Phosphorus - There is a chemistry

 

When phosphate loads are rapidly complexed or not made available, fundamental sugar formation continues to function. Symptoms wave a warning flag that can be seen from great distances. Leaves often become reddish and purplish – a lack of chlorophyll – and tips die off. Seeds, tubers, grains, all suffer since all require phosphorus for adequate metabolism. Growth is slowed accordingly. The corn plant has a sign all its own. When there is a phosphorus deficiency, the kernels drop off about an inch or two from the cob’s end, or they may fail to develop in the first place.

In short, there is a chemistry involved whenever anything is put into the soil, inorganic, organic, salt form, whatever. Rock phosphate is called tricalcium phosphate, and this means it has three calciums, or three negative charges for bonding. This makes it more difficult to disattach from fixation than would be the case with dicalcium phosphate, which has only two charges – thus tri, di! Last, there is the water soluble monocalcium phosphate, which means that as a consequence of acid treatment this form has only one remaining bond.

So if you’re over 6.5 pH, and you want to farm organically for good and obvious reasons, you’re in trouble. You probably shouldn’t be using nonwater soluble phosphorus because the soil does not have enough acid to free it up. If a soil system has a pH of 7.5 the farmer probably shouldn’t be using the di forms. He should go to strictly mono forms of phosphate. Any farmer who doesn’t take into consideration the importance of the active hydrogen ion as being the most important thing to work with thereby authors his own failure.

Acid treatment merely means rock phosphate is being converted from tricalcium phosphate to monocalcium phosphate, and that this highly unstable form is subject to natural reversion back to the stable tricalcium form. The rate of reversion differs. The pH, the free calcium in the soil, the organic matter – all figure in this rate of reversion. But it is safe to say that 75% of the monocalcium phosphate reverts back to stable tricalcium phosphate within 90 days. In some soils the reversion takes place within hours. As soil conditions worsen, release of nutrients from rock phosphate worsens, and the chemical amateur becomes married to buying salt fertilizers, each go-round worsening still further the structure of that soil.

The water soluble phosphates are simply water soluble, not acid. But they are a poor substitute for having the proper pH with calcium, potassium, magnesium and sodium in equilibrium, and form an economic point of view they take on ripoff dimensions.

First, the soluble phosphates come from rock phosphate in any case. By treating, say, 1,400 pounds of rock phosphate with 1,200 pounds of sulfuric acid, the fertilizer industry gets 20% superphosphate – the tricalcium phosphate form being converted into water soluble monocalcium form. This chemical reaction causes 20% superphosphate to be represented by about 45% monocalcium phosphate, and 55% calcium sulfate, or gypsum. This means the bag of 0-20-0 contains about 45 pounds of water soluble monocalcium phosphate, which is presumably desired, and about 55 pounds of calcium sulfate, which may or may not be desired, but which farmers are frequently not aware of.

The fertilizer rating 0-45-0 is quite different material. Farmers who see symptoms of phosphorus deficiency sometimes think a higher rating is the answer, and this one comes styled triple superphosphate. Here the acid used to do the etching is phosphoric. This eliminates the calcium sulfate in the bag, calcium frequently needed to kick up to calcium reserve, sulfate needed to complex an excess of magnesium. By invoking the hotdog concept of plant nutrition a much needed nutrient might be eliminated exactly when it is needed.

Ammonium phosphate such as 8-32-0, 11-48-0, and 80 on, also involve concentrated phosphoric acid in the processing, and this provides a handy outlet for otherwise unsalable fossil fuel company byproducts.

- Excerpted from Eco-Farm An Acres U.S.A. Primer

Calcium - 4. Delayed Appreciation

 

The delayed appreciation of the significance of calcium in plant nutrition may be laid at the doorstep of a confused thinking about liming and soil acidity. The absence of lime in many soils of the non-temperate zone has long been known. Lime in different forms such as chalk, marl, gypsum or land plaster, has been a soil treatment for centuries. Lime was used in Rome in times B.C., and the Romans used it in England in the first century A.D. Chalking the land is an old practice in the British Isles. The calcareous deposits like “The White Cliffs of Dover” were appreciated in soil improvement for centuries before they were commemorated in song. Liming the soil is a very ancient art, but a very recent science of agriculture. It was when Liebig, Lawes and Gilbert and other scientists began to focus attention on the soil as source of chemical elements for plant nutrition that nitrogen, soluble phosphate, and potassium became our first fertilizers. It was then that the element calcium and the practice of liming were put into the background. Unfortunately for the wider appreciation of calcium, this element in the form of gypsum was regularly a large part of the acid phosphate that was applied extensively in fertilizer to deliver phosphorus. Strange as it may seem, superphosphate fertilizer carries more calcium than it does phosphorus, and consequently calcium has been used so anonymously or incidentally that its services have not been appreciated. Fertilizers have held our thought. Calcium was an unnoticed concomitant. It has been doing much for which the other parts of the fertilizers were getting credit. Appreciation of the true significance of calcium in plant nutrition was therefore long delayed.

More recently soil acidity has held attention. This again has kept calcium out of the picture. Credit for the service of liming has been going to the carbonates with which calcium is associated in limestone. It was a case of the common fallacy in reasoning, namely the ascribing of causal significance to contemporaneous behaviors. Here is the line of reasoning: “Limestone put on the soil lessens the acidity, and limestone put on the soil grows clover. Therefore the change in acidity must be the cause of the growing clover.” Therefore the change in acidity must be the cause of the growing clover. At the same time, there was disregarded the other possible deduction, namely: “Limestone put on the soil applies the plant nutrient calcium. Therefore the applied calcium must be the cause of the growth of clover.”

The labeling of calcium as fertilizer element of first importance was delayed because scientists, like other boys, enjoyed playing with their toys. The advent of electrical instruments inducement to measure soil acidity everywhere. The pH values were determined on slight provocations and causal significance widely ascribed to them, when as a matter of fact the degree of acidity like temperature is a condition and not a cause of many soil chemical reactions.  Because this blind alley of soil acidity was accepted as a thoroughfare so long and because no simple instrument for measuring calcium ionization was available, it has taken extensive plant studies to demonstrate the hidden calcium hungers in plants responsible in turn for hidden but more extensive hungers in animals. Fortunately, a truce has recently been declared in the fight on soil acidity. What was once considered a malady is now considered a beneficial condition of the soil. Instead of a bane, soil acidity is a blessing in that many plant nutrients applied to such soil are made more serviceable by its presence, and soil acidity is an index of how seriously our attention must go to the declining soil fertility.

Now we face new concepts of the mechanisms of plant nutrition. By means of studies using only the colloidal, or finer, clay fraction of the soil, it was learned that this soil portion is really an acid. It is also highly buffered or takes on hydrogen, calcium, magnesium, and any other cations in relatively large quantities to put them out of solution and out of extensive ionic activities. It demonstrated that because of its insolubility, it can hide away many plant nutrients so that pure water will not remove them, yet salt solutions will exchange with them. This absorption and exchange activity of clay is the basic principle that serves in the plant nutrition. This concept comes as a by-product of the studies of calcium in relation to soil acidity.

Imagine that a soil consists of some calcium-bearing minerals of silt size mixed with acid clays. The calcium-bearing mineral interacts with the hydrogen of the acid clay. The hydrogen goes to the mineral in exchange for the calcium going to the clay. Imagine further that the plant root enters into this clay and mineral mixture. It does so more readily because of the presence of the clay. It excretes carbon dioxide (possibly other compounds) into this moist mixture to give carbonic acid with its ionized hydrogen to carry on between the root acid and the clay particle and the mineral. The hydrogen from the root exchanges with the calcium absorbed on the clay in close contact.

Thus plant nutrition is a trading business between root and mineral with the clay serving as the jobber, or the “go-between”. The clay takes the hydrogen offered by the root, trades it to the silt minerals for the calcium and then passes the calcium to the root. Thus nutrients, like calcium, and other positive ions as well, pass from the minerals to the clay and to the root, while hydrogen or acidity, is passing in the opposite direction to weather out of the soil its nutrients mineral reserve and leave finally the acid clay mixed with unweatherable quartz sand. Acid soils are, then, merely the indication of nutrient depletion.

 

- Excerpt from Albrecht's Foundation Concepts - The Albrecht Papers Vol. 1 - pgs. 149-150