Potential Nitrogen Loss from Frozen Soil Nitrogen Applications to Wheat

Most wheat (Triticum aestivum L.) producers in Kentucky use a split application of nitrogen (N) and make the first application between growth stages Feekes 2 to 3 (mid-February) and the second application between Feekes 5 to 6 (early March and midto late March). Some wheat producers will make early N applications to wheat on frozen ground to avoid rutting or compacting fields with large sprayers. Kentucky had below average temperatures in 2014 for January and February (UK Ag Weather Center, 2014), resulting in frozen soil until 19 February, which delayed wheat development 2 to 3 weeks. Some producers made early N applications in January to dormant wheat on soil frozen to a depth of 6 to 9 inches. This differed from typical early-season N applications made to actively growing wheat in the morning when the soil is sufficiently frozen to support sprayer traffic and before the soil starts to later thaw. Soil thawing usually allows N to infiltrate the soil profile and reduce runoff potential. An experiment was initiated at the University of Kentucky Research and Education Center in Princeton to determine N loss in wheat when N was applied to frozen soil. A Crider silt loam soil (Typic Paleudalf) with <1% slope and a Zanesville silt loam soil (Oxyaquic Fragiudalf) with a 3% slope were used. Plots were established in existing wheat that was drilled into 7-inch rows at a seeding rate of 168 lb wheat/acre in midto late October 2013. A randomized complete block design with three N rates (0, 40, and 80 lb N/acre as NaNO3), two N application conditions (frozen and thawed soil), and three replications of 25-ft2 plots were used to determine potential N loss from frozen soil applications. The NaNO3 reflected the greatest loss potential of N, and permitted quantifying NO3 loss without confounding by nitrification of fertilizer NH4 +. The soil was frozen from the surface to a depth of 6 to 9 inches for both soil types on 30 Jan. 2014 and remained frozen until 19 February. Nitrogen was applied to frozen soil and dormant wheat (Feekes 2) on 30 Jan. 2014. Soil samples were collected to a depth of 12 inches on 24 February for both soils and analyzed for soil NO3 by cadmium reduction to Published in Crop, Forage & Turfgrass Management DOI: 10.2134/cftm2014.0054 © 2015 American Society of Agronomy and Crop Science Society of America 5585 Guilford Rd., Madison, WI 53711