Sustainable Agriculture Literature Review - Boulder County

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3.2 Irrigation Management
According to the USDA, effective irrigation management requires accurate timing and
regulation of water applications in a way that satisfies crop water requirements while not
wasting water, soil, and plant nutrients or degrading the soil. 227 This involves applying
water:
- According to crop needs
- In amounts that can be held in the soil and be available to crops
- At rates consistent with the intake characteristics of the soil, so as not to
increase erosion
- To ensure water quality is maintained or improved
Crop water use, also known as evapotranspiration (ET), is the combination of
transpiration, the amount of water plants use for growth and cooling purposes, and
evaporation, water evaporated from adjacent soil surfaces. 228, 229 Crop water use is
influenced by a variety of factors including prevailing weather conditions, available water
in the soil, crop species, and the growth stage of the crop. 230, 231 Most crops are more
sensitive to water stresses during one or more critical growth periods in the growing
season. Moisture stress during a critical period can cause an irreversible loss of yields
and reduction in the quality for crops. 232
The main irrigated crops in Boulder County by acreage include: 233
- Forage – 21,319 acres
- Corn (grain) – 2,499 acres
- Barley – 1,263 acres
- Wheat (grain) – 797 acres
- Corn (sillage/greenchop) – 671 acres
- Vegetables and other small grains such as millet to a smaller extent
Method of Irrigation
On a farm or field scale there are a number of water conservation practices that can be
employed to increase the efficiency of irrigation, but due to the specific nature of
agricultural operations no one practice is universally appropriate. 234 The latest soil
survey (2007) conducted by the USDA identified five principal methods of irrigation used
in Boulder County. 235 Working definitions of each of these methods are provided below.
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Furrow irrigation is used with row crops. Water is taken from ditches by siphon
tubes, gated pipes, or cuts in the ditchbank, and is applied in the furrows
between the rows of plants. On sloping soils the use of contour furrows helps to
control erosion by carrying water across the slope. On nearly level soils the
furrows are straight.
Border irrigation is used on nearly level fields that are planted with closegrowing
crops. In border irrigation water soaks into the soil as it advances down
narrow strips between the ridges. Uniform grades are necessary to ensure an
even distribution of water and to prevent ponding.
Controlled flooding is used on close-growing crops. Water is flooded down the
slope between closely spaced field ditches.
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