Method for estimating evapotranspiration of reference crops in greenhouse by using outdoor meteorological information

Abstract

The invention relates to the technical field of agriculture, in particular to a method for estimating the evapotranspiration of reference crops in a greenhouse by using outdoor meteorological information, which comprises the following steps of: 1, selecting a test area and determining basic information of the test area; 2, continuously measuring meteorological parameters inside and outside the greenhouse; step 3, calculating daily-scale evapotranspiration (ETo) inside and outside the greenhouse by adopting an FAO 56 Penman-Monteith formula; and 4, introducing a solar radiation transmittance tau (= Rs, in / Rs, out), a wind speed attenuation rate omega (= Vin / Vout), ETrad, out and ETadv, out to construct a model. According to the method, the ETo inside and outside the greenhouse is calculated by using a standard FAO56-PM equation, the radiation component and advection component change characteristics of the ETo inside and outside the greenhouse are analyzed, and a radiation subitem equation and an advection subitem equation in the equation are respectively improved by introducing a radiation transmittance tau and a wind speed attenuation rate omega. And a simple model for estimating indoor ETo based on outdoor meteorological information is constructed.

Description

Technical Field

[0001] The present invention relates to the field of agricultural technology, and in particular to a method for estimating reference crop evapotranspiration in a greenhouse by utilizing outdoor meteorological information. Background Art

[0002] Currently, greenhouse cultivation in my country is still dominated by traditional structures such as solar greenhouses and plastic greenhouses. Ventilation in traditional greenhouses primarily relies on natural ventilation, which creates air flow within the greenhouse, enabling sufficient mass and heat exchange between the greenhouse's internal and external environments, as well as between crops and the surrounding environment. Accurately predicting greenhouse crop water requirements using conventional outdoor meteorological information would provide effective theoretical support for greenhouse management and improved crop irrigation. Currently, few models use external greenhouse meteorological data to calculate indoor crop water requirements. This is primarily due to parameter estimation errors caused by differences in greenhouse ventilation schemes and energy conversion losses. Traditional greenhouse environmental control in my country primarily relies on natural ventilation, using the open state of vents to exchange indoor and outdoor environments. This creates a strong coupling between greenhouse crops and the outdoor atmosphere, making it feasible to use outdoor meteorological information to calculate indoor crop water requirements.

[0003] Currently, most evapotranspiration models are based on energy balance and mass transfer. As models continue to evolve, greenhouse crop evapotranspiration models have been refined to improve simulation accuracy through parameter refinement. These refinements primarily consider the impact of the greenhouse's unique microclimate on crop water transfer. Studies have shown that crop evapotranspiration is closely related to the vapor pressure difference around leaves. Saturation deficit is related to the degree of ambient air deficit, which is directly affected by outdoor saturation deficit and falls under the advection component of the evapotranspiration model. Radiation is another important component influencing crop evapotranspiration. The radiation intensity received by greenhouse crops differs significantly from that of field crops, primarily due to changes in net shortwave and longwave radiation caused by plastic film coverage. When constructing models to estimate indoor crop water requirements based on outdoor meteorological information, improvements to these two important components—radiation and advection—are crucial considerations.

[0004] Crop evapotranspiration (ETo), a meteorologically driven reference, is an important indicator for calculating actual crop water requirements. The FAO 56 Penman-Monteith (FAO 56 PM) formula, recommended by the Food and Agriculture Organization of the United Nations, is currently the most widely used method for calculating Eto. This formula consists of two components: radiation and advection. Previous studies used the FAO 56 PM formula to calculate greenhouse crop evapotranspiration, requiring continuous measurement of multiple meteorological parameters such as net indoor radiation, air temperature, relative humidity, and wind speed. Subsequently, the PM-energy balance method was developed to estimate indoor crop water requirements using outdoor meteorological data. However, this method involves several difficult-to-obtain parameters, such as ventilation rate, water vapor conversion coefficient, sensible and latent heat transfer coefficients, and the heat exchange coefficient between the inside and outside of the greenhouse. This increases model uncertainty. Therefore, from a practical and economic perspective, this approach is difficult to implement.

[0005] To solve the above problems, the present invention constructs a new model with a simple structure, in order to achieve the goal of calculating the water requirement of indoor crops using outdoor meteorological information, thereby providing reliable theoretical and technical support for greenhouse crop management and the convenience of irrigation. Summary of the Invention

[0006] To address the above-mentioned defects and problems, the present invention provides a method for estimating reference crop evapotranspiration in a greenhouse using outdoor meteorological information. The method improves the radiation component and the advection component in the FAO 56 PM equation. By introducing the radiation transmittance τ (=Rs,in / Rs,out) into the radiation component and the wind speed attenuation rate ω (=Vin / Vout) into the advection component, a new model with a simple structure is constructed to achieve the goal of calculating the water requirement of indoor crops using outdoor meteorological information, providing reliable theoretical and technical support for greenhouse crop management and the facilitation of irrigation.

[0007] The solution adopted by the present invention to solve the technical problem is: a method for estimating reference crop evapotranspiration in a greenhouse using outdoor meteorological information, comprising the following steps: Step 1: Select the experimental area and determine the basic information of the experimental area, including the experimental area location, greenhouse structure, the average annual temperature, average annual precipitation, average annual sunshine hours, soil type, average volume mass of the soil layer and field water holding capacity; Step 2: Continuously measure the meteorological parameters inside and outside the greenhouse, including air temperature ( T a ), relative humidity ( RH ), solar radiation ( R s ) and wind speed ( V ), the water vapor pressure difference is calculated using the measured air temperature and relative humidity ( VPD ), and measure evapotranspiration of reference crops; Step 3: Use FAO 56 Penman-Monteith formula to calculate the daily evapotranspiration inside and outside the greenhouse ( ET o ); In calculation ET o When the soil heat flux is generally considered to be 0 on a daily scale, then ET o The calculation formula is as follows: ; Where, Δ is the slope of the saturated water vapor pressure curve (kPa / ℃), γ is the hygrometer constant (kPa / ℃), R n is the net radiation (MJ / (m 2 d)), parameters T a 、 VPD and V From indoor and outdoor measured data; exist ET o In the calculation formula, the radiation components are defined separately ( ET rad ) and the advection component ( ET adv )for: ; ; Inside the greenhouse ET o The attenuation factors of the radiation component and the advection component are defined as follows: ; Where, ET rad,in and ET rad,out Inside and outside the greenhouse ET o The radiation component; ET adv,in and ET adv,out Inside and outside the greenhouse ET o The advection component of ET o,in and ET o,out The total inside and outside of the greenhouse ET o ; ζ rad 、ζ adv 、 ζ o They are ET o Radiation component attenuation factor, advection component attenuation factor and total flux attenuation factor; Step 4: Introduce solar radiation transmittance τ (= R s,in / R s,out ), wind speed attenuation rate ω (= V in / V out )as well as ET rad,out and ET adv,out Build the model by establishing ζ rad and τ The functional relationship and ζ adv and ω The functional relationship of ET o,in The expression is as follows: ; Function f ( τ )and f ( ω ) is established using daily scale data; Step 5: Build ζ rad and τ as well as ζ adv and ω Relational Substitution ET o,in In the expression of ET rad,out and ET adv,out Substitute the expression ET o,in The expression of indoor weather information is obtained based on outdoor weather information. ET o The expression is as follows: .

[0008] Furthermore, the step three ET o In the calculation formula, R n = Rns - R nl , R ns and R nl They are net shortwave radiation and net longwave radiation (MJ / (m 2 ·d)) are calculated using the following formula: ; ; ; Where, α is the reflectivity, R s is the solar radiation (MJ / (m 2 d))、 σ is the Stefan-Boltzmann constant (4.903× 10 -9 MJ / (K 4 ·m 2 d))、 T max,k and T min,k The highest and lowest absolute temperature values ​​are respectively (K=℃+273.6), e a is the actual water vapor pressure (kPa), R so is the solar radiation on a sunny day (MJ / (m 2 d))、 Z is the altitude of the test area (m), R a is the zenith radiation (MJ / (m 2 ·d)).

[0009] Furthermore, in step one, in order to study the changes in the evapotranspiration of reference crops inside and outside the greenhouse, perennial lawns are laid in the test areas inside and outside the greenhouse, and the lawn height is always kept within the set height range by mowing; the lawns inside and outside the greenhouse are irrigated by micro-sprinkler irrigation, and to ensure that the grass outside the greenhouse is not affected by rainfall, plastic film is used to cover it during rainfall.

[0010] Furthermore, in step 1, the plastic greenhouse used in the experiment is a steel frame structure, covered with a drip-free polyethylene film, and vents are provided on the north and south sides of the top and bottom of the greenhouse, and white insect-proof nets are installed at the vents.

[0011] Furthermore, in step 2, multiple sets of HOBO temperature and humidity sensors are used to measure T a andRH , measured using a solar radiometer R s The anemometer with an accuracy of ±0.02 m / s was used to measure the wind speed inside and outside the greenhouse. V The sensor location is the same as that of the radiometer. All meteorological data are collected every 5 seconds and the average value is calculated every 15 minutes.

[0012] Furthermore, a small weighing lysimeter was installed inside the greenhouse. The soil profile, forage planting method, mowing time and irrigation frequency inside the lysimeter were kept the same as those outside. Data were collected every 30 minutes and recorded in the data logger.

[0013] Furthermore, the zenith radiation parameters can be calculated using the formula recommended in the FAO 56 manual.

[0014] The beneficial effects of the present invention are: the standard FAO-56 Penman-Monteith equation is used to calculate the greenhouse internal and external ET o , and analyzed the inside and outside of the greenhouse ET o The radiation and advection component variation characteristics are introduced by τ and wind speed attenuation rate ω The radiation and advection equations in the equations were improved respectively, and a method for estimating indoor ET o A simple model is constructed to estimate indoor ET o The simple model includes four meteorological factors: outdoor net radiation, air temperature, water vapor pressure difference and wind speed, as well as two greenhouse characteristic factors. τ and ω The model has high accuracy, few parameters and is easy to obtain, providing a methodological reference for facilitating greenhouse group irrigation management. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 A dynamic change diagram of the net radiation, net shortwave radiation and net longwave radiation inside and outside the greenhouse of the present invention; Figure 2 The figure is a dynamic change diagram of the evapotranspiration of reference crops inside and outside the greenhouse of the present invention and its components; Figure 3 is a graph showing the variation of the attenuation coefficients of the radiation component, advection component and total flux of the present invention; Figure 4 is a correlation diagram of the attenuation factor and transmission coefficient of the radiation component and the advection component of the present invention; Figure 5is a correlation diagram between the observed and simulated values ​​of the evapotranspiration of the reference crop in the greenhouse of the present invention; Figure 6 is a correlation diagram between the net shortwave radiation in the greenhouse of the present invention and the outdoor solar radiation; Figure 7 This is a correlation diagram between the net shortwave radiation in the greenhouse and the net indoor radiation of the present invention. DETAILED DESCRIPTION

[0016] The present invention will be further described below with reference to the accompanying drawings and examples.

[0017] The present invention provides a technical solution for estimating reference crop evapotranspiration in a greenhouse using outdoor meteorological information, and uses the standard FAO-56 Penman-Monteith (FAO56-PM) equation to calculate the greenhouse internal and external evapotranspiration. ET o , and analyze the inside and outside of the greenhouse ET o The radiation and advection component variation characteristics are introduced by τ and wind speed attenuation rate ω The radiation partial equation and the advection partial equation in the equation are improved respectively, and a method is constructed to estimate the indoor ET o A simple model.

[0018] Example 1: A method for estimating reference crop evapotranspiration in a greenhouse using outdoor meteorological information includes the following steps: Step 1: Select the test area and confirm the basic information of the test area: The experiments were conducted in 2020 and 2021 in a plastic greenhouse at the Henan Agricultural Efficient Water Use Experimental Base (34°47′N, 113°47′E, ​​81.2 m above sea level). The experimental area has an average annual temperature of 14.7°C, an average annual precipitation of 618 mm, and an average annual sunshine duration of 2370 h. The soil type in the experimental area is primarily clay loam, with an average bulk mass and field water holding capacity of 1.43 g / cm2 in the 0-100 cm soil layer, respectively. 3 and 0.36 cm 3 / cm 3 .

[0019] The plastic greenhouse used in the experiment was a steel frame structure covered with a drip-free polyethylene film. It was 20 m long from east to west and 12 m wide from north to south. Ventilation holes were set on the top and bottom of the greenhouse on both the north and south sides. The maximum opening area of ​​the top vent was 20 m. 2 (20 m ´ 1.0 m), the maximum opening area on one side of the bottom is 24 m 2(20 m x 1.2 m), with 60-mesh white insect screens installed at the ventilation openings. The plastic film used in 2020 was old (3 months old), and was replaced in 2021 (newly replaced on February 10). The plastic film used in 2021 was the same material.

[0020] To study the reference evapotranspiration of crops inside and outside the greenhouse ET o ) changes, perennial lawns were laid in the experimental areas inside and outside the greenhouse. Through mowing, the lawn height was always maintained within the range of 0.12-0.15 m. The lawns inside and outside the greenhouse were irrigated with micro-sprinkler irrigation. The irrigation time was set at 20:00, and the irrigation amount was the water surface evaporation measured by a 20 cm standard evaporation dish on that day. The maximum daily irrigation amount inside and outside the greenhouse was 4.2 and 9.7 mm, respectively. Using this irrigation system, the soil moisture content of 0-60 cm was observed to be between 0.29 and 0.36 cm during the experiment. 3 / cm 3 To ensure that the grass outside the greenhouse is not affected by rainfall, plastic film is used to cover it during rainfall. ET o Correlation of advection sub-items,The observation time of this experiment was mainly set in May and June, that is, the greenhouse vents were fully open (except rainy days).

[0021] Step 2: Measure the meteorological parameters inside and outside the greenhouse: During the experiment, the air temperature inside and outside the greenhouse was continuously measured. T a )、Relative humidity RH ), Solar radiation, R s ) and wind speed V ). Measured using multiple sets of HOBO temperature and humidity sensors (U23-002A, USA) T a and RH , 3 locations are monitored inside the greenhouse, namely the east, middle and west, and 1 HOBO is deployed outside the greenhouse. T a and RH The measurement height is 2 m above the ground surface; T a and RH , calculate the vapor pressure deficitVPD ); measured using two sets of solar radiometers with the same specifications (LI200X, USA) R s The greenhouse was mainly measured at the middle position, and the indoor and outdoor radiometers were installed 2 m above the ground. An anemometer with an accuracy of ±0.02 m / s (Gill Wind Sonic, UK) was used to measure the anemometer inside and outside the greenhouse. V , sensor position and R s All meteorological data are collected every 5 seconds and the average value is calculated every 15 minutes. T a and RH The data is stored in HOBO. R s and V The data were stored in a CR1000 data logger (Campbell Scientific Inc., USA).

[0022] Two small weighing lysimeters (LYS50S, China) were installed inside the greenhouse. They were 50 cm long, 50 cm wide, and 60 cm high, with a maximum capacity of 660 kg and an evaporation resolution of 0.01 mm. The soil profile, pasture planting pattern, mowing schedule, and irrigation frequency inside the lysimeters remained the same as those outside. Data were collected every 30 minutes and recorded in a data logger. ET o It can be calculated using the Penman-Montieth formula.

[0023] Step 3: Use FAO 56 Penman-Monteith formula to calculate the daily evapotranspiration inside and outside the greenhouse ( o ).

[0024] The FAO 56-PM equation is a meteorological method for calculating ET o The most commonly used method, the meteorological data included in the equation is relatively small and easy to measure, and can also be obtained through provincial or municipal meteorological departments or agricultural departments, so it is easy to master ET o The changing pattern of water use efficiency is the key to further improve water use efficiency. In greenhouse environment, the presence of plastic film changes the ET o There are two main driving factors for the solar radiation: net solar radiation and air velocity. The former is mainly manifested in the impact of coverage on net short-wave radiation and net long-wave radiation, while the latter is mainly manifested in the restriction effect of vents. Therefore, the radiation exchange process and the horizontal exchange process in the greenhouse environment have a great influence on the solar radiation.ET o The impact is the focus of discussion.

[0025] In calculation ET o At the daily scale, it is generally believed that the soil heat flux (Soil heat flux, G ) is 0, then ET o The calculation formula is as follows: (1) In the formula, the parameters T a 、 ET and V From indoor and outdoor measured data; VPD is the slope of the saturated water vapor pressure curve (kPa / ℃); Δ is the hygrometer constant (kPa / ℃); R n is the net radiation (MJ / (m 2 d)) R n = R ns - R nl ; R ns and R nl They are net shortwave radiation and net longwave radiation (MJ / (m 2 ·d)) are calculated using the following formula: (2) (3) (4) Where, α is the reflectivity; R s is the solar radiation (MJ / (m 2 d)); γ is the Stefan-Boltzmann constant (4.903× 10 -9 MJ / (K 4 ·m 2 d)); T max,k and T min,k are the highest and lowest absolute temperature values ​​respectively (K=℃+273.6); e a is the actual water vapor pressure (kPa); Rso is the solar radiation on a sunny day (MJ / (m 2 d)); Z is the altitude of the test area (m); R a is the zenith radiation (MJ / (m 2 ·d)) This parameter can be calculated using the formula recommended in the FAO 56 manual.

[0026] In formula (1), the radiation component ( σ rad ) and the advection component ( ET adv ) are defined as follows: (5) (6) Inside the greenhouse ET o The attenuation factors of the radiation component and the advection component are defined as follows: (7) Where, ET rad,in and ET rad,out Inside and outside the greenhouse ET o The radiation component; ET adv,in and ET adv,out Inside and outside the greenhouse ET o The advection component of ET o,in and ET o,out The total inside and outside of the greenhouse ET o ; ET rad 、 ζ adv 、 ζ o They are ζ o Radiation component attenuation factor, advection component attenuation factor and total flux attenuation factor.

[0027] Step 4: To use outdoor weather information to estimate indoor ET o The goal is to introduce solar radiation transmittance ET (= R s,in / R s,out), wind speed attenuation rate τ (= V in / V out )as well as ω rad,out and ET adv,out Build the model.

[0028] Since the meteorological data required by the model can be provided by the agricultural part or the meteorological part, the radiation transmittance ET and wind speed attenuation rate τ Become two key factors affecting the accuracy of the model, ω and τ Determine the radiation component and the advection component in ω o The proportion in ET and τ Make reliable calculations or obtain them through accurate on-site measurements; This application is established by ω rad and ζ The functional relationship and τ adv and ζ The functional relationship of ω o,in The expression is as follows: (8) Function f ( ET )and f ( τ ) is established using daily scale data.

[0029] Step 5: Build ω rad and ζ as well as τ adv and Substitute the relationship into formula (8), and ζ rad,out and ω adv,out Substitute the expression into formula (8) to obtain the indoor weather information estimation based on outdoor weather information. ET o The expression is as follows: (9) The above data can all be provided by agricultural extension departments and meteorological service departments, so the model has the characteristics of few parameters and easy to obtain.

[0030] Example: The data period selected for this study is from May 1 to June 30, 2020 and 2021. During this period, the greenhouse vents are in a long-term open state, and sufficient mass and heat exchange can be carried out between the environmental factors inside and outside the greenhouse, and the influence of the advection component is relatively small.

[0031] Dynamic changes of meteorological factors inside and outside the greenhouse: ET a, b and c are the net shortwave radiation inside and outside the greenhouse ( R ns ), Net longwave radiation ( R nl ) and net radiation ( R n ) changes dynamically over time. Table 1 shows the monthly average values, standard deviations, and variation ranges of these three radiation factors in 2020 and 2021. It can be seen that due to the blocking effect of the plastic film, the outdoor R ns 、 R nl and R n Always higher than indoors, 2 a outdoor and indoor R ns The fluctuation range is 3.79~19.14 MJ / (m 2 ·d) and 2.50~13.22 MJ / (m 2 d), R ns, in / R ns, out The difference between outdoor and indoor R nl The fluctuation range is -0.50~2.73 MJ / (m 2 ·d) and -0.40~1.13 MJ / (m 2 d), R nl, in / R nl, out The difference between outdoor and indoor R n The fluctuation range is 4.19~16.41 MJ / (m 2 ·d) and 3.01~12.09 MJ / (m 2 d), R n, in / R n, out It varies between 0.72 and 0.74, with an average value of 0.71. R ns and Rn By doing linear fitting, we can find that there is a significant linear correlation between the two. When the slope is 1.0, R 2 All greater than 0.98 ( ET ), R ns,out / R n,out and R ns,in / R n,in The two-month average R nl,in / R n,in Comparison R nl,out / R n,out The greenhouse plastic film blocks the output of net long-wave radiation, which is 59.2% lower than that of indoor R nl The relative weight of loss is small.

[0032] Figure 1 d, e and f are the air temperatures inside and outside the greenhouse ( T a )、Water vapor pressure difference( Figure 7 ) and wind speed ( V ) changes dynamically over time. Table 1 shows the monthly mean values, standard deviations, and variation ranges of these three meteorological factors in 2020 and 2021. It can be seen that during the entire experimental observation period, the T a The difference is very small, and the temperature difference between inside and outside varies between 0.08 and 3.03 ℃, which means that when the greenhouse vents are fully opened, the indoor and outdoor temperatures are T a There was no significant difference; during the 2-year observation period, the outdoor Figure 1 Significantly higher than indoor, 2 years average outdoor VPD The temperature varies between 0.49 and 2.48 kPa, indoor VPD The outdoor average temperature varies between 0.11 and 1.48 kPa. VPD The wind speed outside the greenhouse was 46.3% higher than that inside the greenhouse. Due to the influence of the greenhouse vents, the wind speed outside the greenhouse was always higher than that inside the greenhouse. The wind speed outside the greenhouse varied greatly, ranging from 0.63 to 3.85 m / s, while the wind speed inside the greenhouse varied steadily, ranging from 0.07 to 0.38 m / s. The average wind speed difference was 90.5%. VPD = V in / Vout ) varies between 0.02 and 0.28, with an average value of 0.11.

[0033] Table 1 Monthly mean values, maximum and minimum values ​​of greenhouse internal and external meteorological factors

[0034] Note: In the table R ns 、 R nl 、 R n 、 T a 、 VPD and V They are net shortwave radiation, net longwave radiation, net radiation, air temperature, water vapor pressure difference and wind speed; the superscripts a, b, c and d in the table represent the average value, standard deviation, minimum value and maximum value of each meteorological factor in the whole month, respectively, the same below.

[0035] Reference crop evapotranspiration inside and outside the greenhouse and dynamic changes of each component: ω a, b and c are the reference crop evapotranspiration inside and outside the greenhouse ( VPD o )、 Figure 2 o Radiation component ( ET o, rad )and ET o Advection component ( ET o, adv ) changes dynamically over time. Table 2 shows the monthly average values, standard deviations, change ranges, and indoor and outdoor differences of these three factors in 2020 and 2021. It can be seen that ET o Trends over time and R n and R ns Similar, outdoor ET o The average value was 4.98 mm / d, which varied from 0.88 to 9.75 mm / d. ET o The indoor average temperature in May was 2.71 mm / d, ranging from 0.40 to 4.05 mm / d. ET o Compared with the outdoor environment, it decreased by 2.02 mm / d, and decreased by 2.55 mm / d in June. The indoor average temperature in the two months was 2.02 mm / d less than that in the outdoor environment. ET o A decrease of 45.7% compared to outdoors.

[0036] Greenhouse exterior and interior ET o, rad The trend of change is relatively close, outdoor ET o, rad The average value is 3.20 mm / d, which varies from 0.43 to 5.07 mm / d. ET o, rad The indoor average value varied between 0.40 and 3.89 mm / d, with an average of 2.59 mm / d. Calculated on a monthly basis, the difference between the two values ​​was small. ET o,rad Compared with the outdoor environment, it only decreased by 0.39 mm / d, and in June it only decreased by 0.84 mm / d. The average indoor temperature in the two months was ET o,rad A 19.1% decrease compared to the outdoor environment. ET o,adv Trends over time and ET o and ET o, rad There are obvious differences, but similar trends to wind speed changes ( ET f), and outdoor ET o,adv Significantly higher than indoor and outdoor Figure 1 o,adv The average value is 1.85 mm / d, which varies from 0.45 to 5.76 mm / d. ET o, adv The indoor temperature varied between 0.01 and 0.37 mm / d, with an average of 0.11 mm / d. Calculated on a monthly basis, the indoor average temperature in May was o,adv This is a significant decrease of 94.9% compared to outdoor conditions, and a decrease of 93.1% in June.

[0037] Radiative and advective components ET o The contributions of ET rad = ET rad / ET o and ρ adv = ET adv / ET o = 1- ρ rad During the experimental observation period, the indoor ET rad Always higher than outdoor, the average indoor and outdoor ET radIn 2021, they were 0.95 and 0.64 respectively, and the average in 2 years was 0.96 and 0.65 respectively. ρ rad Indoor temperatures are 32.3% higher than outdoor temperatures.

[0038] Table 2 Monthly mean, maximum, and minimum values ​​of evapotranspiration and its components for reference crops inside and outside the greenhouse

[0039] Reference analysis of the distribution of the radiation and advection components of crop evapotranspiration and their correlation with the attenuation factor: ρ is the radiation component of the attenuation factor ( ρ rad ), advection component ( ρ adv ) and total flux ( Figure 3 o ) changes dynamically over time. Table 3 shows the monthly average values, standard deviations, and ranges of variation of these three factors in 2020 and 2021. It can be seen that during the experimental observation period, the attenuation factors generally showed the following characteristics: ζ rad > ζ o > ζ adv , 2020 ζ rad It fluctuates between 0.64 and 0.81, with an average value of 0.72. ζ o It fluctuates between 0.26 and 0.73, with an average value of 0.55. ζ adv It fluctuates between 0.01 and 0.19, with an average value of 0.06. ζ rad The average values ​​of ζ o and ζ adv High 23.6% and 91.7%; 2021 ζ rad It fluctuates between 0.69 and 0.96, with an average value of 0.83. ζ o It fluctuates between 0.18 and 0.78, with an average value of 0.55. ζ adv It fluctuates between 0.01 and 0.13, with an average value of 0.06. ζ rad The average values ​​of ζ o and ζ adv 33.7% and 92.8% higher. 2021ζ rad It is significantly higher than in 2020. This is because the new plastic film was replaced in 2021, which has a higher radiation transmittance. ζ o and ζ adv The changes in 2 years are not much different.

[0040] Table 3 Monthly mean, maximum and minimum values ​​of the attenuation coefficients of the radiation component, advection component and total flux

[0041] By summarizing the data from May to June 2020 and 2021 ( n = 122, and the radiation component attenuation factors were established respectively ( ζ rad ) and radiation transmittance ( ζ ) and the advection component attenuation factor ( ζ adv ) and wind speed attenuation rate ( ζ ) between the ( τ ), it can be seen that there is a very significant linear relationship between the two factors ( P <0.01), [[ID=I99]]ζ rad and ω The coefficient of determination ( R 2 ) is 0.71, and the mean absolute error ( Figure 4 ) and the root mean square error ( ζ ) were 0.046 and 0.066 respectively; [[ID=I03]]τ adv and MAE of R 2 0.86, RMSE and ζ They are 0.044 and 0.049 respectively.

[0042] Evaluation of the model for estimating indoor reference crop evapotranspiration based on outdoor meteorological information: T a 、 ω and V Substitute into formula (9), and calculate MAE o,in Linear fitting with indoor observations ( RMSE ), it can be seen that most of the data points are around the 1:1 line, and the two are highly significantly correlated ( P <0.01), R 2 is 0.95, RH and ETThey are 0.248 and 0.475 mm / d respectively, which shows that the model has high accuracy and robustness.

[0043] Changes in radiation transfer and its components inside and outside the greenhouse: Calculation of the radiation inside the greenhouse Figure 5 o First, we need to accurately obtain the indoor net radiation R n,in ,and R n is the net shortwave radiation ( R ns ) and net longwave radiation ( R nl ), as shown in formula (2), if the grass reflectivity α is 0.23, then the inside of the greenhouse R ns It can be expressed as: (10) This shows R ns,in and R s,out The ratio is 0.77 MAE ,if RMSE is known, then R ns,in The outdoor solar radiation factor can be directly used for deduction. R ns,in and R s,out Linear fitting revealed a significant linear relationship between the two ( ET ), R 2 is 0.95, indicating that the outdoor R s Estimated indoor R ns It is feasible. In addition, R ns and R n There is also a good linear relationship between them. By fitting the two, we can find that R 2 for( τ ), these findings provide further simplification for calculating the greenhouse interior R n In addition, the average indoor R ns It is 67% less than that outdoors, close to R n The attenuation ratio of greenhouse plastic film covering is 70%, which shows that the attenuation rate of net radiation and net shortwave radiation is similar.

[0044] Compared to the outside of the greenhouse, the indoor R nl The losses were significantly reduced during the trial observation period in 2020 and 2021. R nl The average losses were 0.97 and 1.05 MJ / (m 2 d), in other words, observed inside the greenhouse R nl The smaller the value, the R n The larger the value, the water loss is 0.39 and 0.43 mm / d. R nl The amount of loss varies.

[0045] The above mentioned R ns and R nl The difference between indoors and outdoors, and the R n The impact will be on τ o The radiation component ( Figure 6 o,rad ) have a direct impact, during the experimental observation period Figure 7 o,rad right ET o Contribution ( ET rad ) is always higher indoors than outdoors. The main reason is that the indoor advection component ( ET o,adv ) is significantly lower than that of outdoor, resulting in indoor ET o In terms of radiation component attenuation, the experiment found that the inside and outside of the greenhouse R n The ratio of the inside and outside of the greenhouse varies between 0.72 and 0.74, with an average value of 0.71. ρ o,rad The ratio varies between 0.64 and 0.96, with an average value of 0.78, indicating that the radiation component attenuation factor ET rad and ET It is not proportional. By analyzing the correlation between the two, it is found that ET Comparison ζ rad There is a significant shift of 0.29, and the slope is close to 1.5.

[0046] Changes in advection and its components inside and outside the greenhouse: τo The advection component is mainly affected by wind speed, and the indoor and outdoor τ o,adv The change trend is similar to that of wind speed. During the experimental observation period, the outdoor wind speed was much higher than that indoors, so ζ o,adv The same trend of outdoor being higher than indoor is also shown, which leads to the ET adv It fluctuates below 0.2, with an average value of only 0.06, which is much smaller than ET adv and ET o Since the advection component is closely related to wind speed, the wind speed attenuation rate must be considered first when estimating the advection component. ζ Independent variable. This study found ζ Comparison ζ adv The deviation is only 0.006 (negligible), but the slope is 0.64. The reason for the underestimation may be that the advection component is significantly affected by the wind speed as well as the T a and ω Although the impact of greenhouse T a It is relatively close (the maximum relative deviation is only 14.2%), but the inside and outside of the greenhouse ω The differences were significant, with the maximum relative deviation reaching 78.2%. Therefore, it can be seen that the water consumption patterns of crops inside the greenhouse are closely related to the water vapor pressure difference around the plant leaves, and the degree of water vapor pressure deficit is directly affected by the degree of saturation deficit outdoors.

[0047] The results show that the average indoor ζ o 、 VPD o,rad and VPD o,adv Compared with the outdoor environment, the radiation component attenuation factor ( ET rad = ET rad,in / ET rad,out ), advection component attenuation factor ( ζ adv = ET adv,in / ET adv,out ) and the total flux attenuation factor ( ζ o = ET o,in / ET o,out) Overall, it is ζ rad > ET o > ET adv Characteristics, 2 a average ζ rad Comparison ζ o and [[ID=25~]]ζ adv 23.6% to 33.7% and 91.7% to 92.8% higher, respectively; ζ rad and ζ as well as ζ adv and ζ There is a very significant linear relationship between P <0.01), coefficient of determination ( R 2 ) were 0.71 and 0.86 respectively, and the mean absolute error (Mean absolute error, τ ) were 0.046 and 0.044 respectively, and the root mean square error (Root mean square error, ζ ) are 0.066 and 0.049 respectively.

[0048] The invention constructs a method for estimating indoor ω o The simple model includes four meteorological factors: outdoor net radiation, air temperature, water vapor pressure difference and wind speed, as well as two greenhouse characteristic factors. MAE and RMSE ,By comparing with the measured results, it is found that the model accuracy is robust, R 2 is 0.95, ET and τ The model has a simple structure, requires less data and is easy to obtain, and has a high robustness, providing a methodological reference for facilitating greenhouse irrigation management.

[0049] The model constructed in this study was established with the greenhouse vents fully open. When the vents were closed, the wind speed in the greenhouse was zero, and the advection component calculated using formula (6) was also zero, resulting in a 3.8% to 4.9% decrease in model accuracy. Therefore, this situation was not considered in this study (the vents were closed mainly at night and a few days after transplanting). Example

[0050] Zenithal radiation in daily time period ( R a ) is calculated as follows: For different latitudes every day during the year R a , given by the solar constant ( G sc )、Solar declination( ω ) and the ordinal number of the day of the year ( J ) to estimate, as follows: (1-1) Where, R a is the zenith radiation (MJ / (m 2 d)); G sc is the solar constant (=0.082 MJ / (m 2 min)); d r is the reciprocal of the relative distance between the sun and the earth; MAE s is the solar hour angle (rad); RMSE is the geographic latitude (rad); δ ω φ δ is the solar declination (rad).

[0051] (1-2) (1-3) (1-4) Where, J Is the day number of a certain day in the year, J The values ​​and calculation equations are detailed in Appendix 2 (Table 2.5) of FAO 56.

[0052] The above description is only a preferred embodiment of the present invention and does not limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principle of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for estimating reference crop evapotranspiration in a greenhouse using outdoor meteorological information, characterized in that: The steps include: Step 1: Select the test area and determine the basic information of the test area, including the location of the test area, greenhouse structure, average temperature over the years, average annual precipitation, average annual sunshine hours, soil type, average volume mass of the soil layer and field water holding capacity; Step 2: Continuously measure the meteorological parameters inside and outside the greenhouse, including air temperature ( T a )、Relative humidity( RH )、Solar radiation( R s ) and wind speed ( V ), using the measured air temperature and relative humidity to calculate the water vapor pressure difference ( VPD ), and measure evapotranspiration of reference crops; Step 3: Use the FAO 56 Penman-Monteith formula to calculate the daily evapotranspiration inside and outside the greenhouse ( ET o ); In calculation ET o When the soil heat flux is generally considered to be 0 on a daily scale, ET o The calculation formula is as follows: ； In the formula, Δ is the slope of the saturated water vapor pressure curve (kPa / ℃), γ is the hygrometer constant (kPa / ℃), R n is the net radiation (MJ / (m 2 d)) Parameters T a , VPD and V From indoor and outdoor measured data; exist ET o In the calculation formula, the radiation components are defined separately ( ET rad ) and the advection component ( ET adv )for: ； ； Inside the greenhouse ET o The attenuation factors of the radiation component and the advection component are defined as follows: ； In the formula, ET rad,in and ET rad,out Inside and outside the greenhouse ET o The radiation component of ET adv,in and ET adv,out Inside and outside the greenhouse ET o The advection component of ET o,in and ET o,out The total inside and outside of the greenhouse ET o ; ζ rad , ζ adv , ζ o They are ET o Radiation component attenuation factor, advection component attenuation factor and total flux attenuation factor; Step 4: Introduce solar radiation transmittance τ (= R s,in / R s,out ), wind speed attenuation rate ω (= V in / V out )as well as ET rad,out and ET adv,out Build the model by establishing ζ rad and τ The functional relationship and ζ adv and ω The functional relationship is ET o,in The expression is as follows: ； Function f ( τ )and f ( ω ) is established using daily scale data; Step 5: Construct ζ rad and τ as well as ζ adv and ω Relational Substitution ET o,in In the expression of ET rad,out and ET adv,out Substitute the expression into ET o,in The expression of indoor ET o The expression is as follows: 。 2. The method for estimating reference crop evapotranspiration in a greenhouse using outdoor meteorological information according to claim 1, characterized in that: Step three ET o In the calculation formula, R n = R ns - R nl , R ns and R nl They are net shortwave radiation and net longwave radiation (MJ / (m 2 ·d)) are calculated using the following formula: ； ； ； In the formula, α is the reflectivity, R s is the solar radiation (MJ / (m 2 d))、 σ is the Stefan-Boltzmann constant (4.903 × 10 -9 MJ / (K 4 ·m 2 d))、 T max,k and T min,k They are the highest and lowest absolute temperature values ​​(K=℃+273.6), e a is the actual water vapor pressure (kPa), R so is the solar radiation on a sunny day (MJ / (m 2 d))、 Z is the altitude of the test area (m), R a is the zenith radiation (MJ / (m 2 d)).

3. The method for estimating reference crop evapotranspiration in a greenhouse using outdoor meteorological information according to claim 1, characterized in that: In the step 1, in order to study the changes in the evapotranspiration of reference crops inside and outside the greenhouse, perennial lawns are laid in the test areas inside and outside the greenhouse, and the lawn height is always kept within the set height range by mowing; the lawns inside and outside the greenhouse are irrigated by micro-sprinkler irrigation, and in order to ensure that the grass outside the greenhouse is not affected by rainfall, plastic film is used to cover it during rainfall.

4. The method for estimating reference crop evapotranspiration in a greenhouse using outdoor meteorological information according to claim 1, characterized in that: In the step 1, the plastic greenhouse used in the experiment is a steel frame structure, covered with a drip-free polyethylene film, and ventilation holes are provided on the top and bottom north and south sides of the greenhouse, and white insect-proof nets are installed at the ventilation holes.

5. The method for estimating reference crop evapotranspiration in a greenhouse using outdoor meteorological information according to claim 1, characterized in that: In step 2, multiple sets of HOBO temperature and humidity sensors are used to measure T a and RH , measured using a solar radiometer R s The anemometer with an accuracy of ±0.02 m / s was used to measure the wind speed inside and outside the greenhouse. V The sensor location is the same as that of the radiometer. All meteorological data are collected every 5 seconds and the average value is calculated every 15 minutes.

6. The method for estimating reference crop evapotranspiration in a greenhouse using outdoor meteorological information according to claim 1, characterized in that: A small weighing lysimeter was installed inside the greenhouse. The soil profile, forage planting method, mowing time and irrigation frequency inside the lysimeter were kept the same as those outside. Data were collected every 30 minutes and recorded in the data logger.

7. The method for estimating reference crop evapotranspiration in a greenhouse using outdoor meteorological information according to claim 2, characterized in that: Zenith radiation parameters can be calculated using the formula recommended in the FAO 56 manual.

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