- Anytime post harvest until the ground freezes is a good time to do soil testing.
- Experts say fall testing is driven by the fact that a soil nitrate test in the fall is the best way to determine the amount of nitrogen fertilizer a grower needs for each field for the next crop year.
- Annual soil testing provides a record for tracking nutrient levels.
- Soil analysis results also often contain the soil texture, organic matter content and the soil pH.
Experts say fall is an optimum time to conduct soil testing.
Once harvest is finished, there's more downtime than in spring and producers typically have a wider window of time to test – anytime post harvest until the ground freezes. It also gives producers time to either apply fall fertilizers or determine the product they need to buy during the winter. The time is also ideal since fertilizer prices tend to be lower than in spring.
John Lee, a soil scientist with AGVISE Laboratories, says fall testing is driven by the fact that a soil nitrate test in the fall is the best way to determine the amount of nitrogen fertilizer a grower needs for each field for the next crop year.
“Crop nutrients need to be utilized in a manner that suits the local environment, and maintain or improve the soil’s productive capacity,” - Edgar Hammermeister, Western Ag Labs
“Farmers spend most of their fertilizer dollars on nitrogen fertilizer," Lee says. "The fall is the best time to test for nitrate-nitrogen in the zero to 24-inch soil profile. The other macronutrients, like phosphorus and potassium, are very stable in the soil and can be tested at any time of year.
“Sulfur is more like nitrogen and it is probably best to test for sulfur in the fall as well,” he adds.
If producers conduct annual soil testing, they can see if nutrient levels are increasing or decreasing over the years. This is more and more important as crop yields continue to increase because this removes additional nutrients from the soil. Lee uses soybeans as an example.
“A yield of 40 bushels per acre of soybeans removes 60 pounds per acre of potassium, compared to a 60-bushel-per-acre spring wheat crop, which only removes 20 pounds per acre of potassium,” he says. “Soil testing will allow (producers) to monitor the level of potassium in the soil to make sure it does not fall below the critical level.”
As well as providing producers with an inventory of nutrients in their available forms, soil analysis results often contain the soil texture, organic matter content and the soil pH.
Tom Weir, senior agronomist with FarmersEdge, says these results are most accurate when taken from a zero to six-inch depth.
“These values can be used to determine the rates of some soil-applied herbicides as well as predict the likelihood an herbicide may cause residual problems in a dry year,” he says.
Edgar Hammermeister, field services manager for Western Ag Labs, agrees producers have a stewardship role in the environment and soil testing is part of that process.
“Crop nutrients need to be utilized in a manner that suits the local environment, and maintain or improve the soil’s productive capacity,” he says. “Using nutrients in excess can result in environmental loading that can have other repercussions.”
Caring for the land serves to protect the environment but, ultimately, also makes good business sense. A fall soil analysis enables producers to initiate the planning process earlier, enabling them to take advantage of input purchase opportunities and to monitor crop market opportunities.
“Understanding the soil’s potential is fundamental to preparing successful crop plans,” Hammermeister says.