Use of legumes as an alternative to nitrogen (N) fertilization in pasture management improves
forage quality and animal performance and has been suggested to reduce the potential for environmental
pollution. "Kentucky 3l" tall fescue fertilized with 160 kg N ha-1 yr-1 (split application)
was compared to tall fescue grown with alfalfa or red clover in a 5-yr pasture experiment on a mixed
Typic Hapludult. During yr 6, effects of N fertilization or the legume on soil N, forage N concentration,
yield, botanical composition, N intake by esophageally fistulated steers grazing the
pastures and N utilization by wethers fed the harvested forages were investigated. Soil ammonium
was higher (P ≤ .01) in the A and B horizons in the tall fescue-red clover pastures compared to the
other treatments and nitrate was lower (P ≤ .05) in the A horizon, but concentrations differed (P
≤ .01) by date. Nitrate in the A horizon averaged 2.65, 1.38 and 2.21 ppm for tall fescue-N, tall
fescue-red clover and tall fescue-alfalfa, respectively. In the B horizon, average soil NO3 was .43,
.23 and .53 ppm for tall fescue—N, tall fescue-red clover and tall fescue-alfalfa, respectively. Tall
fescue-alfalfa pastures were higher (P ≤ .01) in percentage legume than tall fescue-red clover, overall,
but differed by date (P ≤ .01). Alfalfa was generally higher (P ≤ .05) in N concentration than
red clover. Total kg N accumulated ha-1 in above-ground herbage was higher (P≤ .05) for the
grass-legume mixtures than N-fertilized tall fescue. Esophageally fistulated steers grazing stockpiled
tall fescue-alfalfa selected forage higher (P ≤ .05) in N concentration than steers grazing the
other
pastures. Stockpiled tall fescue-alfalfa fed to wethers in a metabolism trial was higher (P ≤ .01) in
N concentration, dry matter digestibility (DMD), apparent N absorption, and N retention than the
other treatments. All treatments differed, with wethers fed tall fescue-red clover having the lowest
DMD, apparent N absorption and N retention. Wethers fed tall fescue-alfalfa and tall fescue-red
clover had higher blood urea N then those fed tall fescue-N. Results of this research demonstrate
that soil NO3 concentrations were low for all three forage treatments and would not contribute
to ground water contamination. Legumes supplied adequate N to achieve yields similar to tall
fescue fertilized with N and increased N production ha-1 in the above ground biomass.
Digestibility and utilization of the N in stockpiled tall fescue were improved by inclusion of alfalfa
but not red clover.
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