. Cyclopedia of farm crops : a popular survey of crops and crop-making methods in the United States and Canada. Agriculture -- Canada; Agriculture -- United States; Farm produce -- Canada; Farm produce -- United States. Fig. 447. American Elm (Cii/iu* .4 meri-. Fig. 448. Chestnut {Cattanea dentata). Especially significant is the relation of wood and farm crops to nitrogen, the most indispensable ele- ment of plant life. The sources of nitrogen are precipitation, assimilation of the free atmospheric nitrogen, as by the root tubercles of the legumi- nous plants, and fertilizers. Precipitation fu
. Cyclopedia of farm crops : a popular survey of crops and crop-making methods in the United States and Canada. Agriculture -- Canada; Agriculture -- United States; Farm produce -- Canada; Farm produce -- United States. Fig. 447. American Elm (Cii/iu* .4 meri-. Fig. 448. Chestnut {Cattanea dentata). Especially significant is the relation of wood and farm crops to nitrogen, the most indispensable ele- ment of plant life. The sources of nitrogen are precipitation, assimilation of the free atmospheric nitrogen, as by the root tubercles of the legumi- nous plants, and fertilizers. Precipitation furnishes yearly about pounds of nitrogen per acre. An acre of beech forest consumes every year 45 pounds of nitrogen, fir forest 37 pounds, spruce forest 35 pounds, and pine forest 30 pounds; an average crop of potatoes consumes 54 pounds, wheat 55 pounds, rye 47 pounds, and barley 39 pounds. For the building up of leaves, four to five times more nitrogen is consumed than for the building up of the wood itself. The pounds of nitrogen conveyed annually to an acre of soil by precipitation is just sufficient for the production of the wood substance, but not for the leaves. The nitrogen required for the production of the leaf substance is furnished by the forest itself in the form of fallen foliage and needles that have stored up large quantities of nitrogen. In farming, the need of nitrogen above the amount supplied _ by precipitation must be artificially introduced into the soil by manuring or fertilizing, or by the use of legume crops. Since the bulk of all mineral substances is also deposited in the foliage and not in the wood (see table), the forest trees, every fall, return to the soil, in the form of dead leaves, the greater part of what they have taken up through their roots. Thus forest trees, in addition to furnishing their own fertilizer, by bringing up mineral substances from the deeper layers of the .soil and depositing them on the surface, accomplish practica
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