Detection Principles, Method Comparison, and Quality Control of Soil Physicochemical Properties and Nutrient Indicators
Detection Principles, Method Comparison, and Quality Control of Soil Physicochemical Properties and Nutrient Indicators
Soil testing should distinguish among the physical environment, chemical environment, nutrient reserves, available nutrients, and nutrient transformation processes. Different indicators have different measurement targets and scopes of application, and the results must be interpreted together with sampling conditions, soil type, and analytical method.
Keywords: soil testing; water content; bulk density; soil texture; soil pH; electrical conductivity; soil organic carbon; total nutrients; available nutrients; cation exchange capacity; quality control
1 Soil Sample Collection, Storage, and Pretreatment
1.1 Sampling Units and Sampling Depth
Sampling units should be divided according to topography, soil type, crop, fertilization, and irrigation practices. Composite samples are used to evaluate the average condition of a relatively uniform field, whereas single-point or grid samples are used to analyze spatial variation. Long-term monitoring requires fixed sampling locations, depths, and seasons. Results for organic carbon, available phosphorus, nitrate nitrogen, and salinity from different soil layers cannot be directly compared.
1.2 Sample Classification and Storage
Undisturbed soil should be used for bulk density measurement. Fresh soil should be used for ammonium nitrogen, nitrate nitrogen, and enzyme activity assays and should be stored at low temperature for a short period. Air-dried soil can be used for pH, electrical conductivity, total nutrients, and most available nutrient measurements. Air drying, freezing, and long-term storage may alter inorganic nitrogen, soluble nutrients, and enzyme activity. The sample condition must therefore be stated in the report.
1.3 Sieving, Grinding, and Moisture Correction
Soil passed through a 2 mm sieve is generally used for measurements of pH, electrical conductivity, available nutrients, and exchangeable ions. Total carbon, total nitrogen, and total element measurements require further grinding. When fresh or air-dried soil is used, water content should be measured simultaneously, and results should be converted to an oven-dry soil mass basis. Micro methods use smaller sample masses and therefore require more rigorous homogenization and subsampling.
1.4 Sampling Error and Analytical Error
Field replicates reflect spatial variation in soil, whereas laboratory replicates reflect the repeatability of weighing, extraction, and detection. Consistent laboratory results do not demonstrate that the sample is representative of the field. In soil testing, errors caused by sampling and sample preparation are often greater than errors in instrumental readings.
2 Measurement of Soil Water Content, Bulk Density, and Texture
2.1 Water Content and Its Analytical Significance
Soil water content is generally measured using the oven-drying gravimetric method. Water content not only reflects soil moisture status but also provides the basis for converting fresh-soil test results to a dry-mass basis. Without moisture correction, apparent differences in nutrient concentrations among samples may simply result from differences in water content.
2.2 Bulk Density, Porosity, and Soil Compaction
Bulk density is generally measured using the core method and can be used to evaluate soil compaction, aeration, and root-growth conditions. Total porosity can be calculated from bulk density and particle density. However, a uniform particle density of 2.65 g/cm³ should not be assumed for soils with high organic matter contents or unusual mineral compositions.
2.3 Calculation of Bulk Density and Nutrient Stocks
Results for organic carbon, total nitrogen, and similar indicators expressed in g/kg represent mass concentrations. Calculation of stocks per unit area also requires bulk density, soil-layer thickness, and the proportion of coarse fragments. Comparing concentrations alone may lead to incorrect conclusions regarding changes in soil carbon stocks or nutrient reserves.
2.4 Soil Texture and Nutrient Transport
Sandy soils drain rapidly and generally have a relatively low cation exchange capacity. Nitrate nitrogen, potassium, calcium, and magnesium are therefore prone to leaching. Clay soils retain water and nutrients more effectively but may increase phosphorus adsorption and potassium fixation. At the same available nutrient concentration, the duration of nutrient supply and the risk of leaching differ among soils with different textures.
2.5 Differences Among Soil Texture Measurement Methods
The pipette and hydrometer methods classify particles according to settling velocity, whereas laser diffraction calculates equivalent particle diameter from light scattering. These methods differ in their treatment of particle shape, dispersion status, and particle-size boundaries, and their results cannot be directly substituted for one another.
3 Measurement of Soil pH, Electrical Conductivity, and Salinity
3.1 pH and Soil Buffering Capacity
pH reflects the current acid-base condition of soil but does not represent buffering capacity. Soils with the same pH may have different acidification risks and amendment requirements because of differences in clay content, organic matter, exchangeable acidity, and carbonate content.
3.2 pH Measurement Conditions
Water-extractable pH is readily affected by soluble salts. Extraction with KCl or CaCl₂ stabilizes ionic strength and displaces some exchangeable hydrogen and aluminum. Results obtained using different extractants, soil-to-solution ratios, and equilibration times should not be interpreted using the same evaluation criteria.
3.3 pH and Nutrient Availability
In acidic soils, the solubility of aluminum and manganese increases, and phosphorus is readily fixed by iron and aluminum oxides. In calcareous soils, phosphorus may form sparingly soluble calcium compounds, whereas the availability of iron, manganese, and zinc generally decreases. Results for available phosphorus, available boron, and micronutrients should therefore be interpreted together with pH.
3.4 Electrical Conductivity and Soil Salinity
Electrical conductivity reflects the combined concentration of all soluble ions in the extract and cannot identify specific salts. High electrical conductivity may result from salt accumulation or recent fertilization. Electrical conductivity measured in an extract at a fixed soil-to-water ratio is suitable for comparison among samples, whereas electrical conductivity of the saturation-paste extract is more appropriate for salinity evaluation. The two cannot be directly converted.
3.5 Salinization and Sodification
Salinization is mainly caused by the accumulation of soluble salts, whereas sodification is mainly associated with an increased proportion of exchangeable sodium. High exchangeable sodium can cause clay dispersion, reduced infiltration, and soil crusting. Evaluation of saline-sodic soils should incorporate pH, electrical conductivity, sodium adsorption ratio, exchangeable sodium percentage, and soil structure.
4 Measurement of Soil Organic Matter, Organic Carbon, and Total Carbon
4.1 Differences Among Indicators
Soil organic matter contains multiple organic components, with organic carbon serving as its principal quantitative indicator. Total carbon includes both organic and inorganic carbon. In carbonate-containing soils, total carbon cannot be directly regarded as organic carbon.
4.2 Potassium Dichromate Oxidation Method
The potassium dichromate oxidation method is suitable for routine batch measurement of soil organic carbon. However, some charred carbon and mineral-protected organic carbon may not be completely oxidized, and chloride ions and other reducing substances may interfere. When correction factors are used, their applicability to the method and soil type should be confirmed.
4.3 Dry Combustion Method
The dry combustion method provides a relatively complete measurement of total carbon and offers high precision and automation. In calcareous soils, inorganic carbon must be measured separately, or carbonates must be removed before organic carbon measurement. Otherwise, soil organic carbon will be overestimated.
4.4 Loss-on-Ignition Method
The loss-on-ignition method estimates organic matter from the mass difference before and after ignition. However, release of structural water, dehydroxylation of clay minerals, and decomposition of carbonates can all cause positive bias. This method is suitable for rapid assessment after regional calibration but should not directly replace organic carbon measurement.
4.5 Conversion of Organic Matter and Carbon Stock Calculation
Multiplying organic carbon by 1.724 to estimate organic matter is based on the assumption that organic matter contains an average of 58% carbon, which is not applicable to all soils. Evaluation of soil carbon stocks also requires organic carbon concentration, bulk density, soil-layer thickness, and the proportion of coarse fragments.
5 Measurement of Soil Total Nitrogen, Total Phosphorus, and Total Potassium
5.1 Interpretive Limits of Total Nutrients
Total nitrogen, total phosphorus, and total potassium reflect soil nutrient reserves but do not represent the amounts available to crops during the current growing season. Total nutrient indicators are suitable for evaluating parent-material background and long-term accumulation, whereas available nutrient indicators are more appropriate for assessing short-term nutrient supply.
5.2 Soil Total Nitrogen
The Kjeldahl method measures most organic nitrogen and ammonium nitrogen but does not completely include nitrate and nitrite under traditional conditions. Dry combustion covers a broader range of nitrogen forms but requires rigorous sample homogenization and instrument calibration.
5.3 Soil Carbon-to-Nitrogen Ratio
The carbon-to-nitrogen ratio can assist in evaluating organic matter decomposition and nitrogen mineralization trends. When readily decomposable organic matter has a high carbon-to-nitrogen ratio, microorganisms may immobilize inorganic nitrogen. At a lower carbon-to-nitrogen ratio, net nitrogen mineralization is more likely. Actual results are also affected by organic matter degradability, temperature, and moisture.
5.4 Soil Phosphorus Pools
Total phosphorus reflects the total reserve, whereas organic and inorganic phosphorus reflect the composition of the phosphorus pool. Available phosphorus reflects the short-term phosphorus-supply potential under specified extraction conditions. High total phosphorus combined with low available phosphorus may result from fixation by iron and aluminum, precipitation as calcium phosphates, or insufficient mineralization of organic phosphorus.
5.5 Soil Potassium Pools
Soil potassium includes water-soluble potassium, exchangeable potassium, fixed potassium, and mineral-lattice potassium. Available potassium mainly includes water-soluble and exchangeable fractions. High total potassium does not necessarily indicate adequate current potassium supply.
5.6 Other Total Elements
Total boron and total iron mainly reflect soil element reserves and do not directly indicate plant availability. Even when total iron is high, alkaline soils may cause iron deficiency in plants because of low iron solubility.
5.7 Complete and Partial Digestion
Measurement of total elements requires sufficient decomposition of mineral structures. If the digestion system cannot completely break down silicate minerals, the result should be described as acid-soluble or digestible content rather than total content.
6 Measurement of Soil Ammonium Nitrogen, Nitrate Nitrogen, and Available Nutrients
6.1 Ammonium Nitrogen and Nitrate Nitrogen
Ammonium nitrogen can be adsorbed by soil colloids and therefore has relatively low mobility. Nitrate nitrogen is not strongly adsorbed by most soils and is readily leached. Both are affected by mineralization, nitrification, denitrification, plant uptake, and microbial immobilization. Field-moist soil should therefore be extracted as soon as possible after collection; when immediate processing is not possible, samples should be stored at low temperature for a short period.
6.2 Temporal Characteristics of Inorganic Nitrogen Results
Fertilization, rainfall, irrigation, and temperature changes can rapidly alter ammonium and nitrate nitrogen contents. A single measurement reflects only the condition at the time of sampling and cannot represent nitrogen-supply capacity throughout the entire growing season.
6.3 Available Nitrogen
Available nitrogen measured by diffusion or specific extraction methods generally includes part of the inorganic nitrogen and readily hydrolyzable organic nitrogen. Available nitrogen cannot simply be equated with the sum of ammonium and nitrate nitrogen. Results should be interpreted using regional classification criteria appropriate for the analytical method.
6.4 Available Phosphorus in Acidic Soils
Phosphorus in acidic soils is mainly controlled by adsorption and precipitation involving iron and aluminum oxides. An extraction system suitable for acidic soils should therefore be used. Extraction conditions that are too weak may underestimate phosphorus-supply potential, whereas overly strong extraction may dissolve phosphorus that is not readily available to plants in the short term.
6.5 Available Phosphorus in Neutral and Alkaline Soils
Neutral, alkaline, and calcareous soils commonly use bicarbonate-based extraction systems for available phosphorus. Strongly acidic extractants may dissolve some poorly available calcium phosphates and overestimate available phosphorus. Available phosphorus results from acidic soils and those from neutral or alkaline soils cannot be directly compared.
6.6 Soil Available Potassium
Available potassium mainly includes water-soluble and exchangeable potassium. Potassium is readily leached in sandy soils, whereas some clay minerals can fix potassium. Results should be interpreted together with texture, CEC, and crop potassium uptake.
6.7 Available Sulfur, Silicon, and Boron
Available sulfur mainly reflects extractable sulfate, although mineralization of organic sulfur may continue to supply sulfur during the growing season. Available silicon is useful for evaluating silicon supply to crops such as rice. Available boron is affected by pH, organic matter, and water content, and drought may restrict boron transport toward the rhizosphere.
6.8 Soil Enzyme Activities
(1) Enzymes Related to Nitrogen Cycling
N-Acetyl-β-D-glucosaminidase reflects the potential degradation of nitrogen-containing organic matter, urease reflects the potential for urea hydrolysis, and nitrate reductase and nitrite reductase reflect the potential for nitrate and nitrite reduction.
(2) Enzymes Related to Phosphorus Cycling
Acid, neutral, and alkaline phosphatases reflect the potential hydrolysis of organic phosphorus. Increased enzyme activity may indicate enhanced organic phosphorus mineralization or a phosphorus-deficiency response by plants and microorganisms.
(3) Enzymes Related to Sulfur Cycling
Arylsulfatase reflects the potential hydrolysis of organic sulfate esters. Its activity is affected by organic matter, pH, temperature, and microbial biomass and cannot replace measurement of available sulfur.
6.9 Differences Between Available Nutrients and Enzyme Activities
Available nutrient contents indicate how much extractable nutrient is present at the time of sampling, whereas enzyme activities reflect potential reaction rates under defined conditions. High urease activity does not necessarily indicate a high ammonium nitrogen content, and high phosphatase activity does not necessarily indicate sufficient available phosphorus.
7 Measurement of Soil Cation Exchange Capacity and Exchangeable Ions
7.1 Cation Exchange Capacity
Cation exchange capacity (CEC) represents the ability of soil colloids to retain cations. A high CEC indicates a large number of exchange sites but does not mean that those sites are necessarily occupied by beneficial ions such as calcium, magnesium, and potassium.
7.2 Potential and Effective CEC
CEC measured under buffered pH conditions includes some variable-charge sites and represents potential exchange capacity. Effective CEC measured at the original soil pH is closer to the current soil condition. The difference between these values may be substantial in acidic soils.
7.3 Exchangeable Base Cations
Exchangeable calcium, magnesium, potassium, and sodium reflect the composition of exchange sites. Calcium and magnesium promote aggregate stability, potassium is an essential plant nutrient, and an excessive proportion of sodium may cause clay dispersion and structural degradation.
7.4 Exchangeable Acidity and Aluminum
Exchangeable hydrogen and aluminum are major sources of acidity in acidic soils. Exchangeable aluminum can inhibit root growth and reduce phosphorus availability. Lime requirements should be determined from pH, exchangeable acidity, and CEC rather than from pH alone.
7.5 CEC in Relation to Soil Texture and Organic Matter
Clay minerals and organic matter are the principal sources of CEC. Low-CEC sandy soils are prone to leaching of ammonium, potassium, calcium, and magnesium and are more suitable for split fertilizer applications. High-CEC soils retain nutrients more effectively, but nutrient fixation may also be more pronounced.
7.6 Major Interferences in CEC Measurement
The ammonium acetate method may be affected by ammonium fixation, soluble salts, carbonates, and gypsum. Suitable methods should be selected for highly saline soils or soils containing unusual minerals, and soluble ions should be distinguished from exchangeable ions.
8 Applicability and Comparison of Different Soil Testing Methods
8.1 Method Selection According to Analytical Purpose
Total measurements are used to evaluate nutrient reserves, available-form measurements are used to assess short-term nutrient-supply potential, and enzyme activity assays are used to evaluate potential transformation processes. Indicators from these categories cannot replace one another.
8.2 Method Selection According to Soil Type
Different extraction systems should be used for available phosphorus in acidic and calcareous soils. Carbonate-containing soils require differentiation between organic and inorganic carbon. Soluble salt interference must be excluded when exchangeable ions are measured in saline soils.
8.3 Micro Methods and Macro Colorimetric Methods
Micro methods use smaller amounts of samples and reagents but are more susceptible to sample heterogeneity and pipetting errors. Macro colorimetric methods use larger reaction volumes and consume more reagents. The reliability of both approaches depends on extraction conditions, the linear range, and quality control.
8.4 Colorimetric and Instrumental Methods
Colorimetric methods are suitable for routine batch testing, but humic substances, sample color, and turbidity may cause optical interference. Ion chromatography, flow analysis, ICP, and other instrumental methods may improve throughput or detection capability but cannot correct sampling errors, incomplete digestion, or inappropriate extraction methods.
8.5 Method Changes and Continuity of Results
There is generally no universal conversion factor between different analytical methods. When a method is changed during long-term monitoring, representative soils covering different textures, pH values, and concentration ranges should be tested in parallel to evaluate systematic bias.
Table 1 Classification and Interpretive Limits of Soil Indicators
Indicator Category | Representative Indicators | Main Evaluation Content | Interpretive Limits |
Physical foundation | Water content, bulk density, texture | Moisture, aeration, compaction, and transport conditions | Cannot independently represent soil fertility |
Chemical environment | pH, electrical conductivity, exchangeable acidity | Acidity, salinity, and chemical limitations | pH does not equal buffering capacity, and electrical conductivity does not identify specific salts |
Nutrient reserves | Organic carbon, total nitrogen, total phosphorus, total potassium | Total soil nutrient pools | High total content does not necessarily indicate high availability |
Current supply | Ammonium nitrogen, nitrate nitrogen, available phosphorus, available potassium | Current or short-term nutrient-supply potential | Results depend on sample preservation and extraction method |
Transformation processes | Urease, phosphatase, arylsulfatase | Potential nutrient transformation capacity | Cannot be used as nutrient content measurements |
Exchange retention | CEC and exchangeable ions | Nutrient-retention capacity and composition of exchange sites | High CEC does not indicate adequate beneficial ions |
9 Products for Soil Carbon, Nutrient Content, and Nutrient-Cycling Analysis
Table 2 Products for Soil Organic Carbon, Organic Matter, and Total Element Analysis
Catalog # | Product Name | Grade & Purity | Detection Indicator | Main Application |
Soil Organic Carbon (SOC) Content Assay Kit (Micro Method) | BioReagent | Soil organic carbon | Detection of soil organic carbon content | |
Soil Organic Matter (SOM) Content Assay Kit (Micro Method) | BioReagent | Soil organic matter | Detection of soil organic matter content | |
Soil Total Phosphorus, Organic Phosphorus and Inorganic Phosphorus Content Assay Kit (Micro Method) | BioReagent | Total phosphorus, organic phosphorus, and inorganic phosphorus | Analysis of soil phosphorus-pool composition | |
Soil Total Phosphorus, Organic Phosphorus and Inorganic Phosphorus Content Assay Kit (Colorimetric Method) | BioReagent | Total phosphorus, organic phosphorus, and inorganic phosphorus | Colorimetric analysis of soil phosphorus forms | |
Soil Total Phosphate Assay Kit (Micro Method) | BioReagent | Total phosphate | Detection of soil total phosphate | |
Soil Inorganic Phosphate (S-PHOS) Content Assay Kit (MB, Micro Method) | BioReagent | Inorganic phosphorus | Detection of soil inorganic phosphorus | |
Soil Total Boron Content Assay Kit (Micro Method) | BioReagent | Soil total boron | Detection of soil total boron | |
Soil Total Boron Content Assay Kit (Colorimetric Method) | BioReagent | Soil total boron | Colorimetric detection of soil total boron | |
Soil Total Iron Content Assay Kit (o-Phenanthroline, Micro Method) | BioReagent | Soil total iron | Detection of soil total iron | |
Soil Total Iron Content Assay Kit (Phenanthroline, Colorimetric Method) | BioReagent | Soil total iron | Colorimetric detection of soil total iron |
Table 3 Products for Soil Inorganic Nitrogen, Available Nutrients, and Available Element Analysis
Catalog # | Product Name | Grade & Purity | Detection Indicator | Main Application |
Soil Ammonium Nitrogen Content Assay Kit (IPB, Micro Method) | BioReagent | Ammonium nitrogen | Detection of soil ammonium nitrogen | |
Soil Nitrate Nitrogen Content Assay Kit (SA, Micro Method) | BioReagent | Nitrate nitrogen | Microscale detection of soil nitrate nitrogen | |
Soil Nitrate Nitrogen Content Assay Kit (SA, Colorimetric Method) | BioReagent | Nitrate nitrogen | Colorimetric detection of soil nitrate nitrogen | |
Soil Available Nitrogen Content Assay Kit (Diffusion Method) | BioReagent | Soil available nitrogen | Detection of soil available nitrogen | |
Neutral/Alkaline Soil Available Phosphorous Assay Kit (Micro Method) | BioReagent | Available phosphorus in neutral and alkaline soils | Detection of available phosphorus in neutral and alkaline soils | |
Neutral/Alkaline Soil Available Phosphorus Assay Kit (Colorimetric Method) | BioReagent | Available phosphorus in neutral and alkaline soils | Colorimetric detection of available phosphorus in neutral and alkaline soils | |
Acid Soil Available Phosphorous Assay Kit (Micro Method) | BioReagent | Available phosphorus in acidic soils | Detection of available phosphorus in acidic soils | |
Acid Soil Available Phosphorus Assay Kit (Colorimetric Method) | BioReagent | Available phosphorus in acidic soils | Colorimetric detection of available phosphorus in acidic soils | |
Soil Available Potassium Content Assay Kit (Micro Method) | BioReagent | Soil available potassium | Detection of soil available potassium | |
Soil Available Sulfur Content Assay Kit (Micro Method) | BioReagent | Soil available sulfur | Detection of soil available sulfur | |
Soil Available Silicon Content Assay Kit (Micro Method) | BioReagent | Soil available silicon | Microscale detection of soil available silicon | |
Soil Available Silicon Content Assay Kit (Colorimetric Method) | BioReagent | Soil available silicon | Colorimetric detection of soil available silicon | |
Soil Available Boron Content Assay Kit (Micro Method) | BioReagent | Soil available boron | Microscale detection of soil available boron | |
Soil Available Boron Content Assay Kit (Colorimetric Method) | BioReagent | Soil available boron | Colorimetric detection of soil available boron |
Table 4 Products for Auxiliary Evaluation of Soil Nitrogen, Phosphorus, and Sulfur Cycling
Catalog # | Product Name | Grade & Purity | Evaluation Stage | Main Application |
Soil N-Acetyl-β-D-glucosaminidase (S-NAG) Activity Assay Kit (Micro Method) | BioReagent | Organic nitrogen mineralization | NAG activity assay | |
Soil N-Acetyl-β-D-glucosaminidase (S-NAG) Activity Assay Kit (Colorimetric Method) | BioReagent | Organic nitrogen mineralization | Colorimetric NAG activity assay | |
Soil Nitrate Reductase (S-NR) Activity Assay Kit (Naphthylamine, Micro Method) | BioReagent | Nitrate reduction | Nitrate reductase activity assay | |
Soil Nitrite Reductase (S-NiR) Activity Assay Kit (NO₂⁻, Micro Method) | BioReagent | Nitrite reduction | Nitrite reductase activity assay | |
Soil Nitrite Reductase (S-NiR) Activity Assay Kit (NO₂⁻, Colorimetric Method) | BioReagent | Nitrite reduction | Colorimetric nitrite reductase activity assay | |
Soil Urease (S-UE) Activity Assay Kit (Micro Method) | BioReagent | Urea hydrolysis | Soil urease activity assay | |
Soil Urease (S-UE) Activity Assay Kit (Colorimetric Method) | BioReagent | Urea hydrolysis | Colorimetric soil urease activity assay | |
Soil Acid Phosphatase(S-ACP) Activity Assay Kit (DPP, Micro Method) | BioReagent | Hydrolysis of organic phosphorus under acidic conditions | Acid phosphatase activity assay | |
Soil Acid Phosphatase (S-ACP) Activity Assay Kit (DPP, Colorimetric Method) | BioReagent | Hydrolysis of organic phosphorus under acidic conditions | Colorimetric acid phosphatase activity assay | |
Soil Neutral Phosphatase(S-NP) Activity Assay Kit (DPP, Micro Method) | BioReagent | Hydrolysis of organic phosphorus under neutral conditions | Neutral phosphatase activity assay | |
Soil Neutral Phosphatase (S-NP) Activity Assay Kit (DPP, Colorimetric Method) | BioReagent | Hydrolysis of organic phosphorus under neutral conditions | Colorimetric neutral phosphatase activity assay | |
Soil Alkaline Phosphatase(S-AKP/ALP) Activity Assay Kit (DPP, Micro Method) | BioReagent | Hydrolysis of organic phosphorus under alkaline conditions | Alkaline phosphatase activity assay | |
Soil Alkaline Phosphatase (S-AKP/ALP) Activity Assay Kit (DPP, Colorimetric Method) | BioReagent | Hydrolysis of organic phosphorus under alkaline conditions | Colorimetric alkaline phosphatase activity assay | |
Soil Arylsulfatase (S-ASF) Activity Assay Kit (Micro Method) | BioReagent | Organic sulfur mineralization | Arylsulfatase activity assay | |
Soil Arylsulfatase (S-ASF) Activity Assay Kit (Colorimetric Method) | BioReagent | Organic sulfur mineralization | Colorimetric arylsulfatase activity assay |
Soil testing should classify indicators according to physical foundation, chemical environment, nutrient reserves, current nutrient supply, and transformation processes. Total indicators reflect nutrient reserves, available-form indicators reflect short-term supply potential, and enzyme activities reflect potential transformation processes. Results from these categories cannot be used interchangeably.
For more related articles, please see below:
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