Fall provides farmers a chance to get a head start on soil testing and on fertilizer or manure nutrient applications for next year's crop. "Now is an optimum time for soil testing to reveal any potential nutrient deficiencies," says Keith Diedrick, a Pioneer Hi-Bred area agronomist. "By sampling soil and having it tested for phosphorus, potassium and lime this fall, growers can work to increase the nutrient profiles of their fields, spread the workload and prepare for spring."
When agronomists assess poor-growing crops, the first questions usually revolve around basic nutrient availability, especially nitrogen, phosphorous and potassium. Knowing which nutrients are out of balance is the first step in improving conditions for crops. "Soil tests are a good tool to measure existing nutrient levels available to crops," says Diedrick. "The results provide you with a good idea of what may be going on in your fields."
Knowing the current level of nutrients in your soil is valuable information
To maximize profitability, using the right combination of fertilizers is important. "Results from consistent soil tests are critical for growers making those decisions," he adds. A standard soil test provides a measurement of phosphate, potassium, soil pH etc. Knowing the current levels of these nutrients allows you to plan for any necessary applications to prepare fields before spring planting.
Fall soil tests for nutrients such as nitrogen (N) and sulfur (S) may not be as valuable because the nutrient status of these two may change before the crop can take them up. Some growers use soil nitrate tests to fine-tune nitrogen rates in-season, but most N recommendations are based on the previous crop, the N-to-corn price ratio and each grower's personal comfort level for risk.
In-season soil tests also tend to work well for diagnostic purposes - to find out what may be causing a current issue. "If you want to plan ahead, it's important to test at the same time every year for comparability reasons," says Diedrick.
Regular soil sampling and testing every 3 to 4 years is recommended
"It's important to understand the results of the soil test," he adds. "Make sure you know what the lab is basing its results and recommendations on." Verify that the fertilizer recommendations you're getting match your crop needs. Crop plans for the upcoming year will influence your use of the results. Critical nutrient levels are different for every crop. If you're unsure of typical nutrient levels recommended for your area, you should check with your regional agronomy resources and recommendations from your state's Extension soil fertility specialist. Such information is available from your local Extension office.
"Regular soil tests, taken every three to four years, allow you to react to changes and reverse negative trends," says Diedrick. "Shorter test intervals tend not to show any significant benefits. If you wait longer than four years, you don't get a consistent benchmark of soil nutrients."
For accurate results, it is necessary to pull representative soil samples from a proper depth throughout the field. Sampling methods depend on cropping and fertility management practices. Check with your local experts for more information on correct sampling methods.
Consistency in sampling lets you build accurate information over the years
Soil test results can alter a grower's nutrient application rates. For cost-effective application in the fall, Diedrick suggests using a granular, dry fertilizer. "Dry fertilizers will dissolve and react with the soil similarly to liquid fertilizers," he says. "Most dry applications can be soluble with little rainfall, and are easier and more economical to handle in large quantities."However, N application is generally more efficient in the spring. "Fall and winter applications can result in potential losses of significant amounts of nitrogen," says Diedrick. Whether you decide to apply nutrients in the fall, winter or spring, consistent testing from year to year is one of the best ways to ensure a balance between economic and environmental factors. For more information on interpreting soil test results or understanding critical nutrient levels in your area, visit the soil fertility page on www.pioneer.com.