How do plants grow? This might seem like a pretty simple and harmless question, but Jean Baptista Van Helmont was curious about this so he did a pretty basic experiment to find out. The downside to his experiment was that he was arrested for it!
Here is what he did in his own words:
“I took an earthen pot and in it placed 200 pounds of earth which had been dried out in an oven. This I moistened with rainwater, and in it planted a shoot of willow which weighed five pounds. When five years had passed, the tree which grew from it weighed 169 pounds and about three ounces. The earthen pot was wetted whenever it was necessary with rain or distilled water only. It was very large, and was sunk in the ground, and had a tin-plated iron lid with many holes punched in it, which covered the edge of the pot to keep airborne dust from mixing with the earth. I did not keep track of the weight of the leaves which fell in each of the four autumns. Finally, I dried out the earth in the pot once more, and found the same 200 pounds, less about two ounces. Thus, 164 pounds of wood, bark, and roots had arisen from water alone.”
For this experiment, he was arrested for the crime of studying plants and other phenomena. This happened in 1634. At the time, it was believed that plants grew by eating the soil and his research was not received very well. His research was published in Ortus Medicinae (in 1648). This is human nature. Sometimes we get stuck in our paradigms and cannot accept new ideas. I have also seen that sometimes we get stuck in new paradigms and cannot accept old ideas. Let me explain.
His science is a little outdated and we now know that his conclusion was not entirely correct but he did prove an important point that we seem to ignore in today’s agriculture. His point; plants do not grow from the soil. His experiment showed that the makeup of the plant did not come entirely from the soil. It does partially come from the water added to the soil as he stated, but we also now know about the miracle of photosynthesis. Photosynthesis is the process where the plant takes carbon dioxide (CO2) and water (H2O) and combines them by capturing sunlight energy to form a simple sugar called glucose (C6H12O6).
He was almost right; very little of the growth comes from the soil. Over 95 per cent of the elemental makeup of a plant comes from the air. On a wet basis, over 80 per cent of a plant is water, but if we look at the typical dry matter composition breakdown of a plant, it looks something like this: carbon: 45 per cent, oxygen: 45 per cent, hydrogen: six per cent and nitrogen: 1.5 per cent. That’s 97.5 per cent. Any other single element in a plant will make up less than one per cent. Most are measured in parts per million. Most of a plant is carbon which comes from the air, with hydrogen and oxygen from the water (which comes from the air as well) to make sugar through photosynthesis.
Nitrogen is also taken from the air by soil microbes and given to the plant in exchange for sugar. The air we breathe is 78 per cent N. The most common method is by the symbiotic relationship between the legume and the microbes to exchange N for sugar, but there are other bugs that can convert the N in the air as well. The main point is that less than five per cent of the elements we need to grow plants come from the soil.
Yes, I agree, a soil test will show the elemental breakdown of all of the elements in the soil. And adding nutrients to the soil will make plants grow, but at what cost? I’m just saying we can get it for free by recycling. We have degraded our land. We no longer have healthy soils that can function on their own.
Here is a paradigm for you. I hear all the time about nutrients that get “bound up” in the soil and people say this as though it is a bad thing. I am trying to build my soil. I am trying to have nutrients and minerals held in the soil. Are we not constantly trying to promote taking carbon from the air and putting it back into the soil to save the earth? Why is carbon any different than all of the other elements? It is a good thing if we can build up our soil and have all the nutrients become “bound up” in the soil. We just need the right bug to get it for us when we need it.
There are millions and millions of interactions that take place in the soil. Many of them are symbiotic relationships between the plants and the soil organisms that benefit both sides. A major issue with our agricultural soils is that we have been “mining” them for many years. We are taking nutrients from them without replacing them. Most of the nutrients needed to grow a plant come from the air, and we need the soil organisms to get it. I agree, some of the nutrients for the plant might come directly from the soil. Indirectly though, that nutrient needs to recycle through the soil and be replenished. The net change in the soil needs to be neutral.
So my question for you is, if more than 95 per cent of the plant’s elemental makeup comes from the air, why do we spend so much time and money trying to add nutrients to the soil? The soil is only a medium to provide stability and a protected environment for the plants and the soil life. The real magic is in the plants with the process of photosynthesis, and in our amazing soil organisms. Matter cannot be created or destroyed. Every element has a cycle. We need to learn how to effectively recycle nutrients so we do not have to constantly buy them.
Most often in today’s agriculture, these cycles are disturbed by our management practices. One of the biggest reasons why is because we do not take care of the bugs in our soil — 85-90 per cent of plant nutrition is microbiotically mediated. Most soils have a biological issue, not a fertility issue. WE NEED BUGS IN THE SOIL! (I think I have said that a few times before.)
What about the other five per cent of the elements we need? The bugs can get that from the soil for you as well, but only if they are well taken care of. Let’s look at one example of how the soil life can help the plants. The mycorrhiza fungi in a healthy soil acts like the Internet to connect, transfer and exchange nutrients and information within the soil. This massive network connects all of the processes in the soil together. The fungi can extend the reach of the plant’s root systems a thousandfold in searching for nutrients. They can also extract the minerals we need straight from the rocks. They can pass information between the plants for disease and pests to build up resistances. It is amazing what our soil life can do for us. If we let it! I would recommend you look into how to take care of your fungi. I bet you will find that most of it is really just common sense.
We know very little about what happens within our soils. But in reality, the soil is not that complicated. It is silt, sand and clay with organic matter mixed in. It is the millions and millions of soil organisms that do all of the heavy lifting. This includes plants, animals and fungi. Take care of your living soil.
Be aware of your own paradigms. I think more people in agriculture today should be arrested for the paradigms they get stuck in! What some of us do to our soils is a crime.