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7 Conclusions
Dryland crop production is of major importance in North America, with large areas
of dryland farming in Canada, Mexico, and the United States. The Canadian Prairie
and the Great Plains and Inland Pacific Northwest of the U.S. are the areas with the
highest density of dryland farming. In addition, there are less dense areas of dryland
production in nearly every state in the western U.S and in northern and central
Mexico. The traditional production system is a wheat-summer fallow rotation with
conventional or stubble mulch tillage. Sustainability of this practice is limited by
soil degradation and erosion and poor water use efficiency. Where adopted, no-till
practices improve precipitation storage and use efficiency, which has led to crop
intensification and diversification and improvements in soil properties. While wheat
is the most common dryland crop in North America, dryland farming is also impor-
tant for the production of maize, sorghum, pulses, and oilseeds. No-till systems are
being adopted together with more intensive crop rotations that reduce fallow fre-
quency, increase precipitation use efficiency, reduce erosion, and improve soil prop-
erties. No-till adoption is greatest in the northern region of the Great Plains, where
climate conditions are favorable, and least in the Southern Great Plains.
As adoption of reduced tillage practices has grown, dependence on herbicides
for weed control has also increased and has led to weed resistance and weed shifts
that complicate weed management. With a limited array of available herbicide
classes, weed resistance will remain a challenge to wheat production in the future.
Herbicide resistance to glyphosate is creating unique challenges as a result of its
ubiquitous use. Sustainable weed management in dryland wheat production will
best be achieved through continued development and adoption of integrated weed
management and crop production practices.
When reduced or no-till practices are implemented, crop rotations can be intensi-
fied and diversified. In the Northern Great Plains, inclusion of oilseed crops in con-
tinuous crop rotations without fallow is common. Annual forage or pulse crops have
also been successfully integrated into dryland rotations, improving soil health such
as soil carbon levels and nutrient cycling. Gaining the soil improvements associated
with intensified rotations requires a period of time for the system to adapt and also
requires careful management. Choice of a fallow replacement crop is a major deci-
sion for dryland farmers in the Great Plains. Use of a cropping system model has
been demonstrated as a way to test alternative crops and crop rotations with differ-
ent environmental conditions and climate.
Sustainability of dryland cropping systems must consider practices that maintain
soil organic matter and restore soils degraded by past practices. Practices such as
residue burning and fallow period tillage have reduced soil organic carbon levels by
as much as 60 %. Current no-till dryland systems with intensified crop rotations
have been shown to stabilize soil carbon and increase soil organic matter accretion.
Future research using experimentation and modelling should continue to develop
alternative no-till crops and crop rotations that increase precipitation use efficiency,
improve soil properties, reduced dependence on N fertilizers, adapt to climate
change, and develop alternative markets.
N.C. Hansen et al.