Tuesday, September 11, 2018

organic matter

The differences between soil samples in a very rainy time on our farm as shown in the post just below, is connected with the water cycle and the carbon cycle, both of which are involved in the idea of climate change. Returning our soil to good health is a critical part of coping with and mitigating climate change. And it is always easier, when faced with a big problem, if one can grasp a good handle on it.

Earth’s water cycle is denatured because the soil does not hold water well enough. Hence too much runoff to the surface water with attendant flooding and erosion, both field and streambank. Too much surface water in a warming environment leads to excessive rain as well as flooding. You see where this goes.

It is apparent that our pasture soils hold water better than those under a cropping use. Note the crumb structure with its openness between and among fragments. This is evidence of an abundance of little critters in the soil, millions of species, most of them yet unknown. Their presence is in itself evidence of a higher proportion of carbon in the soil. We know this to be true because we have a higher organic matter reading in our pastures than in our cropping areas. Soil organic matter is about 58% carbon. Our farm has high readings in both pastures and cropping practices, which is very encouraging to us. But our levels, at five to six and a half percent organic matter, are still only half of what they were thought to be at the time of white settlement. It is sobering to realize that in the short time of three or four generations that amount of carbon was lost to the air through tillage, which exposes the soil and burns off organic matter. Since organic matter level is generally read in terms of the top six inches of the soil, each tilled acre has contributed a tremendous weight of carbon to the atmosphere in that time. I am not mathematically adept enough to quantify this. It is, in any case, huge.  Is it comparable to the loads dumped by coal burning and petroleum use?

So one of the things we can try to do in order to help stabilize the water cycle is to change the carbon cycle on the farm. We do this, in farm terms, by building organic matter in the soil. And we know that not only does tillage of the soil work against building organic matter, but also that a planned grazing practice encourages organic matter. This is because of the essentially “pulsing” effect of the animal impact. The periodic grazing of the plants cause them to slough off some of the root structure building humus-organic matter-in the soil. It is this event, plus the regrowth of those same roots as the grass grows back, which kicks the activity of the soil critters into high gear and will increase the amount of carbon in the soil over time.

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