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Phosphorus for the Rest of Us

Phosphorus, a much needed macronutrient in plant health, is yet another resource mismanaged in modern agriculture. Traditionally, farm and even municipal wastes were returned to the growing lands to be recycled into the ecological chain. Present in respectable amounts in bones and urine, and lesser amounts in most plant residues, farmers utilized the P in an economical way.

Currently most agricultural systems worldwide rely on geological deposits of phosphate rock, most now on the African continent. The mining is often damaging to the environment, without accounting for transportation.

Some facts:

Closed loop traditional systems recycled phosphorus nearly 50 times before any deficiency was noted.

Nearly 90% of phosphorus worldwide is used in agriculture.

Geographical deposits of phosphorus are finite. (Actual figures are a point of debate currently).

Some things to do:

Since overuse is a common practice on farms and in gardens, get a soil test to determine levels. Also, since P is most usable to plants within a fairly narrow pH range, 6.5 to 6.8,  strive for this level. Although soil microbes and good organic matter levels are helpful, P can more readily be obtained in a mineralized form for plant uptake. Too low a pH and it is tied up with iron or aluminum, higher pH and it is tied up with calcium. Since soils are often not at this level, it stand to reason that there may be a banking of P in the soil through bonding in a less soluble form (immobilized). As with other nutrients, it is about balance and understanding of the system. For those who are interested in nutrient dense farming and other popular approaches, they are only effective if you get the numbers right. Dumping any resource on the land in hopes that it will help can also be mismanagement. When nutrient are in excess, they may either be unavailable for uptake, or worse, available (mineralized) and thus prone to leaching (which in the case of P, leads to pollution and issues like algal blooms ). Re-cycling phosphorus containing farm and family waste products can provide a free source of P. As with all farm inputs, it is uneconomical to misuse them.