Montana State University Extension’s soil fertility specialist Clain Jones said on Mar. 9 that farmers should consider how this year’s warm and dry winter may affect fertilizer decisions for the upcoming growing season.
Most of Montana is experiencing abnormally dry or moderate drought conditions, with some areas in northcentral Montana facing severe or extreme drought, according to the National Weather Service’s drought monitor. The northern part of the state, east of the Continental Divide, has received less than 25% of normal precipitation from Jan. 1 to Mar. 2, while only a small portion of central Montana has seen about normal precipitation. The Montana Climate Office reports that 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.”
Jones explained that phosphorus, potassium and sulfur levels are not expected to change much from last fall due to limited leaching and slowed nutrient release from organic matter and plant residue. However, nitrogen could see more significant changes because it can increase or decrease substantially over winter depending on microbial activity and moisture levels. Despite warmer weather, Jones noted that low rainfall likely prevented nitrate leaching except on very shallow soils and predicted spring nitrate levels would be similar to those measured in the fall.
Given high nitrogen fertilizer costs, low commodity prices and below-average soil moisture, Jones recommended conservative nitrogen rates this spring with possible in-season applications if precipitation improves. He also advised using MSU Extension’s online calculator for determining profitable nitrogen rates and cautioned against overfertilizing due to risks such as soil acidity problems and water contamination.
Recent research by Jones’ team found specific sulfur needs for crops like yellow mustard, canola, wheat and pea based on grain yield. He encouraged producers to contact him with questions about sulfur tests since not all produce consistent results.
Minimal phosphorus or potassium fertilization is needed if soil test results show phosphorus above 16 parts per million or potassium above 250 parts per million; otherwise additions are recommended. Fertilizer applied in seed rows can impact seedling emergence more when soils are dry—especially in coarse soils—so consulting a crop adviser or MSU Extension agent is suggested.
Jones said early scouting for nutrient deficiencies allows for timely rescue applications: “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.” More information about deficiency symptoms is available at https://landresources.montana.edu/soilfertility/nutrientdeficiency.html.
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