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Tuesday, November 2, 2010

Soil

A friend recently told me that my blog was getting a bit didactic. (He really said I should stop trying to bludgeon people into changing and go back to describing what I’m doing. People will follow. ) He’s probably right. But, I’ve hit a place in my thinking and doing where I’m stuck. I can keep doing what I know, probably even get better at it, but it will never fix the fundamental problem with the system. Not even at the level of my little farm and my little family. Sustainability will continue to elude me. So, I’ll be continuing my didactic posts for a while, using them to explore my own thinking and maybe illuminate some possible next steps.

There is a kind of magic in being a farmer. You choose a bit of ground, prepare it, plant a seed, and like magic, a new plant grows. You do your best to provide everything the plant will need and to protect it from harsh conditions and invaders. But what happens underground as the seed grows into a plant and the plant grows to maturity is a bit of black box magic. Yes, we know what happens. The seed sprouts. The roots spread out through the soil and the plant reaches for the sky. The plant draws what it needs from the soil, and through photosynthesis, turns the chemical bits into the sugars and proteins it needs to grow. But beyond that, most of us don’t really know what happens. We know to make sure there is plenty of NPK, and water, and that the temperature is right before we plant. We know that weeds compete and bugs destroy, and that it is our job to prevent these things from harming our chosen plants. But we, except for a few farmers with advanced degrees in chemistry, botany, and microbiology, don’t know how the magic really happens in that black box we call soil. Without knowing what is happening we can’t really predict what effect our actions have. There are four main players in this magic, the soil, the plants, the animals, and us. Understanding the role each plays in a sustainable system will help us develop a more sustainable form of agriculture.

First the soil –

Here’s what I, a farmer without advanced degrees in chemistry, botany, biology, microbiology, or anything relevant, have been able to glean about what’s happening in the soil.

Soil is not DIRT. It is a complex, living, little understood poly-organism. From a farmer point of view, soil is primarily a storage facility for plant nutrients. That’s the part I’ve been trying to understand, how soil works as a fertility storage/production/ exchange medium.

Soil has three components, chemical, organic, and microbial. All of these parts have to be working in balance to produce plants and replenish the soil in a sustainable way.

First the chemistry has to be right. From a plants (famers) p.o.v. soil is a mega warehouse of the building blocks of life. These building blocks are either held in the soil for plants to use, or are snatched by the plants as they flow through the soil matrix. From a sustainability standpoint, holding the components of life within the soil matrix for future use is key. This happens through chemistry. There are two basic chemical components involved in this process, colloids and cations. Colloids have a negative charge, and cations have a positive charge. Colloids are mostly clay particles or humus (a stable organic particle… more on that later.) Cations are mineral ions that have acquired a positive electrical charge. These mineral ions – calcium, magnesium, nitrogen, phosphorus, potassium, sodium, sulfur, copper, zinc, etc., are bound to negative sites on the colloid. That holds them in the soil. (If they are not bound to a colloid they are in solution and wash through the soil matrix quickly.) Each mineral ion fills a percentage of the sites on the colloid. This is the base saturation for that mineral. The nutrient holding capacity of a soil is determined by the number of colloids in that particular soil type. The base saturation determines soil fertility. The ratio of various mineral ions on the colloid determines how what nutrients are available for the plants to use. If the balance is wrong, particularly the balance between calcium and magnesium (these two combined need to occupy about 80% of the sited on the colloid, with calcium occupying 60 to 70% and magnesium occupying 10 to 20 %) the other mineral ions become bound too tightly to the colloid and are not available to the plant.

Humus is the other major colloid in the soil. Humus is an organic particle created by the decomposition of ligneous organic matter. Lignin is the fibrous part of mature plants. It is mostly carbon. It is broken down slowly in the soil by soil microbes. Humus does not include undigested plant remains, woody bits, etc. It also doesn’t include green vegetative material. This material is very low in lignin and will be completely digested by soil microbes rather than turned into humus. Soil microbes live in the humus. The less humus in the soil, the fewer soil microbes. Without humus and the microbes all the nutrients required by the plants would have to be added yearly as soluble fertilizer and the soil would become hard, compacted and prone to erosion.

When humus is exposed to the air it oxidizes rapidly. The nitrogen turns into nitrogen gas and the carbon oxides into carbon dioxide gas. This destroys the humus colloid, releasing the remaining minerals to be washed away. Loss of humus means loss of soil structure, loss of nutrients, loss of microbes and the ability to process organic matter, loss of water holding capacity, more compaction, and more erosion.

A sustainable method of agriculture would have to create chemically balanced soil and build humus. Otherwise we are just mining the soil and quickly becoming dependent on fertility imported from elsewhere.

2 comments:

Barbee' said...

Fascinating, Alan. Thank you for figuring out all of this, and explaining it to some of us who are interested, but didn't know or understand the details. I have always been interested in this. I have felt the magic, but never have had as much land to play with as you have. I enjoy following your thoughts and activities.

Alan said...

Barbee', Thanks for thinking I'm so smart. Just fumbeling through. Most of this information was gleaned from William Albrecht's books. I'd highly recomend The Albrecht Papers Vol 2 for anyone wanting a more indepth look at how soil works and how it impacts health.

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