Fertilizers that Contain Phosphorous

Superphosphate

Superphosphate is usually made from rocks that contain phosphates or from coprolites (fossilized excrement.)

It is treated with sulfuric acid so that it is soluble.

Superphosphate is a friable grey powder.

It contains 13 percent to 18 percent phosphoric acid.

Superphosphate is acidic. It is best used on soils with a good proportion of carbonate of lime, such as loamy or calcareous soils.

Heavy clays, or peats, gravels or sands that have low levels of limes, should be limed before superphosphate is applied to them..

Superphosphate is useful in spring, but is most effective when it is applied in the fall.

1 ½ to 2 ½ ounces of superphosphate should be applied per square yard.

Mineral Phosphate

Mineral phosphate can only be used by some crops.

It is good to use with rutabagas (swedes), turnips, peas and cabbages, but cannot be sued with potatoes, tomatoes or carrots.

Mineral phosphate is finely ground.

Basic Slag

Basic slag is a dense, black powder that is created when iron or meal smelted processes.

It may contain from 8 percent to 18 percent phosphoric acid, as well as magnesium, iron and free line.

The more finely basic slag is ground, the more valuable it is.

You should only purchase basic slag that is guaranteed to have passed through a sieve with 10,000 holes per square inch.

Medium quality slag will contain 12 percent to 16 percent phosphoric acid. At least 80 percent of this should be soluble in citric acid.

When working with peaty or heavy soils, it is better to apply basic slag than to apply superphosphate, as long as the soil is moist.

Basic slag is useless on dry soil.

It works slowly and should be applied in the fall.

2 to 4 ounces of basic slag should be applied per square yard.

Bone Meal and Steamed Bone Flour

Bone meal and steamed bone flour are good sources of phosphorus.

They also contain a small amount of nitrogen, but this is not in a form that can be easily used by plants.

Bone meal contains about 45 percent calcium phosphate, while steamed bone flour has 55 to 60 percent calcium phosphate. This is equivalent to about 27 percent phosphoric acid,

Less than 50% of this can be dissolved in 2 percent citric acid.

Bones work very slowly in heavy soils. They are best used on light soils.

Bone manures are the best phosphatic fertilizers for soils that are too dry for basic slag to be applied and do not have enough lime for superphosphate to be applied.

1 ½ to 3 ounces of bone meal or steamed bone flour should be applied per square yard.

Dissolved Bones

When bones are treated with sulfuric acid, the substance that is created is known as "dissolved bones".

Treating bones with sulfuric acid causes the phosphates in them to become soluble.

Dissolved bones is a sticky, damp substance. To make it easier to handle, you should mix it with dry soil or a similar dry substance.

Dissolved bones usually contains about 20 percent soluble phosphates - about 9 percent phosphoric acid and 2 percent nitrogen.

When working with chalky soil, dissolved bones is the best phosphatic fertilizer to use.

1 ½ to 3 ounces of dissolved bones should be applied per square yard.