Phosphorus (P) plays an important part in how plants and animals form and in how they function and grow. Phosphorus is known to help plants during photosynthesis, P helps plants respire (breathe), P provides energy transfer and storage, and P also helps plants efficiently use water. Seedlings and roots grow more quickly and vegetable and fruit production is increased when plants get enough phosphorus.

Here is a link that might be useful: Soil Fertility: How Does Your Garden Grow?

It is primarily utilized by plants in root production, although it does have beneficial secondary effects as well. Unless you are doing heavy cropping (i.e., farming), there is generally enough phosphorus present in the soil to satisfy most plant requirements. Very rapidly growing crops like greens and legumes are those that most often require phosphorus supplementation. All organic matter contains phosphorus at sufficient levels to address most needs, so the use of compost or other OM as a mulch is typically more than adequate for most situations. Relatively low amounts of applied phosphorus can produce phytotoxic effects in a number of plants, so do some research and exercise care when using as a supplement.

I don't want to sound argumentative, but my soil (previously lawn) is depleted with regard to Phosphorus. I have plenty of Potassium, but no Phosphorus. I amend with bone meal, superphosphate and triple superphosphate when preparing beds. All are sources of Phosphorus.

From my reading, gardeners who add inches of compost, and other organic materials in depth, tend to see a large increase in the potassium levels of their soil. Especially in humid temperate climates which naturally grow forests.

Good compost also supplies nitrogen, and gardeners often actively seek out other nitrogen sources -- used coffee grounds, kitchen wastes, manures, animal bedding, urine, etc., etc.

By contrast, of the three main ingredients of the N-P-K trinity, organic sources of phosphates tend to be undersupplied. To my understanding, plants tend to concentrate phosphorus in their flowers, seeds and fruits. These are important parts of many of the plants we grow to eat, but they are usually less of the total bulk mass of a plant (compared to the bulk of leaves, stems and roots.)

Organic sources of phosphorus tend to release more gradually and when applied with a light hand, are less likely to overdose plants, and/or leach and pollute. Seed meals, bone meal, and the manures of animals fed seed grains, are a few of many natural phosphorus sources.

All the best,
-Patrick

p.s. The above information is primarily based on Steve Solomon's writing, especially his book Organic Gardener's Composting. The full text is available online for free at the Soil And Health Library. I highly recommend it.

BTW, on checking Solomon's personal web page (link right below) there's a PowerPoint presentation dated today, showing photos of his gardens in fall -- he lives in the southern hemisphere. It's pretty damn impressive.

Here is a link that might be useful: Steve Solomon's personal web page

Many people greatly misunderstand what is being said about Phosphorus today and seem to get the idea that because excess quantities of P get into our water system and that the application of unnecessary P is, more and more, being regulated that P is being reviled. It is not, what is being reviled is the unnecessary application of too large quantities of unneeded Phosphorus. At one time most people simply added lots of P to their soil annually because many garden writters said it was necessary because plants used so much, and because of that excess P in soil today is also partly why plants are unhealthy, too much P can inhibit the uptake of other, necessary macro and micro nutrients. A balance of nutrients is needed but the annual addition of say a 10-10-10 may not, and if your soil is properly taken care of even that will not be necessary. However, the only way to know for sure is with a good, reliable soil test.

albert: phosphate plays a role in most plant metabolic pathways; it's crucial in photosynthesis, for instance, and they don't come more basic than that. But remember: Test, Don't Guess, by which I mean that too much is worse than too little, because it's harder to put right. Regards, Peter.

"The full text is available online for free at the Soil And Health Library. I highly recommend it."

There are two people who I never tire of reading their work, Steve Solomon, and Lady Eve Balfour. Members of this forum brought these names as well as others to my attention, and I have studied them intently for a number of years. The extensive list of literature provided on Steves web site offers a wealth of information regarding the history of organic gardening, as well as other themes of the organic movement.

As it relates to phosphate, Lady Eve Balfour did a 10-year study on three farm systems now known as "The Haughley Experiment" (see link below). She preformed soil tests on each farm monthly for a 10-year period; that is 360 soil tests. One of her conclusions states:

"On the Organic Section, which received no fertilizers, the fluctuation was so marked that, for example, in the field with the highest humus content and the longest history of no chemicals, as much as 10 times more available phosphate has been recorded in the growing period of the year than in the dormant period. Potash and nitrogen followed the same general pattern. It was clear, from the fact of the closed cycle, that this seasonal release of minerals could only have been brought about by biological agencies, and it appears to be a natural action-pattern of a biologically active soil."

This is one of the first references (in 1977) to what is now known as "The Soil Food Web". Thus, it is clear to me, that if in fact her data is correct (and it is), the living soil provides nutrition based on the demands of the plant, if indeed the nutrition is available to the plant within the soil. If the nutrition is not available, the plant will send out its root system seeking those needed nutrients. As stated above, this is one of the functions of phosphorus. Another can be to provide antibiotics to protect the plant from disease and/or insect attack. It appears to me that the plant determines what is taken from the soil, if the nutrient is there, and not what a soil test says it thinks should be there.

Then there is the issue of definitions. We provide information, links, experience, and knowledge to each other; yet certain words get in the way of our message as it relates to amendments and compost. Some of the words that come to mind are:

1. Humus
2. Buffer
3. Remediation
4. Covalent Bonding
5. Chelation
6. Water Bridge
7. Electrostatic
8. Transmutation
9. CEC
10. Storage Capacity
11. Remineralization
12. Humic Acid
13. Fulvic Acid

It is the function of P along with the other needed nutrients, in the presence of compost that provides fertility to our soil. Those who practice organic soil building enjoy the benefits of the above list. The definitions of these words get in the way of such words as pollution, leaching, over-feeding, phytotoxic, and good reliable soil test.

Indeed, if I am to become a student of the organic movement, not only am I going to use information provided by those good enough to share, as well as my own observations of what I see outside my back door, and discoveries that may have not been known. It is unrealistic to expect anyone to become an organic robot and become programmed by dogma. The living soil insists I not garden by the test, but garden by the life

Blutranes

Old Farmers' Ryhme-- NPK--Up, down, and all around.