The procedures described in this standard
test rely on overgrazing to prevent escapes and separate entries and are not
meant to be used as grazing recommendations for producers.
PLANT CULTURE
Establishment:
Land preparation, liming, fertilization, and pest control for
establishment and maintenance are the same as those used for any alfalfa yield or
performance trial. All entries to be tested, plus a grazing tolerant and
intolerant check, are sown at the normal planting date for alfalfa in replicated
sward plots (simulate planting with a cultipak seeder) at 15-20 kg ha-1 within a
grazing paddock (range 0.5 to 1.5 ha). A minimum of 1.5 X 4.5 m plots with 6
replications is recommended. The actual test should be surrounded on all sides
by at least 7.5 m of a border area between the test and any fence used to confine
the animals. Drinking water, mineral boxes, supplement feeders, and any shade
for the animals should all be located on the same end of the paddock and away
from the actual plots.
Grazing:
Plants are allowed to reach an early flowering stage before grazing
begins. After initial stands are determined, the test is exposed to intensive,
continuous stocking by beef cattle (entire paddock area constantly grazed to a
stubble height of 5 to 7.5 cm) for the entire grazing season (normally 120 days).
USE A CHEMICAL BLOAT PREVENTATIVE DURING GRAZING. Never use less than 2
animals per paddock (this reduces behavior problems associated with a single
animal). If total forage supply becomes insufficient for a maintenance diet,
then feed hay as a supplement.
Measurements:
Approximately 7-10 days after an
initial hay harvest or graze down, initial stand measurements are made. The most
common method is to count plants or crowns in small quadrats within each plot. A
minimum of 90 plants m-2 are required for adequate initial stands of each entry.
Stands of the tolerant and intolerant checks should be monitored throughout the
grazing season. When the tolerant and intolerant checks separate from each other
in a statistically significant manner (p<0.05) and are within their
acceptable ranges, then grazing can cease. Within 10-14 days after
grazing has ceased, stand
measurements are made similar to the initial
measurements on all entries.
Data Interpretation:
If initial stands are not significantly different among
entries, then use only final stand data to compare entries to the checks. If
initial stands are significantly different among entries, then both final stands
and survival % must be used for comparisons. An entry must, at a minimum, show
significantly (p<0.05) better final stands (and survival % if initial stands are
different) than the intolerant check and be no different from the tolerant check
in order to claim a grazing tolerance (T) rating (Table 1).
Subsequent Year Grazing:
If checks do not significantly separate during the first
grazing season, another season of grazing will be required. In the subsequent
year, initial stand measurements are made again. IF INITIAL STANDS ARE DEPLETED
FOR EITHER THE TOLERANT OR INTOLERANT CHECKS DUE TO WINTER-KILL OR OTHER FACTORS,
THEN THE TEST CAN NOT BE USED FOR A SECOND SEASON. If initial stands are similar
to where they were at the end of the previous season, then grazing can commence
as before.
Table 1. Example of plant counts.
| Variety |
| (Type*) | Initial | Final | Survival** |
| | -plants m-2- | % | | Variety A
(T) | 111.9 | 54.8 | 48.9 | | Variety B
(I) | 112.9 | 19.4 | 17.2 | | Variety C
(T) | 106.5 | 55.9 | 52.5 | | Variety D
(I) | 118.4 | 54.8 | 46.3 | | Variety E
(I) | 116.2 | 40.9 | 36.2 |
| Checks |
| Alfagraze (T) | 125.9 | 67.8 | 53.8 |
| Apollo (I) | 97.9 | 31.2 | 31.8 |
| LSD (5%) | 20.4 | 17.2 | 16.4 |
| Test
Mean | 109.8 | 51.6 | 46.9 | | CV
(%) | 16.5 | 30.0 | 30.3 | *T=grazing
tolerant; I=grazing intolerant. **Survival = Final plant counts/Initial plant
counts X 100.
CHECK CULTIVARS
Approximate Expected Tolerance: | | Final
Stands | Range | | -------------plants
m-2--------------- | | Tolerant | 60 |
40-82 | | Alfagraze (D/SD)* | | AmeriGraze 702 (ND)
| | ABT 805 (ND) | | Intolerant | 20 |
5-38 | | Apollo (D/SD) | | 5432 (D/SD) | | CUF 101 (ND)
| | | Survival** | Range |
| ----------%------------- |
| Tolerant | 44 | 29-60 |
| Alfagraze (D/SD) | | AmeriGraze 702 (ND) |
| ABT 805 (ND) | | Intolerant |
18 | 3-38 | | Apollo (D/SD) | | 5432
(D/SD) | | CUF 101 (ND) |
*D/SD=Recommended
checks to compare dormant and semi-dormant entries; ND=Recommended checks to
compare nondormant entries. **% Survival = Final plant counts/Initial plant
counts X100.
ALTERNATE METHOD
When plots are established as drilled rows, then determining percentage initial
and final stands can also be used instead of plant counts. An entry must, at a
minimum, show significantly (p<0.05) better final stands than the intolerant
check and be no different from a tolerant check in order to claim grazing
tolerance. This method is still in development and more data will be needed to
obtain expected tolerances for the checks.
Table 2. Example of alternate method.
| Variety (Type*) | Initial | Final |
| | ----------%----------- |
| Variety A(T) | 96 | 86 |
| Variety B(I) | 94 | 56 |
| Variety C (T) | 96 | 65 |
| Variety D(I) | 88 | 25 |
| Variety E (I) | 90 | 51 |
| Checks |
| Alfagraze (T) | 96 | 75 |
| Apollo (I) | 92 | 47 |
| LSD(5%) | NS | 17 |
| Test Mean | 94 | 64 |
| CV (%) | 9 | 12 |
*T=grazing tolerant; I=grazing intolerant.
REFERENCES
Bouton, J.H., S.R. Smith, C.S. Hoveland, and M.A. McCann. 1993. Development of
grazing tolerant alfalfa cultivars. p. 416-418. Proc. XVII International
Grassland Congress, 8-11 February 1993. Palmerston North, New Zealand.
Smith, S. R., Jr., J. H. Bouton, and C. S. Hoveland. 1989. Alfalfa persistence
and regrowth potential under continuous grazing. Agron. J. 81:960-965.
Smith, S.R., Jr., and J.H. Bouton. 1993. Selection within alfalfa cultivars for
persistence under continuous stocking. Crop Sci. 33:1321-1328.
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