Rock Phosphate

Phosphorus is another important mineral that is often unavailable in soils with a low organic matter content and with poor biology (microorganisms). Carey Reams believed that both calcium and phosphorus are the limiting elements in soils. This hard rock phosphate should be used when there is a documented deficiency of both calcium and phosphorus.

Phosphate is necessary for photosynthesis and metabolism. It is the major catalyst in all living systems.

Since the most common soil tests are inherently inaccurate, the calcium number should be ignored and instead, the base saturation test should be consulted. Here, the percentage of exchange sites occupied by calcium would ideally be 60-68% (closer to 60% for sandy soil). Even better, a Reams test (aka Lamotte test) more accurately tells us how much calcium is available to plants. Ideally, this would be 2000-8000lbs/acre (1000-4000 ppm and mg/kg), and at least 4000lbs/acre for turf. Further, the ratio of calcium:magnesium would ideally be 10:1 in general, and 7:1 for grasses and sandy soils.

A conventional soil test doesn't tell us much about phosphorus availability, as the number given is inherently inaccurate. A Reams test gives much better information on phosphorus availability, and for this, the ideal number would be 400lbs/acre (200 ppm and mg/kg). For either test, the ratio of phosphorus:potash would ideally be 2:1 in general, and 4:1 for grasses and sandy soils.

If a conventional soil test indicates that there is a lot of phosphorus in the soil, but a Reams test indicates there is not enough available phosphorus, molasses is often applied at 2 gallons/acre to help "loosen" the phosphorus. And since phosphorus uptake is so dependent on microorganisms, particularly mycorrhizal fungi, they should be included in the program.