If there are 150 ppm of available phosphorus in an acre furrow slice, how many pounds per acre does this represent?

To determine how many pounds of available phosphorus 150 ppm represents in an acre furrow slice, it's important to understand the relationship between parts per million (ppm) and pounds per acre.

One ppm of a substance in soil generally translates to one pound of that substance per acre-foot of soil. An acre-foot is the volume of one acre of land to a depth of one foot, which is equivalent to approximately 2.72 million pounds of soil. When considering a furrow slice, which is typically defined as the top 6 inches of soil, the weight of that slice is about half of an acre-foot—roughly 1.36 million pounds.

To convert ppm to pounds per acre for an acre furrow slice, you multiply the concentration in ppm by the weight of the soil in that volume. Since 150 ppm means 150 pounds per million pounds of soil, you would calculate it as follows:

150 ppm = 150 pounds/1,000,000 pounds of soil.

To find how many pounds this equates to in the 1.36 million pounds present in the acre furrow slice, you set up the equation:

150 ppm * (1.36 million pounds) / (1 million pounds) = 150