Nitrate Movement after Anhydrous Ammonia Application in a Ridge Tillage System

Ridge application of N fertilizer has been promoted as a management tool to reduce nitrate movement. However, anhydrous ammonia applicator knives produce slots, which may impact water and nitrate movement. The objective of this study was to determine the effects of N fertilizer placement by an anhydrous ammonia applicator on nitrate movement within a ridge tillage system. Anhydrous ammonia was applied in a subsurface band to the ridge or valley areas of a ridge tillage system at the rates of 0 or 200 kg N ha−1. Rainfall (17 cm) was applied with a drop-type artificial rainfall simulator 3, 10, and 24 d after fertilizer application in a fallowed field. Percolating water was collected in grid lysimeters (15 by 15 cm) located 75 cm below the soil surface of a Brandt silty clay loam (fine-silty over sandy or sandy skeletal mixed Pachic Udic Haploboroll). Rainfall timing and N fertilizer placement influenced N fertilizer loss. The percentage of applied fertilizer collected in lysimeters when rainfall occurred 3 and 10 d after fertilizer application was 0 and 15%, respectively. When rainfall occurred 24 d after application, 49 and 73% of the applied N was leached through the profile from valley and ridge treatments, respectively. Increased N loss in the ridge treatment may have resulted from the fertilizer slot remaining open during the rainfall, while in the valley treatment the slot closed