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 NO₃ leaching with two different N fertilizer formulations applied to forages. For 11 yr, ammonium nitrate (AN) was applied to a large(8.1 m² 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 percolatefrom these 2.4 m-deep lysimeters were measured weekly. Even though N0₃-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, N0₃-N concentrations remained relatively constant until after 8 yr oftreatment, reaching concentrations of 6 mg L^-1. The highest rates of annual N0₃-N transport in percolate were 42.3 and 12.1 kg ha^-1from lysimeters treated with AN and MU, respectively. (Losses from NH, volatilization were measured at 12.0 and44.8 kg N ha^-1for AN and MU, respectively.) Nitrate-N transport in percolate varied seasonally with the greatest amounts beingmoved during the late winter-early spring. Following 11 yr, the N0₃-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 NO₃-N leaching will occur when a slow-release N fertilizer, such as MU, is applied to forages than when AN is applied. [ABSTRACT FROM AUTHOR]