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No matter how food is administered to it, on the ground's surface or down under, a tree's alimentary process remains the same. Like native minerals in the soil, the water-borne nutrients of fertilizer do not go directly into the tree's tissues. They must first be imbibed by rootlets, and then carried aloft by the pumping system to the leaves, to be transformed and elaborated by photosynthesis. The three prime nutrient minerals are nitrogen, phosphorus, and potassium. Nitrogen plays the leading role in forming chloroplasts, the green bodies that change sun energy into chemical energy. Phosphorus is ingested by the leaves in such a way as to stimulate flower, seed, and root growth. Potassium (potash) adds tensile strength to wood cells and, in the leaves, it catalyzes the formation and movement of sugars and starches, formed by carbon, hydrogen, and oxygen from the tree's air and water. In selecting a manufactured fertilizer for trees, the ordinary commercial brands made for farm use will serve, but some of the mixtures prepared expressly for shade trees are better, and probably worth the difference in price. The nitrogen-phosphorus-potassium ratios are usually printed on the bags in bold figures. Most formulas meant for crop tillage (5-10-5, 6-8-6, 10-10-10, and the like) are lower in nitrogen than are most tree formulas, which will run 10-8-6,10-6-4,or maybe 8-6-8. Most field fertilizers come as finely divided powders intended to dissolve rapidly. Tree foods are milled in coarse granules for a slower, longer lasting effect. The better prepared tree foods incorporate at least some of the trace minerals, such as boron, magnesium, and manganese, which trees are now believed to require. |
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