Nitrate Levels in Shallow Groundwater under Pastures Receiving Ammonium Nitrate or Slow-Release Nitrogen Fertilizer
- L.B. Owens *,
- W.M. Edwards and
- R.W. Van Keuren
This study examined the impact on groundwater quality of conventional and slow-release N fertilizer to small, grazed watersheds in eastern Ohio. Three small watersheds (each less than 1 ha) received 56 kg N/ha annually as NH4NO3 for 5 yr. For the next 10 yr, one watershed received 168 kg N/ha annually as NH4NO3 and two others received the same amount of N as methylene urea, a slow-release fertilizer. Shallow groundwater samples were collected from springs and analyzed. After the 5-yr prestudy period, NO3-N levels in the groundwater from the three watersheds were in a 3 to 5 mg/L range. Groundwater NO3-N concentrations increased slightly during the first 3 yr at the higher N fertilizer rate, though they remained in the 3 to 5 mg/L range. Nitrate-N levels increased more sharply during the rest of the study. Although these NO3-N levels varied more between the growing and dormant seasons than when lower rates of fertilizer were applied, they eventually reached a slower rate of increase. During the 9th and 10th yr of the high application, seasonal NO3-N levels in groundwater ranged from 10 to 16 and 7 to 14 mg/L from the watersheds receiving NH4NO3 and methylene urea, respectively. This study showed that 168 kg N/ha was too much for this system, regardless of whether conventional or slow-release N was used.
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