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Nitrogen sources are provided in a variety of ways. Some from the air and dissolved nitrate salts in the rain. Some from manure left

behind because everything from cattle to insects feed on the plants. Some from the plants themselves - called "green manure" or plants that fix nitrogen in their roots and are thus tilled into the soil by nature's farmers, the ants. And some from the plants as

they die or go to sleep season's end.

Almost immediately, macroorganisms start the breakdown of these sources. There are a variety of these macroorganisms,

including millipedes, sow bugs and pill bugs, roaches, earwigs, and even some beetles that feed on these nitrogen sources. At

the same time, beneficial fungi start attacking and a process called decomposition begins. (The process also goes by the name

of "rotting".) When they are done, we have a material called compost, and when mixed with a bit of moisture, is further

processed by Nature's "tillers" - the earthworms.

The result of all this macrobial action is ammonia compounds that the "critters" cannot digest, but that bacteria can and do, thus forming nitrites, although

nitrites must first be turned into nitrates. Nitrates is the form of nitrogen that plants can use, and they do. But in doing so, more beneficial fungi are formed around the

roots of these plants to help them in their uptake of this nitrogen, other nutrients and moisture. As the plant

grows, it of course ages and is eventually consumed, and the process renews once more.

•Nitrogen Fixation•Decay•Nitrification•Denitrification

Microorganisms play major roles in all four of these.

Four processes participate in the cycling of nitrogen through the biosphere:

•

Nitrogen FixationThe nitrogen molecule (N2) is very stable. To break it apart

so that its atoms can combine with other atoms requires the input of a lot of energy.

Three processes are responsible for most of the nitrogen fixation in the biosphere: atmospheric fixation

biological fixation industrial fixation

DecayThe proteins made by plants enter and pass through food webs just

as carbohydrates do. At each trophic level, their metabolism produces organic nitrogen compounds that return to the

environment, chiefly in excretions. The final beneficiaries of these materials are microorganisms of decay. They break down the molecules in excretions and dead organisms into ammonia.

NitrificationAmmonia can be taken up directly by plants - usually through their

roots. However, most of the ammonia produced by decay is converted into nitrates. This is accomplished in two steps: •Bacteria of the genus Nitrosomonas oxidize NH3 to nitrites

(NO2-).

•Bacteria of the genus Nitrobacter oxidize the nitrites to nitrates (NO3

-).

These two groups or autotrophic bacteria are called nitrifying bacteria. Through their activities (which supply them with all their energy needs), nitrogen is made available to the roots of plants.

DenitrificationThe three processes just listed remove nitrogen from the

atmosphere and pass it through ecosystems.Denitrification reduces nitrates to nitrogen gas, thus replenishing

the atmosphere. Once again, bacteria are the agents. They live deep in soil and in

aquatic sediments where conditions are anaerobic. They use nitrates as an alternative to oxygen for the final electron acceptor in

their respiration. Thus they close the nitrogen cycle.

Are the denitrifiers keeping up?

Agriculture may now be responsible for one-half of the nitrogen fixation on earth through

•the use of fertilizers produced by industrial fixation •the growing of legumes like soybeans and alfalfa.This is a remarkable influence on a natural cycle

You can create you own Nitrogen Cycle "factory" by creating a compost bin for your yard

trimmings and kitchen vegetable scraps.Then, after

applying the compost to your garden,watch how the plants

respond to your kindness - providing you

with deep green foliage,beautiful flowers and sweet fruits and seeds.

The EndThe End