Organic phosphorus fertilizers come primarily from mineral sources, like rock dust or colloidal phosphate (also called “soft phosphate”), or from bone sources, such as steamed bone meal or fish bone meal.
Mineral phosphorus sources are cheaper and last longer in the soil. Bone sources are more readily absorbed by plants.
Phosphorus is needed for root development, stem formation, and fruiting in summer vegetables like tomatoes, peppers, eggplants, squash, melons, and cucumbers.
Phosphorus tends to be widely disbursed in soil, so it’s hard for these plants to get enough of it within their limited root zones. To get enough phosphorus to produce fruit, fruiting plants evolved symbiotic relationships with myccorhizal fungi. Almost all plants that bear fruit form myccorhizal associations.
Fungi are creatures of the soil. Their hyphae can spread for hundreds of feet underground (the largest living organisms are fungi), and they can transport nutrients anywhere in the hyphal system. Myccorhizal fungi concentrate phosphorus and other minerals at the roots of plants, and the plants provide the fungi with sugars, starches, and amino acids in exchange.
Gardeners and farmers usually add supplemental organic phosphorus fertilizers to the soil to accommodate crop needs. Inoculating seedling roots with Endo-Myccorhizae increases their ability to absorb soil phosphorus.
Dr. Earth Life (Probiotic) Fertilizer contains both endo- and ecto-mycorrhizae, as well as beneficial bacteria, and is a great soil amendment for summer vegetables. It’s especially useful for growing vegetables in containers, where sterile potting mixes limit plant growth.
The table below lists organic phosphorus fertilizers. Colloidal phosphate is more biologically available than rock dust, but not as readily assimilated by plants as bone sources of organic phosphorus.
|Soil Amendment||N-P-K||Description||Lasts||Application Rate|
|Soft Rock Phosphate||0-18-0||Colloidal Phosphate has a clay base that makes it easier for plants to assimilate than phosphate rock. Releases over months and years in acidic and neutral soils, but breaks down poorly in alkaline soils (pH higher than 7). Peak availability in 2nd year.||2-3 Years||Up to 6lbs/100 sq ft|
|Bat Guano (High-P)||3-10-1||High-Phosphate guano from fruit-eating bats. Excellent P source for container vegetables and gardens.||2-3 Years||2-3lbs/100 sq ft|
|Steamed Bone Meal||3-15-0||Made from ground cattle bones. P in bone meal is highly plant-available. Great mixed into the planting hole with bulbs. Good amendment for allium family plants (onions, garlic). May attract raccoons. P in bone meal not released in alkaline (pH greater than 7) soils.||1-4 Months||10lbs/100 sq ft|
|Fish Bone Meal||3-18-0||Phosphorus from fish bone meal is readily assimilated by microorganisms and plant roots in the soil.||1-2 Years||1-2lbs/100 sq ft|
|Rock Phosphate||0-33-0||Very slow release P source. Releases over several years in acidic and neutral soils, but won’t break down in alkaline soils (pH higher than 7).||3-5 Years||Up to 6lbs/100 sq ft.|
|Rock Dust (Crushed Granite)||0—3-5—0,
|Granite fines, the dust from rock grinding and sorting operations. Very slow releasing P source, good source of trace minerals for plant immunity and tolerance of temperature extremes.||5-10 Years||Up to 8.5lbs/100 sq ft|
|Chicken Manure||1.1-0.8-0.5||Good manure source for P and some K.||3-12 Months|| 1/2-1” layer
(5-10 5-gal buckets/100 sq ft)
|Pig Manure||0.8-0.7-0.5||Good, balanced manure source of N, P, and K. Because some pig parasites and pathogens can infect humans, pig manure is not allowed in many organic protocols. If it is used, it must be hot-composted prior to use.||3-12 Months|| 1” layer
(10 5-gal buckets/100 sq ft)
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