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Superintendent
David Davis
21262 Genoa Road
Linneus, MO 64653
Phone: 660 895-5121
FAX: 660 895=5122
Email:
DavisDK@missouri.edu
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July 1, 2003
Forage Systems Update
Vol 12, No. 3
Influence of Nitrogen Rate and Pasture Composition
on Toxicity, Quality and Yield of Stockpiled Tall Fescue
Robert L. Kallenbach and Robert L. McGraw
Plant Sciences Unit, University of Missouri
More than one-third of Missouri's 60,000 beef producers use
stockpiled tall fescue to extend the grazing season. However, less
than half the producers who stockpile tall fescue apply N in late
summer to encourage fall growth. While previous research has shown
the yield and quality response of tall fescue fertilized with N in
late-summer, producers are reluctant to fertilize and frequently
raise three questions about it. These questions are:
1) How should I adjust my N rate for stockpiling if I have a mixed
tall fescue/red clover versus a pure stand of tall fescue?
2) Does applying N in late summer affect the clover component in my
mixed sward the next spring? And
3) Does applying N in late summer change the toxicity (ergovaline
concentration) of endophyte infected tall fescue?
Two years ago we began a study at FSRC to answer these questions.
The overall objective is to develop research-based recommendations
that help farmers accurately and profitably manage tall fescue for
stockpile grazing. Specific objectives are:
Objective 1: Determine the optimum N rate (late-summer N
application) for tall fescue/red clover versus pure tall fescue
pastures used for stockpile forage.
Objective 2: Determine if a late-summer N application affects the
persistence and productivity of red clover in mixed tall fescue/red
clover pastures the following spring.
Objective 3: Determine the influence of a late-summer N application
on the ergovaline content of tall fescue and tall fescue/red clover
pastures used for stockpile forage.
Methods
This four-year field trial began in August, 2001. The study has 10
treatments; five rates (0, 50, 100, 150 and 300 lb/acre) of N
applied in August and two pasture types (tall fescue with or without
red clover). Table 1 gives a complete listing of the
treatments. Nitrogen is applied as ammonium nitrate, and no N is applied
other than in August. The study is replicated six times.
We established the study using an existing endophyte-infected tall
fescue/red clover pasture. Before treatments were applied, the stand
was approximately 30% red clover and 70% tall fescue. For the tall
fescue treatments without clover, existing red clover plants were
killed in the spring of 2001 by spraying 2,4-D and Remedy. Plots of
tall fescue with red clover are over-seeded annually with 5 lb/acre
of red clover seed in February.
Forage yield was measured five times during the winter; on or about
15th of November, December, January, February and March from uncut
portions in each plot. In addition, forage yield was measured from
all sub-sub plots in May and July to study the residual effects of N
applications and winter harvest dates. Forage yields are determined
by clipping a 4-ft. x 20-ft. strip.
Forage quality and toxicity {crude protein, acid detergent fiber
(ADF), neutral detergent fiber (NDF) and ergovaline} are measured at
the same time as forage yield. Crude protein, ADF, NDF and botanical
composition of the tall fescue/red clover treatments is measured
using NIRS. Ergovaline is determined using standard wet chemistry
procedures.
Red clover plant density of the tall fescue/red clover treatments is
determined in August and June each year. Red clover plant density is
determined by counting the number of plants in five, 1.0-sq. ft.
frames in each sub-subplot.
Results
Because this is a four year study, we are only part-way through the
experiment. However, some preliminary results are:
Forage yields in November increase substantially when N is applied
in August. Despite the dry growing conditions in the autumn of both
2001 and 2002, and regardless of whether plots contained red clover,
we obtained a nearly linear response to N rates up to 100 lb/acre
(Fig. 1). Rates above 100 lb/acre show either little or no increase
in forage yield. Although many producers limit late-summer or fall
applications of N to 50 or 60 lb/acre, our data show that even in
dry years, rates up to 100 lb/acre give yield responses.
Our data suggest that when previous moisture conditions cause
limited on-farm hay supplies, a late summer N application might be
more cost effective than previously thought. However, we have only
two years of data; collecting the data over more years will help
with developing accurate recommendations.
Ergovaline is the principal toxin in infected tall fescue and this
compound causes metabolic problems for almost all classes of
livestock. While we have not had a chance to analyze all of the data
yet, we do have some preliminary data from the November 2002
harvest. The ergovaline content of stockpiled tall fescue increased
linearly with N rate (Fig. 2). When no nitrogen was applied,
ergovaline levels were approximately 175 ppb lower in mixed tall
fescue/red clover treatments than in treatments where no red clover
was present. However, the benefit of red clover declined as N rates
increased. This is probably due to the lower percentage of red
clover in the mixed sward as N rates increased.
The ergovaline concentrations we found are approximately 25 to 50%
lower than those reported by Rottinghaus et al. (1991) for
spring-grown tall fescue. However, the ergovaline concentration in
all treatments was in excess of the 150 ppb threshold for livestock
reported by Stamm et al. (1994). This suggests that while stockpiled
forage has lower ergovaline levels than tall fescue during the
growing season, it still is a potential problem for livestock owners
in winter and that N fertilizer management plays an important role.
Over the next two years we will continue our research on the impact
of N on stockpiled tall fescue. Specifically, we are interested in
determining the rate and extent of forage degradation over winter,
with a special focus on ergovaline concentrations. Based on previous
data published by Kallenbach et al. (2003), ergovaline levels are
expected to drop over winter in stockpiled tall fescue. Although the
influence of N rate on this process is unknown, we would like to
develop prediction equations that could guide producers, fertilizer
dealers, crop consultants and other about the potential toxicity and
use of stockpiled tall fescue in winter. In addition, we will be
able to determine the impact of fall fertilization on red clover
growth in tall fescue pastures the following spring.
References
Kallenbach, R.L., G.J. Bishop-Hurley, M.D. Massie, G.E. Rottinghaus,
and C.P. West. 2003. Herbage mass, nutritive value, and ergovaline
concentration of stockpiled tall fescue. Crop Sci. 43:1001-1005.
Rottinghaus, G.E., G.B. Garner, C.N. Cornell, and J.L. Ellis. 1991.
HPLC method for quantitating ergovaline in endophyte-infested tall
fescue: Seasonal variation of ergovaline levels in stems with leaf
sheaths, leaf blades, and seed heads. J. Agric. Food. Chem.
39:112-115.
Stamm, M.M., T. Delcurto, M.R. Horney, S.D. Brandyberry, and R.K.
Barton. 1994. Influence of alkaloid concentration of tall fescue
straw on the nutrition, physiology, and subsequent performance of
beef steers. J. Ani. Sci. 72:1068-1075.
Table 1. Experimental treatments including nitrogen rates and
pasture composition for the tall fescue stockpile study conducted at FSRC.
| Treatment |
Nitrogen rate
(lb/acre) |
Type of pasture |
| 1 |
0 |
Tall fescue |
| 2 |
50 |
Tall fescue |
| 3 |
100 |
Tall fescue |
| 4 |
150 |
Tall fescue |
| 5 |
300 |
Tall fescue |
| 6 |
0 |
Tall fescue/red clover |
| 7 |
50 |
Tall fescue/red clover |
| 8 |
100 |
Tall fescue/red clover |
| 9 |
150 |
Tall fescue/red clover |
| 10 |
300 |
Tall fescue/red clover |
Fig 1. Yield in mid November of Stockpiled Tall Fescue
at Five Levels of N Applied August
Fig 2. Ergovaline Content of Stockpiled Tall Fescue
in Response to N Applied August
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