A method and system for constructing a comprehensive model of water and heat transfer in agricultural fields covered with mixed canopies

Abstract

The present invention discloses a method and system for constructing a comprehensive model of water and heat transfer in a mulched mixed canopy farmland. The present invention is based on energy balance theory and turbulent transmission theory, combined with agricultural production practice, and fully considers the influence of farmland surface film covering and intercropping on the water and heat transfer process of farmland, and creatively proposes a comprehensive model of water and heat transfer in a mulched mixed canopy farmland. The model only needs conventional meteorological (air temperature, saturated water vapor pressure difference, wind speed, solar radiation, air pressure), soil (soil moisture content and field water holding capacity), and crop growth data (leaf area index) data drive, and can realize the accurate simulation of the water and heat transfer flux (latent heat, sensible heat, net radiation, and soil heat flux) of the whole mulched mixed canopy farmland and each component (each mixed canopy, mulched soil, bare soil) during the whole growth period, filling the gap in the simulation research of water and heat transfer in mulched mixed canopy farmland.

Description

Technical Field

[0001] The present invention relates to the technical field of micrometeorology and plant physiology, and in particular to a method and system for constructing a comprehensive model of water and heat transfer in a mulched mixed canopy farmland. Background Art

[0002] Film covering of farmland has been widely promoted and applied in arid areas of my country because it can significantly save water and retain entropy. However, film covering of farmland significantly changes the surface resistance, greatly reduces soil evaporation, changes the surface reflectivity, and thus changes the water and heat transfer process on the surface, and has an important impact on the regional climate. In recent years, based on the understanding of the response characteristics of different crops to light and water, in order to give full play to the response ability of different crops to light and water, intercropping and interplanting techniques have also been widely promoted and applied. The canopy transpiration composition of intercropped or interplanted farmland plants has changed from one crop to multiple crops, making the water and heat transfer process of farmland more complex. Existing studies have shown that: (1) There have been many simulation studies on water and heat transfer models for vegetation-covered surfaces, but soil evaporation under mulching conditions is often treated as zero flux, which is inconsistent with reality; (2) Traditional water and heat transfer models based on the soil-plant-atmosphere-continuous system (SPAC) often calculate canopy transpiration by treating all vegetation canopies as a whole, thus ignoring the fact that the underlying surface often has multiple plant species mixed, and different plants have different utilization of light energy and water, resulting in large errors in the estimation of various components of water and heat transfer. Establishing a model that can accurately describe the water and heat transfer process in farmland with mulched mixed canopies is of great significance for the efficient use of agricultural water resources and water resources management, simulation of land surface processes in arid areas, and regional climate change. Summary of the invention

[0003] The present invention takes energy balance as the framework, adopts the surface reflectivity model of film-covered farmland to describe the influence of film covering on the short-wave radiation transmission process, introduces the emissivity / absorption rate of film-covered soil to consider the influence of film covering on the long-wave radiation transmission process, and introduces the film covering proportional factor f m and film resistance coefficient Considering the influence of film covering on the water and heat transfer process of soil evaporation; on the basis of the above, the mixed canopy energy interception proportional factor is introduced I i C i Let's consider the energy distribution process in different canopies in a mixed canopy field.

[0004] Based on the above problems, the present invention adopts the following technical solution: a method for constructing a comprehensive model of water and heat transfer in a mulched mixed canopy farmland, which comprises the following steps:

[0005] Step 1. Establish the energy balance equation of the whole mixed canopy farmland and its components, namely, the mixed canopy, bare soil and film-covered soil;

[0006] Step 2. Calculate the latent heat flux of the film-covered mixed canopy farmland as a whole and its components, i.e., each mixed canopy, bare soil, and film-covered soil;

[0007] Step 3. Calculate the sensible heat flux of the film-covered mixed canopy farmland as a whole and its components, i.e., each mixed canopy, bare soil, and film-covered soil;

[0008] Step 4. Calculate the net radiation flux of the film-covered mixed canopy farmland as a whole and its components, i.e., each mixed canopy, bare soil and film-covered soil;

[0009] Step 5. Calculate the soil heat flux of the mulched mixed canopy farmland as a whole and its components, namely bare soil and mulched soil;

[0010] Step 6. Couple the energy balance equation with the soil water and heat transfer process, establish a comprehensive model of the water and heat transfer process in the mulched mixed canopy farmland, determine the model parameters and solve the comprehensive model.

[0011] Furthermore, for the film-covered farmland as a whole, its energy balance equation is:

[0012]

[0013] in, , , and are the net radiation flux, latent heat flux, sensible heat flux and soil heat flux obtained by the film-mulched farmland system, W m -2 ;

[0014] For mixed canopy fields with different crops, different plants i The energy balance equation of the canopy is:

[0015]

[0016] The energy balance equation of film-covered soil is:

[0017]

[0018] The energy balance equation of bare soil between membranes is:

[0019]

[0020] in, , and Plant iCanopy net radiation flux, plant transpiration latent heat flux and plant sensible heat flux, W m -2 ; and are the net radiation flux of bare soil between films and film-covered soil in some film-covered farmland, Wm -2 ; and are the evaporation latent heat flux of bare soil between films and film-covered soil in some film-covered farmland, W m -2 ; and are the soil heat fluxes of bare soil between films and covered soil in some film-covered farmland, W m -2 ; and are the sensible heat fluxes of bare soil between films and film-covered soil in some film-covered farmlands, W m -2 .

[0021] Furthermore, for the film-covered farmland as a whole, the energy balance equation , , and Each is divided into the following components:

[0022] Overall net radiation flux And its components:

[0023]

[0024] Overall latent heat flux And its components:

[0025]

[0026] Overall sensible heat flux H s And its components:

[0027]

[0028] Overall soil heat flux And its components:

[0029]

[0030] in, For the i Mixed canopy light interception factors of crop canopies; is the proportion of film-covered soil to the total farmland area; For the i Latent heat flux in the canopy.

[0031] Furthermore, in step 2,

[0032] Film-covered farmland plants i Latent heat of evaporation , Latent heat of evaporation of bare soil between membranes and latent heat of evaporation of film-covered soil The following formulas are used for calculation:

[0033]

[0034]

[0035]

[0036]

[0037]

[0038]

[0039] In the formula, is the air density, kg m -3 ; is the specific heat capacity of air at constant pressure, J kg -1o C -1 ; is the hygrometer constant, KPa o C -1 ; Plant i Canopy temperature, °C; and are the surface soil temperatures at bare soil between films and at film-covered soil, ℃; , and The temperature is , and Saturated water vapor pressure at , Kpa; is the actual water vapor pressure at the reference altitude temperature of the flux observation; is the saturated water vapor pressure slope, Kpa ℃ -1 ; is the saturated water vapor pressure difference at the reference height of flux observation, Kpa; For plants i Aerodynamic drag from blade to flux observation reference height, m -1 s; For plants i Canopy resistance, m -1 s; is the aerodynamic drag m -1 s; is the overall average canopy leaf-to-flux observation height aerodynamic drag, m-1 s; is soil resistance, m -1 s; is the coating resistance m -1 s, is the air temperature at the observation height.

[0040] Furthermore, in step 3, the film-covered farmland plants i Sensible heat flux Bare soil sensible heat flux between membranes and sensible heat flux of film-covered soil The following formulas are used for calculation:

[0041]

[0042]

[0043]

[0044] Furthermore, the net radiation flux of each mixed canopy, bare soil and film-covered soil in step 4 includes the net shortwave radiation flux and the net longwave radiation flux ;

[0045] Among them, film-covered farmland plants i Net shortwave radiation flux , Net shortwave radiation flux of bare soil between membranes and the net shortwave radiation flux of the film-covered soil They are:

[0046]

[0047]

[0048]

[0049]

[0050] In the formula, is the solar shortwave radiation, W m -2 ; is the canopy shortwave radiation absorption rate, equal to , is the transmittance of solar shortwave radiation in the canopy; is the reflectivity of solar shortwave radiation in the canopy; is the shortwave radiation reflectivity of the film-covered soil; is the short-wave radiation reflectivity of bare soil between membranes;

[0051] In solving the film-covered soil and bare soil between films, thei When calculating the canopy longwave radiation flux, all crop canopies are considered as a whole, and the longwave radiation of the overall canopy radiation is expressed as the film coverage ratio. Assigned to the film-covered soil and bare soil between films, the plants in the film-covered farmland i Net longwave radiation flux , Net long-wave radiation flux of bare soil between membranes and the net longwave radiation flux of film-covered soil They can be expressed as:

[0052]

[0053] + [ ]+ [ ]

[0054] ]

[0055] ]

[0056] In the formula, is the Stefan-Boltzmann constant, which is 5.67×10 -8 W / (m 2 K 4 ); is the sky surface emissivity; is the canopy surface radiation coefficient; is the radiation coefficient of the film-covered soil surface; is the radiation coefficient of the bare soil surface between membranes; is the canopy longwave radiation reflectivity; is the long-wave radiation reflectivity of the film-covered soil; is the long-wave radiation reflectivity of bare soil between films; is the canopy longwave radiation transmittance; is the atmospheric temperature, °C, T r is the air temperature at the observation height; is the surface temperature of the film-covered soil, °C; is the surface temperature of bare soil between membranes, °C;

[0057] Film-covered farmland plants i Net radiation flux , Net radiation flux of bare soil between membranes and the net radiation flux of the film-covered soil They are:

[0058]

[0059]

[0060]

[0061] .

[0062] Furthermore, in step 5, the soil heat flux at the film-covered soil of the film-covered farmland Soil heat flux at bare soil between film and The following formulas are used for calculation:

[0063]

[0064]

[0065] In the formula, and They are the reference soil depth ( , m) of soil heat flux between the film-covered soil and the bare soil between the films, W m -2 ;when When it is more than 1m, and Treated as 0; is the soil heat capacity, WK -1 m -1 .

[0066] Furthermore, in step 6, the latent heat flux, sensible heat flux, soil heat flux and net radiation flux components are solved by bringing them into the energy balance equation to obtain the plant i Energy balance equation for the canopy, film-covered soil, and bare soil between films:

[0067] Plant i The energy balance equation at the canopy is:

[0068]

[0069] Energy balance equation at the film-covered soil:

[0070]

[0071] Energy balance equation for bare soil between membranes:

[0072]

[0073] The above energy balance equations are for plants i Canopy temperature , Film-covered soil temperature and the bare soil temperature between membranes The equation of , so it can be expressed as the following system of equations:

[0074]

[0075] in, n For plant types, n When the plant canopy exists, the temperature function equation is f (T) contains (n+2) unknowns, and the number of equations to be solved is (n+2). The temperature function equation is solved by the energy balance equation established above:

[0076]

[0077]

[0078] .

[0079] Furthermore, the Newton-Simpson iterative method is used to solve the nonlinear equations.

[0080] Solve the temperature function equations f After (n+2) unknown temperatures in (T), the latent heat, sensible heat, net radiation and soil heat flux components of different plant canopies, film-covered soil and bare soil are solved, and the weighted sum of each component can be obtained to obtain the overall latent heat, sensible heat, net radiation and soil heat flux of the film-covered mixed canopy farmland.

[0081] On the other hand, the present invention also provides a system for constructing a comprehensive model of water and heat transfer in a film-covered mixed canopy farmland, comprising:

[0082] Module 1. Establish the energy balance equation for the whole mixed canopy farmland and its components, namely, the mixed canopy, bare soil and film-covered soil;

[0083] Module 2. Calculate the latent heat flux of the film-covered mixed canopy farmland as a whole and its components, namely, the mixed canopy, bare soil, and film-covered soil;

[0084] Module 3. Calculate the sensible heat flux of the film-covered mixed canopy farmland as a whole and its components, namely, the mixed canopy, bare soil, and film-covered soil;

[0085] Module 4. Calculate the net radiation flux of the film-covered mixed canopy farmland as a whole and its components, namely, the mixed canopy, bare soil, and film-covered soil;

[0086] Module 5. Calculation methods for soil heat flux of the mulched mixed canopy farmland as a whole and for each component, namely bare soil and mulched soil;

[0087] Module 6. Establish a comprehensive model of water and heat transfer process in mulched mixed canopy farmland, determine the model parameters and solve the comprehensive model.

[0088] Compared with the prior art, the present invention has the following beneficial effects:

[0089] The present invention is based on the energy balance theory and turbulent transfer theory, combined with agricultural production practice, fully considering the impact of surface film covering and intercropping on the water and heat transfer process of farmland, and creatively proposes a comprehensive model of water and heat transfer in mixed canopy farmland. The model only requires conventional meteorological (air temperature, saturated water vapor pressure difference, wind speed, solar radiation, air pressure), soil (soil moisture content and field water holding capacity), and crop growth data (leaf area index) data to drive it, and it can accurately simulate the water and heat transfer flux (latent heat, sensible heat, net radiation, and soil heat flux) of the entire growth period of the mulched mixed canopy farmland and each component (each mixed canopy, mulched soil, bare soil), filling the gap in the research on water and heat transfer simulation of mulched mixed canopy farmland. The invention can provide a theoretical basis for the water and heat transfer process of the complex underlying surface of the mulched mixed canopy farmland, and provide technical support for improving the simulation of land surface processes of the existing land surface model on the typical complex underlying surface of the mulched mixed canopy farmland, providing a scientific basis for studying the impact of large-scale promotion and application of mulching and mixed canopies on regional climate, and providing a scientific reference for regional agricultural water resources management. BRIEF DESCRIPTION OF THE DRAWINGS

[0090] Figure 1 The latent heat flux ( λET )、Latent heat of evaporation( λT ) and soil evaporation latent heat ( λE )Comparison chart of simulated value and measured value;

[0091] Figure 2 A comparison diagram of simulated and measured values ​​of plant transpiration latent heat of maternal corn and paternal corn in two film-mulched mixed canopy farmlands, i.e., a film-mulched furrow irrigation seed corn farmland (BM) and a film-mulched drip irrigation seed corn farmland (DM) according to an embodiment of the present invention;

[0092] 3 is a comparison diagram of simulated and measured values ​​of soil evaporation latent heat of film-covered soil and bare soil in two film-covered mixed canopy farmlands, namely, a film-covered furrow irrigation seed corn farmland (BM) and a film-covered drip irrigation seed corn farmland (DM) according to an embodiment of the present invention;

[0093] Figure 4 This is a comparison chart between the simulated field sensible heat values ​​and the measured values ​​of the film-mulched mixed canopy farmland simulated by the comprehensive water and heat transfer model of the film-mulched mixed canopy farmland in an embodiment of the present invention.

[0094] Figure 5 It is the sensible heat simulation value of each mixed canopy, film-covered soil and bare soil simulated by the comprehensive model of water and heat transfer in the film-covered mixed canopy farmland in the embodiment of the present invention.

[0095] Figure 6 This is a comparison chart between the simulated value and the measured value of the field net radiation of the film-mulched mixed canopy farmland simulated by the comprehensive model of water and heat transfer in the film-mulched mixed canopy farmland according to an embodiment of the present invention.

[0096] Figure 7 It is the net radiation simulation value of each mixed canopy, film-covered soil and bare soil simulated by the comprehensive model of water and heat transfer in the film-covered mixed canopy farmland in the embodiment of the present invention.

[0097] 8 is a comparison chart of simulated values ​​and measured values ​​of field soil heat flux in a mulched mixed canopy farmland simulated by the comprehensive water and heat transfer model for mulched mixed canopy farmland according to an embodiment of the present invention.

[0098] Fig. 9 The simulated values ​​of soil heat flux of film-covered soil and bare soil simulated by the comprehensive model of water and heat transfer in film-covered mixed canopy farmland according to an embodiment of the present invention. DETAILED DESCRIPTION

[0099] In order to facilitate those skilled in the art to understand and implement the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the implementation examples described herein are only used to illustrate and explain the present invention and are not used to limit the present invention.

[0100] Example 1

[0101] like Figure 1 As shown, an embodiment of the present invention provides a method for constructing a comprehensive model of water and heat transfer in a mulched mixed canopy farmland, which includes the following steps:

[0102] Step 1. Establish the energy balance equation of the whole mixed canopy farmland and its components, namely, the mixed canopy, bare soil and film-covered soil;

[0103] For the film-covered farmland as a whole, its energy balance equation is:

[0104] (1)

[0105] in, , , and are the net radiation flux, latent heat flux, sensible heat flux and soil heat flux obtained by the film-mulched farmland system, W m -2 ;

[0106] For the film-covered farmland in general, the energy balance equation , , and Each is divided into the following components:

[0107] Net radiation flux Components:

[0108] (2)

[0109] Latent heat flux Components:

[0110] (3)

[0111] Sensible heat flux Components:

[0112] (4)

[0113] Soil heat flux Components:

[0114] (5)

[0115] in, For the i Mixed canopy light interception factors of crop canopies; is the proportion of film-covered soil to the total farmland area; For the Latent heat flux in the canopy.

[0116] This embodiment takes a mixed canopy farmland with two crops as an example. For a mixed canopy farmland with two crops, the following are plant f and plant m, respectively. Then, the energy balance equation of the canopy of plant f is:

[0117] (6)

[0118] The energy balance equation of the plant canopy is:

[0119] (7)

[0120] The energy balance equation of film-covered soil is:

[0121] (8)

[0122] The energy balance equation of bare soil between membranes is:

[0123] (9)

[0124] in, , and are the canopy net radiation flux, plant transpiration latent heat flux and plant sensible heat flux of plant f and plant m, W m -2 ; and are the net radiation flux of bare soil between films and covered soil in some film-covered farmland, W m -2 ; and are the evaporation latent heat flux of bare soil between films and film-covered soil in some film-covered farmland, W m -2 ; and are the soil heat fluxes of bare soil between films and covered soil in some film-covered farmland, W m -2 .

[0125] Step 2. Calculate the latent heat flux of the film-covered mixed canopy farmland as a whole and its components, i.e., each mixed canopy, bare soil, and film-covered soil;

[0126] The latent heat of transpiration of the film-covered farmland plants in formulas (6) to (9) is （ ), latent heat of transpiration of plant m ( ), latent heat of evaporation of bare soil between membranes ( ) and latent heat of evaporation of film-covered soil ( ) are calculated using the following formula:

[0127] (10)

[0128] (11)

[0129] (12)

[0130] (13)

[0131] (14)

[0132] (15)

[0133] (16)

[0134] (17)

[0135] In the formula, is the air density, kg m -3 ; is the specific heat capacity of air at constant pressure, J kg -1o C -1 ; is the hygrometer constant, KPa o C -1 ; Plant i Canopy temperature, °C; and are the surface soil temperatures at bare soil between films and at film-covered soil, ℃; , and The temperature is , and Saturated water vapor pressure at , Kpa; is the actual water vapor pressure at the reference altitude temperature of the flux observation; is the saturated water vapor pressure slope, Kpa ℃ -1 ; is the saturated water vapor pressure difference at the reference height of flux observation, Kpa; For plants i Aerodynamic drag from blade to flux observation reference height, m -1 s; For plants i Canopy resistance, m -1 s; is the aerodynamic drag m -1 s; is the overall average canopy leaf-to-flux observation height aerodynamic drag, m -1 s; is soil resistance, m -1 s; is the coating resistance m -1 s, is the air temperature at the observation height.

[0136] Step 3. Calculate the sensible heat flux of the film-covered mixed canopy farmland as a whole and its components, i.e., each mixed canopy, bare soil, and film-covered soil;

[0137] Sensible heat flux of plants in film-covered farmland ( ), plant m sensible heat flux ( ), bare soil sensible heat flux between membranes ( ) and sensible heat flux of film-covered soil ( ) are calculated using the following formula:

[0138] (18)

[0139] (19)

[0140] (20)

[0141] (twenty one)

[0142] Step 4. Calculate the net radiation flux of the film-covered mixed canopy farmland as a whole and its components, i.e., each mixed canopy, bare soil and film-covered soil;

[0143] 4.1 Calculation of net shortwave radiation flux

[0144] Net shortwave radiation flux of plants in film-covered farmland ( ), net shortwave radiation flux of plant m ( ), net short-wave radiation flux of bare soil between membranes ( ) and the net shortwave radiation flux of the film-covered soil ( ) are:

[0145] (twenty two)

[0146] (twenty three)

[0147] (twenty four)

[0148] (25)

[0149] (26)

[0150] In the formula, is the solar shortwave radiation (W m -2 ); is the canopy shortwave radiation absorption rate, equal to , is the transmittance of solar shortwave radiation in the canopy; is the reflectivity of solar shortwave radiation in the canopy; is the shortwave radiation reflectivity of the film-covered soil; is the short-wave radiation reflectivity of bare soil between membranes; , and The MICA model formula can be used to solve it.

[0151] 4.2 Calculation of net longwave radiation flux

[0152] The transmission process of long-wave radiation from mulched farmland is more complicated than that of short-wave solar radiation. The atmosphere, mixed plant canopy, mulched soil and bare soil between films can all emit long-wave radiation, which will be absorbed, transmitted and reflected by each layer. For the convenience of analysis, when solving the long-wave radiation flux from the canopy of plant f and plant m obtained from mulched soil and bare soil between films, all crop canopies are considered as a whole, and the long-wave radiation of the overall canopy radiation is calculated by the mulching ratio ( ) is distributed to the film-covered soil and bare soil between films. Then the net long-wave radiation flux of the film-covered farmland plants ( ), net long-wave radiation flux of plant m ( ), net long-wave radiation flux of bare soil between membranes ( ) and the net longwave radiation flux of film-covered soil ( ) can be expressed as:

[0153] (27)

[0154] +( + )[ ]+ ](28)

[0155] +( + )[ ]+ [ ](29)

[0156] ](30)

[0157] ](31)

[0158] In the formula, is the Stefan-Boltzmann constant, which is 5.67×10 -8 W / (m 2 K 4 ); is the sky surface emissivity; is the canopy surface radiation coefficient; is the radiation coefficient of the film-covered soil surface; is the radiation coefficient of the bare soil surface between membranes; is the canopy longwave radiation reflectivity; is the long-wave radiation reflectivity of the film-covered soil; is the long-wave radiation reflectivity of bare soil between films; is the canopy longwave radiation transmittance; is the atmospheric temperature (°C), and the air temperature at the reference observation altitude is used in this application (℃); is the surface temperature of the film-covered soil (°C); is the surface temperature of bare soil between membranes (℃).

[0159] 4.3 Calculation of net radiation flux

[0160] From the above, the net radiation flux of the film-covered farmland plants f ( ), plant m net radiation flux ( ), net radiation flux of bare soil between membranes ( ) and the net radiation flux of the film-covered soil ( ) are

[0161] (32)

[0162] (33)

[0163] (34)

[0164] (35)

[0165] (36)

[0166] Step 5. Calculate the soil heat flux of the mulched mixed canopy farmland as a whole and its components, namely bare soil and mulched soil;

[0167] Soil heat flux at the film-covered soil of film-covered farmland ( ) and soil heat flux at bare soil between membranes ( ) are calculated using the following formulas:

[0168] (37)

[0169] (38)

[0170] In the formula, and They are the reference soil depth ( , m) of the film-covered soil and the soil heat flux between the films (W m -2 ),when When deep enough, and Can be regarded as 0 processing; is the soil heat capacity (WK -1 m -1 ).

[0171] Step 6. Establish a comprehensive model of water and heat transfer process in mulched mixed canopy farmland, determine the model parameters and solve the comprehensive model.

[0172] The model involves many parameters, but the methods of obtaining them are relatively simple. The following introduces the determination of various parameters of latent heat flux and sensible heat flux, net radiation, soil heat flux and soil heat conduction.

[0173] 6.1: Determination of model parameters.

[0174] 6.1.1: Parameters required for latent heat flux and sensible heat flux calculations

[0175] When calculating the latent heat flux, the air temperature at the observation altitude ( ), local atmospheric pressure (P) and relative humidity (RH) can be obtained from conventional meteorological data monitored by meteorological stations.

[0176] Air Density (kg m -3 ) can be calculated by the following formula:

[0177] (39)

[0178] in, When the air temperature is 0 o C and the air density when the atmospheric pressure is 101.3 Kpa is 1.29 kg / m 3 ; P is atmospheric pressure (Kpa), is the air temperature ( o C).

[0179] Hygrometer constant (Kpa℃ -1 ) can be calculated from the atmospheric pressure,

[0180] P (40)

[0181] The slope of the temperature saturation water vapor pressure relationship curve (Kpa ℃ -1 ) can be calculated from the air temperature,

[0182] (41)

[0183] Air saturation vapor pressure (Kpa) can be calculated from the air temperature,

[0184] (42)

[0185] Actual water vapor pressure of air (Kpa) can be calculated from the air temperature,

[0186] (43)

[0187] in, and are the minimum and maximum air temperatures in a unit period (℃), and They are respectively the minimum and maximum relative humidity of air in a unit time period (%), which can be obtained from conventional meteorological data monitored by meteorological stations. and are the saturated water vapor pressure (Kpa) corresponding to the lowest and highest air temperatures during the time period, respectively.

[0188] Aerodynamic drag and It can be calculated from the vertical wind speed profile,

[0189] (44)

[0190] (45)

[0191] Where k is the Von Karman constant and its value is 0.41. is the average canopy height (m), which is obtained by weighting the canopy height of the mother plant and the canopy height of the father plant by the leaf area index proportional factor.

[0192] (46)

[0193] is the friction wind speed (ms -1 ), can be calculated using the following formula,

[0194] (47)

[0195] in, is the wind speed, which can be obtained from routine observation data of meteorological stations; z is the observation height (m);

[0196] is the momentum roughness length (m), which can be calculated from the canopy height,

[0197] (48)

[0198] d is the zero plane displacement (m), which can be calculated from the canopy height,

[0199] (49)

[0200] K is the turbulence dissipation coefficient,

[0201] (50)

[0202] n is the extinction coefficient, which can be obtained by linear interpolation,

[0203] (51)

[0204] is the turbulence dissipation coefficient at the top of the canopy,

[0205] (52)

[0206] Soil surface resistance It can be calculated by the following formula:

[0207] (53)

[0208] in is the minimum soil surface resistance, here it is taken as 100 sm -1 ; is the surface resistance of the film-covered soil (sm -1 ), which can be obtained by calibration from test data.

[0209] is the average soil volume moisture content in the root active layer (cm 3 cm -3 ). It can be calculated by the following formula:

[0210] (54)

[0211] is the field water holding capacity of the crop root active layer (cm 3 cm -3 ), the experimental sampling value in this study was 0.29cm 3 cm -3 .

[0212] In the SWIM model, the differences in canopy resistance of mixed canopy species are fully considered, and the ERIN model is used to calculate the plant f ( ) and plant m ( ) Canopy light interception factor:

[0213] (55)

[0214] (56)

[0215] (57)

[0216] (58)

[0217] in, and are the leaf area index scaling factors of plant f and plant m, respectively, and are the planting ratios of plant f and plant m respectively.

[0218] and are the light energy interception rates of the canopies of plants f and m, respectively, which can be calculated using the following formula:

[0219] (59)

[0220] )(60)

[0221] F is the promotion factor, between 0 and 1, which is the plant f ( ) and plant m ( ) as a function of canopy height:

[0222] )(61)

[0223] and They are the light interception rates of the two plants when the height of plant f is much higher than that of plant m. The calculation formula is as follows:

[0224] (62)

[0225] (63)

[0226] and They are the light interception rates of the canopies of the two plants when the height of plant m is much higher than that of plant f. The calculation formula is as follows:

[0227] (64)

[0228] (65)

[0229] The aerodynamic drag from the leaves of plants f and m to the reference height for flux observation ( and ) can be calculated by the following formula:

[0230] (66)

[0231] (67)

[0232] in, is the average boundary layer resistance per unit area of ​​the canopy (sm -1 ), here the value is 50 sm -1 .

[0233] Canopy resistance of plant f and plant m ( and ) were calculated using the Jarvis model. The Jarvis model describes the response of stomatal resistance at the leaf and canopy scales to environmental variables. The model quantifies these responses by dividing the minimum stomatal resistance by the leaf area index and a series of stress functions:

[0234] (68)

[0235] (69)

[0236] Where: The average stomatal resistance of leaves under the optimal light and water conditions can be taken as 216 sm -1 ; and The leaf area index of the canopy directly involved in energy exchange of plant f and plant m can be calculated by the following formula:

[0237] (70)

[0238] represents the effect of photosynthetically active radiation (S), calculated using the report of Tourula and Heikinheimo (1998):

[0239] (71)

[0240] (72)

[0241] In the formula, is the maximum canopy resistance, which is 5000 sm -1 . Represents the effect of saturated water vapor pressure difference:

[0242] (73)

[0243] In the formula, and The atmospheric temperature is The saturated water vapor pressure difference and the actual water vapor pressure difference (Kpa); g is an empirical parameter with a value of 0.25Kpa -1 . It reflects the effect of air temperature on canopy resistance and is calculated using the following formula:

[0244] (74)

[0245] The effects of water stress were considered:

[0246] (75)

[0247] SWC is the average soil water content in the root active layer (cm 3 cm -3 ), is the soil moisture content at the wilting point (cm 3 cm -3 ), The critical water content that represents the crop's tolerance to water stress (i.e., the soil water content at which the crop begins to consume readily available water), i.e., the field water holding capacity (cm 3 cm-3 ).

[0248] In terms of the solution of canopy resistance, the aerodynamic resistance from the canopy to the flux observation reference height ( ) can be calculated by the following formula:

[0249] (76)

[0250] in, LAI is the canopy comprehensive leaf area index (cm 2 cm -2 ), is the leaf area index of the plant ( ) and plant leaf area index ( ) by planting ratio ( + =1) Weighted calculation yields:

[0251] (77)

[0252] Canopy resistance ( ) is also calculated using the Jarvis model, where

[0253] (78)

[0254] is the comprehensive effective leaf area index of the underlying surface and is calculated using formula (70).

[0255] 6.1.2: Parameters required for soil heat flux and heat conduction calculations

[0256] When calculating soil heat flux, the soil layer thickness Δz from the soil surface to the first point below the soil surface is taken as 0.2 m; the time step Δt is taken as 1 d; the soil moisture content SWC is taken as the observed value at a depth of 20 cm; and the temperature Tl of the first point below the soil surface is the measured value of the soil temperature at a depth of 20 cm.

[0257] 6.1.3: Parameters required for net radiation calculation

[0258] 6.1.3.1 Parameters required for calculating canopy net radiation

[0259] When calculating shortwave radiation, the solar shortwave radiation (DSR) is the conventional data of the meteorological station. )、Transmittance( ) and absorption rate ( ) changes dynamically with the growth of crops throughout the crop growth period.

[0260] The shortwave radiation reflectivity of the canopy ( ) is calculated by the MICA model, a dynamic parameterized model of the surface reflectance of mulched farmland; canopy shortwave radiation transmittance Approximately equal to photosynthetically active radiation transmittance :

[0261] (79)

[0262] in, is the interception rate of photosynthetically active radiation by the canopy, which can be calculated from the leaf area index:

[0263] (80)

[0264] LAI is the average leaf area index, which is calculated from the leaf area index of the mother plant and the father plant in the planting ratio:

[0265] (81)

[0266] Then, the canopy shortwave radiation absorption rate Then:

[0267] (82)

[0268] When calculating canopy longwave radiation, the emissivity (or infrared absorptivity) of the canopy when it is fully covered is 0.97. The change of canopy due to the influence of crop growth will affect According to previous research, and canopy cover The following relationship can be established:

[0269] (83)

[0270] Canopy Cover The following formula can be used for approximate calculation:

[0271] (84)

[0272] In the formula, is the canopy attenuation coefficient of radiation.

[0273] Since the long-wave radiation reflectivity of the canopy is smaller, assuming it is 0.01. Then the transmittance of canopy longwave radiation is It also changes with the canopy coverage, and its value is:

[0274] (85)

[0275] The emissivity of the sky ( ) can be determined by the air temperature ( ) is calculated to get:

[0276] (86)

[0277] 6.1.3.2 Parameters required for calculating net radiation of film-covered soil

[0278] Shortwave radiation reflectivity of film-covered soil ( ) is calculated by the MICA model; its long-wave radiation reflectivity ( ) is obtained by calibration of test data, long-wave radiation emissivity / infrared absorptivity .

[0279] 6.1.3.3 Parameters required for calculation of net radiation of bare soil between membranes

[0280] Short-wave radiation reflectivity of bare soil between membranes ( ) is calculated by the MICA model; its long-wave radiation reflectivity ( ) is obtained by calibration of test data, long-wave radiation emissivity / infrared absorptivity ( ).

[0281] 6.2 Solution of the comprehensive model

[0282] Substituting the above equations for latent heat flux, sensible heat flux, soil heat flux and net radiation flux into formulas (5) to (8), the energy balance equations for the canopy of plant i, the film-covered soil and the bare soil between the films are obtained:

[0283] Energy balance equation at the canopy of plant f:

[0284] (87)

[0285] Energy balance equation at the canopy of plant m:

[0286] (88)

[0287] Energy balance equation at the film-covered soil:

[0288] (89)

[0289] Energy balance equation for bare soil between membranes:

[0290] (90)

[0291] It is easy to obtain that the four energy balance equations are all plant canopy temperature ( )、plant canopy temperature( )、film-covered soil temperature( ) and the bare soil temperature between films ( ), so it can be expressed as the following system of equations:

[0292] (91)

[0293] Where, corresponding to equations (47) to (50),

[0294] (92)

[0295] (93)

[0296] (94)

[0297] (95)

[0298] The Newton-Simpson iterative method is used to solve the nonlinear square system, and finally the program is written in R language to solve the system of equations.

[0299] This example verifies the comprehensive model of water and heat transfer in mulched mixed canopy farmland.

[0300] Taking the estimation of total surface evapotranspiration of corn fields covered with plastic film and intercropped in the Shiyang River Basin of the Northwest Arid Region as an example, the results are shown in Figures 1 to 9 . Its verification is as follows:

[0301] The parameters of the comprehensive model of water and heat transfer in the mixed canopy farmland with mulched film were analyzed using the field test data from 2015 to 2016: the surface resistance of the mulched soil ( )、Long-wave radiation reflectivity of film-covered soil( ) and the long-wave radiation reflectivity of bare soil between films ( ) and other parameters for calibration. , and The calibration results are 732 m -1 s, 0.259 and 0.152, and the model was verified.

[0302] 1) The latent heat flux is verified as follows:

[0303] When using this model to solve the latent heat flux (λET), many parameters are involved. In order to reduce the input variables as much as possible and reduce the complexity of the model calculation, a relatively direct and simple calculation formula is used in the solution to reduce the optimization parameters and avoid the effect of different parameters with the same effect. Figure 1The simulated values ​​and observed seasonal variation diagrams of the latent heat flux (λET) and plant transpiration latent heat (λT) and soil evaporation latent heat (λE) of the corn seed farmland simulated by the model of this scheme are shown in Figure 1. The results show that the model of this scheme can well describe the seasonal variation of the latent heat flux of the corn seed farmland covered with film irrigation (BM) and drip irrigation under film (DM). At the same time, the results of model evaluation and analysis show that the slope (Slop) of the simulated value and the measured value of the model of this scheme is very close to 1, and the correlation coefficient (R 2 ) is higher, the root mean square error (RMSE) and relative average deviation (PBIAS) are smaller, and the simulation results are accurate.

[0304] Figure 2 In order to simulate the plant transpiration of maternal and paternal maize in two film-mulched mixed canopy farmlands, namely, the film-mulched furrow irrigation seed maize farmland (BM) and the film-mulched drip irrigation seed maize farmland (DM), and compare them with the measured values, it was found that the simulated values ​​had a good fit with the measured values, indicating that the model of this scheme can accurately simulate the plant transpiration of each mixed canopy in the film-mulched mixed canopy farmland.

[0305] Figure 3 In order to simulate the soil evaporation of film-mulched soil and bare soil in two film-mulched mixed canopy farmlands, namely, the film-mulched furrow irrigation seed corn farmland (BM) and the film-mulched drip irrigation seed corn farmland (DM), and compare them with the measured values, it was found that the simulated values ​​had a good fit with the measured values, indicating that the model of this scheme can accurately simulate the soil evaporation of film-mulched soil and bare soil in the film-mulched mixed canopy farmland.

[0306] 2) Verification of sensible heat flux

[0307] The seasonal comparison of simulated and observed values ​​of sensible heat flux (Hs) in seed corn fields under mulch irrigation (BM) and drip irrigation under mulch (DM) is shown in Figure 4 The slopes (Slop) of the simulated and observed values ​​of Hs in the observation areas of mulch irrigation (BM) and drip irrigation (DM) were 0.93 and 1.07, the correlation coefficients were 0.70 and 0.64, and the root mean square errors were 17.06 Wm -2 and 16.91W m -2 , and the relative deviations are 0.37 and 0.32, respectively. In general, the simulated values ​​fit the measured values ​​well, and the model can be used to simulate the sensible heat flux of the mulched mixed canopy farmland. This simulation can not only accurately simulate the total sensible heat flux of the mulched mixed canopy farmland, but also simulate the various components of the sensible heat flux, including the sensible heat flux of each mixed canopy ( and ) and the sensible heat flux of film-covered soil and bare soil between films ( and ),See Figure 5 .

[0308] 3) Verification of net radiation flux

[0309] The seasonal comparison of simulated and observed net radiation flux (Rn) of mixed canopy farmland with mulch irrigation (BM) and drip irrigation (DM) is shown in Figure 6 The slopes of the simulated and observed values ​​of Rn in the BM and DM observation areas were 1.01 and 1.04, the correlation coefficients were 0.95 and 0.97, and the root mean square errors were 11.45 W m -2 and 11.50 Wm -2 , and the relative deviations are 0.07 and 0.07, respectively. In general, the simulated values ​​fit the measured values ​​well, and the model can be used to simulate the net radiation flux of the seed corn farmland covered with film. This simulation can not only accurately simulate the total net radiation flux of the film-covered mixed canopy farmland, but also simulate the various components of the net radiation flux, including the net radiation flux of each mixed canopy ( and ) and the sensible heat flux of film-covered soil and bare soil between films ( and ),See Figure 7 .

[0310] 4) Verification of soil heat flux

[0311] The seasonal comparison of simulated and observed soil heat flux (Gs) in mixed canopy farmland with mulch irrigation (BM) and drip irrigation (DM) is shown in Figure 8 The slopes of the simulated and observed Hs values ​​of the mixed canopy fields in the BM and DM observation areas were 0.96 and 0.97, the correlation coefficients were 0.72 and 0.87, and the root mean square errors were 6.61 W m -2 and 4.01 W m -2 , and the relative deviations are 0.51 and 0.52, respectively. In general, the simulated values ​​fit the measured values ​​well, and the model can be used to simulate the soil heat flux of the mulched mixed canopy farmland. This simulation can not only accurately simulate the total soil heat flux of the mulched mixed canopy farmland, but also simulate the various components of the soil heat flux, including the soil heat flux of the mulched soil and the bare soil between the films ( and ),See Fig. 9 .

[0312] Example 2

[0313] This embodiment provides a system for constructing a comprehensive model of water and heat transfer in a mulched mixed canopy farmland, including:

[0314] Module 1. Used to establish the energy balance equation of the whole mixed canopy farmland and its components, namely, the mixed canopy, bare soil and film-covered soil;

[0315] Module 2. Used to calculate the latent heat flux of the whole mixed canopy farmland and its components, namely the mixed canopy, bare soil, and covered soil;

[0316] Module 3. Used to calculate the sensible heat flux of the film-covered mixed canopy farmland as a whole and its components, namely, the mixed canopy, bare soil, and film-covered soil;

[0317] Module 4. Used to calculate the net radiation flux of the film-covered mixed canopy farmland as a whole and its components, namely, the mixed canopy, bare soil, and film-covered soil;

[0318] Module 5. Calculation methods for calculating soil heat flux of the mulched mixed canopy farmland as a whole and for each component, namely bare soil and mulched soil;

[0319] Module 6. Used to establish a comprehensive model of water and heat transfer process in mulched mixed canopy farmland, determine model parameters and solve the comprehensive model.

[0320] The above are only preferred embodiments of the present invention, and are not intended to limit the implementation methods and protection scope of the present invention. Those skilled in the art should be aware that all solutions obtained by equivalent substitutions and obvious changes made using the contents of the specification of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for constructing a comprehensive model of water and heat transfer in a mulched mixed canopy farmland, characterized in that: It includes the following steps: Step 1. Establish the energy balance equation of the whole mixed canopy farmland and its components, namely, the mixed canopy, bare soil and film-covered soil; For the film-covered farmland as a whole, its energy balance equation is: in, , , and are the net radiation flux, latent heat flux, sensible heat flux and soil heat flux obtained by the film-mulched farmland system, W m -2 ; For mixed canopy fields with different crops, different plants i The energy balance equation of the canopy is: The energy balance equation of film-covered soil is: The energy balance equation of bare soil between membranes is: in, , and Plant i Canopy net radiation flux, plant transpiration latent heat flux and plant sensible heat flux, W m -2 ; and are the net radiation flux of bare soil between films and covered soil in some film-covered farmland, W m -2 ; and are the evaporation latent heat flux of bare soil between films and film-covered soil in some film-covered farmland, W m -2 ; and are the soil heat fluxes of bare soil between films and covered soil in some film-covered farmland, W m -2 ; and are the sensible heat fluxes of bare soil between films and film-covered soil in some film-covered farmlands, W m -2 ; Step 2. Calculate the latent heat flux of the film-covered mixed canopy farmland as a whole and its components, i.e., each mixed canopy, bare soil, and film-covered soil; Step 3. Calculate the sensible heat flux of the film-covered mixed canopy farmland as a whole and its components, i.e., each mixed canopy, bare soil, and film-covered soil; Step 4. Calculate the net radiation flux of the film-covered mixed canopy farmland as a whole and its components, i.e., each mixed canopy, bare soil and film-covered soil; Step 5. Calculate the soil heat flux of the mulched mixed canopy farmland as a whole and its components, namely bare soil and mulched soil; Step 6. Couple the energy balance equation with the soil water and heat transfer process, establish a comprehensive model of the water and heat transfer process in the mulched mixed canopy farmland, determine the model parameters and solve the comprehensive model.

2. The method for constructing a comprehensive model of water and heat transfer in a mulched mixed canopy farmland according to claim 1, characterized in that: For the film-covered farmland in general, the energy balance equation , , and Each is divided into the following components: Overall net radiation flux And its components: Overall latent heat flux And its components: Overall sensible heat flux H s And its components: Overall soil heat flux And its components: in, For the i Mixed canopy light interception factors of crop canopies; is the proportion of film-covered soil to the total farmland area; For the i Latent heat flux in the canopy.

3. The method for constructing a comprehensive model of water and heat transfer in a mulched mixed canopy farmland according to claim 1, characterized in that: In the step 2, Film-covered farmland plants i Latent heat of evaporation , Latent heat of evaporation of bare soil between membranes and latent heat of evaporation of film-covered soil The following formulas are used for calculation: In the formula, is the air density, kg m -3 ; is the specific heat capacity of air at constant pressure, J kg -1o C -1 ; is the hygrometer constant, KPa o C -1 ; Plant i Canopy temperature, °C; and are the surface soil temperatures at bare soil between films and at film-covered soil, ℃; , and The temperature is , and Saturated water vapor pressure at , Kpa; is the actual water vapor pressure at the reference altitude temperature of the flux observation; is the saturated water vapor pressure slope, Kpa ℃ -1 ; is the saturated water vapor pressure difference at the reference height of flux observation, Kpa; For plants i Aerodynamic drag from blade to flux observation reference height, m -1 s; For plants i Canopy resistance, m -1 s; is the aerodynamic drag m -1 s; is the overall average canopy leaf-to-flux observation height aerodynamic drag, m -1 s; is soil resistance, m -1 s; is the coating resistance m -1 s, is the air temperature at the observation height.

4. The method for constructing a comprehensive model of water and heat transfer in a mulched mixed canopy farmland according to claim 3, characterized in that: In step 3, the film-covered farmland plants i Sensible heat flux Bare soil sensible heat flux between membranes and sensible heat flux of film-covered soil The following formulas are used for calculation: 。 5. The method for constructing a comprehensive model of water and heat transfer in a mulched mixed canopy farmland according to claim 4, characterized in that: The net radiation flux of each mixed canopy, bare soil and film-covered soil in step 4 includes the net shortwave radiation flux and the net longwave radiation flux ; Among them, film-covered farmland plants i Net shortwave radiation flux , Net shortwave radiation flux of bare soil between membranes and the net shortwave radiation flux of the film-covered soil They are: In the formula, is the solar shortwave radiation, W m -2 ; is the canopy shortwave radiation absorption rate, equal to , is the transmittance of solar shortwave radiation in the canopy; is the reflectivity of solar shortwave radiation in the canopy; is the shortwave radiation reflectivity of the film-covered soil; is the short-wave radiation reflectivity of bare soil between membranes; In solving the film-covered soil and bare soil between films, the i When calculating the canopy longwave radiation flux, all crop canopies are considered as a whole, and the longwave radiation of the overall canopy radiation is expressed as the film coverage ratio. Assigned to the film-covered soil and bare soil between films, the plants in the film-covered farmland i Net longwave radiation flux , Net long-wave radiation flux of bare soil between membranes and the net longwave radiation flux of film-covered soil They can be expressed as: + + [ ] In the formula, is the Stefan-Boltzmann constant, which is 5.67×10 -8 W / (m 2 K 4 ); is the sky surface emissivity; is the canopy surface radiation coefficient; is the radiation coefficient of the film-covered soil surface; is the radiation coefficient of the bare soil surface between membranes; is the canopy longwave radiation reflectivity; is the long-wave radiation reflectivity of the film-covered soil; is the long-wave radiation reflectivity of bare soil between films; is the canopy longwave radiation transmittance; is the atmospheric temperature, °C, using the air temperature at the reference observation altitude ; is the surface temperature of the film-covered soil, °C; is the bare soil surface temperature between membranes, °C; Film-covered farmland plants i Net radiation flux , Net radiation flux of bare soil between membranes and the net radiation flux of the film-covered soil They are: 。 6. The method for constructing a comprehensive model of water and heat transfer in a mulched mixed canopy farmland according to claim 5, characterized in that: The soil heat flux at the film-covered soil of the film-covered farmland in step 5 Soil heat flux at bare soil between film and The following formulas are used for calculation: In the formula, and The reference soil depth is Soil heat flux between the film-covered soil and the bare soil between the films, W m -2 ;when When it is more than 1m, and Treated as 0; is the soil heat capacity, WK -1 m -1 .

7. The method for constructing a comprehensive model of water and heat transfer in a mulched mixed canopy farmland according to claim 6, characterized in that: In step 6, the latent heat flux, sensible heat flux, soil heat flux and net radiation flux components are solved by bringing them into the energy balance equation to obtain the plant i Energy balance equation for the canopy, film-covered soil, and bare soil between films: Plant i The energy balance equation at the canopy is: Energy balance equation at the film-covered soil: Energy balance equation for bare soil between membranes: The above energy balance equations are for plants i Canopy temperature , Film-covered soil temperature and the bare soil temperature between membranes The equation of , so it can be expressed as the following system of equations: in, n For plant types, n When the plant canopy exists, the temperature function equation is f (T) contains (n+2) unknowns, and the number of equations to be solved is (n+2). The temperature function equation is solved by the energy balance equation established above: 。 8. The method for constructing a comprehensive model of water and heat transfer in a mulched mixed canopy farmland according to claim 7, characterized in that: The Newton-Simpson iterative method is used to solve the nonlinear equations. Solve the temperature function equations f After (n+2) unknown temperatures in (T), the latent heat, sensible heat, net radiation and soil heat flux components of different plant canopies, film-covered soil and bare soil are solved, and the weighted sum of each component can be obtained to obtain the overall latent heat, sensible heat, net radiation and soil heat flux of the film-covered mixed canopy farmland.

9. A system for constructing a comprehensive model of water and heat transfer in a film-covered mixed canopy farmland according to any one of claims 1 to 8, characterized in that: include: Module 1. Used to establish the energy balance equation of the whole mixed canopy farmland and its components, namely, the mixed canopy, bare soil and film-covered soil; Module 2. Used to calculate the latent heat flux of the whole mixed canopy farmland and its components, namely, the mixed canopy, bare soil and covered soil; Module 3. Used to calculate the sensible heat flux of the whole field and each component of the mixed canopy, bare soil and covered soil; Module 4. Used to calculate the net radiation flux of the whole mixed canopy farmland and its components, namely, the mixed canopy, bare soil and covered soil; Module 5. Calculation methods for calculating soil heat flux of the mulched mixed canopy farmland as a whole and for each component, namely bare soil and mulched soil; Module 6. Used to establish a comprehensive model of water and heat transfer process in mulched mixed canopy farmland, determine model parameters and solve the comprehensive model.

Images