A water-saving irrigation method for forest land based on plant water requirement and soil infiltration calculation

Abstract

This invention provides a water-saving irrigation method for forest land based on plant water requirements and soil infiltration calculations, comprising the following steps: (1) determining the effective rainfall utilization coefficient of forest land; (2) calculating the daily evapotranspiration and soil infiltration of forest land; and (3) calculating the daily irrigation volume of forest land. This invention enables refined management of water-saving irrigation and efficient utilization of water resources during the plant growing season. Based on comprehensive observation of rainfall, meteorology, and forest land soil moisture, numerical model simulation technology is applied to refine the calculation of daily water requirements of vegetation, breaking it down into vegetation transpiration and soil evaporation, which can improve the in-depth understanding of the water requirements of vegetation. At the same time, a quantitative relationship between soil infiltration and rainfall is established, and soil infiltration is used as the effective rainfall, replacing the calculation method of the rainfall coefficient constant, which can more realistically reflect the differences in effective rainfall under different rainfall and vegetation conditions.

Description

Technical Field

[0001] This invention relates to the field of land surveying technology, specifically to a water-saving irrigation method for forest land based on plant water requirements and soil infiltration calculations. Background Technology

[0002] In water-scarce regions of northern my country, water scarcity has become a significant factor hindering sustainable ecological, economic, and social development. Water-saving irrigation can significantly reduce the water requirements for plant growth, alleviating local water resource pressures and improving water use efficiency. In recent decades, water-saving irrigation has been widely applied in modern agricultural production, playing a vital role in achieving sustainable water resource utilization, ensuring food security, and maintaining ecological balance in northern regions.

[0003] In arid regions, shelterbelts play a vital role in sand control, oasis farmland protection, and soil and water conservation. Because shelterbelt vegetation is tall and its water consumption exceeds local rainfall, some oasis shelterbelts and windbreak / sand-fixing forests require irrigation to ensure tree growth and proper functioning. Currently, water-saving irrigation for shelterbelts largely draws on theories and methods from agricultural water-saving irrigation, while forest water-saving irrigation technologies are relatively weak, lacking precise water-saving irrigation theories and methods suitable for arid region shelterbelts. With my country's shelterbelt construction now in the crucial sixth phase of the Three-North Shelterbelt Project, coupled with the backdrop of climate change (heating and aridity), there is an urgent need to develop a set of effective precise forest water-saving irrigation technologies. This is of great significance and value for the sustainable management of shelterbelts and ecological security.

[0004] Currently, water-saving irrigation technologies have been widely applied in crop growth and agriculture. Significant progress has been made in areas such as the water requirements of major crops like wheat, corn, and rice at different growth stages, water-saving irrigation for seedling roots, integrated water and fertilizer management, field irrigation, and the development of intelligent water-saving machinery. A paradigm shift from conventional water-saving technologies to intelligent, efficient, and green water-saving technologies has begun. While water-saving irrigation technologies such as the selection of water-saving tree species and drip irrigation equipment are currently used to some extent in forestry production, the development of precise irrigation systems for forest land remains relatively weak.

[0005] At the technical level, water-saving irrigation in forest land largely relies on the theories and methods of water-saving pipe irrigation in agriculture, but it still has the following three shortcomings. First, when calculating the amount of water-saving irrigation for vegetation, the time scale is often too large, only estimating the total irrigation amount for the entire growing season, lacking precise calculations at a smaller scale (such as days). Second, the water-saving irrigation calculation equation only considers rainfall and water demand, but does not adequately consider important processes such as rainfall infiltration in forest land, water absorption by plants, soil evaporation, and changes in soil moisture. Third, the effective rainfall coefficient is only used as a constant, which cannot reflect the differences in water demand under different rainfall and vegetation conditions.

[0006] In conclusion, it is necessary to further innovate existing technologies. Summary of the Invention

[0007] To address the technical problems existing in the background art mentioned above, this invention proposes a method for calculating the daily irrigation amount of forest land based on plant water requirements and soil infiltration. Its concept is reasonable and can realize the refined management of water-saving irrigation and efficient utilization of water resources during the plant growing season. It establishes the quantitative relationship between soil infiltration and rainfall, uses soil infiltration as the effective rainfall, and replaces the calculation method of rainfall coefficient constant, which can more realistically reflect the differences in effective rainfall under different rainfall and vegetation conditions.

[0008] To address the aforementioned technical problems, this invention provides a water-saving irrigation method for forest land based on plant water requirements and soil infiltration calculations, comprising the following steps:

[0009] (1) Determine the effective rainfall utilization coefficient of forest land;

[0010] (2) Calculate the daily evapotranspiration and soil infiltration of the forest land;

[0011] (3) Calculate the daily irrigation amount of the forest land.

[0012] The water-saving irrigation method for forest land based on plant water requirements and soil infiltration, wherein the specific process of step (1) is as follows:

[0013] First define P e The amount of rainfall minus losses such as soil evaporation during the process, E. loss The effective rainfall, also known as the amount of rainwater that actually infiltrates the soil, is calculated using the following formula:

[0014] P e =I net =PE loss (1);

[0015] In equation (1) above, I net P represents net infiltration into the soil surface. e P represents effective precipitation; E represents rainfall amount; P represents effective precipitation amount; P represents rainfall amount; E represents effective precipitation amount. loss This represents the amount of soil evaporation loss during rainfall.

[0016] Then, based on the rainfall P and the effective rainfall P e The effective rainfall utilization coefficient α is determined by fitting the relationship equation (2):

[0017] P e =α*P (2);

[0018] In equation (2) above, P represents daily precipitation; eα represents the effective precipitation; α is the effective utilization coefficient of precipitation.

[0019] Finally, the effective rainfall utilization coefficient for different hydrological years or different vegetation types was fitted.

[0020] The forest water-saving irrigation method based on plant water requirements and soil infiltration, wherein: the net infiltration of the soil surface layer I net and the soil evaporation loss E loss All results were obtained using the Hydrus-D model on an hourly scale.

[0021] The water-saving irrigation method for forest land based on plant water requirements and soil infiltration, wherein the daily evapotranspiration of the forest land in step (2) is the sum of plant transpiration and soil evaporation, i.e.:

[0022] ET = T + E (3);

[0023] In the above formula (3), ET is the daily evapotranspiration; T is the plant transpiration; and E is the soil evaporation.

[0024] The forest water-saving irrigation method based on plant water requirement and soil infiltration calculation, wherein the plant transpiration T and soil evaporation E are calculated on a diurnal scale using the Hydrus-1 D model, as detailed below:

[0025] The Richards equations are applied to simulate the unsaturated water transport and dynamics in soil. The governing equations for this simulation are as follows:

[0026]

[0027] In equation (4) above, θ is the soil volumetric water content; h is the soil water potential; t is time; Z is the vertical ascending coordinate; K is the unsaturated hydraulic conductivity; S(h) is the root water uptake, which is the plant transpiration; S(h) is calculated based on the Feddes model through the water stress response function and potential transpiration, as follows:

[0028] S(h)=a(h)·b(x,z)·L t ·T p (5);

[0029] In equation (5) above, a(h) is the water stress response function, b(x,z) represents the two-dimensional spatial distribution of the root's potential water uptake, Lt is the width of the soil surface, and T p It is the potential evaporation rate;

[0030] Soil hydraulic parameters are estimated using the ROSETTA function in the Hydrus model, which is based on soil texture and bulk density. Specifically, the definitions are as follows:

[0031]

[0032] In equation (7) above, Se represents the effective saturation:

[0033]

[0034] In equations (6)-(8) above, θ s θ represents saturated water content; r Residual moisture content; K s α is the saturated hydraulic conductivity; α, n, and l are empirical coefficients that determine the shape of the function.

[0035] The forest water-saving irrigation method based on plant water requirement and soil infiltration calculation, wherein: the calculation of soil infiltration in step (2) is achieved by setting the upper and lower boundary conditions in the Hydrus model, and the upper boundary condition for soil water infiltration is selected when the precipitation intensity is known, but no water accumulation forms on the surface, that is:

[0036]

[0037] In equation (9) above, θ is the soil volumetric water content; t is time; z is the vertical ascent coordinate; D is the effective diffusion coefficient; K is the unsaturated hydraulic conductivity; and R(t) is the rainfall condition.

[0038] The lower boundary condition for soil moisture infiltration is chosen when the groundwater is buried at a relatively deep depth and the water content at the lower boundary is constant, i.e.:

[0039]

[0040] In equation (10) above, θ is the soil volumetric water content; Z is the vertical ascending coordinate.

[0041] The forest water-saving irrigation method based on plant water requirement and soil infiltration, wherein the daily irrigation amount of the forest land in step (3) is the difference between the forest land water requirement and the effective precipitation, that is:

[0042] I = ET - P e (11);

[0043] In the above formula (11), I is the daily irrigation amount; ET is the vegetation water requirement; P e This refers to the effective precipitation.

[0044] By adopting the above technical solution, the present invention has the following beneficial effects:

[0045] This invention, based on field observations of meteorological elements and soil moisture, applies numerical models to simulate and calculate key hydrological parameters such as vegetation evapotranspiration and rainfall infiltration. This invention enables refined management of water-saving irrigation and efficient utilization of water resources during the plant growing season. Based on comprehensive observations of rainfall, meteorology, and forest soil moisture, numerical model simulation technology refines the calculation of vegetation water demand (evapotranspiration), breaking it down into vegetation transpiration and soil evaporation, thus improving the understanding of vegetation water demand patterns. Simultaneously, this invention establishes a quantitative relationship between soil infiltration and rainfall, using soil infiltration as the effective rainfall amount and replacing the calculation method of the rainfall coefficient constant, which can more realistically reflect the differences in effective rainfall under different rainfall and vegetation conditions.

[0046] Compared with existing technologies, this invention represents a significant breakthrough in fundamental theory and methodology, specifically in the following aspects:

[0047] 1) Theoretical Innovation

[0048] The calculation of water-saving irrigation volume by comprehensively considering both plant water requirements and soil infiltration volume breaks through the limitation of traditional theories that only involve water requirements. In this way, the key hydrological processes such as rainfall infiltration in forest land, plant water absorption, soil evaporation and its moisture content changes can be considered more comprehensively in the technical theoretical framework.

[0049] 2) Methodological advancement

[0050] Existing technologies do not consider the infiltration process of rainfall in forest land and the water loss such as soil evaporation, and cannot reflect the differences under different rainfall and vegetation conditions. Specifically, the effective rainfall coefficient α in past irrigation calculations was assumed to be a constant under different rainfall (P) conditions (α = 1.0 when P < 5 mm; α = 1.0-0.8 when 5 mm ≤ P ≤ 50 mm; α = 0.7-0.8 when P > 50 mm).

[0051] This invention determines α based on the relationship between rainfall and forest infiltration rate. This not only reflects the true extent of rainfall infiltration into the forest soil but also accurately characterizes the differences in rainfall effectiveness under different rainfall and vegetation conditions. Simultaneously, this invention breaks down plant water requirements into plant transpiration and soil evaporation, and proposes a daily-scale calculation method for water-saving irrigation. This more accurately reflects plant water requirements, thereby significantly improving irrigation water resource utilization efficiency. In conclusion, the improvements in the fundamental theory and technical methods of water-saving irrigation presented in this invention are of great significance for achieving precise water-saving irrigation and efficient water resource utilization in forest areas under the dual context of climate change and human activities. Attached Figure Description

[0052] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0053] Figure 1 This is a graph showing the relationship between daily cumulative rainfall and infiltration data related to the water-saving irrigation method for forest land based on plant water requirements and soil infiltration calculations of this invention.

[0054] Figure 2 This is a graph showing the relationship between Julian daily and daily evapotranspiration in the forest water-saving irrigation method based on plant water requirements and soil infiltration calculations of this invention.

[0055] Figure 3 This is a graph showing the relationship between Julian day and daily infiltration volume in the forest water-saving irrigation method based on plant water requirement and soil infiltration calculations of this invention.

[0056] Figure 4 This is a graph showing the relationship between Julian Day and daily irrigation volume in the forest water-saving irrigation method based on plant water requirements and soil infiltration calculations of this invention. Detailed Implementation

[0057] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0058] The present invention will be further explained below with reference to specific embodiments.

[0059] like Figure 1 As shown in this embodiment, a water-saving irrigation method for forest land based on plant water requirements and soil infiltration calculations is provided. Its theoretical basis is as follows: based on forest land hydrological and meteorological observations, the Hydrus-1D soil physical numerical model is applied to calculate key parameters such as vegetation transpiration, soil evaporation, and soil infiltration, increasing the accuracy of the calculations and providing a basis for the formulation of water-saving irrigation systems for forest land. To achieve the above objectives, this invention mainly includes the following three steps.

[0060] (1) Determine the effective rainfall utilization coefficient of forest land

[0061] This invention uses the Hydrus-D model to calculate the net rainwater infiltration on an hourly scale (see the relevant description in step (2)) and accumulates the daily net infiltration (I net), and use it as the daily effective rainfall P e In other words, P e This refers to rainfall minus losses such as soil evaporation during the process (E) loss After that, the effective amount of rainwater that can actually infiltrate into the soil can directly provide effective soil moisture replenishment. e The calculation can be expressed as the following formula:

[0062] P e =I net =PE loss (1);

[0063] In equation (1) above, I net Net infiltration rate of soil surface layer (mm·d) -1 ); P e Effective precipitation (mm·d) -1 P represents rainfall (mm·d); -1 ); E loss Soil evaporation loss during rainfall (mm·d) -1 ).

[0064] Then, based on the rainfall P and the effective rainfall P e The effective rainfall utilization coefficient α is determined by fitting the relationship equation, as follows:

[0065] P e =α*P (2);

[0066] In equation (2) above, P represents daily precipitation (mm); e α represents the effective precipitation (mm); α is the effective precipitation utilization coefficient. Thus, this invention can fit the effective precipitation utilization coefficient for different hydrological years or different vegetation types.

[0067] The net surface infiltration rate (I) in equations (1) and (2) above net ) and soil evaporation loss (E loss All of them were calculated using the Hydrus-D model on the hourly scale (the calculation method of the Hydrus-D model on the hourly scale is the same as that on the daily scale, see the following formulas (4)-(10) for details).

[0068] (2) Calculate the daily evapotranspiration and soil infiltration of the forest land.

[0069] For a specific shelterbelt or plant community, its daily evapotranspiration is the sum of plant transpiration and soil evaporation, that is:

[0070] ET = T + E (3);

[0071] In equation (3) above, ET is the daily evapotranspiration (mm·d). -1 T represents plant transpiration (mm·d); -1 E represents soil evaporation (mm·d); -1 ).

[0072] The plant transpiration and soil evaporation in equation (3) above are calculated on a diurnal scale using the Hydrus-1D model (Version 4.17). The specific method is as follows:

[0073] The Richards equations are applied to simulate the unsaturated water transport and dynamics in soil. The governing equations for this simulation are as follows:

[0074]

[0075] In equation (4) above, θ represents the soil volumetric water content (cm³). 3 ·cm -3 h is the soil water potential (also known as pressure head) (cm); t is time (d); Z is the vertical rise coordinate (cm); K is the unsaturated hydraulic conductivity (cm·d). -1 S(h) is the root water absorption (cm³). 3 ·cm -3 ·d -1 This refers to plant transpiration. S(h) is calculated using the Feddes model through the water stress response function and potential transpiration, as follows:

[0076] S(h)=a(h)·b(x,z)·L t ·T p (5);

[0077] In equation (5) above, a(h) is the water stress response function (dimensionless), and b(x,z) represents the two-dimensional spatial distribution of the root's potential water uptake (cm). -2 Lt is the width of the soil surface (mm·d) -1 ), T p It is the potential evaporation rate (mm·d) -1 Soil hydraulic parameters (i.e., θ) s θ represents saturated water content; r Residual moisture content; K s The saturated hydraulic conductivity (see equation (8) below) was initially estimated based on the ROSETTA function in the Hydrus model, which is based on soil texture and bulk density (Schaap et al., 2001), and is specifically defined as:

[0078]

[0079] Where Se represents the effective saturation:

[0080]

[0081] Where θ s Saturated water content (cm) 3 ·cm -3 );θ r Residual moisture content (cm) 3 ·cm -3 ); K s Saturated hydraulic conductivity (cm·d) -1 ); α(cm -1 ), n (unitless) and l (unitless) are empirical coefficients that determine the shape of the function.

[0082] Soil infiltration is calculated by setting upper and lower boundary conditions in the Hydrus model. In this embodiment, the upper boundary condition for soil water infiltration is selected as the case where the rainfall intensity is known but surface water does not accumulate, i.e.:

[0083]

[0084] In equation (9) above, θ is the soil volumetric water content; t is time; z is the vertical ascending coordinate; D is the effective diffusion coefficient; K is the unsaturated hydraulic conductivity; and R(t) is the rainfall condition.

[0085] In this embodiment, the lower boundary condition for soil moisture infiltration is selected when the groundwater is buried at a relatively deep depth and the water content at the lower boundary is constant, that is:

[0086]

[0087] In equation (10) above, θ is the soil volumetric water content; Z is the vertical ascending coordinate.

[0088] (3) Calculate the daily irrigation amount of the forest land.

[0089] For a specific shelterbelt or plant community, its daily irrigation amount (I) is equal to the difference between the forest land water requirement (evapotranspiration, ET) and the effective precipitation, that is:

[0090] I = ET - P e (11);

[0091] In the above formula (11), I is the daily irrigation amount (mm·d). -1 ); ET is the vegetation water requirement (mm·d). -1 ); P e Effective precipitation (mm·d) -1 The calculation formula is shown in equation (2).

[0092] Example 1: A water-saving irrigation method for forest land based on dual calculation of plant water requirement and soil infiltration - taking Haloxylon ammodendron sand-fixing forest as an example.

[0093] A water-saving irrigation method for forest land based on dual-element calculation of plant water requirement and soil infiltration includes the following steps:

[0094] (1.1) Determine the effective rainfall utilization coefficient

[0095] This invention uses the Hydrus-1D model to calculate the net rainfall infiltration in Haloxylon ammodendron forests on an hourly scale, and accumulates the daily net infiltration (I net ), and use it as the daily effective rainfall P e Based on rainfall and soil infiltration data, the effective utilization coefficient of precipitation α = 0.691 in equation (2) was fitted. The specific results are shown below. Figure 1 .

[0096] (1.2) Calculate the actual evapotranspiration and net soil infiltration.

[0097] This invention establishes a Hydrus-1D numerical model for Haloxylon ammodendron sand-fixing forests. The upper boundary condition is defined as the atmospheric boundary (precipitation and evaporation), and the lower boundary is defined as free drainage at a depth of 200 cm. The influence of groundwater level changes on soil moisture is ignored, and specified initial and boundary conditions are considered for each location. On a diurnal scale, the established Hydrus-1D numerical model is used to calculate the daily evapotranspiration and daily infiltration of Haloxylon ammodendron sand-fixing forests during the growing season (April 15 to October 31). The results are shown below. Figure 2-3 .

[0098] (1.3) Calculate the actual irrigation amount of Haloxylon ammodendron forest land

[0099] The results showed that the effective rainfall during the growing season was 47.89 mm, and the total evapotranspiration of the Haloxylon ammodendron forest during the growing season was 186.74 mm, of which evaporation was 82.93 mm and soil evaporation was 103.81 mm. The cumulative irrigation amount during the growing season calculated according to equation (9) was 138.85 mm, equivalent to 92.61 m³ of supplemental irrigation per mu (approximately 0.067 hectares). 3 See below Figure 4 .

[0100] This invention is well-conceived and can achieve refined management of water-saving irrigation and efficient utilization of water resources during the plant growing season. It establishes a quantitative relationship between soil infiltration and rainfall, uses soil infiltration as the effective rainfall, and replaces the calculation method of the rainfall coefficient constant. This can more realistically reflect the differences in effective rainfall under different rainfall and vegetation conditions.

[0101] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for water saving irrigation of forest land based on plant water requirement and soil infiltration calculation, characterized in that, The method comprises the following steps: (1) determining the effective rainfall utilization coefficient of the forest land First define P e Subtract the amount of soil evaporation loss E during the process of rainfall loss The effective rainfall, which can actually infiltrate into the soil, is the effective rainfall amount, and its calculation formula is: P e = I net =P-E loss (1); In the above formula (1), I net is the net infiltration amount of the soil surface layer; P e is the effective precipitation amount; P is the rainfall amount; E loss is the soil evaporation loss amount during the rainfall process; Then, the effective rainfall utilization coefficient α is determined by fitting according to the relationship (2) between the rainfall P and the effective rainfall P e : P e = α * P (2); In the above equation (2), P is the rainfall amount; P e is the effective rainfall amount; and α is the effective utilization coefficient of the rainfall. The effective rainfall utilization coefficient of different hydrological years or different vegetation types is finally fitted; (2) calculating the daily evapotranspiration of the forest land The daily evapotranspiration of the forest land is the sum of the plant transpiration and the soil evaporation, that is: ET = T + E (3); In the above formula (3), ET is the daily evapotranspiration; T is the plant transpiration; and E is the soil evaporation; The plant transpiration T and the soil evaporation E are calculated by the Hydrus-1D model on a daily scale, and the specific method is as follows: Richards equation is applied to simulate the unsaturated water flow migration and dynamics in the soil, and the control equation of the simulation is as follows: （4）； In the above formula (4), θ is the soil volume water content; h is the soil water potential; t is the time; z is the vertical upward coordinate; and K is the unsaturated hydraulic conductivity; K(h) is the unsaturated hydraulic conductivity of the soil water potential; S(h) is the root water absorption, that is, the plant transpiration; S(h) is calculated according to the Feddes model through a water stress response function and potential transpiration, and the specific method is as follows: （5）； In the above formula (5), a(h) is a water stress response function, and b(x, z) represents a two-dimensional spatial distribution of the potential water uptake amount of the root system, is the width of the soil surface, T p is the potential evaporation rate; The soil hydraulic parameters are estimated according to the ROSETTA function in the Hydrus model based on the soil texture and bulk density, and the specific definition is as follows: and (6); （7）； In the above equation (7), Effective saturation: （8）； In the above equations (6) to (8), θ s is the saturated water content; θ r is the residual water content; K s is the saturated hydraulic conductivity; and α, n and l are empirical coefficients that determine the shape of the function. The calculation of the soil infiltration amount is realized by setting the upper boundary and lower boundary conditions in the Hydrus model, and the upper boundary condition of the soil water infiltration is selected to be the case that the rainfall intensity is known, but the surface does not form waterlogging, that is: （9）; In the above equation (9), θ is the volumetric water content of the soil; t is time; z is the vertical upward coordinate; D is the effective diffusion coefficient; and K is the unsaturated hydraulic conductivity; is the unsaturated hydraulic conductivity of the volumetric water content of the soil; and R(t) is the rainfall condition. The lower boundary condition of the soil water infiltration is selected to be the case that the groundwater is buried deep, and the water content at the lower boundary is constant, that is: ； In the above formula (10), θ is the soil volume water content; and z is the vertical upward coordinate; (3) calculating the daily irrigation amount of the forest land The daily irrigation amount of the forest land is the difference between the daily evapotranspiration and the effective rainfall, that is: I = ET - P e = ET - a * P (11); In the above equation (11), I is the daily irrigation amount; ET is the daily evapotranspiration amount; P e is the effective precipitation amount.

2. The method for calculating water-saving irrigation of forest land based on plant water requirement and soil infiltration according to claim 1, characterized in that: The net infiltration amount I of the surface layer of the soil net and the evaporation loss amount E of the soil loss are both calculated on an hourly scale using the Hydrus-D model.

Images