Title:

Nitrogen Use, Cycling and Losses in
Non-Irrigated Bluegrass Seed Production

Objectives:

1. Compare current nitrogen management with improved management alternatives.

2. Determine a nitrogen budget for bluegrass seed production under current agronomic management practices.

3. Evaluate vertical movement of nitrate and quantify nitrate leaching losses in the vadose zone beneath a bluegrass crop.

4. Disseminate and transfer the technology developed to both growers and the bluegrass seed industry.

Investigators:

John E. Hammel (Soil Physics), Soil Science Division, University of Idaho
Robert Mahler (Soil Fertility), Soil Science Division, University of Idaho
Jon Hutchings (Graduate Student), Soil Science Division, University of Idaho

Cooperators:

Glen Murray, Plant Science Division, University of Idaho, Moscow
Stephen Griffiths, USDA-ARS, Corvallis, Oregon
Alan Mitchell, Oregon State University, Madras, Oregon
Vicki Parker-Clark, Kootenai County Extension Agent, Coeur d'Alene, Idaho
Paul Stern (grower cooperator), Rockford, Washington

Abstract:

A nitrogen fertilizer-bluegrass field experiment was established during Fall 1995 on a grower cooperator field in Kootenai County in northern Idaho. Fertilizer treatments included: 1) 140 Ibs N/ac, traditional rate, fall application, 2) 100 lbs N/ac, alternate rate, fall application, 3) 100/40 Ibs N/ac, fall/spring split, traditional rate, 4) 60/40 lbs N/ac, fall/spring split, alternate rate, 5) 140 Ibs N/ac, traditional fall rate, slow release, and 6) 100 lbs N/ac, alternate fall rate, slow release. Soil-water samplers were placed within each treatment to measure variations in nitrate concentrations during the winter. Initial above ground biomass, root biomass and soil samples were collected in November to be used in conjunction with spring and harvest samples for N budget determination and for estimation of overwinter nitrate leaching losses.

Justification:

Northern Idaho and eastern Washington produce 70 to 80% of the Kentucky bluegrass (Poa pratensis) seed grown in the United States. In non-irrigated areas of northern Idaho, annual N fertilizer applications to bluegrass seed crops range between 120 and 160 Ibs N/ac. Current management practices include fall application of the major portion of N fertilizer to assure seed production the following year. During the winter, little N is utilized by bluegrass and a large fraction of the applied N fertilizer exists in the nitrate form. Since nitrate is highly mobile, a high potential for leaching losses during the wet winter period exists. This poses a threat to the region's groundwater and causes low nitrogen-use efficiencies resulting in an economic loss to growers. Knowledge of nitrogen leaching losses and bluegrass N requirements under current bluegrass seed production is needed to develop effective alternative N fertilizer management.