## Units of measure

Waste production from livestock is expressed in pounds per day per 1,000 pounds of livestock live weight (lb/d/1000#). Volume of waste materials is expressed in cubic feet per day per 1,000 pounds of live weight (ft3/d/1000#). Food processing waste is recorded in cubic feet per day (ft3/d), or the source is included as in cubic feet per 1,000 pounds of apples processed. In this chapter English units are used exclusively for weight, volume, and concentration data for manure, waste, and residue.

The concentration of various components in waste is commonly expressed as milligrams per liter (mg/L) or parts per million (ppm). One mg/L is 1 milligram (weight) in 1 million parts (volume); for example, 1 liter. One ppm is 1 part by weight in 1 million parts by weight. Therefore, mg/L equals ppm if a solution has a specific gravity equal to that of water.

Generally, substances in solution up to concentrations of about 7,000 mg/L do not materially change the specific gravity of the liquid, and mg/L and ppm are numerically interchangeable. Concentrations are sometimes expressed as mg/kg or mg/1000g, which are the same as ppm.

Occasionally, the concentration is expressed in percent. A 1 percent concentration equals 10,000 ppm. Very low concentrations are sometimes expressed as micrograms per liter (mg/L). A microgram is 1 millionth of a gram.

Various solid fractions of a manure, waste, or residue, when expressed in units of pounds per day or as a concentration, generally are measured on a wet weight basis (% w.b.), a percentage of the "as is" or wet weight of the material. In some cases, however, data are recorded on a dry weight basis (% d.w.), a percentage of the dry weight of the material. The difference in these two values for a specific material is most likely very large. Nutrient and other chemical fractions of a waste material, expressed as a concentration, may be on a wet weight or dry weight basis, or expressed as pounds per 1,000 gallons of waste.

Amounts of the major nutrients, nitrogen (N), phosphorus (P), and potassium (K), are always presented in terms of the nutrient itself. Only the nitrogen quantity in the ammonium compound (NH4) is considered when expressed as ammonium nitrogen (NH4-N).

Commercial fertilizer formulations for nitrogen, phosphorus, and potassium and recommendations are expressed in terms of N, P2O5, and K2O. When comparing the nutrient content of a manure, waste, or residue with commercial fertilizer, the conversion factors listed in table 4-2 should be used and comparisons on the basis of similar elements, ions, and/or compounds, should be made.

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