Getting the Dirt on Soil Testing

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Soil testing is a helpful practice for gardeners aiming to achieve healthy plant growth and a bountiful harvest. Understanding the composition of your garden soil helps tailor gardening practices to meet the specific needs of your plants. This article provides an overview of laboratory soil testing, covering its importance, the key elements tested, how to collect a soil sample, and how to interpret the results.

Why Soil Testing is Important

Soil testing is valuable for several reasons:

• Nutrient Management: It provides detailed information about the nutrient content of the soil, enabling gardeners to apply the correct type and amount of fertilizer.
• pH Level Adjustment: Knowing the soil's pH level, which affects nutrient availability, allows gardeners to adjust it to the optimal range for their plants.
• Detecting Contaminants: Tests can reveal the presence of harmful contaminants like lead or other heavy metals, ensuring the safety of your garden produce.
• Cost Efficiency: By applying only the necessary fertilizers and amendments, gardeners can save money and prevent environmental pollution.
• Tailored Gardening Practices: Understanding soil health helps in making informed decisions, leading to better plant growth and yield.
• Troubleshoot Why Plants Aren't Thriving: If you've exhausted your attempts to amend soil with compost, a soil test can provide more detailed information to remedy the problem.

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Key Elements Tested in Soil

A standard soil test can include analysis of the following elements:

• pH Level: Indicates the acidity or alkalinity of the soil.
• Macronutrients: Such as nitrogen (N), phosphorus (P), and potassium (K), which are crucial for plant growth.
• Micronutrients: Including elements like iron (Fe), manganese (Mn), and zinc (Zn), which plants need in smaller amounts.
• Organic Matter Content: Affects soil structure, nutrient availability, and water retention.
• Cation Exchange Capacity (CEC): Reflects the soil's ability to hold onto essential nutrients.

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Collecting a Soil Sample

To obtain accurate soil test results, most labs will have specific instructions to follow. In general, These are the steps for collecting a soil sample:

• Choose the Right Time: The best time for soil sampling is when the soil is moist but not wet, typically in the spring or fall.
• Select the Area: If your garden has distinct areas with different crops, soil types, or problem spots, sample each area separately.
• Collect the Sample: Use a clean tool to take small amounts of soil from several spots within the sampling area. Mix these samples in a clean container to create a composite sample.
• Depth of Sampling: For lawns and gardens, a depth of 6-8 inches is appropriate. For trees and shrubs, sample at a depth of 6-12 inches.

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Interpreting Soil Test Results

Soil test results will provide detailed information about the elements mentioned above. Here's how to interpret some of the key findings:

• pH Level: Most garden plants thrive in a pH range of 6.0 to 7.0. Values outside this range may require the application of lime (to raise pH) or sulfur (to lower pH).
• Nutrient Levels: The report will indicate whether nutrient levels are low, medium, high, or excessive. Low or medium levels suggest the need for supplementation, while high or excessive levels mean you should cut back on those nutrients.
• Recommendations: Most soil tests come with recommendations for amendments and fertilizers. Follow these guidelines to adjust nutrient levels and pH accordingly.

Soil testing is a powerful tool that empowers gardeners to make informed decisions about managing their garden soil. By understanding the specific needs of your soil, you can optimize plant health, improve yields, and contribute to the sustainability of your gardening practices. Whether you are a hobbyist or a professional gardener, soil testing is a practice that yields long-term benefits for your garden and the environment.

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Resources

• Cornell Guide to Soil Testing: https://cwmi.css.cornell.edu/guidetosoil.pdf
• University of California Division of Agriculture and Natural Resources – Soil Testing: https://ucanr.edu/sites/placernevadasmallfarms/files/142586.pdf
• UC Master Gardener Program of Alameda County: https://acmg.ucanr.edu/Over_the_Fence / Whats_In_Your_Soil/
• Soil 101: https://ucanr.edu/sites/soils/Soils_101/
• Soil Test Kits: https://ucanr.edu/sites/gardenweb/files/29075.pdf
• Evaluating and Testing Soil: https://marinmg.ucanr.edu/BASICS/SOIL_813/evaluate/
• Soil Health Testing: https://soilfertility.osu.edu/extension-and-outreach/soil-health-testing

Analytic Testing Laboratories for Home Gardeners

Soils, Water, Plants, Heavy Metals and More

• Contact the labs to confirm offered services, pricing and preferred procedures for sample collection.
• Testing labs vary in the types of available tests and recommendations they provide, if any. Be sure to ask for detailed information regarding tests, test fees and interpretation, and whether recommendations are included. Many of the websites provide supplemental information about tests and sampling.
• Resources regarding soils and soil testing:
  • Soil Testing and Soil Contaminants 
  • Cornell Guide to Soil Testing and Interpreting Results
  • Home Gardens and Lead

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