Agriculture Reference
In-Depth Information
yield improvement from 1968 to 1990 to genetic
gains; however, they attributed 48% of yield
improvement over this same period to improved
management, specifi cally to increased levels of
nitrogen fertilizer. Wheat breeding during this
time did result in signifi cant gains in nonyield
components such as end-use quality, and it is
likely that increased nitrogen fertilizer applica-
tions would not have been possible without
the introgression of semidwarfi ng genes. These
studies reinforce the interdependency of yield
building and yield protecting factors and how
they must be used collectively to form a wheat
management system.
ronmental variation. Similarly, market forces and
grain quality standards sometimes trump raw
yield potential in the decision-making hierarchy
of bread wheat producers.
Quantity is not the only nitrogen-related
consideration for intensive wheat management.
Increased emphasis on input application timing
and accuracy has been a covariate in this success.
Timing, split nitrogen applications, and alloca-
tions to each split are all integral parts of the
overall intensive management scheme. A fall
application of nitrogen in intensive wheat man-
agement systems is generally limited to 15 to
30 kg ha
−1
and is often combined with a preplant
application of phosphorus and potassium. It is
also important to understand that split applica-
tion of nitrogen in intensive wheat management
systems generally refers to a split
spring
applica-
tion, not just a fall-spring split. These applica-
tions typically occur at Feekes growth stage (GS)
3 and 6 (Large 1954). By delaying the bulk of
nitrogen application until just before or at joint-
ing in winter wheat, producers have been able to
better assess crop nitrogen needs and adjust nitro-
gen application accordingly. Further, by having a
precise knowledge of crop nitrogen requirements,
producers are able to increase effi ciency and better
utilize nitrogen as a management tool. Nitrogen
timing, for example, has been shown to be an
effective tool in managing tiller numbers in winter
wheat (Weisz et al., 2001). Management of tiller
numbers is a critical tool in achieving the desired
500-600 wheat heads per square meter at harvest
(Alley et al., 1993).
Just as monitoring of crop fertility needs has
resulted in an increase in wheat yield over the past
couple decades, intensifi ed monitoring of insect
infestations and disease incidence and severity
have helped protect the yield created through
improved cultivars and increased nitrogen rates.
Ransom et al. (2006) attribute much of the geno-
type × management interaction mentioned earlier
in this chapter to differing levels of disease control
with fungicide. Further, increased nitrogen fertil-
izer rates associated with increased nitrogen
fertility and increased wheat head densities can
necessitate the use of foliar fungicides and plant
Fertility and pest management
The fi rst step in optimizing and/or intensifying
wheat management is selecting the right cultivar
and matching nitrogen fertility to the cultivar
(Karlen and Gooden 1990). Finding the correct
combination of these two elements often dictates
the difference between negative and positive cash
fl ow from operations (Karlen and Gooden 1990).
The majority of successes in intensive wheat
management have hinged on improved nitrogen
fertility and fi nding cultivars that respond to
this improved fertility. Austin (1999) attributed
much of the advance in wheat yield in the UK to
shorter-statured wheat cultivars with increased
straw strength, which allowed greater responsive-
ness to nitrogen fertilizer. Abeledo et al. (2003)
made similar observations in winter barley.
Moreover, producers who implement intensive
wheat management strategies often place greater
emphasis on straw strength and tolerance to
high nitrogen fertilizer rates than on disease
resistance.
In this example, the basic assumption is that a
foliar fungicide will be used after fl ag leaf emer-
gence and that disease resistance can be viewed as
subordinate to overall yield potential. In contrast,
low-input wheat producers will view disease
resistance as crucial to wheat cultivar performance
and suitability. These producers are often willing
to sacrifi ce top-end yield potential for consistent
performance despite spatial and temporal envi-
