In my last blog I wrote about soil organic matter and how I work to build more of it. Here are some other things I've learned about soil organic matter that might help you.
I love chocolaty, highly mineralized and sweet-smelling soil that is loaded with earthworms and organic matter (carbon). But the truth is that dirt only becomes topsoil when it contains lots of organic matter and high microbial life.
In my area most soil is not soil. It is dirt and will provide clay with little life that will hold a plant up so it can grow in salt fertilizer, buffered with carbonate, and watered every three to seven days. The nutritional content of the harvest is low.
Here is a less-than-exhaustive list of organic matter facts worth knowing:
- Organic matter is 60% carbon and is the sponge of life in the soil.
- Low organic matter soil can hold almost zero moisture and lacks aggregation and pores (air spaces). It is typically anaerobic and low in production and high in “weed” content. The weeds and their tap roots are there to increase pores, carbon and future aggregation. Declaring war on them is generally a mistake.
- Soil organic matter that is functional has a 12:1 carbon to nitrogen ratio. This is also called humus.
- Litter above the ground or on the surface that is highly functional has a 24:1 carbon to nitrogen ratio. This is the same as quality compost.
- High carbon to nitrogen ratio plants above the surface are slow to be digested and break down. Another reason for a high level of plant diversity.
- Cattle manure has a carbon nitrogen ration of 18:1 which explains why we need its soil and plant nutrition to quickly enter the soil. Dung beetles, earthworms, ants, and other microbes do this job for us after we take the purchased chemicals out.
- Tap rooted plants (forbs) pull minerals from deeper in the soil profile and scavenge and store necessary nutrients including minerals and nitrogen. Their live roots exchange nutrients with fungal growth and dead roots produce organic acids that loosen mineral from the subsoil rocks.
Here are a few other interesting and useful carbon:nitrogen ratios.
- Cattle manure – 18:1
- Poultry manure – 7:1
- Slaughter waste – 2:1
- Horse manure – 12:1
- Clover, vetch – 11:1
- Alfalfa – 25:1
- Grass – 50-80:1
- Newspaper – 50:1
- Leaves – 50:1
- Sawdust – 500:1
- Wood chips – 250:1
- Legume hay – 30:1
- Grass hay – 80:1
- Straw – 100:1
- Corn stalks – 57:1
- Cereal rye – 80:1
- Near perfect compost – 25:1
- Quality litter – 25:1
- Soil bacteria and protozoa – 10,000:1 (by number)
- Soil organic matter (humus) – 12:1
It should become apparent why the natural model principles work when they are properly applied: The key is 25:1 on top and lots of 12:1 in the soil. With high levels of mineralization and the living carbon-nitrogen sponge there is lots of life when we cycle the system quickly with high-density, severe cattle grazing (boom-bust). Notice that everything has an important role in the system.
System crashes due to flood or drought or severe grazing are normal since they later add strength and diversity to the system. Remember that diversity yields system stability. Death is required of all life. The result is new life. But 50% of natural system activity is death. The key is to increase the overall volume of the life-death cycling.
The cattle and other animals add bacteria and impact and recycling that the soil and plant life require. Remove the animals or spread them out and the system begins to fail. Boom-and-bust grazing is a key to organic matter development just as it yields huge plant diversity and microbes that are highly functional.
Quality soils are capable of growing quality plants that are capable of growing quality beef that furnish quality health for our families and patrons. Organic matter of our soil is a key. Two-thirds of soil organic matter comes from roots. If we fail to completely recover pastures we lose much of this potential for soil life. The same is true when cattle are removed from the system. Everything is connected to everything.
The opinions of this writer are not necessarily those of Farm Progress/Informa.