Having The Right Amount Of Nitrogen In Our Soil

Soils rich in organic matter are seldom deficient in nitrogen, since nitrogen is produced during decomposition of organic matter. The amount may not be high enough to produce top yields, however. That's why soil periodically should be planted to a legume that will fix additional nitrogen in the soil by the action of bacteria living on the legume roots. Since there are about 75 million pounds of nitrogen in the air above every acre of land, the amount of nitrogen fixed by legumes Is limited only by the plant's ability to do the fixing.

Some day - and researchers are working at it already - we may have legumes and bacteria which will supply all the nitrogen a soil needs without any help from additional fertilizer. But for now there will be times when a soil needs additional help in building up a sufficient supply
of nitrogen. This is particularly true for gardeners who take over poor ground and want to raise good crops Immediately. It takes nature years to restore a soil's fertility. With organic help, the natural process can be sped up.

Growing and consuming plants, in some other way than allowing them to rot back into the soil from which they sprang, are activities which are by their nature nitrogen depleting. If you don't put back as much as you take out of the soil, you're losing ground - literally. The process is sort of like money and banks. If you establish a savings account and draw no money out of it, the interest keeps accumulating. Your money increases without any particular effort on your part.

If, on the other hand, you don't have a savings account but must borrow money steadily, then you must always be paying back - principal plus interest. If you have more nitrogen "banked" in the soil in the form of organic matter than you are taking out, the soil continues to build up - progressively, like interest on savings. You don't just hang on by the skin of your teeth each year in your gardening. And if a year comes when you can't get extra fertilizer from outside sources, there's enough in your "bank" to tide you over. But if you haven't practiced thrift - if you've taken out more nitrogen than you've left in - you have to pay back from another source with interest. And you can't ride out a bad year of fertilizer shortages.

Balancing The Supply

Plants can't use nitrogen in its raw form. First acids in the soil change it to nitrate forms which the roots then take up. In the plant cells the nitrate salts are converted to ammo acids of many kinds which recombine to form protein. And protein, of course, is the real staff of life.

You can upset the process by which nitrogen becomes protein either by not providing enough of the former or by providing too much. Too little in a vegetable garden makes plants spindly and yellowish; too much and they grow rank, producing too much stem and leaf in relation to fruit, or producing leaf which has small protein value.

Too much nitrogen can make grains, especially wheat, grow so rank that they fall over at the first heavy rain or hard wind. In very dry weather, an excess of nitrogen fertilizer can build nitrate levels in stunted plants high enough to cause nitrate poisoning.

Nitrogen Deficiency

You can spot nitrogen deficiency in your garden sometimes by color. Vegetable plants well supplied with nitrogen are a rich, dark green and grow fast in warm, humid weather. When growth is slow and plant color yellowish-green, you're most likely short on nitrogen. First the leaves yellow, then the stems. In case of nitrogen starvation, the whole plant turns yellow, then brown.

Yellowing of leaves occurs from other causes, so be forewarned. Even experts cannot always tell by sight alone. On ground not properly drained, the yellowing may mean that nitrogen is not available to the plant because of excessive moisture and lack of aeration, even though enough of the nutrient is actually present in the soil.