation treatments. Although the Tc curves for each treatment fluctuated slightly, the positions of the same treatment in the nine curves were not consistent over the same period in two years. Taking July 1st as the dividing point, after July 1st, the main factors affecting the Tc curve trend, in addition to ambient temperature, included irrigation treatment. Therefore, after entering this stage, the Tc ranking of each treatment changed, and some treatments over the two years showed similar changes. The result was that the Tc variation curves of the low-to-medium irrigation frequency treatments MD8 and MD12 (MD quota) were significantly above the trend lines, while the Tc variation curve of the high-to-medium irrigation frequency treatment ND4 (ND quota) was significantly below the trend lines. This regular trend continued until the end of August. Entering September, with the cessation of irrigation, cotton began to enter the boll-opening stage, affecting the Tc of this stage. The main factor influencing the curve trend became environmental factors again. However, the differences in soil moisture content and cotton growth caused by previous irrigation treatments also had a combined impact on Tc at this stage, causing the Tc change curve trend among treatments to change again. At this time, the Tc of the three ND treatments was still significantly lower than that of the other treatments, while the trend of the three MD treatments being at the top compared to the previous stage had disappeared. Furthermore, as the time remaining before water cessation increased, the distribution pattern of the Tc curves of each treatment gradually disappeared.

[0068] (2) Distribution of crown temperature difference at different growth stages

[0069] The canopy temperature difference (TDCA) is the difference between canopy temperature (Tc) and air temperature (Ta). Figure 8 The data shows the distribution of the difference between the average Tc and Ta during the same period from 12:00 to 20:00 for each treatment in the budding stage (BS), flowering and boll-forming stage (FBS), and boll-opening stage (BOS) of 2020-2021. Overall, except for the budding stage in 2020, where the TDCA distribution range of each treatment is relatively large, the TDCA data of other periods are relatively concentrated.

[0070] Comparing different growth stages, there were no regular differences among treatments during the BS period of the two-year experiment. In 2020, the median and mean ranged from -4℃ to 1℃, with some data above 0℃. In 2021, the median and mean distribution was more concentrated than in 2020, mainly within the range of -3℃ to 0℃, with most TDCA data below 0℃. Entering the FBS period, TDCA showed significant and regular differences among different irrigation quotas and frequencies. The mean and median of each treatment were similar, indicating that the fluctuation range of TDCA values ​​was relatively uniform across treatments. Except for a small number of TDCA values ​​above 0℃ in the high-frequency MD treatment (MD4) of the 2021 MD quota, the TDCA values ​​of all other treatments were below 0℃. In 2020, the average temperatures of treatments from MD4 to ND12 were -3.2℃, -3.04℃, -2.77℃, -4.39℃, -4.09℃, -3.6℃, ​​-5.52℃, -4.98℃, and -4.03℃, respectively. In 2021, the corresponding average temperatures were -2.21℃, -1.91℃, -1.66℃, -4.3℃, -3.92℃, -3.31℃, -4.77℃, -4.31℃, and -4.2℃, respectively. From the box plot, average temperature, median, and the average temperatures mentioned above, it can be seen that the TDCA value decreases with increasing irrigation quota. For the same irrigation frequency, the decrease in TDCA with increasing irrigation quota is more pronounced; and for the same irrigation quota, the TDCA value decreases further with increasing irrigation frequency. The TDCA trends of each treatment during the BOS period were basically consistent with those during the FBS period, but they differed from those during the FBS period in terms of data size and distribution. In 2020, the average values ​​for each treatment from MD4 to ND12 were -2.41℃, -2.38℃, -2.11℃, -2.32℃, -2.19℃, -1.82℃, -3.99℃, -3.5℃, and -3.13℃, respectively. In 2021, the corresponding average values ​​were -1.78℃, -1.25℃, -0.64℃, -1.89℃, -1.57℃, -1.03℃, -3.05℃, -2.04℃, and -1.72℃, respectively. From the box plot, average values, median, and the aforementioned average values, it can be seen that the TDCA values ​​for each treatment during the BOS period were greater than those for the corresponding treatments during the FBS period, and the differences in the average TDCA values ​​among all treatments during this period were smaller than those during the FBS period.

[0071] (3) Temperature differences in the canopy during UAV thermal imaging

[0072] Thermal imaging drones were used to acquire the thermal conductivity (Tc) of cotton for each treatment at 16:00 the day before irrigation. The air temperature at that time was recorded at a weather station as 35.53℃. FLIR Tools software was used to extract the Tc values ​​from the captured images. The results are as follows: Figure 9As shown in the results, the average Tc values ​​for treatments MD4 to ND12 are 31.8℃, 30.1℃, 33.5℃, 30.1℃, 30.3℃, 32.0℃, 29.6℃, 29.7℃, and 30.2℃, respectively, with corresponding TDCA values ​​of -3.73℃, -5.43℃, -2.03℃, -5.43℃, -5.23℃, -3.53℃, -5.93℃, -5.83℃, and -5.24℃. These data indicate that, with a fixed irrigation frequency, Tc decreases with increasing irrigation quota, and the decrease is more pronounced at higher irrigation frequencies. With a fixed irrigation quota, the canopy temperature increases with decreasing irrigation frequency for both LD and ND quota treatments, with the LD quota treatment showing a significantly higher Tc value at lower irrigation frequencies. Temperature differences are not significant for other treatments, while different irrigation frequencies have little impact on Tc under the ND irrigation quota. The Tc of different irrigation frequencies under the MD quota differs from the variation pattern under the other two quotas. Under the MD quota, the Tc of each treatment is ranked as MD12>MD4>MD8.

[0073] The results showed that the deficit irrigation quota and frequency affected the cotton canopy temperature and canopy-temperature difference. The canopy temperature in each irrigation treatment reached its lowest point around 7:00 AM and its highest point around 4:00 PM. Irrigation quota and frequency affected the peak Tc value; after irrigation, the peak Tc value decreased and was significantly lower than Ta. After the start of irrigation, the Tc change curves for MD8, MD12, and LD12 were clearly above the trend lines, while the Tc change curve for ND1 was clearly below the trend lines, indicating a negative correlation between Tc and irrigation quota and frequency. During the flowering and boll-forming stage, except for a few TDCA values ​​greater than 0℃ under the MD quota, the TDCA values ​​for all other treatments were less than 0℃. The average TDCA value ranged from -2.77℃ to 5.52℃ in 2020 and from -1.66℃ to 4.77℃ in 2021. Meanwhile, this example obtained the same pattern as the ground-based infrared sensor by using a thermal imaging drone to acquire cotton canopy temperature, indicating that it is feasible to use drone thermal imaging to conduct moisture stress monitoring based on canopy temperature.

[0074] In summary, canopy temperature is most directly affected by air temperature. Therefore, canopy temperature usually follows a diurnal variation curve, with daytime temperatures rising due to the absorption of solar radiation and the increase in temperature. Besides being affected by air temperature, cotton canopy temperature also exhibits a highly significant negative correlation with field water consumption. Therefore, irrigation quota and frequency also have a significant impact on canopy temperature. This is due to the heat energy consumed by evaporation and transpiration, as well as the cooling effect of water vapor generated far from the crop canopy. When the energy irradiated onto the crop surface is used for evaporation (latent heat or transpiration) rather than heating the plant surface, the canopy temperature will decrease. Water-stressed plants reduce transpiration and are usually warmer than unstressed crops. In this study, different irrigation quotas and frequencies lead to different effective soil water content, resulting in different evaporation and transpiration conditions, which in turn affect the changes in canopy temperature. The medium and low irrigation treatments MD8 and MD12 with MD quotas, and the low irrigation frequency treatment LD12 with LD quota, have higher canopy temperatures due to low irrigation quotas or longer irrigation intervals. The above effects can be observed from the distribution of the curves corresponding to each treatment on the canopy temperature change curve throughout the entire growth period.

[0075] The canopy temperature difference (TDCA) is closely related to water deficit and can be used as an indicator of drought stress and irrigation regime. The diurnal variation curves in this study show that both air temperature and TDCA reach their highest levels around 16:00, and TDCA is relatively stable. The TDCA around 16:00 can be used to assess the water status of cotton fields in Xinjiang. Due to the cooling effect of water vapor, the cotton canopy temperature drops below the air temperature; therefore, under good evaporation and transpiration conditions, TDCA is usually below 0℃. The flowering and boll-forming stage is a period of high water demand and water sensitivity for cotton. Water deficiency during this period can cause water stress and affect yield. The TDCA values ​​show that the three treatments under the MD quota and the low-frequency treatment LD12 under the LD quota have larger TDCA values, indicating that cotton is prone to water stress under low irrigation quotas and frequencies. Conversely, the TDCA values ​​for the medium and high irrigation frequencies LD8, LD12, and the three treatments under the ND quota are smaller, indicating that the corresponding irrigation quotas and frequencies can meet the cotton's transpiration requirements. Furthermore, under the same irrigation quota, a higher irrigation frequency is more beneficial for plant transpiration.

[0076] The use of drones equipped with thermal imaging lenses to acquire images of large areas of the canopy can overcome the serious shortcomings of other methods that use sample points to represent the whole. In this experiment, the cotton canopy temperature obtained by drones equipped with thermal imaging lenses showed a pattern consistent with that of ground-based infrared sensors. That is, with a fixed irrigation frequency, Tc decreases as the irrigation quota increases. With a fixed irrigation quota, Tc decreases as the irrigation frequency increases. However, under the MD quota, the MD8 treatment with a medium irrigation frequency has the lowest Tc. This indicates that drone thermal imaging is feasible for monitoring water stress based on canopy temperature.

Claims

1. A high-efficiency irrigation method for cotton-growing areas in Xinjiang based on crown temperature difference, characterized in that, During the cotton flowering and boll-forming stage, the canopy temperature difference (TDCA) in the cotton field was monitored daily from 14:00 to 18:

00. Based on the TDCA of the cotton field ranging from -1.0℃ to -6.0℃, a corresponding irrigation plan was formulated: when -2℃ < TDCA ≤ -1℃, 370–520 m³ of irrigation was carried out on the same day. 3 / hm 2 When -3℃ < TDCA ≤ -2℃, the daily irrigation volume is 250–340 m³. 3 / hm 2 When -4℃ < TDCA ≤ -3℃, the daily irrigation volume is 120–180 m³. 3 / hm 2 When -5℃≤TDCA≤-4℃, the daily irrigation volume is 60~90 m³. 3 / hm 2 When TDCA < -5℃, irrigation is not carried out on that day to meet the needs of irrigation on demand, thereby improving water use efficiency while ensuring cotton yield.

2. The efficient irrigation method for cotton-growing areas in Xinjiang according to claim 1, characterized in that, Obtain the daily crown temperature difference as follows: Select at least three representative monitoring points in the cotton field to be monitored, and set up infrared temperature sensors to continuously monitor the cotton canopy temperature Tc and the ambient temperature Ta in real time. Record a set of data every 10 minutes from 14:00 to 18:00 on the same day, and calculate the canopy temperature difference: TDCA=Tc-Ta. Take the average value, which is the canopy temperature difference for the day.

3. The efficient irrigation method for cotton-growing areas in Xinjiang according to claim 2, characterized in that, To monitor the temperature of the cotton canopy, an infrared temperature sensor was installed 20 cm above the cotton canopy at a 45° angle downwards and slightly northwards to prevent interference from sunlight.

4. The efficient irrigation method for cotton-growing areas in Xinjiang according to claim 1, characterized in that, Obtain the daily crown temperature difference as follows: Using an unmanned aerial vehicle (UAV) platform equipped with an infrared thermal imaging camera, infrared thermal images of the cotton canopy in the cotton field to be monitored were collected from 15:00 to 17:00 on the same day. The thermal images of the leaves and their corresponding temperature information were exported using FLIR Tools software. The canopy temperature was obtained by averaging the temperature of each pixel in the area, and then the ambient temperature was subtracted to obtain the canopy temperature difference for the day.

5. The efficient irrigation method for cotton-growing areas in Xinjiang according to claim 1, characterized in that, In the cotton-growing areas of southern Xinjiang, winter irrigation and spring irrigation are implemented in cotton fields before cotton sowing to suppress salt deposits and create soil moisture. Winter irrigation takes place from November 10th to November 25th, with an irrigation volume of 1500–2500 m³. 3 / hm 2 Spring irrigation takes place from February 15th to February 20th of the following year, with an irrigation volume of 800–1200 m³. 3 / hm 2 .

6. The efficient irrigation method for cotton-growing areas in Xinjiang according to claim 1, characterized in that, The irrigation method is drip irrigation under mulch.

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