Distribution of Applied Anhydrous Ammonia in Soils and Germination Hazard to Winter Wheat

Current changes in residue management systems for winter wheat (Triticum aestivum L.) include anhydrous NH₃ injection combined with herbicide application, planting, and other field operations. The feasibility of NH₃ application during planting is dependent upon potential NH₃ toxicity to germinating seeds. A laboratory experiment was conducted to study anhydrous NH₃ movement in soils by injecting 124 and 180 mg N as NH₃ into a Hollister clay (fine, mixed, thermic Pachic Paleustolls), Grant silt loam (fine-silty, mixed, thermic Udic Argiustolls), and Norge clay loam (fine-silty, mixed, thermic Udic Paleustolls) at 0.124 and 0.181 water (kg kg⁻¹) contents. Soil samples were taken 1, 7, and 14 d after N application. Soil NH⁺₄-N and calculated NH₃(aq) concentrations following NH₃ injection generated a normal distribution curve with N concentrations highest near the injection point and decreasing with increasing distance. Calculated NH⁺₄ diffusion coefficients decreased with time and water content and were soil dependent. Field studies were conducted in 1983 to determine the potential germination hazard from NH₃ applied at 0, 56, 112, 168, 224, and 280 kg N ha⁻¹ while planting, and in 1984 to winter wheat planted 0, 1, 3, 5, 6, and 7 d after applications of 0, 100, and 200 kg N ha⁻¹. Stand counts, forage NO⁻₃-N concentration, and yield were not influenced by NH₃ applications during planting in 1983, but grain N concentration increased linearly up to 24.1 mg g⁻¹ with 280 kg N ha⁻¹. In the 1984 experiment, increasing NH₃ rates did not decrease seedling stand, even though analysis of soil samples reflected increased soil pH and soil NH⁺₄-N concentration. Anhydrous NH₃ placement at a sufficient distance from newly seeded rows will ensure the success of systems which include NH₃ injection in conjunction with other field operations in residue management systems.