1/26/2024 - By Dr. Tom Reed

Soil testing is important in determining proper fertilizer applications to balance the nutrient availability in the soil, and the nutrient requirements of the crop to achieve production goals. A routine sampling and analysis program can be utilized for a precise fertilization program that optimizes plant health and minimizes environmental effects. Current pH levels of soil, nutrient fertility levels, and the amount of fertilizer the crop needs are items that can be determined by soil testing. 

Soil Testing Enhances Crop Productivity

Soil testing can indicate where the soil needs treatment or improvement, however, a soil test is not a substitute for proper cultural practices and good management. Soil testing before planting lets you know the nutrient availability in the soil. By identifying nutrient deficiencies or excesses in the soil, farmers can tailor their fertilizer application to meet the specific needs of the crops. This not only enhances crop health and yield but also prevents over-fertilization, reducing environmental impact and minimizing costs for the farmer. 

Soil Sampling Best Practices

Standard procedures for sampling, preparing, and analyzing soil should be followed for meaningful interpretations of the test results and accurate recommendations. Consistency is key, so standardizing your collection process is essential for useful soil sampling.

How to Take Soil Samples of Your Growing Space

·         For proper soil sampling, divide your farm into fields or areas for sampling.

·         If you have areas with different crops, soil, lime type, or fertilizer histories, take a sample from each area. Keep the samples separated.

·         Be sure that you collect samples that provide a general example of the field.

·         Space out your collection sites throughout the area so the sampling will be characteristic of the entire area.

·         Do not sample areas that are too small to be fertilized or limed separately.

Use a proper sampling tool, such as a sampling probe and if necessary, use a shovel or trowel. Obtain a sample at a depth and width representative of a soil probe, around 6 inches deep core of soil from at least fifteen spots in each field or area to be tested. Your depth of sampling may vary depending on crop and production systems but try to be consistent with each field/growing space.

Mix the cores from one field or area together with uniformity as the goal, so they are well combined. Put approximately a pint of the mixed soil in a sample bag, make a record of field sampling and samples, and air dry before analysis. You may freeze samples before analysis if nitrogen forms will be analyzed to prevent loss of ammonia.

Soil Analysis and Interpretation

Once you’ve collected your samples, send them in for analysis. The basic soil analysis package run by most agricultural laboratories includes soil pH and extractable P, K, Ca, Mg, and micronutrients. Extractable nutrients are measured, and the magnitude of soil-test values may differ between different laboratories, consistency is important when it comes to the soil-testing lab. Variability in results between labs can be attributed to several factors, including differences in technique or extraction solution. 

The soil test extraction solution also influences your results, and there are extraction solutions that are more appropriate for certain soil conditions. Melich-3 tends to be the default extraction solution for many soil testing laboratories due to its ability to provide consistent results in plant availability across the widest range of soil and environmental conditions. It may be possible to request a specific extraction solution on the soil test submission worksheet and you can always consult your local Harrell’s Rep for assistance.

The laboratory interprets each soil test result and may also provide fertilizer recommendations accordingly. Growers can independently interpret the numerical results according to regional sources, for example, in Florida, that would be the University of Florida Institute of Food and Agricultural Sciences guidelines based on the extractant used and crop. Do not follow interpretations from other sources and regions as methods vary depending on your region. An extension agent, crop advisor, or Your Harrell's Rep can help interpret recommendations and determine the best course of action.

The interpretation of soil sample results should be used to make management decisions about soil pH adjustments or fertilizer applications. These recommendations on lime and fertilizer applications will be tailored to the crop type you specified, making it easy to prepare your site for planting. If the soil is lacking essential nutrients, fertilizer application is needed to meet crop requirements, and your Harrell's Rep can help you find your perfect fertilizer formulation. If there is an excess of certain nutrients, you can avoid applying unnecessary fertilizer, which is an added cost that could also impact the environment. Soil testing is a way to avoid both problems.

Application programs may change from season to season even with the same crop and field. Annual soil testing is an excellent way to understand the effects of a fertility program on soil characteristics and nutrient reserves, allowing you to select the best application program for your soil season after season.

Soil Testing Enhances Efficiency

Soil testing involves a comprehensive analysis of soil samples to assess various parameters such as nutrient content, pH levels, organic matter, and texture. This information provides farmers with valuable insights into the soil's fertility and aids in making informed decisions about crop selection, fertilization, and overall farm management. Understanding the composition and health of the soil is fundamental to optimizing crop yield, promoting environmental sustainability, and ensuring long-term agricultural productivity.

Efficient use of resources, as facilitated by soil testing, aligns with the principles of sustainable agriculture. This not only improves the efficiency of resource use but also contributes to cost savings for farmers. In fact, Harrell’s has partnered up with The Nature Conservancy and The Fertilizer Institute to endorse the 4R Nutrient Stewardship Program.

With roots in agriculture, but applicability to all growing markets, 4R Nutrient Stewardship is an innovative and science-based approach that offers enhanced environmental protection, increased crop production and quality, increased grower profitability, and improved soil productivity and sustainability. The concept is to use the right nutrient source, at the right rate, at the right time, and in the right place to support the nutrient needs of plants. But this all starts with proper soil testing.

Contact your Harrell's Rep to find out more about soil sampling for your crops’ success!