Agricultural Research Service (ARS) soil scientist Ardell Halvorson, of the agency's soil, plant and nutrient research laboratory in Colorado, conducted several long-term experiments on farm fields in Montana, Colorado and Nebraska. In Montana, he found that a single application of phosphorus increased soil test levels and crop yields for more than 17 years.
His research in Nebraska and Colorado also showed that farmers can expect improved yields for several years after a single phosphorus treatment.
Since phosphorus is expensive, many farmers tend to use less than the ideal amount each year. Through his research, Halvorson has found economic returns to be greater when applying the correct amount of phosphorus the first year, to eliminate phosphorus deficiency, and then skipping two or three years. Initial cost will be higher, but Halvorson claims that farmers are likely to have greater profits in the long term.
Halvorson recommends applying higher, adequate rates of phosphorus initially, then lower rates as needed to maintain optimum crop yields. Since cropping intensity influences how quickly phosphorus is used, farmers may have to apply it more often if using annual cropping systems, rather than wheat/fallow. But they still don't have to apply it every year.
If a farmer is only renting the land for a short period of time, the investment for an initial large application of phosphorus may not make sense. However, for landowners, applying the optimal amount every few years will likely produce larger yields.
Phosphate is one of the three major components in plant nutrition, along with nitrogen and potassium. It has been used as a supplement in food production for the last 100 years.