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USDA-ARS Northwest Irrigation & Soils Research Lab Station Note #01-96 (Revised)


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).



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 (by weight)

To convert from grams/min to ounces of mass/min, multiply the result by 0.0353 oz/g.