Sustainable Agriculture Literature Review - Boulder County

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from irrigation and precipitation. 268, 269 Reduced- and no-till operations have been shown
to allow for greater soil water availability than conventional tillage practices by building
capillary spaces for water movement and improving water retention. These practices
have reduced water demands by up to 12 percent, according to the USDA.
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270, 271
Covering soil with mulched cover crops can reduce water loss from the soil. Creating a
rough soil surface increases the area available to catch raindrops, thereby maximizing
water availability and retention, and mitigating water losses. 272 Improving soil structure
and organic matter content helps soil to retain water and also improves the availability of
water to plant roots. Increased organic matter can increase water retention 273 and
improve water percolation by up to 25-50 percent. 274 Additionally, improved soil stability
reduces erosion and the resulting runoff.
Efficiency of Ditch Delivery
Unlined or earthen ditches are one of the least efficient irrigation delivery systems due to
seepage losses through the soil (Figure 17). Estimates of water loss through seepage
from unlined ditches have been calculated as high as 45 percent with the U.S.
Department of Interior estimating a 22 percent average. 275 Methods proposed to improve
the water delivery and efficiency of use include lining earthen ditches with impermeable
materials to prevent seepage and replacing unlined ditches with pipeline delivery
systems that can improve the efficiency by 10 percent (Figure 17). 276
Figure 17: Potential On-farm Conveyance Efficiencies 277
Inefficient irrigation from unlined ditches can have offsite benefits, such as providing
habitat for a variety of wildlife, acting as an important source of recharge to shallow
groundwater, and possibly providing groundwater return flow to streams and rivers. 278 In
instances where these unlined ditches provide important off site benefits and the
seepage is reduced by the addition of linings, there may be adverse effects to the
beneficiary systems, which include ground water recharge, wildlife habitats, and wet
areas. According to the USDA “without consideration and careful planning, irrigation
project activities can negatively impact water quantity and quality, wetlands, fisheries,
and wildlife.” 279
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