Editor’s Note: This is a combination of two smaller excerpts from Acres U.S.A. original book, Eco-Farm, An Acres USA Primer, written by Acres U.S.A. founder Charles Walters. Copyright 1979, 2009. #122. Softcover. 462 pages. $30.00 regularly priced.
By Charles Walters
All of the confusion [in labeling fertilizer] is further complicated by the nature of the weighted N-P-K formula system. A bag might say 0-0-60. Does this mean that in a 100-pound bag there are 60 pounds of K, the rest being inert filler? Not exactly.
The fact is that farmers get a lot of things they may not even want when they buy 0-0-60,18-46-0,17-17-17, or whatever.
As an example, take ammonium nitrate—or 33.5-0-0. Here’s how they compute the formula. Ammonium nitrate of course is NH4NO3. Each of the elements in this affair has a Mendeleyeff atomic weight. N has an atomic weight of 14. O has an atomic weight of 16. There are two Ns in the formula, or 2N. There are four Hs, or 4H. There are three 0s, or 3O.
Count them. This means:
2N X 14 = 28
4H x 1 = 4
3O X 16 = 48
Total = 80
The entire compound has a weight of 80. This must be divided into 28 (because we’re presumably interested in the legislated formula for N), and the figure is 35%. There is a bit of tolerance here because of binding agents used. As a result the bag is 33.5 (the fertilizer grade of the product). By law, the H and the O are defined into the designation N.
Potassium can be computed the same way, whatever the designation, but the compound involved must be known. KQ means K x 39 and Q x 35, total 74, with 39 divided by 74, or 52.7% K in 0-0-60.
The general idea holds for all the NPKs. Take the common mix, 18-46-0, diammonium phosphate, or (NH4)2HP04. Here N and P are combined with no K in tow. This means:
2N X 14 = 28
9H x 1 = 9
1P X 31 = 31
4O X 16 = 64
Total = 132
The total for N divided by the total for the compound—28/(28+132)—will equal 21.2%. The P end of the affair is arrived at by dividing 31 by 132 to equal 23.5%. Since the law says P is really P2O5, a further conversion must be made to yield the bag designation. In this case the factor is 2.29 x 23.5%, which equals 53.8%. That’s close enough to 18-46-0 as far as the law is concerned—thus diammonium phosphate is bagged as 18-46-0 instead of the pure stuff, 21-53-0, and the complicated affair styled NP is really (NH4)2HP04.
A lot of water has gone over the dam since von Liebig and the fossil fuel crowd got into the fertilizer game, but those old laws abide as though farming were an industrial procedure rather than a biological procedure.
New knowledge about humates, trace elements, enzymes are proscribed here and there because they don’t fit the formulas and the laws.
The pundits talk about the best science, not remembering that the best science once prescribed holes in the skull to let out the demons, bleeding to dispose of bad humors, laudable pus to exit toxins and the intelligence that the world was flat.
Chemical inspection of factory fertilizers and state regulatory control gained a toehold in agriculture because—in the words of Albrecht—of “the early beliefs that water solubility of them was an index of their absorption by the plant roots.”
It was Albrecht’s argument that soil behavior in nature did not conform to the laws of the laboratory. Some substances tagged as soluble in the laboratory became insoluble when placed into the soil. He pointed out that plain old land plaster—known as the chemical compound calcium sulfate, or the mineral gypsum—is soluble in the laboratory. Yet it can break down lung tissue by a process suggesting calcification. Some of the water-soluble fertilizers are promptly lost because they are water soluble. Some become immediately insoluble and difficult for plants to take in as nutrients.
Management of the cation exchange capacity we visited about in the section on soil audits is not best accomplished with soluble salts. Indeed, calcium, magnesium, nitrogen, phosphorus, potassium and other essential nutrients are not swept into plants because they are flooded into the soil in a water-soluble form. Plants force-fed with solubles alone may seem well fed but remain completely undernourished. Synthetic and hydroponic systems simply are not basic to life essentials.
Charles Walters is the founder of Acres U.S.A., and completed more than a dozen books as he edited Acres U.S.A., while co-authoring several others. A tireless traveler, Walters journeyed around the world to research sustainable agriculture, and his trip to China in 1976 inspired others to travel to this then-mysterious society. By the time of his death in 2009, Charles Walters could honestly say he changed the world for the better.