Innovations in Dryland Agriculture

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Another factor that becomes clear from Fig. 4 is that the range of productive
options for saline agriculture decreases dramatically as ECe values increase. With
ECe values between 0 and 5 dS m−^1 about half the crops surveyed had relative yields
greater than 70 %. We can conclude that salinities in this range should not have a
strong effect on crop selection: many options are available. By contrast, with ECe
values between 20 and 30 dS m−^1 , half the crops surveyed had relative yields of less
than 10 %. We can conclude that salinities in this range should have extreme effects
on crop selection: very few productive options are available.
Increasing salinity causes agriculture to transition from potentially highly profit-
able cropping systems such as horticulture, vegetables, grains, forages and fibres to
lower-value salt-tolerant crops such as barley and halophytes (salt-tolerant grasses
and chenopod shrubs). Additionally, as salinity increases, the feeding value of the
available forage often decreases and issues of nutrient imbalances in the diet of
animals increase (Norman et al. 2013 ).
Many agricultural systems rely on the use of leguminous crops and pastures to
fix nitrogen biologically, thereby decreasing reliance on nitrogenous fertilisers.
However, legumes and their associated rhizobia tend to be salt-sensitive. Increasing
salinity therefore results in the loss of legumes (and therefore biological nitrogen
fixation) from agricultural systems. Unless research focuses on the simultaneous
selection of legumes and rhizobia for salt tolerance then farming systems in highly
salinised landscapes can be expected to be more nitrogen deficient.
One interesting case study of the importance of the selection of legume and rhi-
zobia for salt land comes from studies of the salt tolerant forage legume Melilotus
siculus. This species performed well in pasture trials on salt land in the year it was
planted, but failed to regenerate in subsequent years (Nichols et al. 2008 ). In the
year of planting the Melilotus was established with a commercial line of rhizobium


Fig. 4 Impact of soil salinity (ECe) on the relative yield of 108 crop plants (after Steppuhn et al.
2005 ). The red line indicates the median crop response


D.J. McFarlane et al.
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