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4.2 Major Crops for Dryland Farming
Wheat (Triticum aestivum L.) was the leading crop in the beginning of dryland
farming in the US (Widtsoe 1920 ) and remains so today in most regions. The crop
is not highly drought-resistant and does not tolerate prolonged drought. Wheat is
considered a drought avoidance crop which is well suited to dryland regions because
it can take advantage of soil moisture that accumulates during fallow periods, winter
and early spring, and matures before the hot and dry, late summer when planted at
the appropriate time (Hansen et al. 2012 ). Similarly, under water-stressed growing
conditions, wheat plants produce smaller cells reducing the height of the culm, the
size of the leaves and the stomatal openings, and hence are less adversely affected
by drought (Arnon 1972 ). Maize (Zea mays L.) was also a major crop in the begin-
ning along with sorghum (Sorghum bicolor L.). Maize lost favor in semiarid regions
because it was not considered as drought tolerant as wheat and sorghum. This is
interesting because it was considered the most successful dryland crop in the early
days of dryland farming (Buffum 1909 ; Shaw 1909 ; Widtsoe 1920 ). Widtsoe ( 1920 )
stated that of all the crops tried, maize was the most uniformly successful under
extremely dry conditions and he felt that the dryland community had yet to realize
the value of maize as a dryland crop. He stressed, however, that the value in dry
years was as a fodder crop because grain may not be produced. These early writers
stated that maize grown in dry areas should be planted in hills of multiple plants per
hill. Sorghum is grown largely in regions of Africa, Asia, North America and
Australia that are too dry for successful maize production. Sorghum produces higher
grain yield than maize under dry and hot climatic conditions because it remains
dormant during the period of severe water stress and resumes growth when favor-
able conditions reappear (Leonard and Martin 1963 ).
Cotton (Gossypium hirsutum L.) is also a major crop in dryland areas where
there is a sufficient frost-free growing season of at least 180 to 200 days, ample
sunlight and enough growing heat units accumulated during the growing season.
Sunflower (Helianthus annuus L.) is cultivated in some dryland areas; it has a deep
rooting system capable of extracting water and nutrients to a depth of 3 m, which
contributes to its adaptation to dryland environments (Jones and Johnson 1983 ).
Since there is a close relationship between plant available water in the soil profile
during the reproductive period and total biomass production, plants with high water
use efficiency (WUE) are important for determining crop yield under dryland envi-
ronments (Blum 2009 ). Crop yields have increased significantly in most dryland
farming regions over the years. For example, in Whitman County, Washington win-
ter and spring wheat yields have increased from less than 2000 kg ha−^1 to about
5000 kg ha−^1 over 73 years (Fig. 5 ), an average of 48 kg ha−^1 year−^1. However, the
data points indicate that yields may have plateaued during the 1980s. There are
many reasons for the increased yields, but there is little doubt that the main driver
has been reducing water loss by evaporation and runoff so more water is available
for the plants. This is because the units of water to produce a unit of biomass for
crops have changed little, if any. Widtsoe ( 1920 ) reported that German scientists, in
B.A. Stewart and S. Thapa