Collodial Phosphorus, Cool or Not So Cool?

(The view looking down on one corn plant. The top six inches of roots.

Each square is one-foot square. Applies to the previous blog)

Purplish strips at the edges of corn leaves usually indicates a deficiency in phosphorus. Some organic gardeners use colloidal phosphate as the solution to this deficiency, but consider this: colloidal phosphate is often strip-mined in Florida, washed with water (and Florida has a big problem with supplies of fresh water), loaded on train cars, and shipped to places as far away as California and Washington, where it’s sacked up and shipped to your local garden-supply store.

[As a side note: Florida mines 75 percent of the phosphorous used by American farmers and about 25 percent of the entire world production. Phosphate ore must be chemically processed with sulfuric acid. When sulfuric acid reacts with the phosphate it produces a slightly radioactive byproduct known as phosphogypsum. According to the Florida Department of Environmental Protection, there are a billion tons of phosphogypsum stacked across the state and 30 million tons are generated each year.]

And the total amount of phosphorus (P₂O₅) in the sack is only 16 percent of all the bagged-up bulk, of which a mere two percent is available the first gardening season since the phosphorus is locked up in a mineralized form that requires the activity of soil microbes, soil bacteria, and exudates. (Exudates come from the roots and aid in the nutrient-release process by releasing; sugars, organic acids, and other compounds to dissolve minerals into a soluble state and stimulate the soil’s microbial action.) Unnecessary water use, exploitation of limited resources and wasted energy—all wrapped in a single bag. Add to this the fact that there is a limited supply of easily mined colloidal phosphorus. It’s much like oil: will we have enough in the future? Will we be able to find enough new supplies if the current mines are exhausted? Some say the U.S. supply will be gone by 2035. The world supply make be depleted in 50-100 years.

Choosing to buy commercial colloidal phosphate really means making a very important environmental decision. This is especially clear when one compares the environmental cost of imported amendments to the energy-efficiency of “growing” phosphorus at home by planting legumes and tilling the young foliage into the soil. Thus the gardener has two choices: (1) import nutrients, organic or not, to force an intensive yield, or (2) use wider spacing when planting and/or rotate heavy-feeder crops with a season of legumes to cut down on the competition for available nutrients. Whichever you choose, don’t grow corn in the same spot every year, as it will exhaust much of the nitrogen. Instead, alternate corn crops with green manures—that also increase available phosphorus.

Let me know what you think.

Visit my web site to learn about my new book on drip irrigation and other gardening books.

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Let's Get Real About Sustainability in Gardens

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.

Let me know what you think.

Visit my web site to learn about my new book on drip irrigation and other gardening books.

NOTE: The comments section at the bottom of the post has disappeared. Click on the "___ Comments" button or the title under the "Blog Archives". Thanks, Robert