Fertilizer 15N Presence in Lysimeter Drainage Water

Agricultural and natural N cycling systems have been intensively studied via the stable isotope 15N. Tracing N translocation over time by applying 15N-tagged fertilizer has been used extensively. Our objective was to quantify fertilizer 15N translocation for an extended time in irrigated lysimeters containing sandy loam soil and cropped with corn and potato. Tagged fertilizer was applied to two lysimeters in 1989 and one in 1990. One lysimeter remained untreated. Breakthrough of 15N, above the background level of 0.366 atom %, was detected in drain effluent from 2.3-m-deep drains on treated lysimeters one year after initial preplant 15N application. Drainage water 15N concentration then increased rapidly to about 0.48 atom %, followed by a gradual decrease. However, 9 years after application there was still elevated 15N, 0.39 atom %, in the drainage water and 26-31% of the applied excess 15N remained in the soil profile. Cumulative 15N removed from lysimeters via drainage water during the first 7 years was between 3.0 and 3.7%. Estimated gaseous loss was 16%.