Soil Phosphorus Content Detection: Total Phosphorus, Available Phosphorus, and Inorganic Phosphorus Fraction Analysis

Soil phosphorus content detection is an important method for evaluating the size of the soil phosphorus pool, the phosphorus supply capacity for plants, and the risk of phosphorus accumulation. Total phosphorus reflects soil phosphorus reserves, available phosphorus reflects phosphorus fractions that can be absorbed by plants or readily transformed for use in the short term, and inorganic phosphorus fraction analysis is used to explain the fixation, release, and transformation mechanisms of phosphorus in soil.

Keywords: soil phosphorus; soil total phosphorus; total phosphate; available phosphorus; inorganic phosphorus; phosphorus fractions; molybdenum blue colorimetry; soil fertility evaluation

1 Research Entry Points for Soil Phosphorus Content Detection

1.1 Indicator Boundaries of Total Phosphorus, Available Phosphorus, and Phosphorus Fractions

Phosphorus in soil does not exist in a single form, but is distributed among multiple fractions, including mineral-bound phosphorus, adsorbed inorganic phosphorus, organic phosphorus, and residual phosphorus. Total phosphorus is used to evaluate the overall size of the soil phosphorus pool, but it does not directly represent plant availability. Available phosphorus is closer to the short-term phosphorus supply capacity for crops, but it cannot explain the mechanisms by which phosphorus is fixed or released. Inorganic phosphorus fraction analysis can further distinguish water-soluble phosphorus, weakly adsorbed phosphorus, iron/aluminum-bound phosphorus, calcium-bound phosphorus, and other fractions, and is used to analyze the sources of differences in phosphorus availability.

Detection Indicator	Main Question Answered	Applicable Scenario
Total phosphorus/total phosphate	Total amount of the soil phosphorus pool	Long-term fertilization, soil background values, phosphorus accumulation evaluation
Available phosphorus/rapidly available phosphorus	Short-term plant-available phosphorus level	Fertility evaluation, fertilization management, phosphorus supply assessment
Water-soluble phosphorus	Easily mobile and easily lost phosphorus level	Runoff risk and eutrophication risk evaluation
Inorganic phosphorus fractions	Phosphorus fixation and release mechanisms	Soil amendment, phosphorus fixation mechanisms, fraction transformation analysis
Organic phosphorus estimation	Potential size of the organic phosphorus pool	Organic fertilizer, straw return, soil phosphorus transformation research

1.2 Necessity of Multi-Indicator Combined Detection

A single phosphorus indicator is insufficient to fully reflect soil phosphorus status. High total phosphorus with low available phosphorus usually suggests that soil phosphorus reserves are sufficient but availability is limited. Simultaneous increases in available phosphorus and water-soluble phosphorus may indicate enhanced short-term phosphorus supply capacity along with potential environmental mobility risk. When both total phosphorus and available phosphorus are low, the result more likely reflects an insufficient soil phosphorus pool. By jointly analyzing total phosphorus, available phosphorus, and phosphorus fractions, different issues such as insufficient phosphorus reserves, enhanced fixation, and excessive accumulation can be distinguished.

2 Soil Total Phosphorus and Total Phosphate Detection

2.1 Basic Principle of Total Phosphorus Detection

Soil total phosphorus detection usually requires acid digestion, alkaline fusion, or other complete decomposition methods to convert different forms of phosphorus in soil into measurable orthophosphate, followed by quantification using molybdenum blue colorimetry or instrumental analysis. Therefore, “soil total phosphorus/total phosphate content detection” can be used together in experimental descriptions. However, the pretreatment logic should be clearly stated in the method description: the detection signal usually comes from orthophosphate released after digestion, rather than direct measurement of all original phosphorus forms in soil.

2.2 Digestion-Molybdenum Blue Colorimetric Method

The digestion-molybdenum blue colorimetric method is widely used in soil total phosphorus detection. After acid digestion or other decomposition treatment, orthophosphate reacts with molybdate to form phosphomolybdic heteropoly acid, which is then reduced to form a blue complex. Phosphorus content is calculated based on absorbance.

This method is suitable for batch sample detection and has the advantages of relatively low cost and a mature operating system. Key experimental factors include digestion completeness, stability of reagent blanks, color development time control, the linear range of the standard curve, and correction for sample matrix interference. For soil samples rich in iron oxides, organic matter, or fine mineral particles, attention should be paid to the clarity of the digest, background absorbance, and spike recovery.

2.3 Alkaline Fusion and Instrumental Methods

For soil samples with a high proportion of poorly soluble mineral phosphorus or stable mineral structures, alkaline fusion can be used to improve sample decomposition. Alkaline fusion has strong release capacity, but the procedure is more complex, and reagent blanks and salt matrices may affect subsequent detection. Instrumental methods such as ICP-OES and ICP-MS are suitable for multi-element analysis and can simultaneously detect P, Fe, Al, Ca, and other elements, helping to analyze the relationship between phosphorus fixation and soil mineral composition.

Method	Applicable Samples	Advantages	Limitations
Acid digestion-molybdenum blue colorimetry	Routine agricultural soils and ecological soils	Low cost and suitable for batch detection	Depends on digestion completeness and color development stability
Alkaline fusion-colorimetry	Soils with a high proportion of poorly soluble mineral phosphorus	Strong decomposition capacity	Complex operation, with higher blank and salt interference
Digestion-ICP-OES	Samples requiring multi-element combined detection	Can simultaneously detect P, Fe, Al, Ca, and other elements	Higher instrument requirements and higher cost
Digestion-ICP-MS	Low-content or refined multi-element analysis	High sensitivity	High requirements for matrix interference control and method development

3 Soil Available Phosphorus Detection

3.1 Experimental Significance of Available Phosphorus

Available phosphorus reflects phosphorus fractions in soil that are readily absorbed by plants or can be transformed for use in the short term. It is a commonly used indicator in soil fertility evaluation and fertilization management. Available phosphorus does not represent all releasable phosphorus in soil, but rather the active phosphorus fraction obtained under a specific extraction system. Therefore, it is strongly method-dependent.

Available phosphorus results must be interpreted together with soil type. Acidic soils, calcareous soils, and neutral soils differ in phosphorus fixation mechanisms, and the extraction reagents used are also different. Available phosphorus values obtained by different methods should not be directly compared horizontally.

3.2 Available Phosphorus Detection in Acidic and Neutral/Alkaline Soils

In acidic soils, phosphorus often undergoes adsorption, precipitation, or complexation with iron and aluminum oxides or hydroxides. Therefore, rapidly available phosphorus detection should focus on Fe/Al-bound active phosphorus fractions. In neutral to alkaline soils, calcium-bound phosphorus and carbonate systems have a more pronounced effect on phosphorus availability. The method for rapidly available phosphorus detection should match soil pH and the regional fertility evaluation system.

Soil Type	Main Limiting Factor	Detection Focus	Interpretation Point
Acidic soil	Fe/Al fixation and acidic adsorption sites	Rapidly available phosphorus in acidic soil	Should be interpreted together with pH, Fe/Al background, and fertilization history
Neutral soil	Adsorbed phosphorus and active inorganic phosphorus	Rapidly available phosphorus in neutral soil	Suitable for evaluating short-term phosphorus supply capacity
Alkaline soil	Ca-P formation and carbonate effects	Rapidly available phosphorus in alkaline soil	Calcium-bound phosphorus and pH effects should be considered
Recently fertilized soil	Short-term increase in water-soluble phosphorus	Rapidly available phosphorus + water-soluble phosphorus	Sampling time and fertilization interval should be controlled

3.3 Interpretation of Available Phosphorus Results

Low available phosphorus may indicate insufficient soil phosphorus supply capacity, but it may also be related to poor compatibility of the extraction method. High available phosphorus usually indicates strong short-term phosphorus supply capacity, but long-term high available phosphorus may increase the risk of phosphorus runoff loss and water eutrophication. In agricultural applications, soil pH, organic matter, crop phosphorus uptake, fertilization history, and regional soil fertility grading standards should be considered for comprehensive interpretation.

4 Soil Inorganic Phosphorus Fraction Analysis

4.1 Significance of Inorganic Phosphorus Fraction Analysis

Soil inorganic phosphorus consists of multiple fractions with markedly different activities. Water-soluble phosphorus and weakly adsorbed phosphorus are highly active but usually present at low levels. Iron/aluminum-bound phosphorus is more common in acidic soils; calcium-bound phosphorus is more prominent in calcareous soils; occluded phosphorus and residual phosphorus are slowly released and have low short-term plant availability.

Inorganic phosphorus fraction analysis is suitable for explaining why “total phosphorus is not low but available phosphorus is insufficient.” It can also be used to evaluate the effects of fertilization systems, soil amendments, straw return, biochar application, or long-term cultivation on phosphorus fixation and release.

4.2 Common Inorganic Phosphorus Fractions

Inorganic Phosphorus Fraction	Activity Characteristics	Common Soil Background	Research Significance
Water-soluble phosphorus	Highest activity and easily mobile	Short-term increase after fertilization	Phosphorus supply capacity and environmental loss risk
Weakly adsorbed phosphorus	Relatively easy to desorb	Rhizosphere and soils rich in active surfaces	Short-term source of available phosphorus
Al-P	Moderate activity	Common in acidic soils	Related to aluminum oxides and acidic fixation
Fe-P	Moderate to relatively low activity	Soils rich in iron oxides	Strongly affected by redox conditions
Ca-P	Variable activity	Common in calcareous soils	Affected by pH, organic acids, and carbonate systems
Occluded phosphorus/residual phosphorus	Low activity and slow release	Weathered minerals or strongly fixed soils	Represents long-term stable phosphorus pools

4.3 Sequential Extraction Method

Sequential extraction methods use different extractants to release phosphorus fractions with different activities in sequence and are used to distinguish different binding forms. Common fractionation frameworks include resin phosphorus, bicarbonate-extractable phosphorus, sodium hydroxide-extractable phosphorus, hydrochloric acid-extractable phosphorus, and residual phosphorus.

Sequential extraction results are operationally defined fractions and are not equivalent to absolute chemical species. Different methods, extraction sequences, soil properties, and completeness of residue transfer can all affect the results. Therefore, the same study should maintain a consistent method system and avoid directly comparing data obtained from different fractionation methods.

5 Soil Organic Phosphorus and Total Phosphorus Difference Analysis

5.1 Position of Organic Phosphorus in the Soil Phosphorus Pool

Organic phosphorus includes phytate compounds, phospholipids, nucleic acids, and other organic phosphate esters, and is an important component of the potential soil phosphorus pool. Its plant availability is usually lower than that of active inorganic phosphorus. It must first be transformed into inorganic phosphorus through microbial mineralization or rhizosphere processes before entering the available phosphorus pool.

5.2 Estimation Methods for Organic Phosphorus

In routine research, organic phosphorus can be estimated using the difference between total phosphorus and inorganic phosphorus, or it can be characterized in greater detail using more complex chemical fractionation or nuclear magnetic resonance methods. The difference method is relatively simple and suitable for trend comparison, but its error is affected by both total phosphorus and inorganic phosphorus detection errors. Therefore, it should not be used to overinterpret specific organic phosphorus structures.

Analysis Method	Applicable Scenario	Advantages	Limitations
Total phosphorus minus inorganic phosphorus	Routine organic phosphorus estimation	Relatively simple operation	Error accumulation and inability to identify specific structures
Organic phosphorus fractionation	Organic fertilizer, straw return, ecological soil research	Can distinguish organic phosphorus fractions with different activities	Complex method and operationally defined results
Refined analysis such as NMR	Structural analysis of organic phosphorus	Provides more information	High cost and high requirements for samples and instruments

6 Sample Collection, Pretreatment, and Quality Control

6.1 Sampling Design

Soil phosphorus distribution has obvious spatial heterogeneity and is affected by fertilization position, root distribution, topography, soil depth, and long-term management practices. Farmland soils usually require multi-point composite sampling by plot or field. Rhizosphere studies should distinguish rhizosphere soil from non-rhizosphere soil. Profile studies should clearly define soil layer depth and sampling intervals.

6.2 Air-Drying, Grinding, and Sieving

Air-dried soil samples can usually be used for total phosphorus, available phosphorus, and most phosphorus fraction tests, but pretreatment conditions must be consistent. Plant residues, stones, and obvious impurities should be removed, and samples should be thoroughly mixed before grinding or sieving according to method requirements. Total phosphorus detection requires high sample homogeneity; insufficient grinding may affect digestion representativeness and result stability.

6.3 Dry Weight Correction

Different soil samples vary in moisture content, and detection results should be uniformly converted based on dry soil mass. For wet soils, rhizosphere soils, and long-term refrigerated soil samples, failure to correct for water content may cause bias in concentration results.

6.4 Blanks, Standard Curves, and Recovery

In colorimetric detection, reagent blanks, sample blanks, standard curves, and spike recovery are basic quality control requirements. Soil digests or extracts may contain color, turbidity, or salt interference. When necessary, sample blank correction or matrix-matched standards should be used.

Control Step	Common Problem	Key Handling Point
Sampling	Insufficient sampling points and poor representativeness	Use multi-point composite sampling and record soil layer and field information
Air-drying	High-temperature treatment changes fractions	Air-dry at room temperature and avoid external contamination
Grinding	Sample is not homogeneous	Total phosphorus samples should be fully ground and mixed
Digestion	Incomplete decomposition	Set digestion blanks, reference materials, or spike recovery
Extraction	Inconsistent soil-to-solution ratio and extraction time	Standardize shaking time, temperature, and filtration conditions
Colorimetry	Unstable color development or out-of-range absorbance	Control color development time and keep samples within the standard curve range
Data conversion	Moisture content is ignored	Report results uniformly based on dry soil mass

7 Result Interpretation and Combined Analysis

7.1 High Total Phosphorus and Low Available Phosphorus

This result suggests that the soil phosphorus pool is large, but short-term availability is limited. Common causes include fixation by iron/aluminum oxides, calcium fixation, insufficient organic phosphorus mineralization, or unsuitable soil pH. Subsequent testing of inorganic phosphorus fractions, pH, organic matter, and water-soluble phosphorus can further identify the limiting step.

7.2 Low Total Phosphorus and Low Available Phosphorus

This result usually suggests an insufficient soil phosphorus pool and weak short-term phosphorus supply capacity. If it is accompanied by low crop phosphorus uptake, yield limitation, or poor root development, fertilization history and crop demand can be combined to evaluate phosphorus supplementation measures.

7.3 High Total Phosphorus and High Available Phosphorus

Long-term heavy application of phosphate fertilizer, livestock and poultry manure, or sludge return may cause both total phosphorus and available phosphorus to increase. For such soils, phosphorus accumulation and environmental mobility risk should be emphasized. Water-soluble phosphorus, soil phosphorus saturation, or runoff risk evaluation is recommended.

7.4 Low Available Phosphorus but Non-Low Water-Soluble Phosphorus

This situation may be related to recent fertilization, localized phosphorus input, or insufficient sample mixing. Sampling time, fertilization interval, soil moisture status, and composite sample homogeneity should be checked to avoid misinterpreting short-term fluctuations as stable phosphorus supply capacity.

Result Combination	Possible Explanation	Recommended Follow-Up Analysis
High total phosphorus, low available phosphorus	Strong phosphorus fixation or poorly available forms	Analyze Fe/Al/Ca-bound phosphorus
Low total phosphorus, low available phosphorus	Insufficient phosphorus pool	Judge phosphorus supplementation needs together with fertilization history and crop phosphorus uptake
High total phosphorus, high available phosphorus	Long-term phosphorus accumulation	Add water-soluble phosphorus and environmental risk evaluation
Normal total phosphorus, low available phosphorus	pH or mineral fixation limits release	Detect pH, organic matter, and inorganic phosphorus fractions
High available phosphorus, high water-soluble phosphorus	Strong phosphorus supply capacity but high mobility risk	Focus on runoff, leaching, and phosphorus saturation
High inorganic phosphorus, low organic phosphorus	Phosphorus mainly exists in mineral or adsorbed forms	Determine Fe/Al/Ca fixation type
High organic phosphorus, low available phosphorus	Large organic phosphorus pool but insufficient release	Further study mineralization processes and rhizosphere effects

8 Common Misinterpretations in Soil Phosphorus Content Detection

8.1 Equating Total Phosphorus with Available Phosphorus

Total phosphorus represents the size of the phosphorus pool, not the phosphorus that plants can directly absorb. High total phosphorus with low available phosphorus is common in strongly fixed acidic soils and calcareous soils with calcium fixation.

8.2 Ignoring the Effect of Soil Type on Available Phosphorus Methods

Available phosphorus is a method-dependent indicator. Different soil pH levels and mineral compositions affect extraction efficiency. Acidic soils and calcareous soils should not be interpreted using the same logic.

8.3 Treating Inorganic Phosphorus Fractionation Results as Absolute Chemical Species

Sequential extraction yields operationally defined fractions rather than completely pure single chemical forms. Fractionation results are more suitable for trend comparison and fixation mechanism analysis, and should not be overinterpreted as absolute species contents.

8.4 Ignoring Time Effects After Fertilization

Within a short time after fertilization, water-soluble phosphorus and available phosphorus may increase rapidly and then undergo adsorption, precipitation, or transformation. If sampling times are not standardized, differences among treatments may mainly reflect fertilization timing effects rather than stable soil phosphorus supply capacity.

Common Misinterpretation	Problem	More Reasonable Approach
High total phosphorus = sufficient phosphorus supply	Total phosphorus includes a large amount of poorly available phosphorus	Detect available phosphorus and phosphorus fractions together
Low available phosphorus = definite phosphorus deficiency	The method may not be suitable for the soil type	Select the extraction method according to pH and regional standards
Low water-soluble phosphorus = no environmental risk	Mobility risk may change shortly after rainfall or fertilization	Analyze together with sampling time and runoff conditions
Fractionated phosphorus = true single species	Sequential extraction is operationally defined	Focus on relative changes and mechanistic interpretation
No blanks or recovery tests	Colorimetric methods are easily affected by the matrix	Set reagent blanks, sample blanks, and spike recovery
No dry weight correction	Moisture content affects concentration conversion	Report results uniformly based on dry soil mass

9 Product Selection Related to Soil Phosphorus Content and Fraction Detection

9.1 Reagent Kits for Soil Total Phosphorus, Available Phosphorus, and Phosphate Detection

Cat. No.	Product Name	Grade & Purity	Application Module	Application Positioning
S1521777	Soil Total Phosphorus, Organic Phosphorus and Inorganic Phosphorus Content Assay Kit (Micro Method)	BioReagent	Combined detection of total phosphorus/organic phosphorus/inorganic phosphorus	Used for joint evaluation of the total soil phosphorus pool and different phosphorus fractions; suitable for small-sample or micro-assay systems
S1521776	Soil Total Phosphorus, Organic Phosphorus and Inorganic Phosphorus Content Assay Kit (Colorimetric Method)	BioReagent	Combined detection of total phosphorus/organic phosphorus/inorganic phosphorus	Used for routine colorimetric analysis of soil total phosphorus, organic phosphorus, and inorganic phosphorus
S1522127	Soil Total Phosphate Assay Kit (Micro Method)	BioReagent	Soil total phosphate detection	Used for determining total phosphate content in soil samples; suitable for the core main table of the article
T1522125	Total Phosphate in Water and Soil Assay Kit (Micro Method)	BioReagent	Total phosphate detection in water and soil	Used for micro-detection of total phosphate in water and soil samples; suitable for soil-water migration evaluation
T1522126	Total Phosphate in Water and Soil Assay Kit (Colorimetric Method)	BioReagent	Total phosphate detection in water and soil	Used for routine colorimetric detection of total phosphate in water and soil samples
S1506787	Soil Inorganic Phosphate (S-PHOS) Content Assay Kit (MB, Micro Method)	BioReagent	Soil inorganic phosphorus detection	Used for determining soil inorganic phosphorus content and supporting phosphorus fraction or availability analysis
A1515853	Acid Soil Available Phosphorous Assay Kit (Micro Method)	BioReagent	Available phosphorus detection in acidic soil	Used for determining rapidly available phosphorus in acidic soils; suitable for evaluating phosphorus supply capacity in acidic soils
A1515974	Acid Soil Available Phosphorus Assay Kit (Colorimetric Method)	BioReagent	Available phosphorus detection in acidic soil	Used for routine colorimetric detection of rapidly available phosphorus in acidic soils
N1515854	Neutral/Alkaline Soil Available Phosphorous Assay Kit (Micro Method)	BioReagent	Available phosphorus detection in neutral/alkaline soil	Used for determining rapidly available phosphorus in neutral and alkaline soils; suitable for Olsen-type phosphorus supply evaluation
N1515976	Neutral/Alkaline Soil Available Phosphorus Assay Kit (Colorimetric Method)	BioReagent	Available phosphorus detection in neutral/alkaline soil	Used for routine colorimetric analysis of rapidly available phosphorus in neutral and alkaline soils
I1506776	Inorganic phosphorus content detection kit (ferrous molybdenum blue sulfate, colorimetric method)	BioReagent	Inorganic phosphorus detection	Used for colorimetric detection of inorganic phosphorus in sample extracts or digests; can support soil phosphorus fraction analysis
I1506789	Inorganic Phosphate Content Assay Kit (MMB, Colorimetric Method)	BioReagent	Inorganic phosphorus detection	Used for colorimetric detection of inorganic phosphorus; suitable for comparison of phosphate quantification methods
I1510382	Inorganic Phosphate Content Assay Kit (UV Micro Method)	BioReagent	Inorganic phosphorus detection	Used for inorganic phosphorus detection in micro-assay systems and can be combined with soil extract analysis
I1510435	Inorganic Phosphate Content Assay Kit (UV Colorimetric Method)	BioReagent	Inorganic phosphorus detection	Used for routine UV colorimetric detection of inorganic phosphorus
P1506503	Malachite Green Phosphate Detection Kit	BioReagent, sterile	Phosphate detection	Used for phosphate content detection; suitable for soil extracts, digests, or water-soil migration samples
P1506504	Phosphate Assay Kit (Phosphomolybdic Acid Method)	BioReagent, sterile	Phosphate detection	Used for colorimetric phosphate detection and can support total phosphate or available phosphorus detection
P117898	Water quality total phosphorus standard	Analytical standard, 1.000-2.000 mg/L in water (after dilution)	Total phosphorus quality control	Can be used as a method calibration and quality control reference in water-soil total phosphate detection

9.2 Phosphorus, Phosphate Ion, and Phosphate Standards/Quality Control Products

Cat. No.	Product Name	Grade & Purity	Application Module	Application Positioning
P742303	Phosphorus solution	100 μg/mL (as P)	Phosphorus standard curve	Used for low-concentration phosphorus standard curves or quality control
P118421	Dihydrogen Phosphate in Water	1000 mg/L, matrix: water	Dihydrogen phosphate standard	Used for calibration of dihydrogen phosphate-related detection
P299482	Standard Reference Material for Dihydrogen Phosphate Composition Analysis in Water	1000 μg/mL ±1% (20℃)	Dihydrogen phosphate standard	Used for aqueous dihydrogen phosphate standard curves or method validation
P117459	Phosphate standard	1000 μg/mL in water (20℃)	Phosphate standard	Used for phosphate detection standard curves and quality control
P299417	Phosphate standard	500 μg/mL in water (20℃)	Phosphate standard	Used for quantitative calibration of medium-concentration phosphate ions
P299416	Phosphate standard	100 μg/mL in water (20℃)	Phosphate standard	Used for calibration of low-concentration phosphate ion detection
P742321	Phosphate standard	100 μg/mL	Phosphate standard	Used for standard curves in phosphate colorimetric methods
A299233	Phosphate anion standard solution	1 mg/mL (1,000 ppm)	Phosphate standard	Used for calibration of phosphate anion detection
A299232	Phosphate anion standard solution	0.1 mg/mL (100 ppm)	Phosphate standard	Used for calibration of low-concentration phosphate anion detection

9.3 Auxiliary Products for Mechanistic Interpretation and Result Analysis

Cat. No.	Product Name	Grade & Purity	Application Module	Application Positioning
S1515788	Soil Total Iron Content Assay Kit (o-Phenanthroline, Micro Method)	BioReagent	Fe-P interpretation auxiliary indicator	Used to assist in analyzing the background of iron-bound phosphorus fixation; suitable for mechanistic interpretation in acidic or iron-rich soils
S1515912	Soil Total Iron Content Assay Kit (Phenanthroline, Colorimetric Method)	BioReagent	Fe-P interpretation auxiliary indicator	Used for routine colorimetric detection of soil total iron and assisting in interpreting the possibility of Fe-P formation
S1522275	Soil Organic Matter (SOM) Content Assay Kit (Micro Method)	BioReagent	Organic matter auxiliary indicator	Used to interpret phosphorus adsorption, complexation, organic phosphorus pools, and available phosphorus changes
S1522276	Soil Organic Carbon (SOC) Content Assay Kit (Micro Method)	BioReagent	Organic carbon auxiliary indicator	Used to assist in analyzing soil organic matter background and the transformation environment of phosphorus fractions

The core of soil phosphorus content detection is to distinguish total phosphorus pool size, short-term phosphorus supply capacity, and phosphorus fixation forms. Total phosphorus is used to evaluate soil phosphorus reserves, available phosphorus is used to assess plant availability, and inorganic phosphorus fractions are used to explain phosphorus fixation and release mechanisms.

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