Fertilizer prices in 2021 have increased substantially and these price increases are expected to continue throughout 2022. Increasing fertilizer prices affect the profits farmers can make on a crop, leaving many growers wondering where they can cut costs on their operation. One cost that farmers should not avoid is the cost of a soil test. MU Extension agronomist Tim Schnakenberg notes "If there was ever a time to do a soil test, this is it." In addition to soil testing, MU Extension offers several other laboratory tests that can help you accurately apply the amounts of nutrients your plants need.
The cost of a soil test is a small price to pay to be able to accurately apply the amount of nutrients your crop needs to thrive. This information can help you avoid overapplying nutrients your plants don't need or underapplying nutrients and reducing crop yields, either scenario negatively impacts a farmer's bottom line.
Every soil across the state of Missouri contains a certain amount of the different nutrients which are essential for plant growth. Fertilizer recommendations given on a soil test report are calculated from the requirements of the crop as well as the nutrients already found in your soil. For example, some Missouri soils are high in phosphorous and may require little if any additional phosphorous fertilizer to be added. Other soils in Missouri are high in organic matter content and these soils will require a lower amount of nitrogen to produce a bountiful crop, compared to those low in organic matter. Every 1% of organic matter in the soil will release approximately 20 lbs of nitrogen per acre over the course of the growing season. A soil with 4% organic matter could reduce nitrogen applications by as much as 80 lbs per acre, potentially saving well over $100 per acre in nitrogen fertilizer costs.
Soil test reports will also help you understand your soil pH, which can impact a crop's ability to access nutrients present in the soil. The availability of phosphorous in the soil decreases when soil pH falls below 6.0 or above 7.0. Adjusting your soil pH to optimum levels will help your plants access nutrients that are already present in your soil, saving you money on fertilizer costs. Without a soil test, fertilizing a crop involves a lot of guesswork. Taking a soil sample and following the recommendations given could potentially save you hundreds of dollars per acre on fertilizer costs.
MU Extension offers soil testing for commercial producers of vegetables and fruits and provides detailed recommendations to both optimize soil pH and fertilizer applications for these crops. It is recommended to test soil at a minimum every 2-3 years, however annual testing can better allow farmers to track the impact of their fertilization practices.
Sampling Your Fields
A soil analysis report will be representative of the soil sample that was submitted. The rules of thumb for soil sampling are as follows:
- A flat uniform field of up to 20 acres can be sampled as one field
- Hilly or rolling land should be sampled in 5-acre sections
- Areas with different soil color and texture should be sampled as separate fields
To ensure your soil sample is the best representation of your field, a minimum of 8-12 subsamples should be taken in a random grid pattern across a field for each sample submitted. The subsamples should be pulled from the surface of the soil down to a depth of 6 inches. The subsamples should be dried and mixed thoroughly, and 2 cups of this mixed soil will be necessary for analysis.
Manure and Compost Use and Testing
Farmers who have previously relied on synthetic bagged fertilizer may consider sourcing animal manure and compost to decrease fertilizer costs and improve soils. Manure can be a valuable fertilizer source, but every type of animal manure (broiler chickens, laying hens, turkey, dairy, etc.) contains varying amounts of nutrients essential for plant growth. For example, dried dairy manure may be between .6% and 2.1% nitrogen and between .7% and 1.1% phosphorous by weight; while dried poultry manure may contain between 2% and 4.5% nitrogen, and between 4.5% and 5% phosphorus by weight. Just like soil, the only way to understand what levels of nutrients manure and compost contain is to have it tested by a laboratory. A manure or compost analysis report will provide detailed info on the amounts of nutrients present in sampled manure and compost. This information will ensure you are able to apply the correct amount of manure/compost to supply the amount of nutrients your crops need. Similar to soil sampling, 8-10 subsamples should be taken from throughout a manure or compost pile and mixed thoroughly to provide a representative sample. A quart sample of manure or compost is required for testing, a sealable plastic bag inside of a cardboard box is the best way to package manure or compost for shipping to the laboratory.
In recent years, vegetable producers in Missouri have encountered issues with manure or compost that is contaminated with herbicides. The herbicides of concern are sprayed on pastures for broad leaf weed control. These herbicides pass from hay or forage into manure and/or compost and then into the soil and crop where the manure or compost is applied. These herbicides can remain active for several years, and if contaminated manure is tilled into the soil cash crops could be killed or damaged until the herbicide is neutralized over time. It is important to check with your supplier of manure that animals have not been fed hay or forage treated with the following herbicides: aminopyralid, clopyralid, fluroxypyr, picloram, or triclopyr. If you have concerns related to contaminated compost or manure please reach out to your local MU Extension specialist for more information.
Submitting Soil, Manure and Compost Samples
Soil, manure and compost samples can be dropped off directly at your local extension office and will be shipped to the soil and plant testing lab in Columbia. Request that your soil sample be submitted on a Commercial Fruits and Vegetables form. You can select 3 different crops to receive fertility recommendations for, with each soil sample submitted. Soil, manure and compost samples can also be sent directly to the MU Soil and Plant Testing Laboratory. It is suggested to call the laboratory first before sending samples, to ensure the lab has everything they need to process your samples and return your results. The lab can be reached by phone at 573-882-0623 or by mail at:
Soil and Plant Testing Laboratory
23 Mumford Hall, University of Missouri
Columbia, MO 65211