Soil

The best soils for growing vegetables are well drained, deep, fertile soils, with adequate levels of 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 retention, availability, and uptake of nutrients.

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 USU 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 USU Analytical Laboratory. 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.

Soil Test Interpretation

A soil test evaluates the nutrient-supplying capabilities of a soil. A common misunderstanding is that the test provides you the total amount of nutrients that are available for plant growth. The soil test only provides a prediction of how much fertilizer is required for optimum plant growth. If fertility levels are below optimum, addition of the 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 units of pounds of the particular nutrient per acre. Reading and understanding the soil test depends on knowing what method was used in the test laboratory and what units are 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 P₂O₅ and K₂O 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.

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 a 100 pounds of nitrogen (N), 100 pounds of phosphate (P₂O₅ ), and 100 pounds of potash (K₂O) 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:
1. Divide the percentage of N, P₂O₅ , or K₂O in the fertilizer into the quantity of nutrient needed per acre.
2. Multiply that value by 100.
3. 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 (Utah State University Extension)
• Solutions to Soil Problems: High pH (Utah State University Extension)
• Solutions to Soil Problems: Drainage (Utah State University Extension)
• Solutions to Soil Problems: High Salinity (Utah State University Extension)
• Solutions to Soil Problems: Low Organic Matter (Utah State University Extension)
• Utah Visual Farm Guide: Year-Round Soil Care (Utah State University Extension)
  
• Utah Visual Farm Guide: What is Healthy Soil (Utah State University Extension)
• Preparing and Improving Garden Soil (Utah State University Extension)