Nitrate Leaching from Grassed Lysimeters Treated with Ammonium Nitrate or Slow-Release Nitrogen Fertilizer
- L. B. Owens *,
- W. M. Edwards and
- R. W. Van Keuren
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 percolate from these 2.4 m-deep lysimeters were measured weekly. Even though NO3-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, NO3-N concentrations remained relatively constant until after 8 yr of treatment, reaching concentrations of 6 mg L−1. The highest rates of annual NO3-N transport in percolate were 42.3 and 12.1 kg ha−1 from lysimeters treated with AN and MU, respectively. (Losses from NH3 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 NO3-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.
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