Agriculture Reference
In-Depth Information
are two primary reasons for this. First, added
nitrogen in the fall encourages early wheat growth
and adequate forage production. Second, the
removal of cattle in early March leaves little time
for top-dress applications of nitrogen, as the
plants are quickly approaching the critical time
for canopy closure. Still, most modern dual-
purpose wheat producers choose to make some
type of top-dress nitrogen application in late
winter. Top-dress nitrogen amounts vary by pro-
ducer but extension recommendations indicate
a need for 30 kg ha
−1
of nitrogen for every
1,000 kg ha
−1
of wheat forage produced. This
nitrogen requirement comes despite that 61%-
77% of the nitrogen consumed in wheat forage
by ruminant animals is excreted in feces (33%)
and urine (66%) (Phillips et al., 1995). Nonuni-
form distribution of urine and feces and losses
due to volatilization and runoff necessitate top-
dress nitrogen applications.
Planting date for dual-use wheat is much earlier
than for grain-only systems. Hossain et al. (2003)
demonstrated that optimal sowing dates for forage
production are approximately one month earlier
than for grain-only systems (Fig. 4.2). Early-
September sowing dates have been shown to
increase duration of grazing by as much as 24 days,
but the tradeoff was a 22% reduction in grain yield
relative to a late-September sowing date (Hossain
et al., 2003). Io optimize the forage and grain com-
ponents of the system, a mid-September planting
date was considered optimal.
Actual yield reduction from the act of grazing
is debatable. Georgeson et al. (1892) reported a
wheat grain yield reduction of 202 kg ha
−1
when
wheat pasture was grazed but then reported no
yield reduction in a later study (Georgeson et al.,
1896). Similar mixed results followed for the next
100 years (Swanson 1935; Dunphy et al., 1982;
Winter and Thompson 1987; Redmon et al.,
1996), but most investigators agree that a yield
penalty is associated with grazing wheat pasture.
The severity of the yield reduction, however, is
quite debatable and depends on several factors.
Stocking density is probably the largest animal-
related infl uence on dual-purpose wheat yield.
Arzadun et al. (2003) reported that heavier
Grazing termination and impact on
grain yield
Timing of cattle removal from wheat pasture has
been the subject of investigation since the late
1800s (Redmon et al., 1995). Modern semidwarf
cultivars are more sensitive to timing of grazing
termination than older, taller cultivars. Increases
in cattle weight for grazing past the fi rst-hollow-
stem stage have generally not been suffi cient to
offset reductions in wheat yield; therefore, fi rst-
hollow-stem stage is considered the optimal
developmental period for removal of cattle from
wheat pasture (Redmon et al., 1996). Research by
Fieser et al. (2006) indicates that beef gains for
grazing past fi rst hollow stem can offset grain
yield losses when cattle average-daily-gains are
greater than 1.5 kg steer
−1
day
−1
and wheat yields
are less than 3,000 kg ha
−1
; however, fi rst hollow
stem was still recommended as the optimal timing
for grazing termination of wheat pasture.
Even when cattle are removed from wheat
pasture in a timely fashion, wheat yield reductions
generally occur in a dual-purpose wheat pro-
duction system relative to a grain-only system.
Some of this reduction is due to planting date.
Fig. 4.2
Wheat forage production increases with early
sowing, while grain yield benefi ts from later sowing. Most
dual-purpose producers in the US choose September 15
[day of year (DOY) 258] as the optimal compromise
between forage and grain yield. (Adapted from Hossain
et al., 2003.)
