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Fish as plant food helped create the first Thanksgiving feast

Thanksgiving is a time to think of fish as well as turkey. Fish for planting, that is, not for eating.

Remember, it was scraps of fish "planted" beneath seeds that helped create a good enough corn harvest to warrant that first Thanksgiving feast almost 400 years ago.

Experimentation and observation had taught Native Americans that such buried fish helped corn grow. The Pilgrims were wise enough to follow their lead.

How many of us modern gardeners tailor our gardening practices to noncommercial advice and close observation?



Today, the science behind those buried fish scraps has been spelled out. Fish bones are rich in calcium and phosphorus, but plants cannot "eat" those nutrients until they are solubilized by microorganisms. Phosphorus, important for grain formation, moves slowly through the soil, so burying fish scraps right beneath seeds ensures a good dose of this nutrient early in a plant's life.

Modern farmers typically lay a band of high phosphorus fertilizer — in synthetic form, not as fish waste — just beneath corn seed at sowing.

The muscle of fish or other animals, as you might remember from high school biology, is protein, which is made up of amino acids, rich in nitrogen. Plants cannot absorb nitrogen directly from muscle, or even from amino acids, any more than they can get their calcium and phosphorus directly from bones. But when an animal dies, microorganisms get to work breaking down muscle proteins into their component amino acids, then converting amino acids first to ammonium and then to nitrate.

Ammonium and nitrate are the forms in which plants absorb nitrogen from the soil.



A couple of details highlight just how wonderful this process is. First, because these are microbial reactions, they carry on most rapidly under moist, moderately warm conditions. Eureka! These are the same conditions under which plants grow fastest and need most nitrogen. So this natural process doles out nitrogen food to plants in sync with growing conditions.

Spread or water in a solution of some synthetic fertilizer beneath a plant, and some of the nitrate or ammonium nitrogen contained in it will force-feed the plant, or wash out of the soil before the plant is ready to use it.

Within the constraints of warmth and moisture, the microorganisms that convert amino acids to ammonium are more diverse and work under a broader range of conditions than do the microorganisms that go on to convert ammonium to nitrate. Under very acidic conditions, for instance, ammonium formation chugs along, but nitrate formation grinds to a halt.

Eureka again! Plants that require very acidic conditions — mountain laurel, rhododendron and blueberry, for example — happen to prefer their nitrogen dished out as ammonium, which is just what they get.

In a less pleasant display of their nature, ammonium-forming microorganisms work happily even in the absence of air. These creatures are responsible for the offensive aroma of compost piles that are gasping for air because of waterlogging or because materials are packed too densely.



I'm not suggesting planting fish scraps in your garden. For one thing, neighbourhood dogs and cats would have a field day grubbing around for them.

Deodorized fish emulsion is a commercial substitute used by many gardeners.

Furthermore, fish scraps and fish emulsion are concentrated fertilizers, even if they are natural. As such, they supply the soil with very little organic matter, which is so important for building humus. Humus, besides its direct and indirect benefits to plant nutrition, enhances the physical environment of the soil (its porosity, moistness and temperature) and helps fight diseases.

If you do use fish scraps, fish emulsion or any other concentrated fertilizer, supplement it with abundant compost, leaves, straw and other bulky, organic materials. The confines of a flower pot allow little room for adding bulky materials (except peat moss, compost or coir in the potting mix itself); in this case, use a soluble fertilizer, such as fish emulsion, mixed into your watering can.



Lee Reich, The Associated Press

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