Agriculture Reference
In-Depth Information
2007). With cooler ambient temperatures during
onset of fi rst hollow stem, however, a 2-week
delay in fi rst hollow stem may only translate to
a 2- to 3-day delay in heading and wheat
maturity.
stocking rates decreased wheat grain yield by 29%
but simultaneously increased cattle gains by 38%.
Similar to Fieser et al. (2006) they concluded that
the value of beef cattle gains were enough to offset
the reduction in wheat grain yield. In a later study
Arzadun et al. (2006) indicated that part of the
stocking rate effect was due to the amount of
green leaf area left in the fi eld after grazing events.
They simulated grazing intensity, and thereby
stocking density, by clipping wheat plants to
specifi ed heights and found that a 7-cm clipping
height had no effect on subsequent grain yield
in 2 out of 3 years, but a 3-cm clipping height
reduced grain yield every year of their
experiment.
Rainfall likely played some role in the amount
of yield reduction associated with grazing in these
experiments. Cattle traffi c on wet or waterlogged
soils damages wheat plants and likely increases
the yield penalty associated with grazing (see
Color Plate 7). Of course, the actual yield penalty
is relative to the yield potential of the wheat crop
prior to grazing. This is one reason that dual-
purpose wheat production has found favor in
areas with suboptimal wheat production environ-
ments. The cattle component in the systems
decreases risk by generating cash fl ow even if con-
ditions are not favorable for grain yield.
While later fi rst hollow stem is a desirable trait
for dual-purpose wheat producers, early matu-
rity is frequently the paramount selection
criterion for wheat growers. In areas where
double-cropping is prevalent, early maturity will
allow for earlier sowing of the following crop;
earliness of sowing often translates to increased
double-crop yield. Early maturity is preferred in
areas such as the US southern Great Plains due
to frequent drought. In these areas subsoil mois-
ture is often the only source of water for much
of the grain-fi ll season. Ambient temperatures
are generally lower during grain-fi ll of early-
maturing wheat cultivars than for later-maturing
cultivars. This translates to lower evaporative
demand and frequently to higher yield among
cultivars developed primarily in grain-only
systems. Dual-purpose wheat producers,
however, have had to accept earlier fi rst hollow
stem to achieve early heading (Edwards et al.,
NO-TILL WHEAT PRODUCTION
Conservation tillage refers to soil management
practices that leave at least 30% residue cover on
the soil surface. While adoption of conservation
tillage practices has remained fairly stable since
the mid-1990s, the proportion of all cropland
devoted to no-till crop production steadily
increased from 14.7% in 1996 to 19.6% in 2002
(Fawcett and Towery 2004).
Why no-till has increased
The most likely factor driving the increase of no-
till in the US has been the introduction of herbi-
cide-tolerant, bioengineered crops (Fawcett and
Towery 2004). Specifi cally, the introduction of
glyphosate-tolerant soybean, maize, and cotton
(
Gossypium hirsutum
L.) has driven the adoption
of no-till in the midwestern and southern US.
Thus far, genetically modifi ed wheat has not
reached commercial production, so adoption of
no-till management systems for wheat has been
much slower. In the wheat-dominated southern
Great Plains, for example, no-till practices account
for less than 5% of the acreage and adoption of
conservation tillage remains less than 20% (Ali
2002). In environments where monocrop wheat is
the primary cropping system, the lack of glypho-
sate-tolerant wheat cultivars has hampered the
adoption of no-till systems. Progress is being
made, however. Soft red winter wheat producers
in the southeastern and midsouthern US fre-
quently used no-till practices when seeding
soybean or maize but then tilled before sowing
wheat. These producers found over time, though,
that the long-term benefi ts of no-till systems as a
whole offset temporary reductions in wheat yield
and now operate under continuous no-till for all
crops.
