Why is it necessary to perform a soil analysis?
The soil is one of the most important organic materials on earth, this is because it’s the medium where plants are going to develop, providing space and nutrients. In this medium, roots can grow, anchor and absorb nutrients satisfying some of the most important necessities of plants. In soil we can also find microorganisms like bacteria, fungi, mycorrhiza and nematodes. These microorganisms interact with plants, specially with their roots in a space called “Rhizosphere” where all interactions and symbiosis take place. Talking about microorganisms can be very extensive, that’s why we will discuss it in our next chapter, this time we will talk about soil’s physical and chemical analysis.
The performance of a soil analysis will examine the physical, chemical, and natural properties of this medium to identify soil impediments. This is a great tool to decide what is the most suitable use for this resource, whether if it’s good for crop development or any other project.
This soil analysis or soil sample should be analyzed by collecting sub-samples taken from homogeneous territories to expose compositional patterns rather than normal conditions. The test is very important for a few reasons: optimize crop production, determination of plant nutritional issues, improvement of nutritional balance in plants, and preserve energy by applying the right amounts of fertilizers, compost or other products. This examination gives a sign of potential nutrient deficiencies, pH imbalance, abundance of soluble salts and organic matter determination. Soil examination is a vital practice that permits the proper fertilizers, micro-nutrients and soil conditioners dosage as well as the visualization of changes over time. To perform a soil analysis successfully, you should follow a series of steps to avoid any noise or problem in your sample.
Some of the most common soil analyses include:
- Basic analysis: pH, texture, percent of organic matter, availability of elemental nutrients such as nitrogen, phosphorus, potassium, sulfur, calcium, magnesium, electrical conductivity (salinity), Cation Exchange Capacity.
- An effective tool for evaluating soil fertility and its productivity
- Determines the availability of nutrients in the soil and the response to the fertilizers.
- They allow defining the capacity of use of the grounds, monitoring of fertility variables (nutrient mapping for site-specific management, irrigation in fields, etc.)
- Provide central information for crop planning and crop rotation.
- Improvement of soil management and nutrition plans
- Decisions made by soil analysis results helps to maximize productivity, profitability and sustainability
- Controls plant diseases, insects, and weeds.
Convert decomposed substances and minerals into plant nutrients.
Improves soil structure increasing water retention capacity and nutrients availability.
Improves crop development and increase yields.
Material to perform analysis
Before you start your soil Analysis, you must have with you some important tools, make sure they are totally clean, and free for rusted surfaces to avoid any contamination.
- Earth Drill or Soil Drill,
- Shovel, or Palin,
- Plastic Bags
- Map of the field or orchard map
- Labeling material (stickers, pens or markers).
How to Perform a Soil Analysis:
- Perform a visual inspection of the terrain in order to choose similar areas and before taking each soil subsample remember to remove any trash, vegetation that may be covering the area.
- Define the areas to be sample (color, texture, slope, topography, drainage, vegetation, etc.), if it is a field in production, check the production history
- Define a sampling pattern whether a “square”, “zig-zag”, “x”, “grid” or any other pattern
- Establish your sample parameters, the depth and location in the root zone
- It is important to take into account the sampling depth. This could vary depending on the crop. In general, the soil of the sample should be the one that is near to the crop root system. This could be between 0 to 40 cm, avoiding the first 10-15 cm
- Take a sample every 150 to 500 m2 route, starting with 20cm of depth, 20 cm for transitory crops, and 15 cm for pastures.
- Very deep soils that are easy for roots to penetrate should include a sample of up to 40 to 70 cm. For perennial crops it is recommended to take two subsamples in the same place: one from 0 to 20 cm and the other from 20 to 60 cm.
- Cut down to remove a slice of one side of the hole wall keeping that slice on the blade of the spade. Use a trowel, knife or stick to cut away the sides of the slice leaving only just the center of the section of about 2 cm.
6. Collect samples at more than one point.
- Define a good number of subsamples and the sampling objective. It is important to collect samples at more than one point, and at minimum you should obtain subsamples of 3 different points per lot, this could vary depending on the sampling extension, tying to obtain the most representative sample.
- The soil sample should be label with the name, code or number of the sample, and package in with security.
- Use a permanent or waterproof marker in order to avoid confusion with the sample labels.
- Soil samples can be done any time of the year, but it is recommended before the start of crop cycle, and at the end of the cycle.
- You can obtain free or low-cost soil tests through your local county extension office.
- Avoid conducting a soil analysis if the soil is wet or if you have recently fertilized the area.
Cornell Soil Health Laboratory. (2021). Sample collection. Soil Health Cals Cornell. https://soilhealth.cals.cornell.edu/testing-services/collecting-samples/
Gregorich, E. G. (2006). Soil Sampling Designs. In M. R. Carter , G. T. Patterson, Canadian Society of Soil Science (Eds.), Soil Sampling and Methods of Analysis (2nd Ed, pp. 25–46). Taylor & Francis Group,.
Hue, N V, and M C Ho. 1997, pp. 1–4, Testing Your Soil Why and How to Take a Soil-Test Sample.
Oregon State University Extension Service, Ferry, M., Choate, J., & Murphy, E. (2018). A Guide to Collecting Soil Samples for Farms and Gardens (U.S. Department of Agriculture, Ed.). https://catalog.extension.oregonstate.edu/sites/catalog/files/project/pdf/ec628.pdf
U.S. Environmental Protection Agency & Laboratory Services and Applied Science Division. (2020). Soil Sampling (LSASDPROC-300-R4). https://www.epa.gov/sites/production/files/2015-06/documents/Soil-Sampling.pdf