By rounding 74.94 to 75, it must by understood that the result will not be entirely nor mathematically accurate, but perhaps is close enough for practical purposes. The next step is to multiply the desired PPM by 0.013344, which is 74.94. Therefore, 13,344 ounces per 13,344,000,000 ounces equals 1 part per million, or more simply 0.013344 ounces per 100 gallons of water equals 1 PPM. Multiply 834 pounds by 16 ounces per pound which equals 13,344 ounces per 100 gallons. Therefore, to calculate ppm in 100 gallons of water, first multiply 100 gallons by 8.34 pounds per gallon which equals 834 pounds. The answer is 8.09 ounces of ammonium nitrate which dissolved in 100 gallons of water will yield 200 ppm nitrogen.Ĭonfused? Some examples of what one part per million represents under various conditions are: 1 crystal of salt in 5 lbs., 1 drop in 16 gallons, 1 inch in 158 miles, 1 minute in 1.9 years, 1 pound in 500 tons, and 1 cent in $10,000. To use this equation, assume that the fertilizer recommendation calls for 200 ]ppm of nitrogen from ammonium nitrate (33% N)-Using the above equation, divide 200 ppm by 75 resulting in 2.67,and then divide by 0.33. This results in the number of ounces of fertilizer to use in 100 gallons of water. To calculate the amount of fertilizer required, divide the desired ppm by 75 and then divide by the decimal fraction of the desired nutrient (such as nitrogen, potassium or phosphorous) contained in the fertilizer. Many growers are familiar with the Quick "75" Method for calculating ppm. With a little knowledge, a calculator, and patience, the tables are not necessary. There are fertilizer tables provided by most fertilizer producers for easier reference. The most important concern, no matter which program is used, is accuracy in calculation of fertilizer concentrations.Ĭrop nutrition requirements and most published fertilizer schedules use the terminology "parts per million" or ppm. The program selected is determined by crop requirements, available equipment, and personal preference. Many growers use either a constant feed program fertilizing with each irrigation, while others use a pulse feed program fertilizing on a regular periodic schedule. The use of liquid feed fertilization programs in greenhouse and greenhouse crop production is the standard of our industry. Most fertilizer bags and PGR labels have all the calculations printed on them, but often a refresher on the calculations is in order.
All of these are typically based on parts per million or ppm. While teaching greenhouse and nursery management classes, I have found that students often have the most trouble learning how to calculate fertilizer and plant growth regulator ratios.
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