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Soil Testing

Soil texture affects how well land drains, how effectively the soil holds nutrients and minerals, and how readily the soil can be cultivated. Soil monitoring is used to facilitate the selection of fertilizer composition and dosage for land employed in agricultural as well as horticultural industries.

In agriculture, soil analysis of nutrient and contaminant content is important. Soils under intensive cultivation may have abnormal levels of some nutrients due to previous management practices and fertilizer programs.

In general, soil is analyzed for its pH and for its content of available nitrogen (N), phosphorus (P), potassium (K), magnesium (Mg), and trace elements. Sometimes, soil toxicity has to be assessed as contamination may have occurred from disposal of waste materials and/or pesticide use. Common soil mineral contaminants include arsenic, barium, cadmium, copper, mercury, lead, and zinc. Lead is a particularly dangerous soil component.

Nitrogen Analysis Phosphorus Analysis Trace Elements Analysis Pesticides Detection pH testing

Low nitrogen content weighing boats

Of all the essential nutrients, nitrogen is required by plants in the largest quantity and is most frequently the limiting factor in crop productivity. Nitrogen is not only an essential element for protein building and a component of nucleic acids but also a component of chlorophyll, needed for photosynthesis. Measuring soil nitrogen content can help refine nitrogen fertilizer addition before planting.

Nitrogen content analysis is typically done with Kjeldahl techniques, which involve the sampling of an exact amount of soil before transfer to a digestion tube. Low nitrogen content weighing paper make the sample transfer easy and quick without loss of material and with minimal interference with the end result. The sample may need to be filtered through a qualitative filter paper prior to analysis.

Phosphorus (P) is an essential element for plant growth and is often applied to agricultural land to increase crop production. Through soil phosphorus testing, the amount of phosphorus fertilizer required to achieve maximum plant grow can be determined. Soils with low or medium phosphorus content will likely show higher yields if extra phosphorus is added. However, crops are not likely to respond with a yield increase in soils with high or very high phosphorus content.

To determine the soil phosphorus content, the soil is extracted with a chemical solution and the phosphorus content in the extract is measured by colorimetry. Filtration of the extract through a qualitative filter paper is generally needed before analysis. If an automated method is used for determining phosphorus concentration, acid-resistant filter paper may be needed.

Trace element analysis in soil generally involves determination of essential nutrients for plant growth and detection of potential heavy metal contamination (from for example waste disposal).

Nutrients Analysis

Agricultural nutrients such as potassium (K), magnesium (Mg), and calcium (Ca) are very important for plant growth and development. The analysis of these nutrient elements is thus helpful in assessing the fertility of the soil and improving soil quality prior to planting or during crop growth.

Heavy Metal Contamination of Soils

Sometimes soils may be contaminated by the accumulation of heavy metals through emissions from industrial areas, mine tailings, and disposals of high metal wastes, leaded gasoline, paints, etc. The most common heavy metals in soils are lead (Pb), chromium (Cr), arsenic (As), zinc (Zn), cadmium (Cd), copper (Cu), mercury (Hg), and nickel (Ni). Heavy metals remain in soils for a long time after their introduction.

Toxic metals in soil can pose risks and hazards to humans and the ecosystem through direct contact with contaminated soil and through the food chain.

Methods for Trace Element Testing

Most trace element tests are based on extracting soil and measuring the concentration of trace elements in the soil-free liquid phase using for example inductively coupled plasma atomic emission spectrometry (ICP-AES). Extraction methods can vary between laboratories. The sample then generally needs to be filtered through a qualitative filter paper or glass fiber filter to make sure it will not clog nebulizers or interfere with injection into the analysis instrument. If digested with aqua regia, the sample may be filtered through an ashless filter paper.

Extraction thimbles in Soxhlet extraction
apparatus

Pesticides, such as Glyphosate, Atrazine and Chlorpyrifos, are widely applied to protect plants from disease, weeds, and insect damage, and usually come into contact with the soil, where they undergo a variety of transformations that provide a complex pattern of metabolites.

Pesticides are increasingly tested as environmental contaminants in soil. Prior to analysis by for example gas chromatography (GC), soils may be prepared using Soxhlet extraction or microwave digestion. Extraction thimbles are widely used for Soxhlet techniques. Qualitative filter papers or glass fiber filters can help clear extracts after microwave extraction. Samples may then be refiltered with a 0.45 µm filter to remove small particles and protect your GC. Mini-UniPrep syringeless filter, which is an all-in-one filter and autosampler vial, allows you to process samples faster than traditional syringe filters and eliminates multiple consumables.

The pH of soil is vital for how well it holds minerals. When the soil it too acidic, minerals will be leached out by rainwater before the plants have a chance to use them. Highly alkaline soils are often associated with mineral deficiencies due to the low solubility of minerals under alkaline conditions. Neutral or slightly alkaline soils are ideal for growing plants. However, some plants have very particular pH requirements.

There are many different ways of measuring soil pH. Litmus/pH paper is a quick and inexpensive method to test soil pH when a pH-meter is unavailable or when highly precise values are not necessary. When preparing your soil sample, use a weighing paper to weigh the soil before adding water. Filter papers can be used to remove unnecessary particles from the suspension.

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