ARS | Publication request: NITROGEN MOVEMENT AND WATER QUALITY AT A POORLY-DRAINED AGRICULTURAL AND RIPARIAN SITE IN THE PACIFIC NORTHWEST.

Submitted to: Plant and Soil
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 1, 1997
Publication Date: N/A

Interpretive Summary: Grass seed cropping systems in the Pacific Northwest account for about half of the cool-season forage and turf grass seed production in the world. Grass seed cropping systems are intensely managed with inorganic fertilizers to sustain production. Must of the land where grass seed production occurs in western Oregon is marginally productive for most other crops because of poorly drained soil conditions. The role of riparian areas bordering grass seed fields in moderating surface water and groundwater quality is not well understood. A study site in western Oregon was instrumented to determine how riparian areas bordering grass seed fields process N and thereby influence water quality. The site consisted of a perennial ryegrass (Lolium perenne L.) seed field, a grass riparian area, and an intermittent creek. Collectively, findings show that both crop and riparian processes at the Lake Creek site are responsible for reducing shallow groundwater nitrate to levels below the drinking water standard for nitrate. Data also indicate that grower best management practices appear to minimize nitrate groundwater pollution under these conditions.

Technical Abstract: Grass seed crops are intensely managed with inorganic fertilizers to sustain production. The role of riparian areas bordering grass seed fields in moderating surface water and groundwater quality is not well understood. A study site in western Oregon was instrumented to determine how riparian areas bordering grass seed fields process N and thereby influence water quality. The site consisted of a perennial ryegrass (Lolium perenne L.) seed field, a grass riparian area, and an intermittent creek. Groundwater levels were monitored during the fall of 1995 to the late spring of 1996 and a complete set of samples were collected every two weeks from wells with water and analyzed for NO4**- concentrations for the riparian and field A and C horizons were <0.2 mg L**-1. Annual crop net N accumulation was 144 kg N ha**-1. Riparian soil electrode potentials (Eh)) at 25 and 45 cm average -200 to -100 mV during the wet cycle, whereas the field ranged between 0 to +50 mV. Collectively, findings indicate that both crop and riparian processes at the Lake Creek site are responsible for reducing shallow groundwater NO3**- to low levels.