Fertile soil—rich with minerals, abundant microbial life, humus, and organic matter—produces vibrant plants and healthy crops. The availability of nutrients varies with each growing season due to factors like crop uptake, past fertilizer applications, leaching, denitrification, and more. Rather than speculate about the specific nutrients crops might need in a given year, growers can evaluate soil nutrient composition prior to the season using a soil testing kit. This allows them to base their fertility management decisions on quantifiable results.
Soil testing results, used in combination with a grower’s production goals, can lead to optimal use of a field’s nutrient profile and help growers achieve high yields and the best possible economic outcomes in a growing season.
Soil testing enables growers to:
- Make data-informed fertility management decisions
- Detect nutrient deficiencies
- Fine-tune nutrient applications with site- and crop-specific solutions
- Select amendments that will provide the greatest impact on crop productivity
- Reach higher yield goals
- Achieve a higher return on investment
- Monitor soil health
Prior to testing, choose a lab analysis that targets primary concerns such as deficiencies of plant-available nutrients like nitrogen, phosphorus, potassium, and micronutrients. Analyses that target properties such as pH, cation exchange capacity, texture, organic matter, estimated nitrogen release, and soluble salts can help growers address specific soil issues. The results of these targeted tests provide a roadmap to use throughout the growing season.
How to Sample Soil
Step one is to start digging. Using a clean shovel or probe, collect soil from a depth of 0 to 6 inches and place it in a sealable bucket. Collect a deeper sample, 6 to 12 inches down, to evaluate the subsoil. Then, following any directions provided by the lab, place the samples in labeled containers to send for analysis. Gathering multiple samples can help evaluate conditions across a field and the overall health of the soil.
The Importance of Timing
Pre-season nutrient analysis is key for adequately preparing fields prior to planting. These analyses can be used to help determine how much fertilizer is needed throughout the season to support plant vitality, production goals, and longer-term soil health.
Post-harvest soil tests allow growers to develop a nutrient management plan for the winter season that may include planting cover crops or applying fertilizer in the fall.
Analyzing samples at the same time each year is important for establishing a consistent dataset. Keeping annual records of nutrient levels and comparing soil composition and crop performance year after year can help growers optimize crop performance over time.
Key Nutrients to Evaluate
Nitrogen, phosphorus, and potassium are the primary nutrients that support plant growth, making them important to include in annual soil testing.
Nitrogen is the most important yield-determining nutrient. Crops absorb available nitrogen from the soil by mineralizing organic materials and metabolizing plant-available nitrogen. Research indicates that nitrogen not only enhances photosynthetic processes and supports overall plant health, it is also linked to increased crop production.
Phosphorus is essential for protein synthesis and the development of new plant tissue. Plant-available phosphorus is often low in soils and must be added to prevent deficiencies, which can slow crop growth and result in smaller plants.
Potassium supports the circulation of water, nutrients, and carbohydrates throughout plant tissue and also facilitates enzyme activation within the plant. Enzyme activation affects protein, starch, and adenosine triphosphate (ATP) production, the latter of which regulates the rate of photosynthesis. Low potassium levels can result in stunted plant growth and reduced yield.
Using Data to Improve Soil Health
Nutrient management is one of four strategies recommended by Purdue Extension for improving soil health, with soil reports serving as a fundamental component of a well-designed nutrient management plan. Using the data provided by scientific analyses, growers are able to more accurately adjust the nutrient profile to enhance plant health or—if nutrient levels are sufficient—choose to minimize fertilizer application, reducing costs and protecting natural resources.
Soil testing provides a quantifiable way to inform crop management decisions and maximize crop productivity. With the insight provided, growers are able to gain a clear picture of overall nutrient composition and leverage that to create healthier, more productive soils.