Geo Growers Blog

Organic Fertilizer versus Chemical Fertilizer

Posted by Administrator | Filed under General Gardening

HOW ORGANIC FERTILIZER WORKS

To begin with, let us recall some basic facts about plant nutrition. Green

plants obtain raw materials for their biosynthetic processes in rather

simple forms: carbon dioxide, water, nitrate, phosphate, and ionic forms of

potassium, calcium, and other essential elements. Nitrogen, to choose a

particularly contentious example, almost always enters the roots as nitrate,

becoming assimilated by the plant’s biochemistry into organic compounds

such as amino acids and nucleotides. There is no doubt, then, that nitrate

is a “natural” plant nutrient. Nevertheless, a strict organic farmer does not

wittingly fertilize his crops with nitrate – or with ammonium salts, which

are quickly converted to nitrate by soil bacteria.

Why should a natural plant nutrient such as nitrate be regarded as

unnatural when added to the soil as fertilizer? To appreciate this

argument, we need to go back into soil ecology beyond the immediate

entry of nitrogen into the roots. In a natural system, nitrate in the soil is

derived from the gradual breakdown of humus, the dark, complex,

polymeric material that gives the soil its “tilth.” Nitrogen is integrally bound

to the carbon atoms that make up the organic structure of humus, which

is itself the end product of a complex chain of events that carries nitrogen

into the soil. The main path of entry begins with the deposition of organic

nitrogenous compounds on the soil in the form of animal feces and urine

and the dead remains of animals and plants. These largely organic

materials are subjected to hydrolytic and oxidative degradation by decay

microorganisms, yielding organic low-molecular-weight products that

support the growth of microbial flora. These processes finally yield a mass

of microbial cells, which on their death, together with some other remains,

become humus. The other source of soil nitrogen is nitrogen fixation,

which also delivers the element to the soil system in organic form. Thus, in

a natural soil system, untouched by human technology, nitrogen enters

into the system in organic combination with carbon, largely as the

nutrient for microorganisms that eventually produce humus.

Now a farmer who wishes to add nitrogen fertilizer to the soil to support

crop nutrition has two main alternatives. Nitrogen can be added in a

natural, organic form – as plant residues, manure, sewage, food wastes, or

for that matter, in the form of any nitrogenous organic compound that

can be metabolized by the soil’s microbial flora and thereby yield humus.

Alternatively, nitrogen can be added in an equally natural, but inorganic

form, such as nitrate or ammonia. The first choice is the one made by the

organic farmer; the second is the conventional route of modern

agriculture technology. The strict devotee of natural foods is likely to

reject grain grown with inorganic fertilizer in favor of that grown

“organically” with manure or compost, sometimes claiming that the

nutritional value and keeping qualities are superior – a claim that at this

point can neither be confirmed or denied.

Is there, then, any point in differentiating between the two ways of

supplying fertilizer nitrogen? Indeed there is. Considering the soil as an

integrated system, there is a vast difference in the outcomes of the two

methods. Because nutrient uptake is a working-requiring process, it must

be driven by the root’s oxygen-dependent energetic metabolism. Humus is

much more that a store of nutrients; it is also the chief source of the soil’s

porosity, hence of its oxygen content, and therefore of the efficiency with

which nutrients, such as nitrate, are taken up by the crop.

Thus, the critical difference between the alternative means of supplying

nitrogen fertilizer is that the organic form leads to the production of

humus, while the inorganic form does not. The use of synthetic urea as a

fertilizer provides an informative test of this distinction. Urea is, of course,

an authentic organic compound and is, in fact, an ordinary constituent of

a clearly natural source of nitrogen – urine. The scientific agronomist may

often cite the organic farmer’s objection to pure urea as a fertilizer – it is a

fairly common one in modern agriculture – as evidence of the irrational

basis of organic farming. But is it?

While urea is, indeed, an organic compound, it will not support the

bacterial growth that is essential for the formation of humus. When urea is

metabolized, the products are ammonia and carbon dioxide. Thus, urea

yields carbon in a form that will not support the oxidative metabolism of

solid bacteria. To accomplish that, carbon must be in the reduced state,

combined with hydrogen, as it is in the nearly all more complex organic

compounds. Although urea is an organic compound, by failing to support

the growth of soil bacteria, and therefore the formation of humus, it does

not qualify as an “organic fertilizer.”

The intensive use of inorganic nitrogen fertilizer (or urea) may so overload

a humus-depleted soil with nitrate as to cause it to leach into surface

waters when nitrate levels may readily exceed public health standards.

Leached nitrate also wastes expensive fertilizer synthesized from an

increasingly diminished supply of natural gas. Apart from any other

possible and yet to be established virtues, the use of organic fertilizer (as

defined above) avoid these difficulties and holds the promise of restoring

the natural source of soil fertility – humus. While it remains to be seen

whether food grown in such naturally fertile soil contributes distinctively

to the health of people, the practice can, it seems to me, contribute

significantly to the health of the soil and the economy.

Dr. Barry Commoner

Director, Center for the Biology of Natural Systems

Used with permission from Hospital Practice magazine

Vol. 10, No. 4

Comments (0) | January 29th, 2010