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II. PROCEDURE
Consumptive Use EquationExpressed mathematically, U = KF = sum of kf
where
- U = Consumptive use of crop for a season
F = seasonal consumptive use factor; or sum of the monthly consumptive use factors for the season or period
K = seasonal consumptive use coefficient
t = mean monthly temperature in degrees Fahrenheit
p = monthly percent of daytime hours for the latitude of the Weather Bureau station (Table I)
f = (t x p)/100 = monthly consumptive use factor
k = monthly consumptive use coefficient
u = kf = monthly consumptive use in inches
r = mean monthly precipitation or rainfall
re = mean monthly effective precipitation
Consumptive irrigation requirement = u - re
The computer will not print lower case letters, therefore, in Table IV (p. 22) which is the computer printout of the consumptive use calculations, only capital letters represent the lower case letters in the above discussion.
TABLE I - MONTHLY PERCENTAGE OF DAYTIME HOURS (p) OF
THE YEAR FOR LATITUDES 18° TO 65° NORTH OF THE EQUATORa
---------------------------------------------------------------------------------------------
Latitude
North Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec.
---------------------------------------------------------------------------------------------
65° 3.52 5.13 7.96 9.97 12.72 14.15 13.59 11.18 8.55 6.53 4.08 2.62
64° 3.81 5.27 8.00 9.92 12.50 13.63 13.26 11.08 8.56 6.63 4.32 3.02
63° 4.07 5.39 8.04 9.86 12.29 13.24 12.97 10.97 8.56 6.73 4.52 3.36
62° 4.31 5.49 8.07 9.80 12.11 12.92 12.73 10.87 8.55 6.80 4.70 3.65
61° 4.51 5.58 8.09 9.74 11.94 12.66 12.51 10.77 8.55 6.88 4.86 3.91
60° 4.70 5.67 8.11 9.69 11.78 12.41 12.31 10.68 8.54 6.95 5.02 4.14
59° 4.86 5.76 8.13 9.64 11.64 12.19 12.13 10.60 8.53 7.00 5.17 4.35
58° 5.02 5.84 8.14 9.59 11.50 12.00 11.96 10.52 8.53 7.06 5.30 4.54
57° 5.17 5.91 8.15 9.53 11.38 11.83 11.81 10.44 8.52 7.13 5.42 4.71
56° 5.31 5.98 8.17 9.48 11.26 11.68 11.67 10.36 8.52 7.18 5.52 4.87
55° 5.44 6.04 8.18 9.44 11.15 11.53 11.54 10.29 8.51 7.23 5.63 5.02
54° 5.56 6.10 8.19 9.40 11.04 11.39 11.42 10.22 8.50 7.28 5.74 5.16
53° 5.68 6.16 8.20 9.36 10.94 11.26 11.30 10.16 8.49 7.32 5.83 5.30
52° 5.79 6.22 8.21 9.32 10.85 11.14 11.19 10.10 8.48 7.36 5.92 5.42
51° 5.89 6.27 8.23 9.28 10.76 11.02 11.09 10.05 8.47 7.40 6.00 5.54
50° 5.99 6.32 8.24 9.24 10.68 10.92 10.99 9.99 8.46 7.44 6.08 5.65
49° 6.08 6.36 8.25 9.20 10.60 10.82 10.90 9.94 8.46 7.48 6.16 5.75
48° 6.17 6.41 8.26 9.17 10.52 10.72 10.81 9.89 8.45 7.51 6.24 5.85
47° 6.25 6.45 8.27 9.14 10.45 10.63 10.73 9.84 8.44 7.54 6.31 5.95
46° 6.33 6.50 8.28 9.11 10.38 10.53 10.65 9.79 8.43 7.58 6.37 6.05
45° 6.40 6.54 8.29 9.08 10.31 10.46 10.57 9.75 8.42 7.61 6.43 6.14
44° 6.48 6.57 8.29 9.05 10.25 10.39 10.49 9.71 8.41 7.64 6.50 6.22
43° 6.55 6.61 8.30 9.02 10.19 10.31 10.42 9.66 8.40 7.67 6.56 6.31
42° 6.61 6.65 8.30 8.99 10.13 10.24 10.35 9.62 8.40 7.70 6.62 6.39
41° 6.68 6.68 8.31 8.96 10.07 10.16 10.29 9.59 8.39 7.72 6.68 6.47
40° 6.75 6.72 8.32 8.93 10.01 10.09 10.22 9.55 8.39 7.75 6.73 6.54
39° 6.81 6.75 8.33 8.91 9.95 10.03 10.16 9.51 8.38 7.78 6.78 6.61
38° 6.87 6.79 8.33 8.89 9.90 9.96 10.11 9.47 8.37 7.80 6.83 6.68
37° 6.92 6.82 8.34 8.87 9.85 9.89 10.05 9.44 8.37 7.83 6.88 6.74
36° 6.98 6.85 8.35 8.85 9.80 9.82 9.99 9.41 8.36 7.85 6.93 6.81
35° 7.04 6.88 8.35 8.82 9.76 9.76 9.93 9.37 8.36 7.88 6.98 6.87
34° 7.10 6.91 8.35 8.80 9.71 9.71 9.88 9.34 8.35 7.90 7.02 6.93
33° 7.15 6.94 8.36 8.77 9.67 9.65 9.83 9.31 8.35 7.92 7.06 6.99
32° 7.20 6.97 8.36 8.75 9.62 9.60 9.77 9.28 8.34 7.95 7.11 7.05
31° 7.25 6.99 8.36 8.73 9.58 9.55 9.72 9.24 8.34 7.97 7.16 7.11
30° 7.31 7.02 8.37 8.71 9.54 9.49 9.67 9.21 8.33 7.99 7.20 7.16
29° 7.35 7.05 8.37 8.69 9.50 9.44 9.62 9.19 8.33 8.00 7.24 7.22
28° 7.40 7.07 8.37 8.67 9.46 9.39 9.58 9.17 8.32 8.02 7.28 7.27
27° 7.44 7.10 8.38 8.66 9.41 9.34 9.53 9.14 8.32 8.04 7.32 7.32
26° 7.49 7.12 8.38 8.64 9.37 9.29 9.49 9.11 8.32 8.06 7.36 7.37
25° 7.54 7.14 8.39 8.62 9.33 9.24 9.45 9.08 8.31 8.08 7.40 7.42
24° 7.58 7.16 8.39 8.60 9.30 9.19 9.40 9.06 8.31 8.10 7.44 7.47
23° 7.62 7.19 8.40 8.58 9.26 9.15 9.36 9.04 8.30 8.12 7.47 7.51
22° 7.67 7.21 8.40 8.56 9.22 9.11 9.32 9.01 8.30 8.13 7.51 7.56
21° 7.71 7.24 8.41 8.55 9.18 9.06 9.28 8.98 8.29 8.15 7.55 7.60
20° 7.75 7.26 8.41 8.53 9.15 9.02 9.24 8.95 8.29 8.17 7.58 7.65
19° 7.79 7.28 8.41 8.51 9.12 8.97 9.20 8.93 8.29 8.19 7.61 7.70
18° 7.83 7.31 8.41 8.50 9.08 8.93 9.16 8.90 8.29 8.20 7.65 7.74
a After SCS USDA, 19679
U. S. Weather Bureau records were used to define the growing season. Perennial forage crops, such as alfalfa and grass, consume water for the entire season as long as moisture is available for plant growth. A common definition for growing season for forage crops is the number of days between the last spring killing frost (28°F) and the first killing frost in the fall4. Observations have indicated that forage crops begin to grow and consume water as soon as the maximum daily temperatures stay well above the freezing point for an extended period of days3. The season continues despite later freezes. The end of the season occurs when the daily minimum temperature repeatedly falls below freezing and mean dally temperatures recede. The growing season for alfalfa and grass was assumed for this report to be the period when mean daily temperatures are above 40°F. Table II gives the forage crop growing season at the Wyoming weather stations.
TABLE II - GROWING SEASON FOR ALFALFA AND
GRASS AT WYOMING WEATHER BUREAU STATIONS
---------------------------------------------------------------------------
Normal Date of 40°F Length of
Mean Daily Temperature Growing Season
Station County Spring Fall (Days)
---------------------------------------------------------------------------
Afton Lincoln 4-21 10-23 185
Alta 1 NNW Teton 4-22 10-22 183
Arvada 3N Sheridan 4-3 10-31 211
Basin Big Horn 3-27 11-3 221
Bedford 2SE Lincoln 4-21 10-24 186
Big Piney Sublette 4-25 10-10 168
Border 3N Lincoln 4-17 10-23 189
Buffalo Johnson 4-6 11-1 209
Casper AP Natrona 4-8 11-2 208
Cheyenne AP Laramie 4-11 11-1 204
Chugwater Platte 4-3 11-1 212
Cody Park 4-4 11-5 215
Colony Crook 4-5 11-3 212
Diversion Dam Fremont 4-7 10-30 206
Dixon Carbon 4-9 10-26 200
Douglas Converse 4-4 10-30 209
Dubois Fremont 4-21 10-24 186
Dull Center 1SE Converse 4-3 11-2 213
Encampment 10ESE Carbon 4-16 10-28 195
Evanston 1E Uinta 4-19 10-23 189
Farson Sweetwater 4-16 10-19 186
Ft. Washakie 2S Fremont 4-5 10-29 207
Gillette 2E Campbell 4-8 10-31 206
Green River Sweetwater 4-5 10-29 207
Jackson Teton 4-19 10-22 186
Kaycee Johnson 4-9 10-31 205
Kemmerer Lincoln 4-18 10-22 187
Kendall Sublette 5-5 10-12 160
LaGrange Goshen 3-30 11-7 222
Lake Yellowstone Yellowstone NP 5-18 10-7 142
Lamar RS Yellowstone NP 4-29 10-14 168
Lander AP Fremont 4-7 10-30 206
Laramie Albany 4-18 10-27 192
Lovell Big Horn 4-4 10-31 210
Lusk Niobrara 4-6 11-2 210
Midwest Natrona 4-2 11-4 216
Moran 5WNW Teton 5-2 10-14 165
Newcastle Weston 4-4 11-2 212
Pathfinder Dam Natrona 4-6 11-2 210
Pine Bluffs Laramie 3-30 11-3 218
Pinedale Sublette 5-2 10-13 164
Powell Park 4-3 11-1 212
Rawlins AP Carbon 4-12 10-28 199
Riverton Fremont 4-3 10-28 208
Sage 4NNW Lincoln 4-18 10-20 185
Saratoga Carbon 4-15 10-26 194
Sheridan AP Sheridan 4-7 11-2 209
South Pass City Fremont 5-8 10-8 153
Spencer 10NE Niobrara 3-16 10-31 229
Sundance Crook 4-10 10-30 203
Sunshine 2ENE Park 4-19 10-23 187
Thermopolis Hot Springs 3-31 10-31 214
Torrington Exp. Farm Goshen 3-28 11-3 220
Wamsutter Sweetwater 4-11 10-25 197
Wheatland 4N Platte 3-26 11-8 227
Worland Washakie 3-31 10-27 210
------------------------------------------------------------------------
The growing season for other crops was estimated with the assistance
of specialists in the College of Agriculture, University of Wyoming. The
season for these crops is regarded as between the planting date and harvest.
Planting dates were determined to be ten days earlier than the 40°F date
(Table II) for small grains, fifteen days later than the 40°F date for
sugar beets, thirty days later for corn, forty days later for beans, and
fifty days later for potatoes. The harvest dates were estimated to be
August 1 for small grain, October 10 for sugar beets, October 1 for corn,
September 1 for beans, and September 15 for potatoes.
Consumptive Use Coefficients
The monthly consumptive use coefficients used for this report are
shown on Figures 1 through 7 (pp. These values were assumed to
be applicable to Wyoming after considering all available sources of data.
Effective Precipitation
Not all of the precipitation that falls on an area is effective for
meeting consumptive use needs of plants. This is because of many factors.
Showers of small intensity and duration are commonly evaporated. The
rainfall intercepted by plants before reaching the ground is likewise
evaporated directly from leaves. Runoff and groundwater accretion remove
portions of the rainfall from large storms, reducing the amount of water
retained in the soil for plant use from these storms.
A method suggested in the U. S. Bureau of Reclamation Manual and in the U. S. Department of Agriculture Technical Bulletin No. 12751 to estimate effective rainfall was used in this study. Mean monthly precipitation is divided into one inch increments, and the effective rainfall is calculated from the following percentages:
TABLE III - METHOD FOR ESTIMATING MONTHLY EFFECTIVE PRECIPITATION
------------------------------------------------------------------------
Total Amount Monthly Precipitation Considered Effective
of Precipitation ------------------------------------------
in Any Month Part of each Accumulated Total
inch increment
------------------------------------------------------------------------
Inches Percent Inches
1 95 0.95
2 90 1.85
3 82 2.67
4 65 3.32
5 45 3.77
6 25 4.02
Over 6 5 ----
-----------------------------------------------------------------------
For an example, with an average monthly precipitation value of an inch and one-half at a weather station, the effective rainfall for the month would be 1.40 inches.
During some of the early months of the growing season, the effective rainfall may exceed the consumptive use yielding a negative value for irrigation requirement. In these cases, the consumptive irrigation requirement was assumed equal to zero.
At the start of the growing season, regardless of the beginning date, the amount of effective rainfall for the entire first month was subtracted from the consumptive use to determine consumptive irrigation requirement. This assumes that the precipitation prior to the start of the growing season is stored in the soil and is available to satisfy the requirements, At the end of the growing season, the fractional portion of the month within the growing season was multiplied by the effective rainfall and this value was subtracted from the estimated consumptive use.
Calculation of Consumptive Use
A computer program in Fortran IV for the Blaney-Criddle Method was
written for the computer at the University of Wyoming. The program is
included herein as Appendix 1.
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