Plants Don't Need Soil, But Soil Needs Plants

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posted on

May 22, 2017

By Steve Kenyon 


BUSBY, Alberta: Did you know that a plant could grow without soil?  In a crack in a rock on a mountainside, a spruce tree can grow. How does it grow and where does it get its nutrients? 

The tree’s nutrients come from the air. Over 95 percent of the elemental makeup of any plant comes from the air. If we look at the typical dry matter composition of a plant, it looks something like this: Carbon: 45 percent, Oxygen: 45 percent, Hydrogen: 6 percent and Nitrogen: 1.5 percent. (That’s actually 97.5 percent). Any other element in a plant will make up less than one percent and most are measured in parts per million.   

All of these four elements, the plants, with assistance from our soil organisms, can capture from the air. Less than five percent of the elements we need to grow plants come from somewhere else. This could be from the soil or it could be straight from rock, with the help of our friends the mycorrhiza fungi.   

My point is that the plants do not need the soil to grow. The soil, however, needs the plants to grow. The photosynthesizing of the plants produces sugars, which are the foundation to life. It is the plants that push sugar out of the root tips as they grow that glues the soil particles together causing good aggregation. 

The plants build the soil. The plants take H, O, C and N from the air and add it to the soil. We do also have to give credit to the soil microbes. In symbiotic relationships with the plants, (the soil life needs sugar from the plants) many of our micro biotic employees also help to build the soil.   

For example, mycorrhizal fungi produce glomalin, which is a glycoprotein.  Most tests greatly underestimate the amount of glomalin in our soils, which can accountfor up to one third of the organic carbon stored in agricultural land. However, we need healthy soils with good organic life to do so.  I have heard the recommendation many times that producers need to cultivate their pastures every 8-10 years in order to release the “bound up” nutrients. I totally disagree with this practice. I am trying to build my soil, trying to make nutrients become “bound up” in my soil. I am building soil.  

 Yes, when you break up that pasture, nutrients are released. This only allows you to mine the land and deplete it faster. The problem is that it works, as producers get a really good crop for the next few years by mining the nutrients out of the soil.  This is a short term gain only at the cost of depleting the soil.   

One of the biggest breakthroughs that I have had on my farm is in the realization that plants do not grow from the soil; it is the soil that grows from the plants. We need to build the soil by managing the plants. The magic is in the photosynthesis.   

Building soil also increases the water holding capacity by putting more carbon back into the soil.  Humus can hold up to nine times its weight in water.   

The best way to put organic carbon back into the soil is through exudation from the actively growing roots of plants in the Poaceae family. This includes pasture grasses and cereals. Exudation is when the root tips are pushing out sugars as they grow, which glues the soil together. 

The breakdown of plant material and their fibrous roots is also an important source of carbon in soils. The more active the plant roots are, the more carbon is added. Also, the more diverse the plants, the better it is for your soil life. We need to stay away from monocultures. Polycultures create healthy ecosystems. 

I am experimenting with pasture cropping; I want to have perennial pasture grasses and cereals together.  The ongoing carbon inputs from the perennial grasses create highly stable forms of soil carbon, while the short-term, high sugar forms of carbon exuded by the roots of the cereal crop stimulate microbial activity. This is a good combination in building soil.   

I also want to have some legumes to fix nitrogen as well as some plants that open up the soil like tillage radish and sweet clover. These are not meant to be a forage, but more of a soil amendment. These big roots can dig down and open up the soil allowing water and air infiltration.   

In a healthy ecosystem, plants grow the soil, not the other way around. Of course, this is all tied together with the recycling of nutrients provided to us by our livestock, who recycle 80 percent of what they consume. I am sure glad that they are so inefficient; it is almost like they were meant to be that way. 

My lesson learned: Use plants to build soils and use livestock to manage the plants. It’s been working for centuries without us. 

♦  Steven Kenyon can be reached at Greener Pastures Ranching on Facebookor 

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