A summer maize nitrogen nutrition diagnosis method based on infrared thermal imaging technology

Abstract

The application discloses a summer maize nitrogen nutrition diagnosis method based on infrared thermal imaging technology, and is applied to the technical field of summer maize nitrogen nutrition diagnosis. The method comprises the following steps: obtaining summer maize canopy thermal imaging data under different heights, angles and time shooting modes at different growth periods respectively; synchronously measuring the above-ground plant biomass, nitrogen accumulation amount, leaf area index, leaf SPAD value and absorbed photosynthetically active radiation component of summer maize at different growth periods; analyzing the difference of summer maize canopy temperature image information and the relationship between the nitrogen nutrition index; determining the influence effect of the shooting mode on the canopy temperature and determining the optimal shooting mode; determining the critical temperature according to the relationship between the canopy temperature and the relative yield, and constructing a summer maize nitrogen fertilizer real-time topdressing model at different growth periods, so as to provide theoretical support and thought reference for the application and development of the near-ground infrared thermal imaging precision diagnosis of summer maize nitrogen nutrition.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of summer corn nitrogen nutrition diagnosis, and more particularly to a summer corn nitrogen nutrition diagnosis method based on infrared thermal imaging technology. BACKGROUND

[0002] Nitrogen is the most demanding nutrient element in the process of crop growth and development, and is also the basic component element of signal transduction material and crop secondary metabolism. Nitrogen plays an important role in biological inheritance, protein synthesis, and photosynthetic material storage and transport. When plants are short of nitrogen, they usually show dwarf plant type, decreased biomass accumulation, chlorophyll synthesis and photosynthesis, and early leaf senescence. Excessive nitrogen is easy to cause crops to be late in maturity, poor in stress resistance, and "luxurious absorption" of nutrients. At present, in order to continuously increase crop yield, excessive nitrogen is still commonly used in production practice. Excessive nitrogen not only reduces crop yield and quality, but also causes a large amount of nitrogen residue in soil, resulting in pollution of underground water and atmosphere, and further endangering human health and sustainable development of ecological environment. Therefore, sufficient and reasonable nitrogen supply is very important for promoting crop growth, yield formation, quality construction and green agricultural development.

[0003] Real-time and accurate nitrogen management is one of the most critical nutrient management measures in crop production practice aiming at high yield and nutrient efficiency. Using crop light and temperature response specificity to quickly monitor and accurately diagnose crop nitrogen nutrition has been a research hotspot in smart agriculture and real-time field nutrient integrated management and application. At present, the traditional crop nitrogen nutrition monitoring is mainly based on laboratory chemical analysis. Although this method can obtain relatively accurate results, it is time-consuming, costly and difficult to implement on a macro scale due to sample collection, pre-treatment and indoor analysis, etc. affecting the timeliness and objectivity of agricultural decision-making. At present, infrared thermal imaging technology, as one of the most convenient tools for thermal infrared remote sensing, has been rapidly developed and widely applied due to its rapid, non-destructive and accurate advantages. However, the application of thermal imaging technology in crop nitrogen nutrition diagnosis is easily affected by weather and operation methods (such as shooting time, shooting height, shooting angle, etc.), and crop canopy thermal infrared image acquisition mainly follows the fixed or original recommended method. The standardization of instrument shooting parameters and the construction of quantitative diagnosis model are relatively less studied. How to obtain relatively accurate crop canopy thermal infrared image information is the key to the real-time monitoring of crop nitrogen nutrition by using this technology, and obtaining high-quality temperature images is the premise and guarantee for establishing nitrogen nutrition parameters and quantitative diagnosis model. Summer maize is a nitrogen response sensitive crop with short growth period, significant changes in biomass, leaf area index, canopy width and other population structure indicators, which in turn causes large differences in nitrogen nutrition and canopy temperature information at different growth stages. When using infrared thermal imaging technology to carry out accurate monitoring of summer maize nitrogen nutrition, the changes in canopy structure caused by the difference effects of nitrogen nutrition and growth period, the standardization of inversion parameters and the internal plant nutrition-spectrum information mechanism should be fully considered. Therefore, how to provide a summer maize nitrogen nutrition diagnosis method based on infrared thermal imaging technology is a problem that needs to be solved by those skilled in the art. SUMMARY

[0004] Therefore, the present application provides a summer maize nitrogen nutrition diagnosis method based on infrared thermal imaging technology, which obtains the canopy temperature of summer maize by infrared thermal imaging technology and then establishes a real-time diagnosis equation for summer maize nitrogen nutrition.

[0005] In order to achieve the above purpose, the present application provides the following technical scheme:

[0006] A summer maize nitrogen nutrition diagnosis method based on infrared thermal imaging technology, comprising the following steps:

[0007] S1, obtaining summer maize canopy thermal imaging data under different height, angle and time shooting modes at different growth stages; wherein the height is 0.5 m, 1.5 m and 2.5 m, the angle is 30°, 60° and 90°, and the time is 9:00, 12:00, 14:00 and 16:00;

[0008] S2, synchronously determining the above-ground plant biomass, nitrogen accumulation amount, leaf area index, leaf SPAD value and absorbed photosynthetically active radiation component of summer maize at different growth stages;

[0009] S3, analyzing the relationship between the nitrogen fertilizer application rate and yield, above-ground biomass, nitrogen accumulation amount, leaf area index, leaf SPAD value and absorbed photosynthetically active radiation component of summer maize, and determining the influence of the nitrogen fertilizer application rate on the growth and development of summer maize;

[0010] S4, analyzing the relationship between the canopy temperature and nitrogen fertilizer application rate, yield, above-ground biomass, nitrogen accumulation amount, leaf area index, leaf SPAD value and absorbed photosynthetically active radiation component of summer maize under different shooting modes, judging the influence of different shooting modes on the canopy temperature and determining the optimal shooting mode;

[0011] S5, determining the critical temperature at different growth stages according to the relationship between the canopy temperature and relative yield of summer maize under the optimal shooting mode;

[0012] S6, constructing a canopy temperature nitrogen fertilizer real-time topdressing model based on the optimal shooting mode of summer maize at different growth stages.

[0013] Optionally, S1 is specifically: setting different vertical heights of the summer maize canopy as the shooting height, setting different shooting times, setting different angles between the infrared thermal imager and the horizontal plane as the shooting angle, and shooting at the jointing stage, the big bell mouth stage, the silking stage and the grain filling stage of summer maize, respectively.

[0014] Optionally, S2 is specifically:

[0015] At the jointing stage, the big bell mouth stage, the silking stage and the grain filling stage of summer maize, respectively, 4 representative maize plants are selected in each planting plot, 105°C is used for 30 minutes of fixation, 75°C is used for drying to constant weight, the above-ground biomass is calculated, the maize samples after drying at each growth stage are crushed and sieved, H2SO4-H2O2 method is used for digestion, and AA3 flow injection analyzer is used for determining the plant nitrogen content, the plant nitrogen accumulation amount is calculated, 15m2 of quadrats are selected in each plot at the mature stage, threshing and airing are performed to constant weight, and the grain yield is calculated; 2

[0016] The maize plant leaves collected at each growth stage are all removed and laid on a black background cloth, one 10cm*10cm standard white plate is placed at each corner, a digital camera is used for shooting, and then the leaf area index is analyzed and calculated;

[0017] At each growth stage, 10 maize plants with similar growth vigor are selected in each planting plot, a daily chlorophyll meter is used to measure the leaf SPAD value, and the average value is obtained by testing the results of each planting plot;

[0018] ​The photosynthetically active radiation of the summer corn canopy and the base is measured by using a canopy analyzer in each growth period, and the absorbed photosynthetically active radiation component is calculated.

[0019] Optionally, the calculation of the absorbed photosynthetically active radiation component is specifically as follows:

[0020]

[0021] In the formula, FPAR is the absorbed photosynthetically active radiation component, PAR is the canopy incident photosynthetically active radiation, PAR is the canopy reflected photosynthetically active radiation, PAR is the base incident photosynthetically active radiation, and PAR is the base reflected photosynthetically active radiation. ci cr gi gr

[0022] Optionally, S3 is specifically as follows:

[0023] The Person correlation analysis method is used to quantitatively analyze the relationship between the nitrogen fertilizer amount and the yield, the nitrogen fertilizer amount and the above-ground biomass, the nitrogen fertilizer amount and the nitrogen accumulation amount, the nitrogen fertilizer amount and the leaf area index, the nitrogen fertilizer amount and the leaf SPAD value, the nitrogen fertilizer amount and the absorbed photosynthetically active radiation component, and the nitrogen fertilizer amount and the summer corn canopy temperature, and the change trend of each parameter with the increase of the nitrogen fertilizer amount is analyzed.

[0024] Optionally, S4 is specifically as follows:

[0025] The Person correlation analysis method is used to quantitatively analyze the relationship between the summer corn canopy temperature and the nitrogen fertilizer amount, the yield, the above-ground biomass, the nitrogen accumulation amount, the leaf area index, the leaf SPAD value, and the absorbed photosynthetically active radiation component under different shooting angles, different shooting heights, and different shooting times, and the best shooting angle, the best shooting height, and the best shooting time of the summer corn in different growth periods are determined according to the correlation coefficients and the determination coefficients.

[0026] Optionally, S5 is specifically as follows:

[0027] A monomial quadratic equation is used to fit the summer corn canopy temperature in each growth period and the relative yield in the maturation period under the best shooting mode, the critical value is determined according to the fitting classification standard, the relative yield calculation method is the ratio of the summer corn yield in the maturation period to the highest yield, 95% of the relative yield is taken as the critical value, and the nitrogen fertilizer is deficient when the value is lower than 95%, and the nitrogen fertilizer is rich when the value is higher than 95%, so as to determine the critical temperature value in each growth period.

[0028] Optionally, S6 is specifically as follows:

[0029] ​​​​The relationship between the nitrogen fertilizer consumption and yield of summer corn at each growth period is fitted by using a monomial quadratic equation, the fitting relationship between the total nitrogen fertilizer consumption and yield during the whole growth period is obtained, the partial derivative of the fitting relationship is obtained to obtain the maximum yield and the corresponding nitrogen fertilizer consumption, the nitrogen fertilizer consumption is taken as a reference value of the total amount of nitrogen topdressing, and the amount of nitrogen topdressing is:

[0030] N top = N c -N fer

[0031]

[0032] In the formula, N top is the amount of nitrogen topdressing, N c is the reference value of the total amount of nitrogen topdressing, N fer is the current nitrogen fertilizer level, T ca is the current canopy temperature, and a, b and c are constants, the a, b and c values of each growth period are substituted into the amount of nitrogen topdressing calculation equation to obtain the amount of nitrogen topdressing calculation equation of each growth period.

[0033] Compared with the prior art, the summer corn nitrogen nutrition diagnosis method based on the infrared thermal imaging technology has the following beneficial effects: the present application deeply and systematically analyzes the influence and difference effect of factors such as shooting time, shooting height and shooting angle on the canopy temperature of summer corn, determines a convenient and accurate optimal acquisition method of the canopy thermal image of summer corn, and constructs a real-time diagnosis equation of the nitrogen nutrition of summer corn, so as to provide theoretical and practical references for the real-time and accurate diagnosis of the nitrogen nutrition of summer corn and the accurate application of nitrogen fertilizer. BRIEF DESCRIPTION OF DRAWINGS

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced as follows. Obviously, the drawings in the following description are only embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of the provided drawings.

[0035] Figure 1 The flow chart of the summer corn nitrogen nutrition diagnosis method of the present application;

[0036] Figure 2 The schematic diagram of the analysis results of the nitrogen fertilizer consumption and yield in the embodiment of the present application;

[0037] Figure 3 The schematic diagram of the analysis results of the nitrogen fertilizer consumption and above-ground biomass in the embodiment of the present application;

[0038] Figure 4 The schematic diagram of the analysis results of the nitrogen fertilizer consumption and nitrogen accumulation in the embodiment of the present application;

[0039] Figure 5 Figure is a schematic diagram of the analysis results of nitrogen fertilizer use amount and leaf area index in the embodiment of the present application;

[0040] Figure 6 Figure is a schematic diagram of the analysis results of nitrogen fertilizer use amount and leaf SPAD value in the embodiment of the present application;

[0041] Figure 7 Figure is a schematic diagram of the analysis results of nitrogen fertilizer use amount and absorbed photosynthetically active radiation component in the embodiment of the present application;

[0042] Figure 8 Figure is a schematic diagram of the fitting results of the relationship between canopy temperature and yield in the embodiment of the present application;

[0043] Figure 9 Figure is a schematic diagram of the fitting results of the relationship between nitrogen fertilizer use amount and yield in the embodiment of the present application;

[0044] Figure 10 Figure is a summer corn canopy thermograph under different shooting heights in the embodiment of the present application;

[0045] Figure 11 Figure is a summer corn canopy thermograph under different shooting angles in the embodiment of the present application;

[0046] Figure 12 Figure is a summer corn canopy thermograph under different shooting times in the embodiment of the present application. DETAILED DESCRIPTION

[0047] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0048] The embodiment of the present application discloses a summer corn nitrogen nutrition diagnosis method based on infrared thermal imaging technology, as shown in the figure, comprising the following steps: Figure 1

[0049] S1, summer corn canopy thermal imaging data under different shooting modes of different heights, angles and times in different growth periods are obtained respectively; wherein the heights are 0.5 m, 1.5 m and 2.5 m respectively, the angles are 30°, 60° and 90° respectively, and the times are 9:00, 12:00, 14:00 and 16:00 respectively;

[0050] S2, the above-ground plant biomass, nitrogen accumulation amount, leaf area index, leaf SPAD value and absorbed photosynthetically active radiation component of summer corn in different growth periods are determined synchronously;​

[0051] S3, analyze the relationship between the nitrogen fertilizer application rate of summer corn and yield, aboveground biomass, nitrogen accumulation, leaf area index, leaf SPAD value and absorbed photosynthetically active radiation component, and determine the influence of nitrogen fertilizer application rate on the growth and development of summer corn;

[0052] S4, analyze the relationship between canopy temperature and nitrogen fertilizer application rate, yield, aboveground biomass, nitrogen accumulation, leaf area index, leaf SPAD value and absorbed photosynthetically active radiation component under different shooting modes of summer corn, determine the influence of different shooting modes on canopy temperature and determine the best shooting mode;

[0053] S5, according to the relationship between canopy temperature and relative yield of summer corn under the best shooting mode, determine the critical temperature at different growth stages;

[0054] S6, construct a canopy temperature nitrogen fertilizer real-time topdressing model based on the best shooting mode of summer corn at different growth stages.

[0055] Further, S1 is specifically: set different vertical heights of summer corn canopy as shooting height, set different shooting times, set different angles between infrared thermal imager and horizontal plane as shooting angle, and shoot at the jointing stage, large trumpet stage, silk stage and grain filling stage of summer corn respectively.

[0056] In an embodiment of the present application, summer corn nitrogen fertilizer effect field test is carried out for two consecutive years (2022-2023), and five treatments are set in two years of test, which are 0 (N0), 70 (N70), 140 (N140), 210 (N210) and 280 (N280) kg / hm 2 , each plot area is 30m 2 (5.0m×6.0m), three times of repetition, random block arrangement. The nitrogen, phosphorus and potassium fertilizer varieties are ordinary urea (N 46%), ESN resin coated urea (containing N 44%), superphosphate (P2O512%) and potassium chloride (K2O60%). The nitrogen fertilizer is applied according to the ratio of ordinary urea to coated urea 5:5, and the phosphorus and potassium fertilizer application rates are P2O590 kg / hm 2 and K2O75 kg / hm 2 . All fertilizers are base fertilizer and are applied at once at the five-leaf stage (V5) of summer corn to avoid the influence of fertilizer topdressing on the continuity of summer corn canopy temperature and nitrogen nutrition.

[0057] The TiX640 infrared thermal imager (Fluke, TiX640, USA) produced by the United States Fluke Company was used to collect the summer corn canopy temperature data at the jointing stage, the big trumpet stage, the silk stage and the grain filling stage of summer corn, respectively, in clear, cloudless, windless or small wind weather. The instrument waveband range is 7.5um-14um, the image resolution is 640x480 (307200 pixels), the IFOV (spatial resolution) is 0.8mRad, the thermal sensitivity is ≤0.03℃ at the target temperature of 30℃, and the field of view angle is 30.9°x23.1°. In order to obtain more representative canopy temperature information, the air temperature was obtained before and after shooting of each plot to correct;

[0058] In the embodiment of the application, different shooting modes are as follows:

[0059] 1) Shooting time: the infrared thermal imager was adjusted to an angle of 60° with the horizontal plane at a vertical height of 1.5m from the summer corn canopy, and shooting was performed at four time periods of 9:00, 12:00, 14:00 and 16:00, with three photos taken for each plot;

[0060] 2) Shooting was performed at 12:00-14:00 of the above growth periods, the infrared thermal imager was adjusted to an angle of 60° with the horizontal plane, and shooting was performed at a height of 0.5m, 1.5m and 2.5m from the summer corn canopy, with three photos taken for each plot;

[0061] 3) The shooting angle was also 12:00-14:00 of the above growth periods, the infrared thermal imager was adjusted to an angle of 30°, 60° and 90° with the horizontal plane at a vertical height of 1.5m from the summer corn canopy, and shooting was performed, with three photos taken for each plot.

[0062] Further, S2 is specifically:

[0063] At the jointing stage, the big trumpet stage, the silk stage and the grain filling stage of summer corn, four representative corn plants were selected in each plot, killed at 105℃ for 30min, dried at 75℃ to constant weight, and the above-ground biomass (kg / hm 2 ) was calculated, the corn samples after drying at each growth period were crushed and sieved, digested by H2SO4-H2O2 method, and the plant nitrogen content (%) was measured by AA3 flow injection analyzer (Germany SEAL), and the plant nitrogen accumulation (kg / hm 2 ) was calculated, and 15m 2 of quadrat were selected in each plot at the mature stage, threshed and dried to constant weight, and the grain yield (kg / hm 2 ) was calculated;

[0064] All the leaves of the corn plants collected in each growth period were respectively laid on black background cloth, 1 10cm*10cm standard white board was placed in each corner, leaf area index (LAI) was analyzed and calculated after taking pictures by a digital camera;

[0065] 10 corn plants with similar growth vigor were respectively selected in each growth period in each planting plot, SPAD value of the leaves was measured by a daily chlorophyll meter, and average values were obtained by testing results of each planting plot;

[0066] The photosynthetically active radiation of the summer corn canopy and the base was measured by a canopy analyzer in each growth period, and the absorbed photosynthetically active radiation component (FPAR) was calculated.

[0067] Further, the absorbed photosynthetically active radiation component is specifically as follows:

[0068]

[0069] In the formula, FPAR is the absorbed photosynthetically active radiation component, PAR ci is the canopy incident photosynthetically active radiation, PAR cr is the canopy reflected photosynthetically active radiation, PAR gi is the base incident photosynthetically active radiation, and PAR gr is the base reflected photosynthetically active radiation.

[0070] Further, S3 is specifically as follows:

[0071] The Person correlation analysis method was used to quantitatively analyze the relationship between the nitrogen fertilizer use amount and yield, the nitrogen fertilizer use amount and aboveground biomass, the nitrogen fertilizer use amount and nitrogen accumulation amount, the nitrogen fertilizer use amount and leaf area index, the nitrogen fertilizer use amount and leaf SPAD value, the nitrogen fertilizer use amount and absorbed photosynthetically active radiation component, and the nitrogen fertilizer use amount and summer corn canopy temperature, and the change trend of each parameter with the increase of the nitrogen fertilizer use amount was analyzed.

[0072] The basic data input and the previous processing were performed by using Microsoft Excel 2016; variance analysis and significance test (LSD method) were performed by using SPSS 20.0 software, and the significance level was set to P<0.5;

[0073] In an embodiment of the present application, the analysis results of the nitrogen fertilizer use amount and yield of the summer corn are as shown in Figure 2 The two-year summer corn yields are respectively highest at N210 and N280, and are 12655 and 11707kg / hm 2Compared to nitrogen-free (N0), the average increase in grain yield of summer maize treated with nitrogen in 2022 and 2023 was 30.7% and 30.9%, respectively, showing significant effects. A fertilizer effect function was used to fit the relationship between nitrogen application rate and yield in summer maize; the relationship exhibited a linear + plateau trend, with a coefficient of determination (R²) of [missing value]. 2 The values ​​were 0.849 and 0.941 respectively, and the optimal nitrogen application rates were 174 and 215 kg / hm² respectively. 2 The corresponding yields are 12,589 and 11,707 kg / hm, respectively. 2 ;

[0074] The analysis results of nitrogen fertilizer application and aboveground biomass are as follows: Figure 3 As shown, the aboveground biomass of summer maize at each growth stage is significantly affected by nitrogen fertilizer application. With increasing nitrogen application, the aboveground biomass initially increases and then slightly decreases at each stage, reaching its peak at N210. There is no significant difference between N210 and N280. A comprehensive analysis over two years shows that compared to no nitrogen application (N0), the average increases in aboveground biomass at the jointing, tasseling, silking, grain-filling, and maturity stages after nitrogen application were 57.87%, 51.86%, 41.71%, 52.07%, and 50.61%, respectively. During the growth period, the average aboveground biomass at the jointing, tasseling, silking, grain-filling, and maturity stages were 2009.9, 5794.2, 8828.9, 18183.6, and 22049.5 kg / hm², respectively. 2 ;

[0075] The analysis results of nitrogen fertilizer application and nitrogen accumulation are as follows: Figure 4 As shown, consistent with the biomass change trend, the nitrogen accumulation in the aboveground parts of summer maize also increased significantly with increasing nitrogen fertilizer application, and then tended to stabilize as the growth stage progressed. In 2022, the average aboveground nitrogen accumulation for each nitrogen application treatment at the jointing stage, large trumpet stage, silking stage, grain-filling stage, and maturity stage were 48.1, 164.1, 182.1, 265.3, and 234.9 kg / hm², respectively. 2 The values ​​for 2020, 2021, and 2022 were 83.5, 98.9, 163.5, 270.5, and 314.9 kg / hm², respectively. 2 In the treatment group, the average nitrogen accumulation of summer maize plants in the nitrogen-treated group during each growth stage in 2022 was 192.7 kg / hm². 2 This represents a 55.70% increase compared to NO treatment; the figure for 2023 was 207.7 kg / hm². 2 This represents an increase of 106.83% compared to N0.

[0076] The analysis results of nitrogen fertilizer application and leaf area index are as follows: Figure 5As shown, with the development of the growth period, the LAI of summer maize showed a trend of first increasing and then decreasing. Among the treatments, the LAI of summer maize was significantly different under different nitrogen application rates, and the effects of N210 and N280 were the most significant in 2022 and 2023. Compared with N0, the average increase of LAI in each period in 2022 was 13.51%-47.39%, 12.01%-34.83%, 10.24%-29.84%, and 15.13%-41.27%, respectively; in 2023, the LAI increased by 26.58%-85.47%, 25.78%-65.09%, 9.07%-28.34%, and 26.91%-60.88%, respectively;

[0077] The analysis results of nitrogen fertilizer application rate and leaf SPAD value are shown in Figure 6 As shown, with the development of the growth period, the SPAD value of summer maize in 2022-2023 showed a trend of filling period > silk stage > large bell stage > jointing stage. Different nitrogen fertilizer application rates had a significant effect on the SPAD value of summer maize leaves. With the increase of nitrogen fertilizer application rate, the SPAD value of leaves showed a trend of first increasing and then stabilizing. In both years, N210 and N280 were significantly higher than other treatments, and the increase of nitrogen application treatment in 2022 was 4.18%-16.85%, 4.34%-14.67%, 4.26%-18.54%, and 3.33%-12.25%, respectively; in 2023, the increase of N0 treatment was 4.19%-14.01%, 6.03%-21.41%, 4.49%-13.34%, and 5.97%-13.92%, respectively;

[0078] The analysis results of nitrogen fertilizer application rate and absorbed photosynthetically active radiation component are shown in Figure 7 As shown, the FPAR value of summer maize canopy was significantly affected by nitrogen fertilizer effect, and showed certain differences during different growth periods. Among different nitrogen fertilizer application rates, the FPAR value showed a trend of first increasing and then stabilizing with the increase of nitrogen fertilizer application rate. Based on the analysis of nitrogen fertilizer effect in each period, the FPAR value of summer maize canopy was 0.700, 0.739, 0.779, 0.820, and 0.827 under nitrogen fertilizer application rates of 0, 70, 140, 210, and 280 kg / hm 2 During the growth period, the FPAR values of summer maize canopy in the jointing stage, large bell stage, silk stage, filling stage, and mature stage were 0.674, 0.778, 0.823, and 0.817, respectively, in the test years (2022 and 2023), with a large difference;

[0079] The analysis results of nitrogen fertilizer application rate and summer maize canopy temperature under different shooting heights are shown in Table 1, and the thermal imaging map of summer maize canopy is shown in Figure 10As shown in the table, with the increase of shooting height, the average canopy temperature in 2022 showed a gradually decreasing trend, and the average canopy temperature was 29.63, 29.51 and 29.47℃ when the shooting height was 0.5m, 1.5m and 2.5m respectively; the average canopy temperature in 2023 showed a first decreasing and then increasing trend with the increase of shooting height, and the average temperature was 31.13, 31.04 and 31.18℃ when the shooting height was 0.5m, 1.5m and 2.5m respectively.

[0080] As shown in the table, with the increase of shooting height, the average canopy temperature in 2022 showed a gradually decreasing trend, and the average canopy temperature was 29.63, 29.51 and 29.47℃ when the shooting height was 0.5m, 1.5m and 2.5m respectively; the average canopy temperature in 2023 showed a first decreasing and then increasing trend with the increase of shooting height, and the average temperature was 31.13, 31.04 and 31.18℃ when the shooting height was 0.5m, 1.5m and 2.5m respectively.

[0081] Table 1 Nitrogen fertilizer amount and summer corn canopy temperature at different shooting heights

[0082]

[0083] The analysis results of nitrogen fertilizer amount and summer corn canopy temperature at different shooting angles are shown in Table 2, and the summer corn canopy thermal imaging diagram is shown in Figure 11 As shown in the table, with the increase of shooting height, the average canopy temperature in 2022 showed a gradually decreasing trend, and the average canopy temperature was 29.63, 29.51 and 29.47℃ when the shooting height was 0.5m, 1.5m and 2.5m respectively; the average canopy temperature in 2023 showed a first decreasing and then increasing trend with the increase of shooting height, and the average temperature was 31.13, 31.04 and 31.18℃ when the shooting height was 0.5m, 1.5m and 2.5m respectively.

[0084] Table 2 Nitrogen fertilizer amount and summer corn canopy temperature at different shooting angles

[0085]

[0086] The analysis results of nitrogen fertilizer amount and summer corn canopy temperature at different shooting times are shown in Table 3, and the summer corn canopy thermal imaging diagram is shown in Figure 12It can be seen that the summer corn canopy temperature increases first and then decreases with the shooting time within the day. Overall, the summer corn canopy temperature is the lowest at 9:00 am and the highest at 14:00. Compared with 9:00, the average temperature of summer corn canopy at 12:00, 14:00 and 16:00 in 2022 increased by 11.38%, 17.03% and 14.03% respectively. The change trend in 2023 is opposite, and the average temperature of summer corn canopy increases by 3.91%, 5.46% and 3.38% respectively. The results in 2022 show that with the increase of nitrogen application rate, the canopy temperature of summer corn at 12:00 shows a gradually decreasing and then stable change, while there is no consistent change rule at other shooting times. In 2023, the canopy temperature of summer corn at different shooting times gradually decreases and then tends to be stable with the increase of nitrogen application rate.

[0087] Table 3 Nitrogen application rate and summer corn canopy temperature at different shooting times

[0088]

[0089]

[0090] With the increase of nitrogen application rate, the canopy temperature of summer corn decreases first and then gradually tends to be stable, and the decreasing speed slows down between N210 and N280. Compared with N0 treatment, the average canopy temperature of summer corn in nitrogen treatments N70, N140, N210 and N280 in 2022 decreases by 0.48, 0.95, 1.44 and 1.55℃ respectively; the average canopy temperature of summer corn in nitrogen treatments in 2023 decreases by 0.52, 1.17, 2.18 and 2.52℃ respectively;

[0091] Further, S4 is specifically:

[0092] The relationship between the canopy temperature of summer corn and nitrogen application rate, yield, aboveground biomass, nitrogen accumulation, leaf area index, leaf SPAD value and absorbed photosynthetically active radiation component at different shooting angles, different shooting heights and different shooting times is quantitatively analyzed by Person correlation analysis method, and the best shooting angle, the best shooting height and the best shooting time of summer corn at different growth stages are determined according to the correlation coefficient and the determination coefficient.

[0093] In an embodiment of the present application, the relationship between the average canopy temperature of summer corn at different shooting heights and nitrogen nutrition indicators almost reaches a very significant level (P<0.01). When the shooting height is 0.5m, 1.5m and 2.5m, the determination coefficients (R 2) were 0.898, 0.916, 0.894 and 0.779, 0.807, 0.789, respectively. During the growth period, the canopy temperature at the height of 0.5 m at the jointing stage was better correlated, the height of 2.5 m at the booting stage was best, and the height of 1.5 m at the silking stage to the grain filling stage was best. Comprehensive analysis showed that the R 2 value at each stage in two years was the highest at the height of 1.5 m, and the average was 0.826. Therefore, the embodiment of the application selected 1.5 m as the best shooting height;

[0094] The canopy temperature of summer corn at three shooting angles of 30°, 60° and 90° was significantly correlated (P<0.01) with eight nitrogen nutrition indicators. In 2022, the average R 2 between the canopy temperature of summer corn at the shooting angle of 60° and the nitrogen nutrition indicators was the highest, which was 0.830; in 2023, the correlation was the best at the shooting angle of 90°. Comprehensive analysis of the test results of two years and the growth of summer corn in the field showed that 60°-90° was the best shooting angle;

[0095] The canopy temperature of crops changes with time within a day due to the influence of air temperature. In 2022, the relationship between the canopy temperature of summer corn at 12:00 and the nitrogen nutrition indicators reached a significant level (P<0.01); at 14:00, the canopy temperature of summer corn at the jointing stage reached a significant correlation level, and the correlation between the other shooting times and the remaining indicators was not significant. In 2023, the correlation between the nitrogen nutrition indicators at different shooting times reached a significant level, and the correlation between the canopy temperature of summer corn at 12:00 and the indicators was the highest, with an average R 2 of 0.848 in each period. Based on the test results of two years, 12:00 was determined as the best shooting time for the nitrogen nutrition thermal imaging diagnosis of summer corn.

[0096] Further, S5 specifically is:

[0097] A quadratic equation is used to fit the canopy temperature of summer corn at each growth stage and the relative yield at the mature stage under the best shooting mode, and the critical value is determined according to the fitting classification standard. The relative yield calculation method is the ratio of the yield of summer corn at each nitrogen fertilizer treatment at the mature stage to the highest yield, and 95% of the relative yield is taken as the critical value, which is less than 95% for nitrogen deficiency and higher than the value for nitrogen abundance. The critical temperature value at each growth stage is determined in this way.

[0098] In an embodiment of the application, the fitting results of the relationship between the canopy temperature of summer corn and the yield are as follows: Figure 8As shown, the critical canopy temperatures for summer maize at the jointing stage, large trumpet stage, silking stage, and grain-filling stage are 30.0℃, 31.0℃, 30.5℃, and 28.3℃, respectively. When the canopy temperature is higher than the critical temperature, it indicates that the nitrogen fertilizer supply is insufficient and nitrogen fertilizer should be applied.

[0099] Furthermore, S6 specifically refers to:

[0100] A quadratic equation was used to fit the relationship between nitrogen fertilizer application and yield at different growth stages of summer maize, such as... Figure 9 As shown, the fitting relationship between total nitrogen fertilizer application and yield over the entire growth period was obtained. The partial derivative of the fitting relationship was calculated to obtain the maximum yield and the corresponding nitrogen fertilizer application. This nitrogen fertilizer application was used as a reference value for the total amount of nitrogen fertilizer applied as topdressing. The topdressing amount was:

[0101] N top =N c -N fer

[0102]

[0103] In the formula, N top To supplement nitrogen, N c This is a reference value for the total amount of nitrogen fertilizer applied as topdressing, N fer For the current nitrogen fertilizer level, T ca Given the current canopy temperature, and with a, b, and c being constants, the values ​​of a, b, and c for each growth stage are substituted into the nitrogen application calculation equation to obtain the nitrogen application calculation equation for each growth stage.

[0104] In one embodiment of the present invention, the fitting results of the relationship between nitrogen fertilizer application and yield at different growth stages of summer maize are as follows: Figure 12 As shown, the highest yield was 12244.7 kg / hm². 2 The corresponding nitrogen fertilizer application rate is 299.6 kg / / hm. 2 299.6 kg / / hm 2 This represents the total nitrogen application amount for summer maize throughout its entire growth period, and can be used as a reference value for the total amount of nitrogen fertilizer applied as topdressing.

[0105] Based on the above calculation results, the equation for calculating the nitrogen supplementation amount can be obtained as follows:

[0106]

[0107] Substituting the values ​​of a, b, and c corresponding to each growth stage into the above equation, we finally obtained the recommended nitrogen fertilizer application model for each growth stage. The values ​​of a, b, and c corresponding to each growth stage are shown in Table 4.

[0108] Table 4. Values ​​of a, b, and c corresponding to each reproductive stage.

[0109]

[0110] The various embodiments described in this specification are presented by way of example, and each embodiment is not necessarily composed of all features described with respect to other embodiments. Each embodiment describes a distinct aspect of the present application, and each aspect can be used in combination with one or more other aspects.

[0111] The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein can be applied to other embodiments without departing from the spirit or scope of the application. Thus, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for diagnosing nitrogen nutrition in summer maize based on infrared thermal imaging technology, characterized in that, Includes the following steps: S1. Acquire thermal imaging data of summer maize canopy at different heights, angles, and times during different growth stages; where the heights are 0.5m, 1.5m, and 2.5m, the angles are 30°, 60°, and 90°, and the times are 9:00, 12:00, 14:00, and 16:

00. S2. Simultaneously measure aboveground plant biomass, nitrogen accumulation, leaf area index, leaf SPAD value, and absorbed photosynthetically active radiation component of summer maize at different growth stages. S3. Analyze the relationship between nitrogen fertilizer application rate and yield, aboveground biomass, nitrogen accumulation, leaf area index, leaf SPAD value and absorbed photosynthetically active radiation component of summer maize, and determine the effect of nitrogen fertilizer application rate on the growth and development of summer maize. S4. Analyze the relationship between canopy temperature and nitrogen fertilizer application, yield, aboveground biomass, nitrogen accumulation, leaf area index, leaf SPAD value and absorbed photosynthetically active radiation component under different shooting modes for summer maize, determine the influence of different shooting modes on canopy temperature and determine the optimal shooting mode. S5. Based on the relationship between canopy temperature and relative yield of summer maize under the optimal shooting mode, determine the critical temperature for different growth stages; S6. Construct a real-time topdressing model for canopy temperature and nitrogen fertilizer at different growth stages based on the optimal shooting mode for summer maize.

2. The method for diagnosing nitrogen nutrition in summer maize based on infrared thermal imaging technology according to claim 1, characterized in that, S1 specifically involves setting different vertical heights of the summer maize canopy as shooting heights, setting different shooting times, and setting different angles between the infrared thermal imager and the horizontal plane as shooting angles, and taking pictures at the jointing stage, the large trumpet stage, the silking stage, and the grain-filling stage of summer maize.

3. The method for diagnosing nitrogen nutrition in summer maize based on infrared thermal imaging technology according to claim 1, characterized in that, S2 specifically refers to: Four representative maize plants were selected from each planting plot at the jointing, tasseling, silking, and grain-filling stages of summer maize. The plants were blanched at 105℃ for 30 minutes and dried at 75℃ to constant weight. Aboveground biomass was calculated. The dried maize samples from each growth stage were pulverized, sieved, and digested using the H2SO4-H2O2 method. Nitrogen content was determined using an AA3 flow injection analyzer, and nitrogen accumulation was calculated. At maturity, 15m² plants were selected from each plot. 2 For contiguous plots, thresh and dry the grains to constant weight, then calculate the grain yield. All leaves of corn plants collected at each growth stage were picked and laid flat on a black background cloth. A 10cm×10cm standard whiteboard was placed at each of the four corners. The leaf area index was then analyzed and calculated after taking photos with a digital camera. Ten corn plants with similar growth were selected and planted continuously in each planting plot at each growth stage. The SPAD value of their leaves was measured using a day chlorophyll meter, and the average value of the test results of each planting plot was calculated. The photosynthetically active radiation (PADR) of summer maize canopy and base was measured using a canopy analyzer at each growth stage, and the absorptive PADR component was calculated.

4. The method for diagnosing nitrogen nutrition in summer maize based on infrared thermal imaging technology according to claim 3, characterized in that, The specific calculation of the absorbable photosynthetically active radiation component is as follows: In the formula, FPAR is the absorbable photosynthetically active radiation component, and PAR is... ci For photosynthetically active radiation incident on the canopy, PAR cr To reflect photosynthetically active radiation from the canopy, PAR gi For basal incident photosynthetically active radiation, PAR gr It is effective radiation for photosynthesis reflected from the base.

5. The method for diagnosing nitrogen nutrition in summer maize based on infrared thermal imaging technology according to claim 1, characterized in that, S3 specifically refers to: Person correlation analysis was used to quantitatively analyze the relationships between nitrogen fertilizer application and yield, aboveground biomass, nitrogen accumulation, leaf area index, leaf SPAD value, absorbed photosynthetically active radiation, and canopy temperature of summer maize. The changing trends of each parameter with the increase of nitrogen fertilizer application were also analyzed.

6. The method for diagnosing nitrogen nutrition in summer maize based on infrared thermal imaging technology according to claim 1, characterized in that, S4 specifically refers to: Person correlation analysis was used to quantitatively analyze the relationship between summer maize canopy temperature and nitrogen fertilizer application, yield, aboveground biomass, nitrogen accumulation, leaf area index, leaf SPAD value, and absorbed photosynthetically active radiation component under different shooting angles, shooting heights, and shooting times. Based on the correlation coefficient and the coefficient of determination, the optimal shooting angle, optimal shooting height, and optimal shooting time for summer maize at different growth stages were determined.

7. The method for diagnosing nitrogen nutrition in summer maize based on infrared thermal imaging technology according to claim 1, characterized in that, S5 specifically refers to: A quadratic equation was used to fit the relative yield of summer maize canopy temperature at each growth stage under the optimal shooting mode to the relative yield at maturity. The critical value was determined according to the fitting grading standard. The relative yield was calculated as the ratio of the yield at maturity of summer maize under each nitrogen fertilizer treatment to its highest yield. 95% of the relative yield was taken as the critical value. Below 95% was nitrogen fertilizer deficiency, and above 95% was nitrogen fertilizer abundance. The critical temperature value for each growth stage was determined in this way.

8. The method for diagnosing nitrogen nutrition in summer maize based on infrared thermal imaging technology according to claim 1, characterized in that, S6 specifically refers to: A quadratic equation was used to fit the relationship between nitrogen fertilizer application and yield at each growth stage of summer maize, obtaining the fitting relationship between total nitrogen fertilizer application and yield over the entire growth period. The partial derivative of the fitting relationship was then calculated to obtain the maximum yield and the corresponding nitrogen fertilizer application. This nitrogen fertilizer application was used as a reference value for the total amount of nitrogen fertilizer applied as topdressing. The topdressing amount was: N top =N c -N fer In the formula, N top To supplement nitrogen, N c This is a reference value for the total amount of nitrogen fertilizer applied as topdressing, N fer For the current nitrogen fertilizer level, T ca Given the current canopy temperature, and with a, b, and c being constants, the values ​​of a, b, and c for each growth stage are substituted into the nitrogen application calculation equation to obtain the nitrogen application calculation equation for each growth stage.

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