Montana State University Extension specialist discusses soil fertilization after warm, dry winter

BOZEMAN -Montana State University Extension's soil fertility specialist suggests considering how a warm, dry winter might affect farmers' fertilizer decisions for the upcoming growing season.

According to Clain Jones, MSU Extension soil fertility specialist and a professor in the Department of Land Resources and Environmental Sciences, most of Montana is considered to be abnormally dry or in moderate drought. And, some places in northcentral Montana are in severe or extreme drought, according to the National Weather Service's drought monitor. Most of the northern part of the state, east of the Continental Divide, has received less than 25% of normal precipitation from Jan. 1, 2026, to Mar. 2, 2026, according to drought.gov. Only a small portion of central Montana has received about normal precipitation. The Montana Climate Office reports temperatures were well above average across the state for most of the winter.

"In general, drier conditions will result in less soil nutrient release and availability, though warmer conditions might have counteracted this to some degree," Jones said. "The question is how these conditions have affected soil nutrient levels and whether it's worth re-sampling soil if it was sampled last fall."

In general, phosphorus, potassium and sulfur levels aren't expected to change much from last fall, as dry conditions have likely prevented leaching of sulfur and likely slowed any release of these three nutrients from soil organic matter and plant residue, Jones said.

Nitrogen could have a bigger change because it can increase or decrease substantially over winter, according to Jones' research. Microbes can release substantial amounts of nitrate, the plant-available form of nitrogen, from soil organic matter and plant residue if the soil is warm and moist enough. Even though it has been warmer than normal, Jones said, soil temperatures at 2 to 4 inches are still generally below 40 degrees, which is a temperature where microbial activity is very low, likely minimizing nitrogen release. In addition, low rainfall in most areas has likely prevented nitrate leaching except on very shallow soils. Considering all factors, Jones predicts that spring nitrate levels won't be substantially different than fall levels, and that re-testing soil this spring for those who sampled in the fall may not be necessary.

Given relatively high nitrogen fertilizer costs, low commodity prices and below-average soil moisture, Jones suggests applying conservative nitrogen rates this spring. Nitrogen could be applied in-season if spring has average-to-above-average precipitation. In-season nitrogen application can be especially helpful at increasing wheat grain protein, but equipment, time or weather constraints often minimize its use.

A calculator on MSU Extension's soil fertility website can be used to determine nitrogen rates that maximize profit. Overfertilizing nitrogen can lead to soil acidity problems, water contamination and reduced profit, so it is important to only apply what is necessary, Jones said. Because urea fertilizer can be lost to the air as ammonia, urea should either be applied 2 inches or more below the surface or surface-applied before a predicted large rain event of at least ½ inch.

Recent research by Jones and his colleagues on sulfur fertilizer has found that yellow mustard needs about 2.5 pounds of available sulfur per 100 pounds of grain, canola needs approximately 0.65 pounds of available sulfur per bushel, and wheat and pea need about 0.3 pounds of available sulfur per bushel. Available sulfur equals the amount of sulfur fertilizer plus the amount of plant-available soil sulfur in the top 2 feet of the soil, expressed in pounds per acre. Not all sulfur soil tests produce the same results, so individuals are invited to contact Jones with any questions on sulfur tests.

Minimal phosphorus and potassium fertilization is necessary if a soil test shows that soil phosphorus is above 16 parts per million or that potassium is above 250 parts per million. If phosphorus or potassium levels are below these thresholds, it is recommended that additions of these nutrients be made to the soil.

Jones noted that fertilizer applied in the seed row can impact seedling emergence more when soils are dry, especially in coarse soils. He recommends contacting a crop adviser, MSU Extension agent or Jones himself to determine seed-safe fertilizer rates.

Jones said producers or crop advisers should scout crops early for signs of nutrient deficiencies, as rescue nutrient applications can be made if deficiencies are spotted early enough.

"Nitrogen deficiency is likely if the older leaves are uniformly light green or yellow. Sulfur deficiency symptoms are similar but show up on the newer leaves first," Jones added.

More detailed descriptions and pictures of nutrient deficiency symptoms are available at https://landresources.montana.edu/soilfertility/nutrientdeficiency.html.

Individuals can contact a crop adviser or local MSU Extension agent for help making fertilizer decisions. Questions about soil fertility can also be directed to Jones at [email protected] or 406-994-6076 or addressed by visiting the MSU Extension soil fertility website at landresources.montana.edu/soilfertility/.