BLACKFOOT CHALLENGE
WEEKLY IRRIGATION REPORT
Friday June 3, 2011
All crops except new plantings used more water again this week than the effective rainfall and so upper soil
profiles are dry if not yet irrigated. Some irrigators are applying their first water while others have finished one
application. Many irrigators are checking equipment, application amounts and uniformity while at this time.
WEATHER
Rainfall across the drainage was about ¼ inch this last week with rising temperatures which
are expected to keep rising to seasonal normal this week.
CROP WATER USE
Crop water use rose this last week due to less rainfall and warmer weather. The table below
lists crop water use for the common local crops and for lawns. Attached is a summary of crop
water use for this entire growing season (updated each week).
WATER USE IN INCHES
ALFALFA HAY
GRASS HAY & PASTURE
SMALL GRAINS
LAWNS
LAST 7 DAYS
.8
.75
.25
.9
NEXT 7 DAYS1
1 (.8 -.1.2)
.9 (.7-1.1)
.3 (.25-.5)
1.2 (.8-1.4)
1
Expected water use (potential range if weather becomes cooler or hotter than expected)
SOIL MOISTURE
Soil moisture levels have continued to fall as crop water use increased and rainfall decreased
the past few weeks. Some soils that have not been irrigated have fallen below 50% of their
available water holding capacity, especially sandy and rocky soils in the drier parts of the
drainage. Soil moisture levels will begin dropping rapidly. Early season is a good time to fill
up your soil while temperatures and crop water use is low. However, be aware that early
irrigation may increase risks for fungal diseases, especially during cool, moist springs like this
one.
WEEKLY TIPS
Effective or Net Rainfall and Irrigation
Gross Rainfall is what falls in the rain gauge while Effective Rainfall or Net Rainfall is what makes it into the soil
for use by the crop. The same goes for Gross Irrigation and Effective or Net Irrigation. Early in the season, the
first ¼ inch or so simply evaporates from crop and soil surfaces. In the hot and windy part of the season up to
½ inch can be lost. This means that most summer rainstorms do not contribute much to soil moisture and crop
water. Only about 3 of the 6-8 inches of rain that falls during the local growing season is effective. Be sure to
apply enough extra water to account for this loss when irrigating.
How Much Water Should I Apply?
It is most efficient to apply as much as you can at one time since you lose some to evaporation each time and
since it costs to run the system. Apply at least 1-1 ¼ inch (gross) so you get at least ¾-1 inch in the soil (net).
Don’t apply more than your soil will hold (your available water capacity minus the amount of soil moisture you
have now).
For further information contact Barry Dutton, Registered Professional Soil Scientist, 406-240-7798, dbarry13@q.com -orBrian McDonald, Blackfoot Challenge Project Coordinator, 406-493-0033, brian@blackfootchallenge.org.
BLACKFOOT AREA GROWING SEASON RAINFALL AND CROP WATER USE
RAIN
MIXED GRAINS
ALFALFA HAY &
5-15
HAY
PASTURE START
3
3
2
CROP ROOT DEPTH IN FEET
Friday, May 06, 2011
Friday, May 13, 2011
Friday, May 20, 2011
Friday, May 27, 2011
Friday, June 03, 2011
Friday, June 10, 2011
Friday, June 17, 2011
Friday, June 24, 2011
Friday, July 01, 2011
Friday, July 08, 2011
Friday, July 15, 2011
Friday, July 22, 2011
Friday, July 29, 2011
Friday, August 05, 2011
Friday, August 12, 2011
Friday, August 19, 2011
Friday, August 26, 2011
Friday, September 02, 2011
Friday, September 09, 2011
Sunday, September 16, 2001
Friday, September 23, 2011
Sunday, September 30, 2001
TOTAL
ACTUAL 2011 WEEKLY CROP WATER USE
0.01
0.70
0.40
0.50
0.25
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
1.86
0.40
0.50
0.60
0.70
0.80
0.30
0.40
0.50
0.60
0.75
3.00
2.55
0.25
0.25
0.30
0.80
GRAINS
6-1
START
2
-
LAWNS
1
0.50
0.60
0.70
0.80
0.90
0.00
3.50
(ALL VALUES ARE INCHES OF WATER)
ESTIMATED CROP WATER USE
AVERAGE
WEEK
HOT WEEK COOL WEEK
ALFALFA HAY ALFALFA HAY ALFALFA HAY
WATER USE WATER USE WATER USE
0.40
0.50
0.60
0.70
0.90
1.00
1.20
1.30
1.40
1.50
1.60
1.50
1.40
1.40
1.30
1.20
0.90
0.70
0.60
0.50
0.40
0.30
21.30
0.70
0.80
0.90
1.10
1.40
1.50
1.90
2.00
2.20
2.30
2.50
2.30
2.20
2.20
2.00
1.90
1.40
1.10
0.90
0.80
0.70
0.60
33.40
0.20
0.30
0.40
0.50
0.60
0.70
0.90
1.00
1.10
1.10
1.20
1.10
1.10
1.10
1.00
0.90
0.60
0.50
0.40
0.30
0.20
0.20
15.40