A hyperspectral inversion method for estimating nitrogen absorption by aboveground parts of Chinese cabbage during the closing period

Abstract

The present invention discloses a hyperspectral inversion method for estimating the nitrogen absorption of the aboveground part of Chinese flowering cabbage during the closing period, and relates to the technical field of application of hyperspectral data in the planting industry. The method of the present invention uses a near-infrared spectrometer or a hyperspectral camera to measure the light reflectance of the Chinese flowering cabbage during the closing period in a specific band, and calculates the spectral parameters Sec value and Sabd value. Two prediction models are established based on the Sec value or Sabd value to predict the nitrogen absorption (Nap) of a single Chinese flowering cabbage. This method overcomes the defects of traditional sampling methods such as damage to plants, long measurement cycle and high cost. It has the characteristics of being non-destructive to crops, fast and real-time, low cost, and simple operation steps. After comparison with the measured data, the Nap value has a good correlation with the measured value, and the prediction effect is good.

Description

Technical Field

[0001] The present invention relates to the technical field of application of hyperspectral data in planting industry, and in particular to a hyperspectral inversion method for estimating nitrogen absorption of aboveground parts of Chinese flowering cabbage during the closing period. Background Art

[0002] Late choy sum is typically planted in late November after the late rice harvest, and the rows are closed when the new leaves reach 6-9. By this time, two to three fertilizations have typically been applied, including a base fertilizer consisting primarily of organic and compound fertilizers, one to two topdressings, one of which is a seedling-slowing fertilizer consisting of a small amount of quick-acting nitrogen fertilizer or compound fertilizer, and another topdressing based on growth conditions. From the row closure period until the main moss harvest, two to three topdressings are generally required, with the nitrogen application accounting for 50-70% of the total nitrogen applied during the entire growing period. Therefore, understanding the nitrogen absorption profile of late choy sum during the row closure period provides a scientific basis for formulating subsequent topdressing measures to achieve fertilizer conservation and increased efficiency.

[0003] Currently, there are two traditional methods for measuring crop nitrogen status. The first involves collecting the latest fully expanded leaves of Chinese choy sum during the critical growth period for chemical analysis to determine the dry nitrogen content. Since there are currently no reports on nutritional diagnostic indicators for late-growing Chinese choy sum leaves, the results are usually compared with those from the same part of high-yielding Chinese choy sum during the same period to formulate subsequent nitrogen management measures. This method is significantly affected by external adverse factors (such as drought, pests and diseases), and the nitrogen content may show abnormal values. The second method involves collecting fresh aboveground parts of Chinese choy sum during a specific period, mixing them, and determining their dry weight and dry nitrogen content. The aboveground nitrogen uptake of Chinese choy sum during the closed-row period is then calculated and compared with the aboveground nitrogen uptake of high-yielding Chinese choy sum during the closed-row period to formulate subsequent nitrogen management measures. Since high yield and high quality of crops are based on the sufficient accumulation of nutrients absorbed at different growth stages, estimating the aboveground nitrogen nutrient uptake of late-growing Chinese choy sum can be used to assess the absorption and utilization of nitrogen in Chinese choy sum during the closed-row period. Comparing this with high-yielding Chinese choy sum can also determine whether nitrogen uptake is deficient, sufficient, or excessive, providing a reference for subsequent nitrogen management. However, these two methods require the collection of a large number of individual plants, and sample pretreatment and testing are time-consuming, which affects the formulation of subsequent nitrogen management measures for late Chinese cabbage. Therefore, there is an urgent need to explore fast and simple methods. Summary of the Invention

[0004] The present invention aims to solve at least one of the above-mentioned technical problems existing in the prior art. To this end, the present invention aims to provide a hyperspectral inversion method for estimating the aboveground nitrogen absorption of late Chinese cabbage during the closure period. During the closure period, a near-infrared spectrometer or a hyperspectral camera is used to measure the light emissivity of the late Chinese cabbage in a specific band. The aboveground nitrogen absorption is then calculated based on a model inverted from a large amount of data. The method is simple and can quickly estimate the nitrogen absorption status of late Chinese cabbage during the closure period.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] The present invention provides a method for measuring nitrogen absorption by the aboveground part of Chinese cabbage during the closing period, comprising the following steps:

[0007] S1. Using a near-infrared spectrometer or a hyperspectral camera to measure the light reflectance of the late Chinese cabbage plants during the closed-row period; wherein the light reflectance is obtained by selecting five bands within the range of 681 to 802 nm for data collection;

[0008] S2. Calculate the spectral parameters Sec and Sabd using the following formulas (1) and (2):

[0009] Sec=(ec) / c (1);

[0010] Sabd=(db) / (ba) (2);

[0011] Where a, b, c, d, and e represent Bj or Bw for the five wavelength bands between 681 and 802 nm, respectively; Bj is the average value of the light reflectance of each of the five wavelength bands measured by the infrared spectrometer; and Bw is the light reflectance of a wavelength point within the five wavelength bands measured by the hyperspectral camera.

[0012] S3. Calculate the nitrogen absorption (Nap) of the aboveground part of the vegetable heart using the Sec and the relational expression A; the relational expression A is as follows:

[0013] Nap=m*Sec+n (3);

[0014] The Sabd and relational formula B are used to calculate the nitrogen absorption amount (Nap) of the aboveground part of the Chinese cabbage; the relational formula B is as follows (4):

[0015] Nap=k*Sabd+p (4);

[0016] Wherein, Nap in the relational expressions A and B is the nitrogen absorption amount of the aboveground part of the Chinese cabbage heart, in mg / plant; m, n, k, and p are all constants;

[0017] S4. Calculate the average value Nm of all Nap obtained by the relational expression A and the relational expression B; calculate the deviation Db between Nap and Nm, and the calculation formula is formula (5):

[0018] Db=Abs((Nap-Nm)*100 / Nm) (5);

[0019] Among them, Abs represents absolute value operation; discard the Nap value with Db above 10, and recalculate the average value of Nap Nmx, which is the nitrogen absorption amount of the aboveground part of a single late Chinese cabbage plant, in mg / plant.

[0020] The data obtained by the present invention using a near-infrared spectrometer or a hyperspectral camera are light reflectance data in the visible light wavelength range and the infrared range. In the present invention, nitrogen absorption is used as the data object measured by the chi cai xin. After correlation regression, multiple regression statistics, support vector machine, random forest, neural network and other data processing methods, the results are compared to establish models with better prediction effects, namely, relational formula A and relational formula B. Unlike complex models (such as multiple regression, support vector machine, random forest, neural network) that are easily affected by data capacity, the model A (i.e., relational formula A) and model B (i.e., relational formula B) obtained by regression analysis in the present invention are simple and easy to use, can predict nitrogen absorption, and the predicted data differences are not large, and can complement each other.

[0021] Equations (1) to (4) are based on a large amount of light reflectance data obtained by near-infrared spectrometers or drone-mounted hyperspectral instruments during the closure period of the Chinese cabbage. The calculation parameters Sec and Sabd values ​​were further selected and correlated with the measured data on aboveground nitrogen uptake by individual Chinese cabbage plants. The Sec and Sabd values ​​had the highest correlation coefficients with Nap, so equations (3) and (4) were selected.

[0022] In some embodiments of the present invention, the five wavelength bands in step S1 are 681-685 nm, 709-703 nm, 720-724 nm, 754-758 nm and 798-802 nm.

[0023] The specific wavelengths further defined in step S1 are not determined solely based on the characteristic absorption wavelength of nitrogen, but are obtained by combining a large amount of data such as the fresh (dry) weight, nitrogen content, and nitrogen absorption of the Chinese cabbage.

[0024] In some embodiments of the present invention, in step S1, the data collected by the near-infrared spectrometer is the average value of the light reflectance displayed at different wavelength points within each wavelength band.

[0025] In some embodiments of the present invention, in step S1, the data collected by the hyperspectral camera is the light reflectance corresponding to a wavelength point within the interval of each band.

[0026] In some embodiments of the present invention, a, b, c, d, and e in step S2 correspond to Bj or Bw of the 681-685 nm segment, the 709-703 nm segment, the 720-724 nm segment, the 754-758 nm segment, and the 798-802 nm segment, respectively.

[0027] In some embodiments of the present invention, in step S2, the average value of the light reflectance at different wavelengths within each band measured by the near-infrared spectrometer is recorded as Bv, and Bj is the average value of Bv at different detection parts of a single late Chinese cabbage plant.

[0028] In some embodiments of the present invention, when a hyperspectral camera is used for measurement, the data collection bands of the light reflectance are 682 nm, 712 nm, 723 nm, 756 nm and 800 nm.

[0029] In some embodiments of the present invention, in the relational expression A of step S3, the value of m is 452.41; the value of n is 146.30.

[0030] In some embodiments of the present invention, in the relational expression B of step S3, the value of k is 162.71; the value of p is 139.66.

[0031] In some embodiments of the present invention, in step S1, the near-infrared spectrometer measures 2 to 3 newly emerged fully expanded leaves of a single plant of Chi Cai Xin.

[0032] When using a near-infrared spectrometer for measurement, due to the small probe and limited scanning area, leaf data needs to be collected within a very small range. The newly emerged fully expanded leaves are the growth and metabolic center of the late Chinese cabbage heart. At this time, the leaf area is the largest and it is the most representative part of the plant. Therefore, it is possible to choose to sample the fully expanded leaves to obtain data.

[0033] In some embodiments of the present invention, the hyperspectral camera measures the site of the canopy of the Chinese flowering cabbage.

[0034] In some embodiments of the present invention, the height of the hyperspectral camera is 50-100 m.

[0035] When using a hyperspectral camera for measurement, due to its certain height and large scanning area, the scanning area is the part visible to the naked eye in the horizontal direction, that is, the canopy of the late Chinese cabbage. When the late Chinese cabbage is closed, the area of ​​the newly emerged fully expanded leaves is the largest. The canopy light reflectance measured by the hyperspectral camera carried by the drone basically represents the light reflectance of the newly emerged fully expanded leaves.

[0036] In some embodiments of the present invention, when the near-infrared spectrometer is used for measurement, 5 sampling units are taken, and the 5 sampling triplets show a five-point plum blossom-shaped distribution.

[0037] In some embodiments of the present invention, each sampling unit includes 3 to 4 plants of Chi Cai Xin.

[0038] In some embodiments of the present invention, the intervals between individual late flowering Chinese cabbage plants in the sampling unit are 1 to 3 meters.

[0039] In some embodiments of the present invention, the interval between individual late flowering Chinese cabbage plants in the sampling unit is 1.5 to 2.5 meters.

[0040] In some embodiments of the present invention, within the range of ≤2 cm from the edge of the fully expanded leaf, a near-infrared spectrometer is used to measure the light reflectance of the upper, middle and lower parts of the leaf respectively, and the average light reflectance displayed at different wavelength points in each band is calculated.

[0041] In some embodiments of the present invention, when the hyperspectral camera is used for measurement, five data acquisition units are provided, and each data acquisition unit includes three to four acquisition points.

[0042] In some embodiments of the present invention, the 3 to 4 collection points each cover a surface area of ​​20 to 30 m 2 .

[0043] In some embodiments of the present invention, the late Chinese flowering cabbage plots selected for the measurement are plots with uniform fertilization, uniform management, and uniform plant appearance.

[0044] In some embodiments of the present invention, the Nmx is used to calculate the nitrogen absorption of the aboveground part of the late Chinese cabbage per mu, and the calculation formula is as follows: nitrogen absorption of the aboveground part of the late Chinese cabbage per mu = Nmx* planting density per mu / 1000, in grams / mu.

[0045] In some embodiments of the present invention, the hyperspectral camera is carried by a drone.

[0046] In some embodiments of the present invention, the method for determining nitrogen absorption by the aboveground part of Chinese cabbage during the closing period comprises the following steps:

[0047] S1.1. Selection of sampling plants: When using a near-infrared spectrometer, set up five sampling units in the field to display a five-point plum blossom-shaped distribution, with 3 to 4 late cauliflower plants in each unit. Select healthy late cauliflower plants that are free of pests and diseases and drought stress. Plants should be dispersed as much as possible, with a distance of 1 to 3 m between individual plants, and avoid selecting plants that are too large or too small. When using a hyperspectral camera, set up five data collection units in the field, with each data collection unit having three points, and each point covering a surface area of ​​20 to 30 m. 2 , collect data respectively;

[0048] S1.2. Use a near-infrared spectrometer or a hyperspectral camera mounted on an unmanned aerial vehicle to measure the light reflectance of early Chinese cauliflower plants during the closed-row period. The light reflectance data is collected in the 681-685nm, 709-703nm, 720-724nm, 754-758nm, and 798-802nm bands, and the average light reflectance at different wavelengths within each band is calculated. The near-infrared spectrometer measures the two to three newly emerged, fully expanded leaves of a single early Chinese cauliflower plant; the hyperspectral camera measures the canopy of the early Chinese cauliflower plant.

[0049] S2. Calculate the parameters Sec and Sabd using the following formula:

[0050] Sec=(ec) / c (1);

[0051] Sabd=(db) / (ba) (2);

[0052] Among them, a, b, c, d, and e represent Bj or Bw in the 681-685 nm, 709-703 nm, 720-724 nm, 754-758 nm, and 798-802 nm bands, respectively; Bj is the light reflectance of the late Chinese cabbage heart measured by an infrared spectrometer; Bw is the light reflectance of the late Chinese cabbage heart measured by a hyperspectral camera;

[0053] S3.1. Calculate the predicted nitrogen uptake by the aboveground part of the Chinese cabbage using the relationship A: Use the relationship A between Sec and the predicted nitrogen uptake by the aboveground part of the Chinese cabbage (Nap):

[0054] Nap=m*Sda+n (3);

[0055] Where m is 452.41 and n is 146.30;

[0056] S3.2. Calculate the predicted nitrogen uptake by the aboveground part of the Chinese cabbage using equation B: Use equation B between Sabd and the predicted nitrogen uptake by the aboveground part of the Chinese cabbage (Nap):

[0057] Nap=k*Sabd+p (4);

[0058] Wherein the value of k is 162.71 and the value of p is 139.66;

[0059] S4. Calculate the average value Nm of the Nap values ​​calculated in steps S31 and S32, and calculate the deviation (Db) of each Nap value from Nm. The calculation formula is:

[0060] Db=Abs((Nap-Nm)*100 / Nm) (5),

[0061] Where Abs is the absolute value operation; if the Db value of a certain value is above 10, indicating that the value deviates from the average value by more than 10%, then the value is discarded, and after screening, the new average value Nmx of Nap is recalculated as the final nitrogen absorption of the aboveground part of a single plant.

[0062] In some embodiments of the present invention, the measurement in step S12 is performed under cloudless conditions with good sunlight.

[0063] The method for estimating nitrogen absorption by the aboveground part of the Chinese flowering cabbage during the row-closing period of the present invention can be applied to nitrogen nutrient management and optimized fertilization after the row-closing period of the Chinese flowering cabbage.

[0064] Compared with the prior art, the present invention has the following beneficial effects:

[0065] The present invention provides a method for estimating the aboveground nitrogen absorption amount of late Chinese cabbage during the closing period by using hyperspectral data and model calculations. The method overcomes the defects of traditional sampling methods such as damage to plants, long measurement period and high cost. The method has the characteristics of being non-destructive to crops, real-time and fast, and low cost. At the same time, the aboveground nitrogen absorption amount of late Chinese cabbage during the closing period obtained has a good correlation with the measured value after testing, and has a good prediction effect. It can provide a scientific basis for formulating subsequent nitrogen fertilizer application measures for late Chinese cabbage and achieving fertilizer saving and efficiency improvement. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] Figure 1 is the correlation between the predicted values ​​and the measured values ​​of models A and B in Examples 1 and 2 of the present invention; wherein, Figure 1 A is the correlation between the predicted value and the measured value of Model A in Example 1; Figure 1 B is the correlation between the predicted value and the measured value of model B in Example 1; Figure 1 C is the correlation between the predicted value and the measured value of model A in Example 2; Figure 1 D is the correlation between the predicted value and the measured value of model B in Example 2. DETAILED DESCRIPTION

[0067] The present invention is further described in detail below using specific examples. Unless otherwise specified, the raw materials, reagents, and apparatus used in the examples and comparative examples are available from conventional commercial sources or by conventional methods. Unless otherwise specified, all experimental or testing methods are conventional in the art.

[0068] Example 1

[0069] This embodiment provides a method for calculating the aboveground nitrogen absorption of late Chinese cabbage during the row-closing period. A professional cooperative in a town in Lianzhou City, Guangdong Province was selected to plant late Chinese cabbage. Local varieties were planted after the late rice was harvested, with a planting density of 3,000 plants per mu. The row-closing period of Chinese cabbage was 35 days after transplanting. The area of ​​the vegetable field involved in this embodiment was about 3 mu. The fields were uniformly fertilized and managed, and the plants had a relatively uniform appearance.

[0070] This embodiment adopts near infrared spectrometer to measure, and comprises the following steps:

[0071] S1.1. Select Sampling Plants: Set up five sampling units in a five-point plum blossom pattern in the field, with three late cauliflower plants in each unit. Select healthy late cauliflower plants that are free of pests, diseases, and drought stress. Plants should be dispersed as much as possible, with spacing of 1.5-2.5 meters between plants. Avoid selecting plants that are too large or too small to maintain representativeness of the sample.

[0072] S1.2. Select representative parts of individual plants and measure reflectance using a near-infrared spectrometer to calculate individual plant reflectance data: Use a near-infrared spectrometer to measure the reflectance of two newly emerged, fully expanded leaves of representative plants of the Chinese cabbage heart under cloudless, sunny conditions. Within a range of 2 cm from the leaf edge and avoiding the leaf veins, use the infrared spectrometer probe to measure the reflectance of the upper, middle, and lower parts of the leaves. The measured wavelength ranges are 681-685 nm, 709-713 nm, 720-724 nm, 754-758 nm, and 798-802 nm. The average value Bv of the reflectance displayed at different wavelengths in each band is calculated. The average value of the six Bv values ​​measured for the two fully expanded leaves is calculated as the individual plant reflectance Bj of the Chinese cabbage heart. A total of 15 individual plant reflectance data are obtained for each band, as shown in Table 1 below, marked as a, b, c, d, and e according to the band range;

[0073] Table 1 Average reflectance data of individual leaves in step S12

[0074]

[0075]

[0076] Note: The Bj values ​​of each band are arranged in order of plant number 1 to 15.

[0077] S2. Further calculate the parameter value of each individual plant: Based on the data parameters Sec and Sabd in Table 1, the calculation formula is:

[0078] Sec=(ec) / c (1),

[0079] Sabd=(db) / (ba) (2),

[0080] The calculation results are shown in Table 2;

[0081] Table 2 Sec values ​​and Sabd values ​​of each individual plant calculated in step S2

[0082] Single plant number Sec Sabd 1 0.86523 2.49753 2 0.86414 2.50081 3 0.76328 2.16431 4 0.94481 2.6795 5 0.8915 2.57084 6 0.69804 1.97048 7 0.88215 2.42041 8 0.94461 2.68885 10 0.87965 2.54428 11 0.87291 2.49528 12 0.94694 2.70354 13 0.86097 2.46518 14 0.85974 2.46392 15 0.88371 2.44902

[0083] S3.1. Calculate the predicted value of nitrogen uptake by the aboveground part of the Chinese cabbage using Model A: Use Model A for the relationship between Sec and the predicted value of nitrogen uptake by the aboveground part of the Chinese cabbage (Nap):

[0084] Nap=m*Sda+n (3);

[0085] Where m is 452.41 and n is 146.30. This relationship is derived by regression statistics of the Sec value calculated from a large number of Bj values ​​obtained from hyperspectral measurements of the late Chinese cabbage during the closing period and the corresponding measured data on the aboveground nitrogen uptake of individual late Chinese cabbage plants.

[0086] S3.2. Calculate the predicted value of nitrogen uptake by the aboveground part of the Chinese cabbage using Model B: Use Model B for the relationship between Sabd and the predicted value of nitrogen uptake by the aboveground part of the Chinese cabbage (Nap):

[0087] Nap=k*Sabd+p (4);

[0088] The value of k in the formula is 162.71, and the value of p is 139.66. This relationship is derived by regression statistics based on the Sabd values ​​calculated from a large number of Bj values ​​obtained from hyperspectral measurements of the late Chinese cabbage during the closing period and the corresponding measured data on the aboveground nitrogen uptake of individual late Chinese cabbage plants.

[0089] S4. Calculate the average value Nm of the Nap values ​​calculated in steps S31 and S32, and calculate the deviation (Db) of each Nap value from Nm. The calculation formula is:

[0090] Db=Abs((Nap-Nm)*100 / Nm) (5),

[0091] Among them, Abs is the absolute value operation; if the Db value of a certain value is above 10, indicating that the value deviates from the average value by more than 10%, then the value is discarded, and the new average value Nmx of Nap is recalculated after screening as the final aboveground nitrogen absorption of a single plant. If the aboveground nitrogen absorption of late Chinese cabbage per mu (unit: grams / mu) needs to be converted, according to the formula: aboveground nitrogen absorption of late Chinese cabbage per mu (unit: grams / mu) = the final calculated Nap average value * planting density per mu / 1000, where the planting density per mu in this example is 3000 plants / mu.

[0092] Table 3 Predicted values ​​of nitrogen uptake per plant (Nap) and indicator discrimination calculations calculated by Model A and Model B

[0093]

[0094] Note: The predicted values ​​are arranged in order of plant number 1 to 15.

[0095] It can be seen from Table 3 that the average value Nm is 541.68 mg / plant, of which 2 data deviate from Nm by more than 10%. After removing the unqualified data, the Nmx value is 547.43 mg / plant. The calculated nitrogen absorption of the aboveground part of the late Chinese cabbage per mu is 1642.29 g / mu.

[0096] The following further examines the degree of agreement between the predicted values ​​and the measured values:

[0097] Goodness of fit assessment: After step S2 is completed, immediately collect 3 individual plants of the measured late Chinese flowering cabbage, cut off the aboveground parts and mark them with labels to avoid mistakes, take them back to the laboratory, wash them, and dry them at a temperature of 100-105°C. The oven-dried weight W (unit: g / plant) of the sampled parts is measured, and all the samples are ground evenly. The nitrogen content N (unit: % dry matter) of the aboveground parts of the individual plants is measured. The nitrogen absorption amount Nt of the aboveground parts of the individual plants is calculated based on the oven-dried weight and nitrogen content. The unit is mg / plant. The calculation formula is as follows: Nt = 1000*W*Nt; the Nt data of the 15 measured samples are shown in Table 4.

[0098] Table 4 The measured results of 15 individual plants in the investigation

[0099] Strain No. Dry weight (g / plant) nitrogen(%) Single plant of Chi Cai Xin N (absorption amount mg / plant) 1 13.93 3.85 536.21 2 14.53 3.76 546.35 3 13.9 3.52 489.36 4 15.11 3.77 569.47 5 14.12 3.92 553.59 6 13.39 3.47 464.47 7 14.94 3.59 536.42 8 14.32 4.02 575.56 9 14.11 3.90 550.46 10 14.51 3.56 516.69 11 14.13 3.98 562.33 12 13.52 4.00 540.6 13 13.74 4.05 556.28 14 14.31 3.61 516.72 15 14.54 3.87 562.89

[0100] Draw a scatter plot on the rectangular coordinate system according to the measured value Nt and the predicted value Nap of the same sample. The Nap values ​​calculated in step S5 or the goodness of fit test are plotted separately. The results are shown in Figure 1 A and Figure 1 B. The oblique line in the figure is the ideal oblique line when the measured value is equal to the predicted value. The oblique line passes through the origin and forms a 45-degree angle with the horizontal axis or the vertical axis.

[0101] from Figure 1 A and Figure 1 B shows that the measured values ​​and predicted values ​​of Model A and Model B are well correlated, R 2 The relative accuracy (R / R) of the two models was 0.89 and 0.81, respectively, and the root mean square error (RMSE) was 10.27 and 18.08, respectively. This indicates that both models are effective in predicting nitrogen uptake by the aboveground part of Chinese cabbage using near-infrared spectroscopy. These models overcome the disadvantages of traditional sampling methods, such as plant damage, long measurement cycles, and high costs, and are non-destructive, fast, and inexpensive.

[0102] Example 2

[0103] This embodiment provides a method for calculating the nitrogen absorption of the aboveground part of Chinese cabbage during the late row closing period. The method is carried out at the same location and the same planting density as in Example 1. The row closing period of Chinese cabbage is 38 days after transplanting. The vegetable field area involved in this embodiment is about 4 mu. The fields are uniformly fertilized and managed, and the plants have relatively uniform appearance.

[0104] This embodiment uses a drone equipped with a hyperspectral camera for measurement, including the following steps:

[0105] S1.1. Select data collection units: Based on the principle of uniform plant growth, five data collection units are set up in the field. Each data collection unit has three points, and each point covers a surface area of ​​20 to 30 m 2 , collect data respectively;

[0106] S1.2. Measurements were made using a drone-mounted hyperspectral camera under cloudless, sunny conditions. The canopy reflectance (Bw) was collected at wavelengths of 682 nm, 712 nm, 723 nm, 756 nm, and 800 nm. The hyperspectral camera stored the canopy reflectance data (Bw) for each band. A total of 15 canopy reflectance data points (Bw) were obtained for each band, as shown in Table 5. These data points are labeled a, b, c, d, and e according to the band range.

[0107] Table 5 Canopy reflectance data of each sampling unit in step S12

[0108]

[0109] Note: The Bj values ​​of each band are arranged in order of unit numbers 1 to 15.

[0110] S2. Further calculate the parameter values ​​of each data acquisition unit: Calculate the parameters Sec and Sabd based on the 15 data points in each band in Table 1. The calculation formula is:

[0111] Sec=(ec) / c (1),

[0112] Sabd=(db) / (ba) (2),

[0113] The calculation results are shown in Table 6;

[0114] Table 6 Sec values ​​and Sabd values ​​of each measurement unit calculated in step S2

[0115]

[0116]

[0117] S3.1. Calculate the predicted value of nitrogen uptake by the aboveground part of the Chinese cabbage using Model A: Use Model A for the relationship between Sec and the predicted value of nitrogen uptake by the aboveground part of the Chinese cabbage (Nap):

[0118] Nap=m*Sec+n (3);

[0119] In the formula, the value of m is 452.41, and the value of n is 146.30. This relationship is derived by regression statistics based on a large number of Sda values ​​calculated by near-infrared spectrometer measurement during the closing period of the Chinese cabbage and the corresponding measured data on the aboveground nitrogen absorption of individual Chinese cabbage plants.

[0120] S3.2. Calculate the predicted value of nitrogen uptake by the aboveground part of the Chinese cabbage using Model B: Use Model B for the relationship between Sabd and the predicted value of nitrogen uptake by the aboveground part of the Chinese cabbage (Nap):

[0121] Nap=k*Sabd+p (4);

[0122] The value of k in the formula is 162.71, and the value of p is 139.66. This relationship is derived by regression statistics based on a large number of Sabd values ​​calculated by near-infrared spectrometer during the closing period of the early Chinese cabbage and the corresponding measured data on the aboveground nitrogen absorption of individual early Chinese cabbage plants.

[0123] S4. Calculate the average value Nm of the Nap values ​​calculated in steps S31 and S32, and calculate the deviation (Db) of each Nap value from Nm. The calculation formula is:

[0124] Db=Abs((Nap-Nm)*100 / Nm) (5),

[0125] Where Abs is the absolute value operation. If the Db value of a certain value is above 10, indicating that the value deviates from the average value by more than 10%, then the value is discarded, and after screening, the new average value Nmx of Nap is recalculated as the final single plant aboveground nitrogen absorption. If the aboveground nitrogen absorption of the late Chinese cabbage per mu (in grams per mu) needs to be converted, the formula is: aboveground nitrogen absorption of the late Chinese cabbage per mu (unit: grams per mu) = the final calculated Nap average value * planting density per mu / 1000, where the planting density per mu in this example is 3000 plants per mu.

[0126] Table 7 Predicted values ​​of nitrogen uptake per plant (Nap) calculated by Model A and Model B and the discriminant calculation of indicators

[0127]

[0128]

[0129] Note: The predicted values ​​are arranged in order of unit numbers 1 to 15.

[0130] It can be seen from Table 7 that the average value Nm is 543.91 mg / plant, of which 3 data deviate from Nm by more than 10%. After removing the unqualified data, the Nmx value is 551.77 mg / plant. The calculated nitrogen absorption of the aboveground part of the late Chinese cabbage per mu is 1655.31 g / mu.

[0131] The following further examines the degree of agreement between the predicted values ​​and the measured values:

[0132] Goodness of fit investigation: In the data collection area selected in step S1, three evenly growing and representative late Chinese cabbage plants were collected from each area, the aboveground parts were cut and labeled to avoid mistakes, and the plants were brought back to the laboratory, washed and dried at a temperature of 100-105°C. The oven-drying weight W (unit: g / plant) of each individual sampling part was measured, and the whole plant was ground evenly, and the aboveground nitrogen content N (unit: % dry matter) of each plant was measured. The nitrogen absorption amount Nt of the aboveground part was calculated based on the oven-drying weight and nitrogen content. The calculation formula is as follows: Nt = 1000*W*Nt; the Nt data measured for 15 individual plants are shown in Table 8.

[0133] Table 8 Measured results of 15 individual plants in the consistency investigation

[0134] Strain No. Dry weight (g / plant) nitrogen(%) N absorption amount of single Chinese cabbage plant (mg / plant) 1 13.9 3.86 536.65 2 15.64 3.7 578.8 3 12.72 3.92 498.52 4 15.76 3.75 590.85 5 14.37 3.88 557.73 6 11.73 4.03 472.56 7 14.13 3.9 551.25 8 15.28 3.82 583.69 9 13.78 3.93 541.75 10 13.7 3.97 543.8 11 15.5 3.72 576.61 12 13.25 3.99 528.82 13 14.41 3.82 550.48 14 14.08 3.86 543.55 15 14.17 3.9 552.49

[0135] Draw a scatter plot on the rectangular coordinate system based on the measured Nt and predicted Nap values ​​of the same individual plant. The Nap values ​​calculated in step 5 or step 6 are plotted separately. The results are shown in Figure 1 C and Figure 1 D. The oblique line in the figure is the ideal oblique line when the measured value is equal to the predicted value. The oblique line passes through the origin and forms a 45° angle with the horizontal axis or the vertical axis.

[0136] from Figure 1 C and Figure 1 D shows that the measured values ​​and predicted values ​​of model A and model B have a good correlation, R 2 The RRs were 0.82 and 0.88, respectively, and the root mean square errors (RMSEs) were 12.65 and 11.69, respectively. This indicates that both models are effective in predicting nitrogen uptake by the aboveground part of Chinese cabbage, when measured using a drone-mounted hyperspectral camera. These models overcome the disadvantages of traditional sampling methods, such as plant damage, long measurement cycles, and high costs, and are non-destructive, fast, and inexpensive.

[0137] In summary, the method for estimating nitrogen absorption of the aboveground part of late Chinese cabbage during the closing period of the crop overcomes the defects of traditional sampling methods such as damage to plants, long measurement period and high cost, and has the characteristics of being non-destructive to crops, real-time and fast, and low cost. In addition, the method has simple operation steps, can be used to quickly estimate the nitrogen absorption status of the aboveground part of late Chinese cabbage during the closing period, and has good prediction effect, providing a scientific basis for formulating subsequent nitrogen management measures for late Chinese cabbage and achieving fertilizer saving and efficiency improvement.

[0138] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A method for estimating nitrogen absorption by the aboveground part of Chinese cabbage during the closing period, characterized in that: The steps include: S1. Measure the light reflectance of late Chinese cabbage plants during the closed-row period using a near-infrared spectrometer or a hyperspectral camera; the light reflectance is obtained by collecting data from five wavelengths between 681 and 802 nm; the five wavelengths are 681-685 nm, 709-713 nm, 720-724 nm, 754-758 nm, and 798-802 nm. S2. Calculate the spectral parameters Sec and Sabd using the following formulas (1) and (2): Sec=(ec) / c(1); Sabd=(db) / (ba)(2); Among them, a, b, c, d, and e correspond to Bj or Bw in the 681-685 nm, 709-713 nm, 720-724 nm, 754-758 nm, and 798-802 nm bands, respectively; Bj is the average light reflectance of each of the five bands measured by the near-infrared spectrometer; Bw is the light reflectance of each of the five bands measured by the hyperspectral camera; S3. Calculate the nitrogen absorption (Nap) of the aboveground part of the Chinese cabbage heart using the Sec and the relational expression A; the relational expression A is as follows: Nap=m*Sec+n(3); The aboveground nitrogen absorption amount (Nap) of the Chinese cabbage was calculated using the Sabd and the relational expression B; the relational expression B is as follows (4): Nap=k*Sabd+p(4); Wherein, Nap in the relational expressions A and B is the nitrogen absorption amount of the aboveground part of the Chinese cabbage heart, in mg / plant; m, n, k, and p are all constants; S4. Calculate the average value Nm of all Nap obtained by the relationship A and the relationship B; calculate the deviation Db between Nap and Nm, using the formula (5): Db=Abs((Nap-Nm)*100 / Nm)(5); Among them, Abs represents absolute value operation; discard the Nap value with Db above 10, and recalculate the average value of Nap Nmx, which is the nitrogen absorption amount of the aboveground part of a single late Chinese cabbage plant, in mg / plant.

2. The method according to claim 1, characterized in that In step S1, the data collected by the near-infrared spectrometer is the average value of the light reflectance displayed at different wavelength points within each band.

3. The method according to claim 1, characterized in that In step S1, the data collected by the hyperspectral camera is the light reflectance corresponding to a wavelength point within the interval of each band.

4. The method according to claim 1, wherein In step S2, the average value of the light reflectance at different wavelengths within each wavelength range measured by the near-infrared spectrometer is recorded as Bv, and Bj is the average value of Bv at different detection parts of a single late Chinese cabbage heart plant.

5. The method according to claim 3, characterized in that When a hyperspectral camera is used for measurement, the data collection bands of the light reflectance are 682 nm, 712 nm, 723 nm, 756 nm and 800 nm.

6. The method according to claim 1, wherein In the relational expression A of step S3, the value of m is 452.41; the value of n is 146.

30.

7. The method according to claim 1 or 3, characterized in that In the relational expression B of step S3, the value of k is 162.71; the value of p is 139.

66.

8. The method according to claim 1, characterized in that The Nmx is used to calculate the nitrogen absorption of the aboveground part of the Chinese cabbage per mu, and the calculation formula is as follows: nitrogen absorption of the aboveground part of the Chinese cabbage per mu = Nmx * planting density per mu / 1000, in grams per mu.

Images