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Vol. 17, No. 2
Article 4 of 10
February 20, 2007
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Potential For Fall-Applied Nitrogen Losses Not Eliminated By
Recent Cold Snap By John Lory The recent cold snap has caused the lowest soil temperatures registered in nine years in six-inch soil temperature data recorded at Novelty, Missouri. Soil temperatures have remained below freezing since late January, the longest period of sub-freezing temperatures in the nine-year record. Typically, soil temperatures averaged 2.7 degrees above freezing during this period. This cold spell represents a sharp contrast to warm soil temperatures in late December and early January. During a three-week period, 14 days had the highest soil temperatures recorded in the nine-year record. During this period, soil temperatures averaged over eight degrees above freezing compared to a long-term average of just over three degrees above zero. Farmers who apply fall nitrogen depend on cold soils to hold nitrogen in the soil over-winter. Ideally, anhydrous ammonia is injected into soils that rapidly reach near-freezing temperatures. Cold soil temperatures inhibit the conversion of the anhydrous to nitrate, which is highly mobile in the soil. Applying anhydrous ammonia too early in the fall, or unusually warm winter soil temperatures coupled with excessively wet soils in winter or spring, can lead to significant losses of fall-applied nitrogen. Despite the cold snap, the potential to convert anhydrous to nitrate has been above average since mid-November. There is a high probability that anhydrous ammonia applied without inhibitors before mid-November in northern Missouri has converted to nitrate. Be aware that a wet late winter or spring could lead to significant losses of fall-applied nitrogen despite the current cold snap. To see current six-inch soil temperatures underneath soybean stubble at nine locations across northern Missouri, visit the Website http://agebb.missouri.edu/weather/reports/soysoil6.asp.
John A. Lory |
