WSP10689

• File Number: 8273.600
• Description: Colorado River Basin Salinity Control - Federal Agencies - USDA
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 1/1/1994
• Author: USDA
• Title: Grand Valley Salinity Project - 1993 Annual Monitoring and Evaluation Report
• Water Supply Pro - Doc Type: Annual Report

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2. Over-irrigation seems to have been a common practice in
fields that were monitored because of abundant supply of
inexpensive irrigation water. In 1993, about one-half of
the farmers practiced a high degree of irrigation water
management (IWM).

3. Poor irrigation efficiencies at some sites are due to over
irrigation, i.e. fields are irrigated too soon and too
long. All.of the monitored surface irrigation systems are
capable of irrigating at 50% or greater efficiency with
.:proper management.

4 During pre-irrigation of annual crops and first irrigation
of perennial crops for stand establishment (e.g. alfalfa),
many farmers in the Grand Valley apply a large amount of
water to "black over" the soil so that seeds have adequate
moisture for germination and establishment. The
elimination of this practice would reduce deep percolation
substantially (see 16). However, farmer accepted
alternative cultural or management practice'would pe.needed
to ensure stand establishment. Farmers are reluctant to
accept.practices which are not economically beneficial.

5. Excess pre-irrigation, or the first irrigation, is the
biggest contributor to seasonal deep percolation losses.
This is directly related to high infiltration rate during
these irrigations, which subsequently decreases after .the
first irrigation. This'is supported by the "advance.time"
data obtained from some of the monitored sites. When.
infiltration is high, it take~ longer for water to reach
the end of the furrow. The "advance time" is less during
later irrigations because of the decrease in infiltration
rate due to sealing of the soil surface. .

I
6. The 1993 data for surface irrigated monitored sites .
indicate that, on the average, about 20% of the seasonal
.deep percolation losses occurred during the first .
irrigation event and about 31% by the end of second .
irrigation. For annual crops (small grain and corn), 23%
of deep percolation occurred during the first irrigation
and about 33% by the completion of the second irrigation.

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7. The 1993 data also shows that surface irrigated perennial
crop sites had 2.4 inches less deep percolation than annual
crops. Deep percolation for perennial crops fluctuated
throughout the season, due to changes in infiltration rates
and scheduling. Among annual crops, the deep perCOlation
decreased subtantially from the first to the second
irrigation event, stayed uniform for three to four
irrigations, and then decreased towards the end of the
irrigation season. 1

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