Soil
The best soils for growing vegetables are well drained, deep, fertile soils, with adequate organic matter. Soil textures like sandy loam or loamy sand are suitable for early market crops since they are accessible to machinery and workers even when wet. Loam and silt loam soils are better suited for growing crops for later fresh-market use. Regardless of the soil type, develop a best management practices (BMP) plan for the farm, which includes a good soil management program, proper fertilization, good tillage practices, suitable crop rotations, strategies to increase organic matter, and managed irrigation. Consider integrating cover crops between vegetable plantings to maintain or improve soil structure and retain topsoil.
Many factors influence the nutrient requirements of a given vegetable. Soil textural classification, cation exchange capacity, organic matter content, and drainage are important properties that influence the nutrient needs of vegetables. Rainfall, irrigation methods and management, and environmental conditions during the growing season can alter the nutrient retention, availability, and uptake.
Soil Tests
One way to determine the soil type and fertilizer need is to have your soil tested. Soil sample kits and instructions are available in every county Extension office. The local Extension educator can help with sampling approaches, testing needs, and provide you with the costs of the various soil testing services performed by the Utah State University (USU) Analytical Laboratory (USUAL). Knowledge of the current soil fertility can reduce fertilizer application rates and better match soil fertility level, past cropping history, and soil management practices to the crops grown. To minimize potential soil damage and water pollution, nutrient recommendations are based on the soil test results and past cropping and fertilization practices. For more information on soil testing and interpreting results, visit the USU Analytical Laboratories website.
Soil Test Interpretation
A soil test evaluates the nutrient-supplying capabilities of a soil. A common misunderstanding is that the test provides you with the total amount of nutrients available for plant growth. The soil test only predicts how much fertilizer is required for optimum plant growth. If fertility levels are below optimum, the additional nutrient should enhance or increase plant growth and productivity (provided something else is not limited). If the soil test indicates that a nutrient is at adequate or excessive levels, no applications are needed.
The basic soil test determines the soil texture (sandsilt-clay), soil pH, salinity, and phosphorus (P) and potassium (K) levels. A “complete” analysis also tests for nitrates, micronutrients, sulfate, and organic matter. Soil test recommendations are commonly expressed in pounds of the particular nutrient per acre. Reading and understanding the soil test depends on knowing the method used in the test laboratory and the units used to express the soil nutrient levels. If the soil test report does not state the method used, call the laboratory to find out. This information is needed before interpreting the soil test results.
Soil Test Categories for Nutrients
Test Category | Soil Test Value (mg/Kg) Phosphorus (P) |
Soil Test Value (mg/Kg) Potassium (K) |
---|---|---|
Very Low | 0-10 | 0-70 |
Low | 11-20 | 70-125 |
Adequate | 21-30 | 126-300 |
High | 31-60 | 300+ |
Very | High 60+ | - |
Nutrient Recommendations
Always base nutrition applications on a current soil test. When soil test results are not available, use recommended amounts of P2 O5 and K2 O listed under adequate phosphorus and potassium soil test levels for the crop to be grown. This is not as accurate, but is a conservative approach that minimizes the chance of over-application. Refer to Table 2.1 to interpret the relative levels of phosphorus and potassium in the soil based on the soil test report from the laboratory. When a current soil test is available, use the crop specific recommendations or consult your local county Extension educator.
Use the fertilizer recommendation from the soil test to determine the rate of fertilizer needed to fulfill these requirements.
EXAMPLE: If the soil test recommends 100 pounds of nitrogen (N), 100 pounds of phosphate (P2 O5 ), and 100 pounds of potash (K2 O) per acre, you would need a fertilizer with a 1:1:1 ratio, such as a 16-16-16. To determine the quantity of fertilizer to apply:
- Divide the percentage of N, P2O5 , or K2O in the fertilizer into the quantity of nutrient needed per acre
- Multiply that value by 100
- Total fertilizer required to provide 100 pounds of N per acre would be 625 pounds of the 16-16-16 (100/16=6.25 x 100 = 625)
More Information
- Solutions to Soil Problems: Soil Structure
- Solutions to Soil Problems: High pH
- Solutions to Soil Problems: Drainage
- Solutions to Soil Problems: High Salinity
- Solutions to Soil Problems: Low Organic Matter
- Utah Visual Farm Guide: Year-Round Soil Care
- Utah Visual Farm Guide: What is Healthy Soil?
- Preparing and Improving Garden Soil
Soil Health
Basics of Soil Health Testing
How to Build Soil Health
USU Analytical Laboratory Tour
How to Prepare a Garden
How to Take a Representative Soil Sample