An evaluation method for utilization potential and approach of natural selenium-rich land resources

Abstract

This invention relates to the field of land resource evaluation and discloses a method for evaluating the utilization potential and pathways of naturally selenium-rich land resources. The method includes collecting surface soil samples, soil samples from geological profiles, rock samples, and agricultural product samples at designated sampling points; testing the selenium content and physicochemical indicators of each sample and obtaining the selenium enrichment rate of agricultural products to obtain multi-dimensional test data; classifying the selenium enrichment level of the surface soil based on the selenium content, physicochemical indicators, and selenium enrichment rate of the agricultural products; determining whether the surface soil has a stable source of selenium based on the selenium content, physicochemical indicators, and selenium content of the soil samples from geological profiles and the rock samples; and combining the above determination results with the physicochemical indicators of the agricultural product samples to classify the development potential level. This invention overcomes the limitations of relying solely on surface soil data by introducing soil profile and rock data, accurately reflecting the continuous in-situ supply capacity of selenium-rich resources, and improving the accuracy of development potential classification.

Description

Technical Field

[0001] This invention relates to the field of land resource evaluation, specifically to a method for evaluating the utilization potential and pathways of naturally selenium-rich land resources. Background Technology

[0002] Selenium, an essential trace element for the human body, plays a vital physiological role. The primary route of selenium intake for humans is through the food chain, obtained from the soil. The selenium content of the soil directly affects the selenium content of agricultural products. With the development of specialty agriculture, selenium-enriched agriculture occupies an important position in the development and utilization of agricultural resources. Soil selenium sources in nature are divided into natural and anthropogenic sources. Agricultural products from selenium-enriched lands of different sources exhibit differences in quality. The rational development and utilization of selenium-enriched land relies on scientific land resource evaluation methods. Currently, relevant technical standards have established a series of evaluation systems related to selenium-enriched land, mainly defining and classifying it from the perspectives of selenium content, pH, and the content of certain heavy metals in the soil.

[0003] Existing methods for evaluating selenium-rich land are mostly limited to the measurement of surface soil indicators, typically classifying land grades based solely on thresholds for total or available selenium content under different pH conditions. This approach fails to consider the source characteristics of selenium and the vertical spatial distribution patterns of the soil profile. It cannot determine the true thickness of the selenium-rich soil layer, nor can it distinguish between shallow enrichment caused by localized anthropogenic inputs without a stable selenium source, and primary enrichment resulting from weathering of deeper parent rocks with a stable selenium source. Due to the lack of systematic investigation of the rock background and the soil layers at different strata, existing methods struggle to objectively assess whether surface soils possess a stable selenium source, neglecting the continuous in-situ supply capacity of selenium-rich land resources. This leads to insufficient accuracy and rigor in evaluating the utilization potential of natural selenium-rich land resources.

[0004] Existing selenium-rich land classification systems are not comprehensive enough in terms of ecological and environmental risk control. They typically define clean land only by simply comparing soil heavy metal content with preset risk screening values, failing to deeply and logically couple organic pollutant indicators, preset risk control values, and the actual selenium enrichment rate of agricultural products. There is a complex correlation between agricultural products and soil pollutant content. Existing evaluation standards lack comprehensive consideration of pollutant content in agricultural product samples and the feasibility of implementing agronomic adjustments. They cannot integrate natural selenium-rich quality with ecological safety baselines, making it difficult to provide direct classification guidance for the safe development of selenium-rich land and easily leading to blind agricultural development in areas with environmental pollution risks. Therefore, proposing a method for evaluating the utilization potential and pathways of natural selenium-rich land resources that takes into account the thickness of the selenium-rich soil layer, the stable source of selenium, and comprehensive ecological safety risks is a problem that needs to be solved in this field. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for evaluating the utilization potential and pathways of natural selenium-rich land resources. This method solves the problems of existing selenium-rich land evaluation methods that rely solely on surface soil analysis and cannot determine the thickness of the selenium-rich soil layer or the source of stable selenium substances. Furthermore, these methods fail to systematically consider the comprehensive ecological and environmental risks and the actual quality of agricultural products, resulting in low accuracy in evaluating the development potential of selenium-rich land and the risk of blind agricultural development in areas prone to environmental pollution.

[0006] To address the above problems, the present invention provides the following technical solution: A method for evaluating the utilization potential and pathways of naturally selenium-rich land resources includes the following steps: Sampling points were set up to collect surface soil samples, soil samples from different soil layers, rock samples, and agricultural product samples. The surface soil sample, the profile soil sample, the rock sample, and the agricultural product sample were tested to obtain the selenium content and physicochemical indicators of each sample, and the selenium enrichment rate of the agricultural product was obtained, thus obtaining multi-dimensional test data. Based on the selenium content of the surface soil samples, the physicochemical indicators, and the selenium enrichment rate of the agricultural products in the multi-dimensional test data, the selenium enrichment level of the surface soil is classified, and the selenium enrichment level determination result is obtained. Based on the selenium content of the soil samples from the profile occurrence layer, the physicochemical indicators, and the selenium content of the rock samples in the multi-dimensional test data, it is determined whether the surface soil has a stable source of selenium, and the result of the determination of the stable source of selenium is obtained. Based on the results of the selenium enrichment level determination, the results of the determination of the source status of stable selenium substances, and the physicochemical indicators of the agricultural product samples in the multi-dimensional test data, the development potential level of natural selenium-rich land resources is classified, the development potential level results are obtained, and a selenium-rich land survey report is prepared based on the development potential level results.

[0007] By adopting the above-mentioned technical solution, and by using the topsoil, the soil profile, the rocks, and the agricultural products as multi-dimensional comprehensive survey objects, and integrating the selenium content of each carrier with physicochemical environmental index data, the following technical effects are achieved: On the one hand, this method overcomes the spatial limitations of judging solely by topsoil. By introducing tests on soil profiles and rocks, the geochemical evolution and migration patterns of selenium are clarified from the perspectives of geological origin and spatial vertical distribution, enabling accurate identification of the deep-seated sources and stability of natural selenium-rich anomalies. On the other hand, this method incorporates soil pH, heavy metal and organic pollutant environmental and ecological risk indicators into the evaluation system. Combined with the selenium enrichment rate of the agricultural products, it objectively couples and calculates the total abundance, bioavailability, and ecological safety of selenium, providing a scientific and quantitative benchmark for the rational, safe, and sustainable development and utilization of selenium-rich land, and avoiding blind agricultural development in high-environmental-risk areas.

[0008] Preferably, the physicochemical indicators include soil pH, total organic carbon content, heavy metal content, organic pollutant content, and pollutant content of agricultural product samples; wherein the heavy metal content includes the content of cadmium, mercury, arsenic, lead, and chromium.

[0009] By adopting the above technical solution, a test item matrix is ​​set according to the classification of evaluation objects. The physicochemical indicators such as soil pH and total organic carbon content are used as environmental factors to explore the existence state of trace elements. Combined with multiple heavy metal and organic pollutant indicators, the key control factors affecting the valence state transformation and bioavailability of selenium are comprehensively quantified, and an evaluation underlying database covering both nutrient abundance and ecotoxicology is constructed.

[0010] Preferably, in the steps of separately setting up sampling points to collect surface soil samples, profile soil samples, rock samples, and agricultural product samples, the sampling point density satisfies the following: At a scale of 1 / 50000, the density of surface soil sampling points ranges from 4 points / km² to 16 points / km²; at a scale of 1 / 10000, the density of surface soil sampling points ranges from 20 points / km² to 64 points / km²; and the density of agricultural product sampling points ranges from 1 point / 4km² to 1 point / 1km².

[0011] By adopting the above technical solution, the sampling density of the surface soil and agricultural products can be set differently according to the scale of different exploration accuracies. This can ensure that sampling and testing costs are reasonably controlled while ensuring the representativeness of spatial sampling and the accuracy of geostatistical interpolation, and ensure that the sampling point distribution scheme forms complete data coverage for different parent materials and landform types.

[0012] Preferably, in the steps of separately setting up sampling points to collect surface soil samples, profile soil samples, rock samples, and agricultural product samples, the specific operation for collecting the surface soil samples includes: setting up surface soil sampling points in an X-shape, controlling the sampling depth to 0cm to 20cm above the surface, and after mixing, using the quartering method to collect 1000g to 1500g of the surface soil sample.

[0013] By adopting the above technical solution, using an X-shaped layout of sampling points and mixing them using a quartering method, the occasional micro-topographical errors of a single sampling point are eliminated, and the spatial homogeneity and representativeness of the surface soil samples are improved; thus ensuring the baseline accuracy of subsequent testing and analysis data for trace elements and organic matter indicators.

[0014] Preferably, in the steps of separately setting up sampling points to collect surface soil samples, profile soil samples, rock samples, and agricultural product samples, the specific operations for collecting the profile soil samples, the rock samples, and the agricultural product samples include: when collecting the profile soil samples, the profile depth is controlled to be 200cm to 300cm, and 3 to 5 samples from different layers are collected from a single soil profile; a mixed sample of rock composition of the same stratum and lithology is collected, with a total weight of 400g to 500g, to obtain the rock sample; the edible parts are collected during the peak harvest period of crops, and the amount of agricultural product samples collected is 3 to 5 times the amount of the sample to be tested, to obtain the agricultural product sample.

[0015] By adopting the above technical solutions and setting reasonable profile sampling depth and hierarchical sampling rules, the vertical leaching and secondary enrichment characteristics of selenium between different soil-forming layers can be fully characterized and recorded. By limiting the collection of mixed rock samples of the same strata and lithology, the initial background abundance of trace elements in the parent rock of soil-forming soil can be accurately determined. By setting collection quantity standards for crops, the statistical base of the tested biological samples is ensured to be sufficient, and the actual bioaccumulation rate and transformation capacity of the main economic crops in the study area for available selenium in the soil can be objectively and quantitatively reflected.

[0016] Preferably, in the step of obtaining the selenium enrichment level determination result, the selenium enrichment level of the surface soil is classified as clean selenium enrichment, general selenium enrichment, or no selenium enrichment. The specific conditions for obtaining the selenium enrichment level determination result include: When the soil pH is ≤7.5 and the selenium content of the surface soil sample is ≥0.40 mg / kg, or when the soil pH is >7.5 and the selenium content of the surface soil sample is ≥0.30 mg / kg, if the heavy metal content and the organic pollutant content are both lower than the preset risk screening value, and the selenium enrichment rate of the agricultural product is ≥30%, then the selenium enrichment level determination result is clean selenium enrichment. When the soil pH is ≤7.5 and the selenium content of the surface soil sample is ≥0.40 mg / kg, or when the soil pH is >7.5 and the selenium content of the surface soil sample is ≥0.30 mg / kg, if the contents of cadmium, mercury, arsenic, lead and chromium are higher than the preset risk screening value but lower than the risk control value, and the contents of organic pollutants are lower than the preset risk screening value, and the selenium enrichment rate of agricultural products is ≥30%, then the selenium enrichment level determination result is generally selenium enriched. When the soil pH is ≤7.5 and the selenium content of the surface soil sample is <0.40 mg / kg, or when the soil pH is >7.5 and the selenium content of the surface soil sample is <0.30 mg / kg, the selenium enrichment level is determined to be non-selenium-rich.

[0017] By adopting the above technical solution, the regulatory mechanism of soil pH on the bioavailability of selenium was considered. Under alkaline conditions, the mobility of selenate is enhanced and the absorption efficiency by plants is increased, thereby allowing for the differentiated and scientific setting of selenium enrichment thresholds at different pH levels. At the same time, the test results of heavy metals and organic pollutants were compared in a stepwise manner with preset risk screening values ​​and risk control values. Combined with the selenium enrichment rate of agricultural products, a dual assessment was conducted on the natural selenium-enriched quality of the soil and the baseline of agricultural ecological safety, ensuring that the defined selenium enrichment level has both development nutritional value and food safety baseline.

[0018] Preferably, in the step of obtaining the determination result of the stable selenium source status, the specific conditions for obtaining the determination result of the stable selenium source status as having no stable selenium source include: when only the selenium content of the soil samples from the profile occurrence layer at a depth of 0cm to 20cm reaches the selenium enrichment standard, the determination result of the stable selenium source status is obtained as having no stable selenium source. The specific conditions for obtaining the determination result of the stable selenium source status as having a stable selenium source include: when only the selenium content of the soil samples from the profile occurrence layer at a depth of 0cm to 50cm reaches the selenium enrichment standard, and the total organic carbon content is greater than 11.6g / kg, and the heavy metal content and the organic pollutant content both meet the preset risk screening values, the determination result of the stable selenium source status is obtained as having a stable selenium source; when the selenium content of all soil samples from the profile occurrence layer at a depth of 0cm to 50cm and below reaches the selenium enrichment standard, and the selenium content of the rock sample is ≥1.0mg / kg, the determination result of the stable selenium source status is obtained as having a stable selenium source.

[0019] By employing the aforementioned technical solution, a comprehensive judgment model for natural and stable selenium sources was constructed based on the selenium content and total organic carbon content of soil samples from different depths of the profile, combined with the selenium abundance of the underlying parent rock. This logical judgment rule can distinguish the essential difference between exogenous shallow-source enrichment caused by human fertilization and the intrinsic endowment bestowed by weathering of deep parent rock, objectively and rigorously assessing the sustainable in-situ supply capacity of selenium-rich land resources.

[0020] Preferably, in the step of obtaining the development potential level result, the development potential level of the natural selenium-rich land resources is classified as highly suitable or moderately suitable. The specific conditions for obtaining the development potential level result include: if the selenium enrichment level determination result is clean selenium-rich and the stable selenium source status determination result is that there is a stable selenium source, the development potential level result is highly suitable; if the selenium enrichment level determination result is clean selenium-rich and the stable selenium source status determination result is that there is no stable selenium source, the development potential level result is moderately suitable.

[0021] Preferably, the development potential level of naturally selenium-rich land resources is classified as moderately suitable, generally suitable, or unsuitable. Specific conditions for obtaining the development potential level result include: if the selenium enrichment level is determined to be moderately selenium-rich and the stable selenium source status is determined to have a stable selenium source, and the pollutant content of the agricultural product sample is below the limit value or the exceeding agricultural product is adjusted to a non-exceeding agricultural product through agronomic measures, the development potential level result is moderately suitable; if the selenium enrichment level is determined to be moderately selenium-rich and the stable selenium source status is determined to have no stable selenium source, and the pollutant content of the agricultural product sample is below the limit value or the exceeding agricultural product is adjusted to a non-exceeding agricultural product through agronomic measures, the development potential level result is generally suitable; if the selenium enrichment level is determined to be non-selenium-rich, or the selenium enrichment level is determined to be moderately selenium-rich but does not meet the requirement that the pollutant content of the agricultural product sample is below the limit value and the exceeding agricultural product is not adjusted to a non-exceeding agricultural product through agronomic measures, the development potential level result is unsuitable.

[0022] By adopting the above technical solution, a progressive evaluation system is constructed by logically combining the previously determined selenium enrichment level assessment results with the stable selenium source status assessment results, and supplementing this with assessment indicators for the feasibility of agronomic measures to remediate heavy metal pollutants. This system directly transforms the test results into a decision-making model to guide actual agricultural development, providing direct and quantifiable implementation classification standards for land planning layout, crop variety structure adjustment, and the implementation of agronomic interventions to block and deactivate heavy metals.

[0023] This invention provides a method for evaluating the utilization potential and pathways of naturally selenium-rich land resources. It has the following beneficial effects: 1. This invention collects surface soil samples, soil samples from different soil layers, rock samples, and agricultural product samples. It then tests the selenium content and physicochemical indicators of these samples to obtain multi-dimensional test data. This data is used to construct an evaluation system that classifies the selenium enrichment level of surface soil, determines whether the surface soil has a stable source of selenium, and ultimately classifies the development potential level of natural selenium-rich land resources. This system not only relies on the test data of surface soil and agricultural product samples to determine the selenium enrichment level but also incorporates the selenium content of soil samples from different soil layers and rock samples. By clarifying different depth layers and the condition of the parent rock, it determines whether the surface soil has a stable source of selenium, overcoming the limitations of relying solely on surface soil and improving the accuracy of classifying the development potential level of natural selenium-rich land resources.

[0024] 2. This invention comprehensively determines whether the surface soil has a stable source of selenium by combining the selenium content of soil samples from different depths in multi-dimensional test data with the selenium content and total organic carbon content of rock samples. It distinguishes between shallow enrichment without a stable source of selenium that only appears on the surface and primary occurrence with a stable source of selenium, which is endowed by weathering of deep parent rocks. The determination of the stable source of selenium is used for the subsequent classification of development potential levels. In the evaluation of development potential levels, it objectively reflects the continuous in-situ supply capacity of selenium-rich land resources, making the evaluation results of the utilization potential of natural selenium-rich land resources more rigorous.

[0025] 3. This invention classifies the selenium enrichment level of topsoil into clean selenium-rich, general selenium-rich, or non-selenium-rich levels by comparing soil pH, heavy metal content, and organic pollutant content with preset risk screening and control values, and combining this with the selenium enrichment rate of agricultural products. Furthermore, when classifying the development potential level of natural selenium-rich land resources, it further incorporates the specific conditions of pollutant content in agricultural product samples being below the limit value or adjusting substandard agricultural products to within the limit through agronomic measures. This integrates the quality of natural selenium enrichment with the bottom line of ecological safety, providing direct classification guidance for the safe development of selenium-rich land and avoiding blind agricultural development in areas with environmental pollution risks. Attached Figure Description

[0026] Figure 1 This is a multi-dimensional index profile evolution diagram of a typical selenium-rich plot according to an embodiment of the present invention; Figure 2 This is a comparison and determination benchmark diagram of selenium abundance at different depth levels according to an embodiment of the present invention; Figure 3This is a comparison chart of spatial exploration accuracy and agricultural product safety evaluation according to an embodiment of the present invention. Detailed Implementation

[0027] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. 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.

[0028] Examples 1-3: Example 1: This embodiment provides a method for evaluating the utilization potential and pathways of naturally selenium-rich land resources, including the following steps: S1. The survey subjects are determined to be topsoil, soil layers in the soil profile, rocks, and agricultural products; at a scale of 1 / 50000, the density of topsoil sampling points is 4 points / km. 2 At a scale of 1 / 10000, the density of surface soil sampling points is 20 points / km². 2 The sampling density for agricultural products is 1 point per 4 km. 2 Surface soil sampling points were arranged in an X-shape, with sampling depths ranging from 0cm to 20cm. After mixing, 1000g of surface soil sample was collected using the quartering method. When collecting soil samples from different soil layers, the profile depth was controlled at 200cm, and three samples from different layers were collected from a single soil profile. A mixed sample of rock composition of the same stratum and lithology was collected, with a total weight of 400g. Edible parts were collected during the peak harvest season of crops, and the amount of agricultural product samples collected was three times the amount of samples to be tested. The selenium content, soil pH, total organic carbon, and the content of heavy metals including cadmium, mercury, arsenic, lead, and chromium, as well as the content of organic pollutants, were tested for each sample, and the selenium enrichment rate of agricultural products was obtained. S2. When the soil pH is ≤7.5 and the selenium content of the surface soil sample is ≥0.40 mg / kg, or the soil pH is >7.5 and the selenium content of the surface soil sample is ≥0.30 mg / kg, if the heavy metal content and organic pollutant content are both lower than the preset risk screening value, and the selenium enrichment rate of agricultural products is ≥30%, the surface soil is classified as clean selenium-rich; when the soil pH is ≤7.5 and the selenium content of the surface soil sample is ≥0.40 mg / kg, or the soil pH is >7.5 and the selenium content of the surface soil sample is ≥0.30 mg / kg, the surface soil is classified as clean selenium-rich. 5. When the selenium content of the surface soil sample is ≥0.30 mg / kg, if the contents of cadmium, mercury, arsenic, lead, and chromium are higher than the risk screening value but lower than the risk control value, and the content of organic pollutants is lower than the risk screening value, and the selenium enrichment rate of agricultural products is ≥30%, it is classified as generally selenium-rich; when the soil pH is ≤7.5 and the selenium content of the surface soil sample is <0.40 mg / kg, or when the soil pH is >7.5 and the selenium content of the surface soil sample is <0.30 mg / kg, it is classified as non-selenium-rich. S3. When only soil samples from the strata of occurrence at a depth of 0cm to 20cm meet the selenium enrichment standard, it is determined that there is no stable source of selenium. When only soil samples from the strata of occurrence at a depth of 0cm to 50cm meet the selenium enrichment standard, and the total organic carbon content is greater than 11.6g / kg, and the heavy metal content and organic pollutant content both meet the preset risk screening values, it is determined that there is a stable source of selenium. When soil samples from the strata of occurrence at a depth of 0cm to 50cm and below all meet the selenium enrichment standard, and the selenium content of the rock samples is ≥1.0mg / kg, it is determined that there is a stable source of selenium. S4. If a land is designated as clean and selenium-rich with a stable source of selenium, it is classified as highly suitable; if it is designated as clean and selenium-rich but without a stable source of selenium, it is classified as moderately suitable; if it is designated as generally selenium-rich with a stable source of selenium, and the contaminant content in agricultural product samples is below the limit value or the exceeding agricultural products are adjusted to within the limit through agronomic measures, it is classified as moderately suitable; if it is designated as generally selenium-rich without a stable source of selenium, and the contaminant content in agricultural product samples is below the limit value or the exceeding limit is adjusted to within the limit through agronomic measures, it is classified as generally suitable; if it is designated as not selenium-rich, or as generally selenium-rich but does not meet the contaminant conditions for agricultural products, it is classified as unsuitable. Finally, a selenium-rich land survey report is prepared based on this.

[0029] Example 2: This embodiment provides a method for evaluating the utilization potential and pathways of naturally selenium-rich land resources, including the following steps: S1. The survey subjects are determined to be topsoil, soil layers in the profile, rocks, and agricultural products; at a scale of 1 / 50000, the sampling density for topsoil is 10 points / km². 2At a scale of 1 / 10000, the density of surface soil sampling points is 42 points / km². 2 The sampling density for agricultural products is 1 point per 2 km. 2 The surface soil sampling points were arranged in an X-shape, with a sampling depth of 0cm to 20cm. After mixing, 1250g of surface soil sample was collected using the quartering method. When collecting soil samples from different soil layers, the profile depth was controlled at 250cm, and four samples from different layers were collected from a single soil profile. A mixed sample of rock composition of the same stratum and lithology was collected, with a total weight of 450g. Edible parts were collected during the peak harvest period of crops, and the amount of agricultural product samples collected was four times the amount of samples to be tested. The selenium content, soil pH, total organic carbon, and the content of heavy metals including cadmium, mercury, arsenic, lead, and chromium, as well as the content of organic pollutants, were tested for each sample, and the selenium enrichment rate of agricultural products was obtained. S2. When the soil pH is ≤7.5 and the selenium content of the surface soil sample is ≥0.40 mg / kg, or the soil pH is >7.5 and the selenium content of the surface soil sample is ≥0.30 mg / kg, if the heavy metal content and organic pollutant content are both lower than the preset risk screening value, and the selenium enrichment rate of agricultural products is ≥30%, the surface soil is classified as clean selenium-rich; when the soil pH is ≤7.5 and the selenium content of the surface soil sample is ≥0.40 mg / kg, or the soil pH is >7.5 and the selenium content of the surface soil sample is ≥0.30 mg / kg, the surface soil is classified as clean selenium-rich. 5. When the selenium content of the surface soil sample is ≥0.30 mg / kg, if the contents of cadmium, mercury, arsenic, lead, and chromium are higher than the risk screening value but lower than the risk control value, and the content of organic pollutants is lower than the risk screening value, and the selenium enrichment rate of agricultural products is ≥30%, it is classified as generally selenium-rich; when the soil pH is ≤7.5 and the selenium content of the surface soil sample is <0.40 mg / kg, or when the soil pH is >7.5 and the selenium content of the surface soil sample is <0.30 mg / kg, it is classified as non-selenium-rich. S3. When only soil samples from the strata of occurrence at a depth of 0cm to 20cm meet the selenium enrichment standard, it is determined that there is no stable source of selenium. When only soil samples from the strata of occurrence at a depth of 0cm to 50cm meet the selenium enrichment standard, and the total organic carbon content is greater than 11.6g / kg, and the heavy metal content and organic pollutant content both meet the preset risk screening values, it is determined that there is a stable source of selenium. When soil samples from the strata of occurrence at a depth of 0cm to 50cm and below all meet the selenium enrichment standard, and the selenium content of the rock samples is ≥1.0mg / kg, it is determined that there is a stable source of selenium. S4. If a land is designated as clean and selenium-rich with a stable source of selenium, it is classified as highly suitable; if it is designated as clean and selenium-rich but without a stable source of selenium, it is classified as moderately suitable; if it is designated as generally selenium-rich with a stable source of selenium, and the contaminant content in agricultural product samples is below the limit value or the exceeding agricultural products are adjusted to within the limit through agronomic measures, it is classified as moderately suitable; if it is designated as generally selenium-rich without a stable source of selenium, and the contaminant content in agricultural product samples is below the limit value or the exceeding limit is adjusted to within the limit through agronomic measures, it is classified as generally suitable; if it is designated as not selenium-rich, or as generally selenium-rich but does not meet the contaminant conditions for agricultural products, it is classified as unsuitable. Finally, a selenium-rich land survey report is prepared based on this.

[0030] Example 3: This embodiment provides a method for evaluating the utilization potential and pathways of naturally selenium-rich land resources, including the following steps: S1. The survey subjects are determined to be topsoil, soil layers in the soil profile, rocks, and agricultural products; at a scale of 1 / 50000, the density of topsoil sampling points is 16 points / km². 2 At a scale of 1 / 10000, the density of surface soil sampling points is 64 points / km². 2 The sampling density for agricultural products is 1 point / 1km. 2 The surface soil sampling points were arranged in an X-shape, with a sampling depth of 0cm to 20cm. After mixing, 1500g of surface soil sample was collected using the quartering method. When collecting soil samples from different soil layers, the profile depth was controlled at 300cm, and five samples from different layers were collected from a single soil profile. A mixed sample of rock composition of the same stratum and lithology was collected, with a total weight of 500g. Edible parts were collected during the peak harvest period of crops, and the amount of agricultural product samples collected was five times the amount of samples to be tested. The selenium content, soil pH, total organic carbon, and the content of heavy metals including cadmium, mercury, arsenic, lead, and chromium, as well as the content of organic pollutants, were tested for each sample, and the selenium enrichment rate of agricultural products was obtained. S2. When the soil pH is ≤7.5 and the selenium content of the surface soil sample is ≥0.40 mg / kg, or the soil pH is >7.5 and the selenium content of the surface soil sample is ≥0.30 mg / kg, if the heavy metal content and organic pollutant content are both lower than the preset risk screening value, and the selenium enrichment rate of agricultural products is ≥30%, the surface soil is classified as clean selenium-rich; when the soil pH is ≤7.5 and the selenium content of the surface soil sample is ≥0.40 mg / kg, or the soil pH is >7.5 and the selenium content of the surface soil sample is ≥0.30 mg / kg, the surface soil is classified as clean selenium-rich. 5. When the selenium content of the surface soil sample is ≥0.30 mg / kg, if the contents of cadmium, mercury, arsenic, lead, and chromium are higher than the risk screening value but lower than the risk control value, and the content of organic pollutants is lower than the risk screening value, and the selenium enrichment rate of agricultural products is ≥30%, it is classified as generally selenium-rich; when the soil pH is ≤7.5 and the selenium content of the surface soil sample is <0.40 mg / kg, or when the soil pH is >7.5 and the selenium content of the surface soil sample is <0.30 mg / kg, it is classified as non-selenium-rich. S3. When only soil samples from the strata of occurrence at a depth of 0cm to 20cm meet the selenium enrichment standard, it is determined that there is no stable source of selenium. When only soil samples from the strata of occurrence at a depth of 0cm to 50cm meet the selenium enrichment standard, and the total organic carbon content is greater than 11.6g / kg, and the heavy metal content and organic pollutant content both meet the preset risk screening values, it is determined that there is a stable source of selenium. When soil samples from the strata of occurrence at a depth of 0cm to 50cm and below all meet the selenium enrichment standard, and the selenium content of the rock samples is ≥1.0mg / kg, it is determined that there is a stable source of selenium. S4. If a land is designated as clean and selenium-rich with a stable source of selenium, it is classified as highly suitable; if it is designated as clean and selenium-rich but without a stable source of selenium, it is classified as moderately suitable; if it is designated as generally selenium-rich with a stable source of selenium, and the contaminant content in agricultural product samples is below the limit value or the exceeding agricultural products are adjusted to within the limit through agronomic measures, it is classified as moderately suitable; if it is designated as generally selenium-rich without a stable source of selenium, and the contaminant content in agricultural product samples is below the limit value or the exceeding limit is adjusted to within the limit through agronomic measures, it is classified as generally suitable; if it is designated as not selenium-rich, or as generally selenium-rich but does not meet the contaminant conditions for agricultural products, it is classified as unsuitable. Finally, a selenium-rich land survey report is prepared based on this.

[0031] Comparative Examples 1-3: Comparative Example 1: Compared with Example 2, the difference is that: the soil and rock of the profile generation layer were not included as the investigation objects, the operation of collecting soil samples of the profile generation layer and the operation of collecting rock samples in step S1 were omitted, the analysis and testing steps for soil and rock samples of the profile generation layer in step S1 were omitted, and the judgment step on whether the selenium-rich soil has a stable source of selenium in step S3 was not performed. The evaluation was based only on the test data of the surface soil sample. All other parameters and steps are the same.

[0032] Comparative Example 2: Compared with Example 2, the difference is that in step S2, when classifying selenium-rich soil as clean selenium-rich or general selenium-rich, the classification is based solely on the pH of the surface soil sample and its corresponding soil selenium standard threshold, heavy metal content, and organic pollutant content, without introducing the selenium enrichment rate of agricultural products as a basis for classification; and in step S4, when classifying the selenium-rich soil as having the potential for selenium resource development and utilization, the agricultural product samples are not subjected to compliance testing for the limits of agricultural product pollutants, while the other parameters and steps are the same.

[0033] Comparative Example 3: Compared with Example 2, the difference is that in step S1, the density of surface soil sampling points at a scale of 1 / 10000 is changed to 2 points / km. 2 In step S1, the mass of the topsoil sample collected by the quartering method is changed to 500g; in step S1, when collecting the stratified soil sample using a trough-type sampling drill, the profile depth is changed to 50cm, and the other parameters and steps are the same.

[0034] Test Example 1-3: Test Example 1: Experimental description: To verify the accuracy and feasibility of the evaluation scheme for the utilization potential and development pathways of natural selenium-rich land resources in actual geological surveys and agricultural development, a farmland plot with potential development value in a low mountain and hilly area was selected as the verification area. The parent material of this area is mainly weathered colluvial deposits, with good vegetation cover. By obtaining multi-dimensional spatial and compositional measured data of this plot, the logical rigor and practical effectiveness of the multi-level evaluation model provided by this invention in actual exploration scenarios were comprehensively verified.

[0035] Experimental steps: Samples of surface soil, profile soil, deep rock, and bulk agricultural products grown in situ on the plot were extracted according to the sampling density and sampling weight specified in Example 2. The samples obtained from each of the above-mentioned levels were sent to the laboratory for pretreatment and analysis. The total content of selenium and heavy metal elements in soil and rocks was tested by inductively coupled plasma mass spectrometry, the total organic carbon content in soil was tested by potassium dichromate capacity method, the pH of surface soil was tested by potentiometric method, and the content of corresponding elements in agricultural product samples was determined by liquid chromatography-tandem mass spectrometry. Test data at various depths were compiled and a vertical spatial distribution sequence was established. Based on the chemical indicators of various elements in the surface layer and the enrichment of agricultural products, the basic selenium enrichment level was determined. Then, the thickness of the effective enriched soil layer was verified along the profile depth direction and the source of the underlying selenium was traced. Finally, the long-term development potential level of the land plot was comprehensively evaluated based on the full-chain data.

[0036] Experimental data: Table 1. Distribution Results of Multidimensional Test Indicators in Typical Selenium-Rich Plots Note: "Not tested" in the table above means that, according to the specifications of this evaluation scheme, agricultural products only grow in the topsoil, and there is no need to analyze and test non-essential evaluation indicators such as soil pH and total organic carbon for rock samples.

[0037] Experimental conclusion: Based on the profile distribution results recorded in Table 1 and the attached... Figure 1 The evaluation indicators dynamically evolve with stratum depth. The surface soil of this plot exhibits a slightly acidic environment, and the measured selenium content is significantly higher than the selenium enrichment threshold for acidic soils. Simultaneously, the cadmium heavy metal index in the surface soil is far below the nationally stipulated threshold for agricultural land pollution risk screening, and the measured selenium enrichment rate of agricultural products exceeds the lower limit of the benchmark. These multidimensional apparent data collectively support the preliminary classification of this surface soil as clean and selenium-rich.

[0038] Combining the unique three-dimensional soil formation mechanism analysis of this scheme, attached... Figure 1 The profile evolution patterns of key geochemical indicators are visually illustrated. (Appendix) Figure 1 The solid line with circular markings represents the spatial distribution trend of selenium, while the dashed line with square markings represents the spatial distribution trend of total organic carbon. Observing the trajectory of the solid line with circular markings reveals that selenium abundance remains at a high level in the surface and shallow layers, with a subsurface enrichment peak appearing near a relative depth of 35 cm in the stratigraphic profile. Subsequently, it maintains a gradual transition in deeper soil layers, while exhibiting a distinctly high value characteristic in the bottom parent material layer at a relative depth of 250 cm. This vertical distribution trend clearly indicates that the high selenium anomaly at the surface is not a short-term cumulative effect of human fertilization activities, but rather an in-situ release evolution from the selenium-rich parent rock through long-term geological weathering and soil formation processes.

[0039] Meanwhile, observation of the dotted line trajectory marked with squares reveals that the total organic carbon content exhibits a typical natural decrease with profile depth. Combining the two sets of curves verifies the core source tracing and occurrence mechanism of this scheme: the abundant organic carbon on the surface and in the shallow layer significantly complexes and retains selenium, which is continuously released from the weathering of the underlying rock layers and migrates upwards, thus forming a stable selenium-rich zone with a long-term material supply in the shallow layer. Based on this, this evaluation method accurately determines that the selenium-rich soil possesses a long-term and stable natural selenium source, effectively avoiding the risk of blind land grabbing and development that can easily occur with traditional methods relying solely on surface sampling. Considering both the qualified surface quality and the stable deep material supply, this evaluation scheme ultimately scientifically classifies this plot as a highly suitable natural selenium-rich land resource for development.

[0040] Test Example 2: Experimental description: To verify the technical advantages of introducing multi-dimensional surveys of soil and subsurface rocks at different selenium profile levels in determining the long-term stability of selenium sources, a shallow-layer enriched farmland with a long history of agricultural planting and recent application of exogenous selenium-containing fertilizers was selected as a comparative verification area. By comparing the full-chain evaluation method provided in Example 2 with the single-layer evaluation method provided in Comparative Example 1, the necessity and scientific validity of this invention in preventing the risk of blind development of selenium-rich plots without long-term selenium sources are demonstrated.

[0041] Experimental steps: According to the survey criteria defined in Example 2, topsoil, multi-layer profile soil and bottom fresh rock samples were collected simultaneously at this site. In accordance with the survey baseline defined in Comparative Example 1, soil samples were collected from only the shallow surface area of ​​the same plot, ignoring the exploration of deep strata and parent rock. The samples collected by the two sets of evaluation models were sent to the detection platform and the total selenium abundance and basic physicochemical indicators of each level of samples were determined using analytical instruments such as inductively coupled plasma mass spectrometry. The corresponding test data were processed according to the evaluation logic of Example 2 and Comparative Example 1, respectively, and the judgment results of the two in terms of material source stability traceability and final development potential rating were compared.

[0042] Experimental data: Table 2. Comparison of Selenium Element Measurement Data and Judgment Results at Different Depth Levels under Different Evaluation Models Note: In the table above, "not measured" means that according to the evaluation specifications of Comparative Example 1, only the shallow surface area was sampled, and no soil profile or bottom rock was sampled and investigated; "missing" means that the rock sample does not need to be analyzed and tested for non-essential evaluation indicators such as total organic carbon.

[0043] Experimental conclusion: Based on the multi-level test data recorded in Table 2 and the attached... Figure 2 The vertical profile abundance evolution trend presented in Example 2 demonstrates how multi-level exploration can reflect the true physicochemical characteristics of the geological background. (Combined with appendix...) Figure 2 As indicated by the solid line marked with an asterisk, the selenium abundance in the top 0-20 cm soil layer measured in Example 2 was 0.414 mg / kg, exceeding the natural selenium enrichment threshold of 0.40 mg / kg represented by the horizontal dashed line. The total organic carbon content was also 12.10 g / kg, indicating selenium enrichment. However, when the profile depth reached 20-50 cm and beyond, the asterisked line dropped below the horizontal dashed line, and the selenium abundance decreased to 0.358 mg / kg, failing to meet the selenium enrichment standard. The selenium levels in the deep profile and the bottom parent rock were 0.234 mg / kg, 0.160 mg / kg, and 0.180 mg / kg, respectively, indicating a lack of physical conditions for the continuous release of the corresponding chemical element.

[0044] This longitudinal distribution characteristic indicates that the elevated selenium content in the surface layer of this plot is not the result of natural soil formation, but rather a cumulative effect of agricultural activities such as the application of exogenous selenium-containing fertilizers. A comparison with the attached figures shows that Comparative Example 1... Figure 2 Individual scatter plots marked with diamonds show surface data of 0.56 mg / kg, higher than the baseline. Due to the lack of deep exploration steps, the underlying source cannot be identified, potentially leading to misjudgments in the evaluation model. Example 2, relying on multi-level profiles and rock analysis, identified the actual situation of the site: enrichment in the shallow layer (0cm to 20cm) and a lack of underlying material sources. Given that the surface organic carbon content meets the standard, this evaluation method determines that the area lacks a stable source of selenium and downgrades its overall development potential. This test verifies the effectiveness of this invention in eliminating human interference, preventing blind development, and ensuring the objectivity of natural selenium-rich evaluations.

[0045] Test Example 3: Experimental description: To verify the comprehensive effectiveness of spatial sampling accuracy control and agricultural product quality evaluation indicators in ensuring the accuracy of land resource spatial delineation and the safety of industrial development in this evaluation specification, a natural agricultural area with strong spatial heterogeneity and local fluctuations in heavy metal background values ​​was selected for testing. Through testing and evaluating different data outputs and judgment results under a real exploration environment, the role of rigorous sampling density and a full-process safety verification system in eliminating food safety hazards and avoiding the risk of misjudgment during development was demonstrated.

[0046] Experimental steps: Based on the spatial survey benchmarks defined in Example 2 and Comparative Example 3, topsoil sampling and profile sampling operations with corresponding densities were carried out on the same plot. The elemental abundance of soil samples at each level obtained under different sampling criteria was determined using relevant testing instruments, and the differences in the use of different grid densities in delineating selenium-rich boundaries and probing the depth of bottom material sources were evaluated. Based on the evaluation procedures defined in Example 2 and Comparative Example 2, samples of agricultural products grown in situ on this plot were collected for elemental analysis and quality inspection. The evaluation data were summarized and reconstructed along the spatial distribution cross-section to assess the technical reliability of Example 2 in identifying hidden pollution risks and classifying final development potential levels.

[0047] Experimental data: Table 3. Comparison of Exploration and Safety Evaluation Results of Different Evaluation Schemes in Complex Sites Note: The evaluation system of comparison ratio 2, which did not conduct limit compliance testing, did not include heavy metal indicators of agricultural products in the mandatory testing process; the corresponding point exceeding the standard comparison ratio 3 failed to obtain the corresponding point exceeding the standard because the grid layout was too sparse and the high background heavy metal associated areas were missed in the physical sampling stage, which made it impossible to carry out subsequent high-risk point testing in a targeted manner.

[0048] Experimental conclusion: Based on the exploration data recorded in Table 3 and the attached... Figure 3 The dynamic evolution of spatial cross-sectional chemical indicators presented in Example 2 demonstrates clear technical feasibility in ensuring industrial safety and evaluation accuracy. (Combined with Appendix) Figure 3 As can be observed from the solid line trajectory marked with a circle, Example 2, relying on the high-density spatial layout specification, can reflect the real fluctuation details of soil selenium content along the transverse section, thereby accurately defining the effective high-concentration enrichment range and avoiding the omission of local associated heavy metal anomaly areas.

[0049] At the same time, attached Figure 3 The dotted line marked with a plus sign visually illustrates the spatial distribution of cadmium in agricultural products simultaneously measured in Example 2. Data in the lateral spatial distance range of 450m to 600m clearly exceeds the baseline safety limit for agricultural products represented by the horizontally intersecting dotted line. Example 2, relying on a robust data verification loop, successfully detected substandard batches of agricultural products within the accurately delineated selenium-rich area. Based on the actual pollution distribution, Example 2 can halt development processes with potential food safety risks and assess the overall development potential of the site as moderately suitable. This test demonstrates the rationality of Example 2 in terms of spatial sampling representativeness and end-to-end safety quality control, achieving a safe balance between high-precision exploration and high-quality development.

Claims

1. A method for evaluating the utilization potential and pathways of naturally selenium-rich land resources, characterized in that, Includes the following steps: Sampling points were set up to collect surface soil samples, soil samples from different soil layers, rock samples, and agricultural product samples. The surface soil sample, the profile soil sample, the rock sample, and the agricultural product sample were tested to obtain the selenium content and physicochemical indicators of each sample, and the selenium enrichment rate of the agricultural product was obtained, thus obtaining multi-dimensional test data. Based on the selenium content of the surface soil samples, the physicochemical indicators, and the selenium enrichment rate of the agricultural products in the multi-dimensional test data, the selenium enrichment level of the surface soil is classified, and the selenium enrichment level determination result is obtained. Based on the selenium content of the soil samples from the profile occurrence layer, the physicochemical indicators, and the selenium content of the rock samples in the multi-dimensional test data, it is determined whether the surface soil has a stable source of selenium, and the result of the determination of the stable source of selenium is obtained. Based on the results of the selenium enrichment level determination, the results of the determination of the source status of stable selenium substances, and the physicochemical indicators of the agricultural product samples in the multi-dimensional test data, the development potential level of natural selenium-rich land resources is classified, the development potential level results are obtained, and a selenium-rich land survey report is prepared based on the development potential level results.

2. The method for evaluating the utilization potential and pathways of naturally selenium-rich land resources according to claim 1, characterized in that, The physicochemical indicators include soil pH, total organic carbon content, heavy metal content, organic pollutant content, and pollutant content of agricultural product samples; wherein, the heavy metal content includes the content of cadmium, mercury, arsenic, lead, and chromium.

3. The method for evaluating the utilization potential and pathways of naturally selenium-rich land resources according to claim 1, characterized in that, In the steps of separately setting up sampling points to collect surface soil samples, profile soil samples, rock samples, and agricultural product samples, the sampling point density must satisfy the following: At a scale of 1 / 50000, the density of surface soil sampling points ranges from 4 points / km2 to 16 points / km2; At a scale of 1 / 10000, the density of surface soil sampling points ranges from 20 points / km2 to 64 points / km2; The sampling density for agricultural products is 1 point / 4km2 to 1 point / 1km2.

4. The method for evaluating the utilization potential and pathways of naturally selenium-rich land resources according to claim 1, characterized in that, In the steps of separately setting up sampling points to collect surface soil samples, profile soil samples, rock samples, and agricultural product samples, the specific operations for collecting the surface soil samples include: The surface soil sampling points were arranged in an X-shape, and the sampling depth was controlled from 0cm to 20cm in the surface layer. After mixing, 1000g to 1500g of the surface soil sample was collected using the quartering method.

5. The method for evaluating the utilization potential and pathways of naturally selenium-rich land resources according to claim 1, characterized in that, In the steps of separately setting up sampling points to collect surface soil samples, profile soil samples, rock samples, and agricultural product samples, the specific operations for collecting the profile soil samples, the rock samples, and the agricultural product samples include: When collecting soil samples from the stratified profile, the profile depth is controlled to be 200cm to 300cm, and 3 to 5 samples from different layers are collected from a single soil profile. Collect a mixed sample of rocks of the same stratum and lithology, with a total weight of 400g to 500g, to obtain the rock sample; Edible parts of crops are collected during the peak harvest season. The amount of agricultural product samples collected is 3 to 5 times the amount of the sample to be tested, thus obtaining the agricultural product samples.

6. The method for evaluating the utilization potential and pathways of naturally selenium-rich land resources according to claim 2, characterized in that, In the step of obtaining the selenium enrichment level determination result, the selenium enrichment level of the surface soil is classified as clean selenium enrichment, general selenium enrichment, or no selenium enrichment. The specific conditions for obtaining the selenium enrichment level determination result include: When the soil pH is ≤7.5 and the selenium content of the surface soil sample is ≥0.40 mg / kg, or when the soil pH is >7.5 and the selenium content of the surface soil sample is ≥0.30 mg / kg, if the heavy metal content and the organic pollutant content are both lower than the preset risk screening value, and the selenium enrichment rate of the agricultural product is ≥30%, then the selenium enrichment level determination result is clean selenium enrichment. When the soil pH is ≤7.5 and the selenium content of the surface soil sample is ≥0.40 mg / kg, or when the soil pH is >7.5 and the selenium content of the surface soil sample is ≥0.30 mg / kg, if the contents of cadmium, mercury, arsenic, lead and chromium are higher than the preset risk screening value but lower than the risk control value, and the contents of organic pollutants are lower than the preset risk screening value, and the selenium enrichment rate of agricultural products is ≥30%, then the selenium enrichment level determination result is generally selenium enriched. When the soil pH is ≤7.5 and the selenium content of the surface soil sample is <0.40 mg / kg, or when the soil pH is >7.5 and the selenium content of the surface soil sample is <0.30 mg / kg, the selenium enrichment level is determined to be non-selenium-rich.

7. The method for evaluating the utilization potential and pathways of naturally selenium-rich land resources according to claim 1, characterized in that, In the step of obtaining the determination result of the source status of stable selenium substances, the specific conditions for obtaining the determination result of the source status of stable selenium substances as having no stable selenium substance source include: When the selenium content of the soil samples from the profile with a depth of only 0cm to 20cm reaches the selenium enrichment standard, the result of the determination of the source status of the stable selenium substance is that there is no stable selenium substance source.

8. The method for evaluating the utilization potential and pathways of naturally selenium-rich land resources according to claim 2, characterized in that, In the step of obtaining the determination result of the source status of stable selenium substances, the specific conditions for obtaining the determination result of the source status of stable selenium substances as having a stable selenium source include: When the selenium content of the soil samples from the profile with a depth of 0cm to 50cm reaches the selenium enrichment standard, and the total organic carbon content is greater than 11.6g / kg, and the heavy metal content and the organic pollutant content both meet the preset risk screening values, the result of the determination of the source status of the stable selenium substance is that it has a stable selenium substance source. When the selenium content of the soil samples from the profile at depths of 0cm to 50cm and below all meet the selenium enrichment standard, and the selenium content of the rock samples is ≥1.0mg / kg, the result of the determination of the source status of the stable selenium substance is that it has a stable selenium substance source.

9. The method for evaluating the utilization potential and pathways of naturally selenium-rich land resources according to claim 2, characterized in that, In the step of obtaining the development potential level result, the development potential level of natural selenium-rich land resources is classified as highly suitable or moderately suitable. The specific conditions for obtaining the development potential level result include: If the selenium enrichment level is determined to be clean and selenium-rich and the stable selenium source status is determined to be a stable selenium source, then the development potential level is determined to be highly suitable. If the selenium enrichment level is determined to be clean and selenium-rich, and the stable selenium source status is determined to be without a stable selenium source, then the development potential level is determined to be moderately suitable.

10. The method for evaluating the utilization potential and pathways of naturally selenium-rich land resources according to claim 9, characterized in that, In the step of obtaining the development potential level result, the development potential level of natural selenium-rich land resources is classified as moderately suitable, generally suitable, or unsuitable. The specific conditions for obtaining the development potential level result include: If the selenium enrichment level is determined to be generally selenium-rich and the stable selenium source status is determined to be a stable selenium source, and the pollutant content of the agricultural product sample is lower than the limit value or the agricultural product exceeding the standard is adjusted to a non-exceeding agricultural product through agronomic measures, the development potential level is determined to be moderate and suitable. If the selenium enrichment level is determined to be generally selenium-rich and the stable selenium source status is determined to be without a stable selenium source, and the pollutant content of the agricultural product sample is lower than the limit value or the agricultural product exceeding the standard is adjusted to a non-exceeding agricultural product through agronomic measures, the development potential level is determined to be generally suitable. If the selenium enrichment level determination result is "not selenium-rich", or if the selenium enrichment level determination result is "generally selenium-rich" but does not meet the requirement that the pollutant content of the agricultural product sample is below the limit value and the agricultural product exceeding the standard has not been adjusted to a non-exceeding agricultural product through agronomic measures, then the development potential level result is "unsuitable".

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