Nitrate Leaching from Grassed Lysimeters Treated with Ammonium Nitrate or Slow-Release Nitrogen Fertilizer

Nitrate leaching is a potential in humid regions when crops and forages are fertilized. This study was conducted to compare NO 3 leaching with two different N fertilizer formulations applied to forages. For 11 yr, ammonium nitrate (AN) was applied to a large (8.1 m 2 surface area), undisturbed, monolithic lysimeter Y101B at an annual rate of 168 kg N ha -1 , and methylene urea (MU), a slow-release fertilizer, was applied to a similar lysimeter (Y101D) at the same rate. Nitrate-N concentrations in the percolate from these 2.4 m-deep lysimeters were measured weekly. Even though NO 3 -N levels increased steadily with the AN applications, the greatest increases occurred during the eighth year of treatment and reached levels above 20 mg L -1 . With the MU, NO 3 -N concentrations remained relatively constant until after 8 yr of treatment, reaching concentrations of 6 mg L -1 . The highest rates of annual NO 3 -N transport in percolate were 42.3 and 12.1 kg ha -1 from lysimeters treated with AN and MU, respectively. (Losses from NH 3 volatilization were measured at 12.0 and 44.8 kg N ha -1 for AN and MU, respectively.) Nitrate-N transport in percolate varied seasonally with the greatest amounts being moved during the late winter-early spring. Following 11 yr, the NO 3 -N concentrations in each lysimeter declined to approximately 1 mg L -1 . Based on this study with a 168 kg N ha -1 annual application rate, less NO 3 -N leaching will occur when a slow-release N fertilizer, such as MU, is applied to forages than when AN is applied.