Introduction
Understanding soil health is necessary for effective environmental management. Comprehensive soil analysis provides detailed insights into various factors that influence land use and productivity. A summary of these factors can be found in Table 1.
Additionally, soil analysis can detect the presence of contaminants such as heavy metals, pesticide residues, and other pollutants, helping to assess the safety and environmental integrity of a site.
Table 1. Components of soil tested for soil testing and analysis.
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Physical properties |
Chemical characteristics |
Biological indicators |
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Texture Structure Compaction |
pH Salinity Nutrient content |
Microbial activity Organic matter levels |
What is soil testing and soil fertility testing?
Agricultural soil testing provides information on the soil's chemical, physical, and biological properties. Knowledge of soil characteristics, especially in terms of its nutrients, allows for planned fertilizer programs that are accurate, efficient, and environmentally responsible.
Soil fertility refers to the soil's ability to sustain agricultural plant growth by providing plant habitat that results in sustained and consistent high-quality yields. It can also refer to the soil's ability to supply the correct plant and crop nutrients over a sustained period.
Fine retention for accurate soil filtration and sample preparation with Whatman™ Grade 42
Objectives and importance of soil testing
Soil testing is performed for various purposes:
- Assessing land capability for different forms of agriculture.
- Identifying and quantitating soil constraints.
- Monitoring soil fertility.
- Providing fertilizer guidelines to optimize plant/crop growth.
- Diagnosing reasons for poor performance.
Benefits of soil testing
In plant and crop production, soil testing analysis is needed to build nutrient management plans and develop cost-effective fertilizer programs. By understanding the nutrient availability of soil in each location, a farmer can use the appropriate type and amount of fertilizer to maximize crop production without unnecessary environmental effects or costs.
Types of soil analysis and soil testing
Basic soil analysis: Examines the main macronutrients, nitrogen (nitrate), phosphorous (phosphate), potassium, and magnesium. Along with pH, these provide an insight into some of the most important aspects of soil health in terms of crop production.
Full broad-spectrum analysis: Tests for additional macronutrients and a range of micronutrients. Chemical, physical, and biological analysis and investigations into the presence of heavy metals can also be useful.
NPK soil testing: Examines the three key fertilizer components, which are nitrogen (N), phosphorous (P) and potassium (K). The total or available N, P, and K directly impacts on a farmer's fertilizer requirements in each region, for a crop type, and yield.
Most soil sample testing is performed by central laboratories that have the capacity and capability to offer different packages of soil tests depending on requirements. Each laboratory uses soil testing methods that are applicable to the region. Table 2 summarizes common types of soil analysis performed in these central facilities.
Table 2. Types of soil analysis.
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Type of soil analysis |
Examples of soil tests |
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Nutrient analysis |
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Chemical and physical analysis |
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Biological analysis |
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Heavy and toxic metal analysis |
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Process of soil testing
A selection of soil testing methods are available for each element of interest depending on the properties of the geographical region of interest. Soil testing laboratories will choose an analytical method that meets a farmer's specific needs, adjusting for crop type, geography, any known crop responses, and target yield.
The Food and Agriculture Organization of the United Nations (FAO) published a guide to laboratory plant nutrient analysis, which includes a review of analytical methods available for different soil tests.
How to take soil samples for testing
Soil testing involves taking samples from cultivable areas (vegetable row crops), near trees (e.g., orchards), and plain areas (e.g., pasture). Samples are taken at a depth of 3 inches from fields and 8-12 inches near trees. Adequate samples are taken to represent an average of the area. Surface debris and stones are removed, and any large lumps are broken up. The samples are then dried in an oven at approximately 1000°C and ground. Fine ground samples are further processed in laboratories depending upon the nutrients to be tested.
Although filter papers are not directly associated with soil sampling, they play an important part in post processing of the samples collected. For post processing, Whatman qualitative filter paper Grade 40/41 can be used for gravimetric estimation. Similarly, Whatman glass microfiber grade GF/B or GF/C can be used for testing total solids, total suspended solids and total dissolved solids. For trace metals analysis and macro- and micronutrient analysis using high end instruments like ICP-MS, our syringe filters can be used for sample preparation.
How to read a soil test
Working with soil and agricultural experts helps farmers achieve maximum crop output. By understanding the soil testing reports, the levels of nutrients can be adjusted according to the flowering, fruiting, or growing cycles of the plant.
A soil test can reveal several factors which affect which crops are best suited to be grown, the levels of nutrients, and fertilizers to be used. Both macro- and micronutrients are important factors in growth of food crops. Additionally, a soil test can reveal the level of pH, organic matter, and cation exchange capacity of soil.
Conclusion
Determining the nutrient quantities in a soil sample is crucial to develop a rational fertilizer program that provides the right amount of fertilizer to maximize profitability and minimize environmental impact. Soil testing laboratories also need to operate cost effectively while maintaining accuracy and reliability. Efficient filtration plays a key part in this as a first step in sample preparation before analysis. A laboratory that can make sure it is using optimum filtration practices and materials can simplify soil testing workflows, provide accurate and reliable results, and maximize its profitability.
Cytiva provides a variety of quantitative ashless filter papers, including Grade 42, as well as ready-to-use, pre-folded soil analysis filter papers made from the same high-quality materials. The Whatman filter selector app provides a guide for identifying the most appropriate filter for an application, while the Cytiva scientific support team is available for all other support.
FAQs
Why is filtration important in soil testing and what types of filtration products are used in soil testing?
Laboratory filtration protocols need to accurately separate solids and liquids for various analyses.
Clarification: Paper filters and glass fiber filters are used to remove particulates and suspended solids from aqueous soil extracts. These filters provide a clear sample by retaining unwanted debris that could interfere with downstream analyses or damage sensitive instrumentation.
Solids retention: Retaining specific particulate matter allows for targeted testing of soil components, such as organic matter or residual fertilizers.
Analytical sample preparation: Filtration protects the instrumentation for high-performance liquid chromatography (HPLC) and ion chromatography (IC) so detection and quantification of ions, nutrients, heavy metals, or organic compounds are accurate and reproducible.
What considerations should be made when selecting a filter paper grade for a soil testing application?
Particle retention: Soil samples often contain a range of particle sizes, including fine clay and silt. A finer grade filter paper will offer better retention of small particles but may significantly slow down the filtration process, which could be a drawback in high throughput testing environments.
Filtration speed: Faster filtration can improve efficiency, particularly when processing multiple soil samples. Balancing speed and retention is critical, especially for tests requiring clear filtrates for accurate chemical analysis.
Mechanical strength and handling properties: Soil samples can be heavy or gritty, and the filter paper needs to withstand handling without tearing or collapsing. Wet strength is particularly important, as many papers lose structural integrity when saturated.
Soil analysis labs often process hundreds of soil samples per day, are there ways to improve efficiency of soil testing workflows?
To simplify soil testing workflows, analysts can target the filtration steps of soil sample preparation. Although filtration itself plays a small part in the overall method of soil testing, during peak periods, analysts are likely to hand-fold hundreds of circles of filter paper each day. A simple switch to pre-folded filters in place of flat circles or sheets negates the need for manual folding, saving significant time in sample preparation.
We offer cone, pyramid, fluted and quadrant folded paper formats. In addition to improving overall lab efficiency, reduced paper handling reduces the risk of cross contamination.
References
- Guide to laboratory establishment for plant nutrient analysis, FAO Fertilizer and Plant Nutrition Bulletin 19, ISSN 0259-2495 (2008).
- Sahu, V. et al. Soil test based fertilizer recommendation for targeted yield of crops: A review Int. J. Chem. Stud. 5(5), 1298-1303 (2017)