How plants eat


If it isn’t in the soil, it isn’t in your food
If it isn’t in your food, it isn’t in you

People and animals are fairly self-contained. We carry our stomachs wherever we go and can digest what we find to eat on the spot. It’s a handy feature.

Plants however, have their stomachs in the soil. Their digestion is external to their root system, in the area surrounding their feeder roots. They don’t have the option to get up and move, unless they grow into a new area. It’s an interesting difference.

How plants take nutrients out of the soil

There are several different mechanisms:

  • Plants can absorb dissolved nutrients directly. This is the mechanism that conventional agriculture (and some organic agriculture) uses. Large amounts of soluble fertilizers are applied to the soil so that the plants always have more than enough dissolved nutrients to grow as large as possible as quickly as possible. The trouble with this approach is the toxicity of the fertilizer to soil life, the excessive water usage, the tendency for fertilizer runoff to contaminate waterways and the loss of micro-nutrient fertility in the soil, to name a few.
  • The soil life web can release nutrients from the soil, even if they are not readily available. These nutrients may be taken up by the plants and help to build up soil reserves. And plants can form symbiotic relationships with mycorrhizae to aid in the uptake of nutrients. The trouble with this approach is that the soil life may not be entirely up to the task, especially on marginal or worn-out soils, or arid soils, or soils with low organic matter or poor bio-activity. The result may be poor growth or low nutritional content of the food grown on these soils.
  • Balanced minerals work in concert with soil life to provide optimum nutrition to the plants. If minerals are available and in the right balance, they may be taken up directly both by the plants and by the soil life. This is a resilient system — if the soil life is non-optimum it tends towards direct absorption by the plants. If the minerals are not balanced, soil life will help to provide the extra nutrients from the soil parent material. And the result is a nutrient-dense, vibrant plant that is able to develop to its genetic potential. The health of these plants can be then transferred up the food chain.
Liebig’s Law of the minimum

The great 19th century chemist, Justis von Liebig, found that plant growth is limited by the least available nutrient. Just as the barrel bearing his name shows, the lowest stave (the least available nutrient, depicted as the lowest piece of wood in the barrel) will limit the amount the barrel will hold (the growth of the plant). Once the least available nutrient is supplied, another nutrient becomes the least available.

As gardeners and growers, we often are searching for the silver bullet… that one thing that will make our gardens flourish. You will hear a lot of stories about other people’s silver bullets. They will tell you what worked for them, in their situation. But everyone has their own barrel and their own lowest stave. You’ll need to see what works for you, in your situation.

If a little is good, more is better? Not really…

The trouble with Liebig’s barrel is that it doesn’t tell the whole story. While it correctly illustrates the limiting factor, it reveals nothing about the soil balance needed to allow plants to grow to their full potential.

next… Soil In Balance