WHERE IT ALL BEGINS: THE SOIL - Growing Chinese Vegetables in Your Own Backyard - page 211

I prefer organic fertilizers because they supply a wider range of nutrients and are
less apt to harm plants or soil organisms. Synthetic fertilizers do not enrich the soil, nor
do they nourish the soil bacteria or earthworms essential to the production of quality
topsoil. Quite the contrary; high doses of concentrated synthetic fertilizers can harm soil
organisms, and even more normal doses can stun them into ceasing their activity. Con-
centrated synthetics can burn plants (but then, so can chicken manure — even though
it's organic, it's too concentrated). That's not to say that synthetic fertilizers aren't use-
ful. When used in conjunction with abundant organic matter, and when used in moder-
ation, synthetic fertilizers can produce good gardens.
Nitrogen
Nitrogen is the first element in a fertilizer formula (5-3-3, for example). The chief func-
tion of nitrogen is healthy leaf growth. In addition to iron, nitrogen is responsible for
the dark-green color of foliage, and a lack of nitrogen may be indicated by pale-green
or yellow leaves. (A lack of iron may have the same effect; as with the human body, the
same symptom may result from more than one disease.)
Organic matter slowly releases nitrogen, thanks to the work of soil micro-organ-
isms. That's one of the reasons organic matter is so beneficial. But it's difficult to es-
timate how much nitrogen the soil organisms will release (it varies with temperature,
among other things). Nitrogen is easily leached out by rain and watering, and it's used
up in various natural soil processes. Vegetable plants use a lot of nitrogen, so soil tests
almost always recommend applying this nutrient.