Applying P & K

A question for people in the know. What is the best time to apply P & K during a plants growing cycle?
especially in relation to seeding plants like cucumbers & tomatos or root vegetables like potatos etc.
Many thanks. rob
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When they flower or start to set fruit for the cukes and 'maters. Some one should be along shortly about 'taters or you could "google" growing potatoes.
- Billy Coloribus gustibus non disputatum (mostly)
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wrote:

most I could get on google was early spring which is quite general. The setting fruit bit I can understand, also thinking about the lawn and setting seed. That happens very early spring.
rob
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George.com wrote:

Phosphorus does not dissolve and leach through the soil. Instead, it needs to be dug into the soil to where plant roots will find it. Thus, phosphorus should be applied before planting.
--
David E. Ross
Climate: California Mediterranean
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PO4 3- doesn't dissolve?
Pure anhydrous phosphoric acid is a white solid that melts at 42.35C to form a viscous liquid. In solution, phosphoric acid behaves as a triprotic acid, having three ionizable hydrogen atoms. The hydrogen ions are lost sequentially. H3PO4(aq) H+(aq) + H2PO4(aq) Ka1 = 7.5 ~ 10 3 H2PO4(aq) H+(aq) + HPO42 (aq) Ka2 = 6.2 ~ 10 8 HPO42 (aq) H+(aq) + PO43(aq) Ka3 = 1.7 ~ 10 12
Phosphoric acid is not a particularly strong acid as indicated by its first dissociation constant. It is a stronger acid than acetic acid but weaker than sulfuric acid and hydrochloric acid. Each successive dissociation step occurs with decreasing ease. Thus, the ion H2PO4 is a very weak acid and HPO42 is an extremely weak acid.
Replace the hydronium (H+) with a Na+ and you have essentially the same thing, only it is in the east.
Phosphoric acid is used primarily in the manufacture of fertilizers, detergents, and pharmaceuticals. In the steel industry, it is used to clean and rust-proof the product. It is also used as a flavoring agent in carbonated beverages (read the ingredients list on a can of Coca-Cola), beer, jams and jellies, and cheeses. In foods, phosphoric acid provides a tart, acidic flavor.
In the manufacture of detergents, phosphoric acid is used to produce water softeners. Water softeners remove Ca2+ and Mg2+ ions from "hard" water. If not removed, these hard-water ions react with soap and form insoluble deposits that cling to laundry and the washing machine. Phosphates produced from phosphoric acid are used extensively as water softeners (builders) in detergents. The most widely used phosphorus compound in solid detergent mixtures is sodium tripolyphosphate, Na5P3O10. As a water softener, sodium tripolyphosphate binds to Ca2+ and Mg2+, forming soluble chemical species, called complexes or chelates. These complexes prevent the Ca2+ and Mg2+ from reacting with soap and forming deposits.
Most phosphoric acid is used in the production of fertilizers. Phosphorus is one of the elements essential for plant growth. Organic phosphates are the compounds which provide the energy for most of the chemical reactions that occur in living cells. Therefore, enriching soils with phosphate fertilizers enhances plant growth.
Increasing the phosphate concentration in surface waters also enhances the growth of aquatic plant life. Run-off from fertilized farm lands can stimulate plant growth in lakes and streams. Waste water that contains phosphates from detergents can have the same effect. Lakes that are rich in plant nutrients suffer from accelerated eutrophication. When the lush aquatic plant growth in a nutrient-rich lake dies, the decomposition of the dead plant material consumes dissolved oxygen. This consumption reduces the level of dissolved oxygen to a point where it is insufficient to support animal life. To reduce the threat of lake eutrophication, many localities have banned the use of phosphates in detergents. In some cases, the phosphates have been replaced by carbonates. In others, new detergents have been developed that do not react with the Ca2+ and Mg2+ ions of hard water.
Bone meal (an organic source of phosphates), on the other hand, is not very soluable a should be worked lightly into the soil so as not to damage the roots.
- Billy Coloribus gustibus non disputatum (mostly)
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wrote:

Bill. When you say bone meal is not very soluable, are we talking here about:
1. Something that time will resolve, ie is it is slow release? 2. Or are we talking about something that is distance related, ie it will not work down into the soil & plants root systems if used as a top dressing (unless dragged down by worms maybe)?
Thanks rob
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We are talking not very, when talking about bone meal. Which is to say it doesn't dissolve as quickly as sugar but much more quickly than glass. Depending on its' formulation, phosphates can dissolve slowly or quickly. Rock Phosphate, Bone Meal, Single Super Phosphate, Triple Super Phosphate are your choices. Use half as much as the instructions say. These folks depend on return customers, and the faster you use it, the sooner you'll be back.
Hope I helped.
- Billy Coloribus gustibus non disputatum (mostly)
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wrote:

yeah, sort of, thanks. Maybe just given me an extra variable to think about but so be it. I use blood & bone on the lawn sometimes however the phosphoros likely doesn't break down quickly enough to benefit grass seeding in early spring. I ain't going to till it in neither as it is the lawn. Obviously dig in a little when planting veges however.
I also use wood ash which is good for K but which I think is much more readily available to plants. I am considering trying that out on the lawn as well in smallish amounts. It will slightly alter the soil ph but that is ok given slightly acidic soils.
rob
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wrote:

though maybe a mid autumn application may do the job.
rob
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Billy Rose wrote:

In alkaline soils such as commonly found in southern California and other arid areas of the U.S. southwest, phosphoric acid is quickly neutralized. This prevents phosphorus even from that source traveling through the soil.
--
David E. Ross
Climate: California Mediterranean
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Look mate, we are talking fertilizer. We are talking PO4 -3 (phosphate, not phosphorous which our military is keen on firing into highly populated areas like Fallujah, which is a war crime because it kills indiscriminately when it explodes into fire on contact with air. Do not add phosphorous to your garden. ) Think, Rock Phosphate, Bone Meal, Single Super Phosphate, or Triple Super Phosphate.
- Billy Coloribus gustibus non disputatum (mostly)
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In article

[...]

Okay, here's an oddball question for you: can I use di-calcium phosphate in the garden? I have a bunch of it, but the horse that I bought it for (as a feed supplement) died. (He was in his 30's.)
I tried looking it up and couldn't find anything.
I'm using codfish bonemeal right now. Stinky stuff, but the organic diva next door swears by it.
TIA,
Jan
"Civilization is the interval between Ice Ages." -- Will Durant.
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http://en.wikipedia.org/wiki/Dicalcium_phosphate
Dicalcium phosphate, also known as calcium monohydrogen phosphate, is a dibasic, calcium phosphate.It is usually found as the dihydrate, with the chemical formula of CaHPO4 2H2O, but it can be thermally converted to the anhydrous form. It is practically insoluble in water, with a solubility of 0.02 g per 100 ml at 25C. It contains about 23 percent calcium (dihydrate form), and is mainly used as a dietary supplement in prepared breakfast cereals, enriched flour, and noodle products, and as a tableting agent (re: filler).
http://www.springerlink.com/content/t33v55v1h45n0814 /
G. J. Racz1 and R. J. Soper1 (1) Department of Soil Science, University of Manitoba, Winnipeg, Manitoba
Received: 9 July 1968 Summary The solubility of phosphorus was found to approximate that of dicalcium phosphate dihydrate and/or dimagnesium phosphate trihydrate when KH2-PO4, H3PO4 and K2HPO4 were added to four Manitoba soils. Eighty to one hundred, seventy to ninety and sixty to eighty per cent of the phosphorus added remained in solution when H3PO4, KH2PO4 and K2HPO4 were added, respectively. The solubility of the added phosphorus was high in all samples and relatively soluble compounds, dicalcium phosphate dihydrate and dimagnesium phosphate trihydrate, were most likely formed in the samples indicating that phosphorus added to these soils would be readily available to plants. Associate Professor and Professor respectively.
The short answer is yes.
I want to look at the disassociation constants but from the two articles above, I don't see a problem.
- Bill Coloribus gustibus non disputatum (mostly)
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Typically applied pre-planting to the expected root zone. But save yourself the trouble of applying too much (many soils have plenty) -- get a soil test. Saves water pollution, too.
Kay
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Glacial soils tend to have very little. The upper midwest enjoyed extensive glaciation in the recent past. Like Kay says, do a soil test. (And shop around for one. The price can vary considerably.)
Fine Gardening carried an article on soil testing, written by a soil scientist, last year. It might be on their website: www.finegardening.com The article gave good instructions on how to gather and prepare your sample.
Jan
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