Method for estimating permanent wilting point based on moisture absorption and water content

Abstract

The invention discloses a method for estimating a permanent wilting point based on moisture absorption and water content, and relates to the field of soil water content calculation. The method comprises the steps of obtaining moisture absorption and water content of to-be-estimated soil; the permanent wilting point is calculated through a permanent wilting point estimation model based on the moisture absorption and water content, and the expression of the permanent wilting point estimation model is shown in the specification, namely the permanent wilting point, the matrix potential under the drying condition and the moisture absorption and water content of the soil to be estimated. According to the method, the permanent wilting point of the to-be-measured soil can be rapidly obtained, reliable data support is provided for agricultural soil moisture content monitoring, irrigation decision making and crop moisture management, and the problems that in the prior art, estimation precision is low, errors are large, measurement is time-consuming, and labor cost is high are solved.

Description

Technical Field

[0001] This invention relates to the field of soil moisture content calculation, and specifically to a method for estimating the permanent wilting point based on hygroscopic moisture content. Background Technology

[0002] The soil moisture content at the permanent wilting point, as the lower limit of available water for plant roots, has a very important impact on irrigation formulas, irrigation timing, variety density selection, drought monitoring and assessment, nutrient pesticide efficiency, and soil improvement in different regions with variations in annual precipitation and soil texture.

[0003] For irrigation formulas, the soil moisture content at the permanent wilting point determines the lower limit of the soil's "water tank" and is an indispensable benchmark for assessing the amount of water available to crops in the root zone. The higher the soil moisture content at the permanent wilting point, the more water the soil can "lock in" under extremely dry conditions, and the less water is available to crops. Therefore, when formulating irrigation quotas, the water volume must be determined based on the soil moisture content at the permanent wilting point to avoid including water that is not available to plants, which would lead to inaccurate water use formulas.

[0004] Regarding the timing of irrigation, the soil moisture content at the permanent wilting point provides a baseline for initiating irrigation. When root moisture rapidly approaches this baseline, plants respond quickly, transitioning from mild physiological stress to significant growth restriction. Mastering the soil moisture content at the permanent wilting point quantifies the degree of water shortage as a baseline, allowing for optimal timing and balancing water conservation with yield.

[0005] Regarding "variety and density selection", incorporating the soil moisture content at the permanent wilting point into cultivation decisions can help identify water-deficient plots. In such plots, more drought-resistant or deeper-rooted varieties can be selected, density can be appropriately reduced, and mulching and moisture-retention strategies can be optimized to match the needs of the crop population with the soil's water supply capacity. In water-rich plots, higher density and yield targets can be achieved.

[0006] For "drought monitoring and risk zoning", the soil moisture content at permanent wilting points unifies the basic conditions of different soil layers and plots onto the same "available water scale". This allows managers to see intuitively which plots are close to irreversible wilting risk and which plots still have room for allocation, thereby enabling zoned management and graded response, and prioritizing the allocation of limited water resources to truly "critical" areas.

[0007] Regarding "nutrient and pesticide efficiency," the soil moisture content at the permanent wilting point serves as a "dry-end red line," reminding us to arrange fertilization, pesticide application, and water replenishment in a suitable range away from this red line, so that water, fertilizer, and pesticides can resonate in unison and complement each other.

[0008] For "soil improvement targets and acceptance," the soil moisture content at the permanent wilting point provides a key factor for evaluating the effectiveness of the improvement. By observing the relative changes in soil moisture content at the permanent wilting point and field capacity after improvement, soil water storage can be determined. Incorporating the soil moisture content at the permanent wilting point into the acceptance process shifts the focus from "quantitative moisture conservation to qualitative moisture conservation," guiding subsequent inputs and technology optimization.

[0009] The permanent wilting point moisture content is typically determined and a transfer function established using five methods: pressure plate / membrane method, water potential meter indirect method, plant indicator method, centrifugation equivalent method, and empirical estimation method. Directly measuring the permanent wilting point soil moisture content is time-consuming and labor-intensive. Methods for estimating the permanent wilting point soil moisture content using transfer functions often suffer from significant errors. Traditional methods for obtaining permanent wilting point moisture content are time-consuming and labor-intensive. The establishment of transfer functions is usually based on soils under specific soil formation conditions. Due to the spatial heterogeneity of soil, although the estimated permanent wilting point moisture content is within a reasonable range, its accuracy is often limited. Summary of the Invention

[0010] To address the aforementioned shortcomings in existing technologies, this invention provides a method for estimating the permanent wilting point based on hygroscopic moisture content, which solves the problems of low estimation accuracy, large errors, time-consuming measurement, and high labor costs associated with existing technologies.

[0011] To achieve the aforementioned objectives, the present invention employs the following technical solution: a method for estimating the permanent wilting point based on hygroscopic moisture content, comprising: Obtain the hygroscopic moisture content of the soil to be estimated; The permanent wilting point is calculated based on the hygroscopic moisture content using a permanent wilting point estimation model. The expression for the permanent wilting point estimation model is as follows:

[0012] in, For permanent wilting points, The matrix potential under drying conditions. The hygroscopic moisture content of the soil to be estimated.

[0013] The beneficial effects of this invention are as follows: This invention establishes an estimation model based on the hygroscopic moisture content of soil to estimate the permanent wilting point, overcoming the shortcomings of traditional methods for determining the permanent wilting point, such as low efficiency and insufficient accuracy. It also avoids the dependence of the permanent wilting point on soil particle size distribution and organic matter content, thereby reducing systematic errors caused by differences in soil type and enhancing applicability and universality. Through model estimation, the measurement accuracy is improved, labor costs are reduced, and the permanent wilting point of the soil to be measured can be quickly obtained. This provides reliable data support for agricultural soil moisture monitoring, irrigation decisions, and crop water management, and has significant practical value for promoting the development of precision agriculture and improving water resource utilization efficiency. Attached Figure Description

[0014] Figure 1 A flowchart illustrating a method for estimating the permanent wilting point based on hygroscopic moisture content, provided as an example; Figure 2 The diagrams show the prediction of permanent wilting points for different models, where (a) is the prediction of permanent wilting points for the model provided by this invention, (b) is the prediction of permanent wilting points for the AP model, (c) is the prediction of permanent wilting points for the vdB model, and (d) is the prediction of permanent wilting points for the SH model. Detailed Implementation

[0015] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0016] like Figure 1 As shown, in one embodiment of the present invention, a method for estimating the permanent wilting point based on hygroscopic moisture content includes the following steps: S1. Obtain the hygroscopic moisture content of the soil to be estimated.

[0017] The hygroscopic moisture content of soil samples was obtained by measuring the dry and wet ends of a simulated soil moisture retention curve (SWRC) or by direct measurement.

[0018] S2. Calculate the permanent wilting point based on the hygroscopic moisture content using the permanent wilting point estimation model.

[0019] Specific methods for establishing a permanent wilting point estimation model include: The water characteristic curve, which describes the relationship between soil water potential (soil water absorption capacity) and soil moisture content, has its wet and dry ends connected at the permanent wilting point. This can be represented by the CS model (Campbell & Shiozawa) as follows: (1) Wherein, 4.18 is the common logarithm of the negative matrix potential (unit: cm H2O) at the permanent wilting point. The dimensionless slope of the linear model. For permanent wilting points, This represents the matrix potential under drying conditions.

[0020] When the relative humidity (RH) of the soil is 50%, the common logarithm of the negative matrix potential (unit: cm H2O) at the permanent wilting point is 5.98. Therefore, the CS model expression at a relative humidity (RH) of 50% is: (2) Eliminate by combining formulas (1) and (2) The permanent wilting point estimation model is obtained as follows: (3) in, The hygroscopic moisture content of the soil to be estimated.

[0021] From the above formula, we can see that... and The relationship is linear, and its proportionality coefficient is from Decision. In practical applications, It is usually regarded as a constant (i.e., -10). 7 -10 6.91 and -10 6.8 (Unit: cm H2O), yielding corresponding proportionality coefficients of 2.8, 2.9, and 3.2. In this embodiment, the proportionality coefficient is set to 3.0, resulting in... and The relationship is: (4) This invention is based on Estimate the permanent wilting point for the input variables.

[0022] To verify the beneficial effects of the present invention, the following comparative experiments were conducted: Forty-eight soil samples with clay content ranging from 0% to 61% were selected, including nine from Prebble, six from Campbell & Shiozawa, one from the UNSODA Unsaturated Soil Hydraulic Database (Nemes et al. 1999), seven from Lu et al., four from Schelle et al., and twenty-one from Jensen et al. Dry-end data under matric potential < -1500 kPa suction were determined using a WP4-T dew point water potential meter, a saturated salt solution desiccator, or a dew point water activity meter; wet-end data under matric potential > -1500 kPa suction were determined using a Tempe cell, a pressure plate device, an indoor hygrometer, and a combination of a sandbox and a pressure plate device. Most water retention data were measured at ~25°C.

[0023] Based on the obtained soil samples and their corresponding parameters, the permanent wilting points were estimated using the Aina & Periaswamy model (AP model), the van den Berg et al. model (vdB model), the Seybold & Harms model (SH model), and the present invention. The estimation results are as follows: Figure 2 As shown in Table 1, the four models were evaluated using mean absolute error (MAE) and root mean square error (RMSE).

[0024] Table 1

[0025] Compared to the AP, vdB, and SH models, the model proposed in this invention reduces the mean absolute error (MAE) by 70.83%, 81.08%, and 75.86%, respectively, and the root mean square error (RMES) by 72.22%, 83.87%, and 75.00%, respectively. Furthermore, it avoids the dependence of permanent wilting points on soil particle size distribution and organic matter content. This invention overcomes the shortcomings of traditional methods for determining permanent wilting points, which suffer from low efficiency and insufficient accuracy. It also avoids the dependence of permanent wilting points on soil particle size distribution and organic matter content, thereby reducing systematic errors caused by differences in soil type and enhancing applicability and universality. Through model estimation, the measurement accuracy is improved, labor costs are reduced, and the permanent wilting point of the soil to be measured can be obtained quickly. This provides reliable data support for agricultural soil moisture monitoring, irrigation decision-making, and crop water management, and has significant practical value for promoting the development of precision agriculture and improving water resource utilization efficiency.

Claims

1. A method for estimating the permanent wilting point based on hygroscopic moisture content, characterized in that, include: Obtain the hygroscopic moisture content of the soil to be estimated; The permanent wilting point is calculated based on the hygroscopic moisture content using a permanent wilting point estimation model. The expression for the permanent wilting point estimation model is as follows: in, For permanent wilting points, The matrix potential under drying conditions. The hygroscopic moisture content of the soil to be estimated.

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