By Jason Vance

As producers across the country prepare for the next growing season, fall offers an opportunity to evaluate soil fertility in hayfields and pastures and make informed decisions about fertilizer applications.

Soil testing can help forage producers identify nutrient deficiencies, correct soil acidity and better target fertilizer dollars. Christie Preston, a Kansas State University Sustainable Cropping Systems agronomist based in Parsons, said fall is an especially useful time to assess forage ground before the next growing season.

“This year we’re focusing mainly on forage, hayfields and pastures,” Preston said.

Although soil conditions and nutrient recommendations vary by region, the basic principles of soil testing apply to forage producers nationwide. Testing in the fall allows time to receive results, plan fertilizer purchases and address soil pH problems before spring growth begins.

“One of the reasons why we’re looking at soil sampling this fall, particularly if there are recommendations for liming, is we’re able to apply that lime and get it to react within the soil and raise the soil pH before next spring,” Preston said.

Fall sampling also gives producers time to develop fertilizer plans rather than waiting until spring, when planting, calving, grazing management and other seasonal responsibilities may compete for attention.

For most hayfields and pastures, Preston recommends soil sampling every three to four years. Fields with significant nutrient deficiencies or substantial pH adjustments may require more frequent testing to monitor progress.

In fields with very low pH, lime applications may need to be repeated over multiple years to gradually improve soil conditions. Selecting lime with a finer particle size can help it react more quickly, depending on the product and soil conditions.

Producers should also recognize that a single soil sample may not accurately represent an entire farm or pasture.

“I’m a firm believer that farmers know their fields the best,” Preston said. “So if you see differences within the field, those need to be sampled separately.”

Differences in soil type, drainage, productivity and forage species can affect nutrient requirements. Sampling distinct areas separately can help producers avoid applying the same amount of lime or fertilizer across fields with different needs.

Recommendations may range from 10 to 40 acres for a composite sample, depending on the situation. The appropriate sampling area can vary by region, field variability and local soil-testing recommendations, but sampling smaller, more uniform areas can provide a clearer picture of fertility needs.

“It’s just a way to dial in the inputs and potentially increase the ROI for our producers,” Preston said.

When test results arrive, Preston recommends evaluating soil pH first. Soil pH influences nutrient availability, meaning a field can contain adequate nutrients but still struggle to make them available to growing plants if acidity or alkalinity is outside the desired range.

Phosphorus and potassium should also receive close attention. Nitrogen often gets the most attention in forage production because of its potential to increase growth and yields, but the other nutrients remain essential to maintaining productive stands.

Soil tests are particularly helpful in determining phosphorus and potassium needs. Nitrogen management can be more complicated because nitrate moves through the soil profile, and recommendations may depend on soil characteristics, expected forage production and management practices.

In areas with deeper soils, producers may be able to collect profile samples to measure nitrate levels and improve nitrogen recommendations. A claypan layer can limit the ability to collect samples two feet deep. Other regions face different soil conditions that influence the appropriate sampling method.

Keeping accurate yield records is another important part of managing fertility. The amount of forage harvested provides information about nutrient removal and helps producers determine whether fertilizer applications are replacing what leaves the field.

“Anytime you’re removing the majority of the above-ground biomass, you’re removing high amounts of phosphorus and potassium,” Preston said.

Over time, those nutrients can become depleted if they are not replaced. Soil testing helps identify declining levels before they become a more significant limitation on forage production.

Producers have several nitrogen fertilizer options, including liquid nitrogen solutions, urea, ammonium nitrate and anhydrous ammonia. Availability, cost, application equipment, soil conditions and regional management practices all influence which source makes the most sense.

Timing also depends on the intended use of the forage. Nitrogen may be applied in late summer to encourage stockpiled fescue for winter grazing, in the fall to prepare for spring production or during spring green-up. The best approach depends on the forage species, growing conditions and the producer’s management goals.

Regardless of location, producers should avoid applying fertilizer to frozen ground because of the increased risk of nutrient losses. Local recommendations and weather conditions should guide decisions about application timing and rates.

For producers across the major hay- and pasture-producing regions of the United States, fall soil testing offers a chance to make fertility decisions based on field conditions rather than assumptions. Regular testing, representative samples and accurate yield records can help improve nutrient management while making better use of limited input dollars.

“The take-home message is we need to try to capture as much information as possible, and we can do that through fall soil sampling,” Preston said.