Consider corn as a way to look at true sustainability. Corn plants produce a massive root system that consumes large amounts of moisture and nutrients. The root system forms quickly: by the time a corn plant has formed just eight leaves it has produced 15 to 23 main roots with a total of 8,000 to 10,000 lateral roots. A mature plant can generate roots that have “ramified” (grown through) as much as 180 cubic feet of soil. (As seen in my book Roots Demystified, 2009.)
Corn plants need lots of nitrogen, and leguminous plants, as long as they’re not too crowded can provide it with all the nitrogen required. In a “natural” garden, the ultimate goal would be to eliminate almost all imported nutrients and other “inputs”. Horse manure, cow manure, sacks of bone meal, blood meal, green sand, bat guano, phosphates, or many other options—all add additional fertility, can qualify as “natural,” but come with various environmental costs attached; such as mining, transportation, energy use, and wasted bulk.
As an example of the energy invested in nitrogen for corn, consider blood meal. According to the Food and Agriculture Organization’s regulations, blood is introduced into the (processing) tank as a coagulated mass, previously obtained by a steam-action process. Ideally, as much liquid as possible should be squeezed from the coagulum. Heating is initiated at 82°C (180°F) and progressively raised to 94°C (200°F) for about three hours, then elevated to 100°C (212°F) for 7 hours. (That’s a LOT of energy). Drying is complete when the final moisture level in the dried product is about 12 percent.
Choosing blood meal at the nursery or organic supplier really means making a very important environmental decision compared to “growing” nitrogen at home by planting legumes and tilling the young foliage into the soil.
No matter what your source of imported nitrogen, whether for soil preparation or as a summer application for growth. It’s most effective to spread it relatively far from the cornstalk itself in order to feed the massive width of the corn root system most efficiently. One method of doing this would be to fertilize between the rows rather than on the rows themselves or at the base of each plant. If you plant intensively, be sure to add plenty of nutrients for this hungry crop.
Thus the gardener has three choices: import nutrients for intensive yields, or use a wider spacing and/or, rotate your crops to cut down on the competition for available nutrients. Don’t grow corn in the same spot every year, as it will exhaust much of the nitrogen. Instead, alternate it with green manures—legumes like fava beans (the flowers pictured above) tilled into the soil to provide nitrogen from the atmosphere. A good green manure should be tilled in before too much blooming.
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