Morphological
and physiological determinants of persistence of alfalfa genotypes in
response
to grazing method were studied on a Kandiudalfic Eutrudox in
Piracicaba,
Brazil. In a mob-grazing study, under a
randomized complete block design, treatments were replicated six times
and combined
two grazing methods (main plot; rotational stocking simulated by
grazings every
4-wk in the "warm season" and 6-wk during the "cool
season", or continuous stocking simulated by weekly grazings) and five
alfalfa genotypes (subplots). Genotypes (ABT-805, Alfagraze, Crioula,
CUF-101
and Pioneer 5432) were agronomically contrasting (dormancy, origin, and
grazing
tolerance), and were grazed to a 7-cm stubble for 295 days (last
evaluations on
the 330th day). Genotypes differed on
final stand counts, plant survival, percent alfalfa in pregraze forage
mass,
and concentration and pool of total non-structural carbohydrates (TNC)
and
nitrogen (N) in roots and crowns. Crioula and CUF-101 did not survive
under either
grazing method. Alfagraze had the highest persistence under continuous
stocking, although stand counts declined from 246 to 64 plants m-2
(26%
survival). Under rotational stocking, ABT-805 had the highest
persistence (250 to 112.3 plants m-2;
45%
survival). Of the two dormant, non
grazing-tolerant genotypes, CUF-101 persisted less.
After 210 d of grazing, the mean proportion of CUF-101 alfalfa
in
the total pregraze forage mass was only 9.6%, a harbinger of stand
degradation,
which materialized at the end of the experiment. Mean
root TNC pools for the three grazing-tolerant cultivars
(Alfagraze, ABT-805, and Pioneer 5432) were reduced by 57% (651 to 281
g m-2)
and by 75% (610 to 156 g m-2) for Crioula and CUF-101, by
the 214th
day of grazing. Alfagraze stored more N (28 g kg-1 OM) in
plant
crowns than all the other genotypes, together with a higher N pool (55
g m-2),
already by the 86th day of grazing