See more from this Session: Geneal Soil Fertility and Plant Nutrition: II
Laboratory studies were conducted on four soil types (Raub, Mesic Argiudolls; Pinhook , Mesic Endoaqualfs; Chalmers, Typic Endoaquolls; Pewamo, Typic Argiaquolls) from Indiana to quantify the distribution patterns of fixed and exchangeable N forms (NH4+-N, NO3--N) after anhydrous ammonia (AA) application under specific temperature and moisture content. Application rate of AA equivalent to 170 kg N/ha on a 76 cm spacing was injected at a pressure of 0.14 MPa into the center of 21 soil boxes (30 x 30 x 5 cm) arranged in a split block design and packed at a bulk density of 1.3 Mg/m3. Following application, soils were incubated in a growth chamber at a moisture tension of 0.05 MPa, 22 oC, and 100 % relative humidity. Soil samples were collected from seven concentric zones from the injection point at 1, 7, 14, 21, 28, 35, and 42 days after application. Upon injection of AA, the concentration of exchangeable NH4+-N was increased up to 5-6 cm from the injection point. Increases in fixed NH4+-N occurred up to 2-2.5 cm from the injection point and dissipated by 7 days after application. Production of NO3--N was more rapid from 2.5-4 cm outward and was observed beginning 7 days after application for Raub and Pinhook and at 14 days after application for Chalmers and Pewamo. Fixed and exchangeable NH4+-N concentrations decreased as NO3--N concentrations increased with time, but approximately 25 to 60% of the measured N pools remained in the NH4+-N form 42 days after application.