USDA-ARS Northwest Irrigation & Soils Research Lab Station Note #01-96
Determining The Dry PAM Application Rate For Head Ditch or Pipe Flow
R.D. Lentz and R.E. Sojka
USDA-Agricultural Research Service; 3793 N 3600 E, Kimberly, ID 83341
PH:(208)423-6531, FAX (208)423-6555
INSTRUCTIONS: Determine the PAM concentration desired in the head ditch or pipe flow.
The standard method treats irrigation inflows with 10 ppm PAM from the
beginning of the irrigation until water advancesto the end of the field and begins to runoff. After this advance phase, the PAM injection is stopped, and untreated water is run for the remainder
of the set. In some cases, an irrigation water PAM content < 10 ppm
may be satisfactory. Find your total head ditch or pipe flow rate on the
bottom horizontal axis and move up until you intersect the diagonal line
corresponding to the desired PAM concentration in the irrigation water.
Then move horizontally toward the right axis to find the PAM-product application
rate in ounces-of-mass/minute. Adjust for active ingredient concentration.
Example and computational details are presented on the back page
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Suppose the farmer has 50 miners inches (Idaho) of water flowing in the
head ditch and wishes to treat the flow with 10 ppm. How much dry PAM should
be metered into the flow to attain the target concentration of 10 ppm PAM?
Since the head ditch flow is known in miners inches we would enter the
chart along the bottom horizontal axis at 50 miners inches. Next, move
straight upward until you intersect the diagonal line corresponding to
10 ppm PAM in the irrigation water. Then move horizontally, toward either
the left or right vertical axis, depending on the units with which you
desire the answer reported. If, after intersecting the 10 ppm diagonal
line, one moves toward the left axis, the answer is given as 17 grams/minute.
If one moves to toward right axis instead, the answer is given as 0.6 ounces
of mass/minute. Therefore, to attain a PAM concentration of 10 ppm in a
flow of 50 miners inches, one must meter 17 grams PAM/minute or 0.6 ounces
PAM/minute into the head ditch stream. If product's active ingredient concentration is substantially less than
100%, you may want to adjust the application rate. This is done by multiplying
the rate by the fraction 100/AI, where AI is the percent active ingredient
in the product (by weight). (Note: if the head ditch flow was known in gallons/minute, ie. 448 gpm
= 50 miners inches, the chart could be entered at the top horizontal axis
at 448. Then you would move vertically downward, until the 10 ppm diagonal
line was intersected).
CALCULATING PAM APPLICATION RATES
FOR DITCH/PIPE FLOWRATES AND PAM CONCENTRATIONS BEYOND THE CHART RANGE:
The following formula can be used to compute PAM application rates for
any ditch flowrate and target PAM concentration desired.
Dry PAM application rate (grams/min) to head ditch or gated pipe flow
(Target PAM conc. in ppm [= mg/L]) x (head ditch or pipe flow in Idaho
miners in.) x
(8.96 gpm/miners in.) x (3.785 L/gal) x (0.001 g/mg).
To adjust the rate for the product's active concentration, multiply by
the fraction 100/AI, where AI is the percent active ingredient in the product
To convert from grams/min to ounces of mass/min, multiply the result by