Monday, July 25, 2011

Plant Nutrition

We have been having discussions on Crop Talk about how to feed plants or Plant Nutrition. I have always taught healthy soil equals healthy plant, healthy plant equals healthy animals, healthy animals equals healthy humans. This is a very basic description of the cycle farmers face to produce food.

There are a million ways to do this from strict organic to spraying every week, from pure notill to full tillage and from dryland to irrigation. Since every soil and soil history is different we see different results and lots of lack of understanding of why we get what we get.

My friend John Haggard posted this in 2010 and it is a good review on how he applies his knowledge of plant nutrition to the farmers he consults for.

"North Central Ohio, across the Corn belt ! soil basics - how it works

1. The Symbiotic Decay-Nutrition Cycle

The soil works as a dynamic plant-growing system. Good soil is rich in organic matter and microbes that, together with the atmosphere, precipitation and sunshine, provide all the needed elements and conditions for strong plant growth.

Plants are known to need at least 16 elements to live, grow and reproduce (See Table 1). Recent research has shown that most plants also require very small amounts of nickel, and some plants require silicon. Like animals, plants need a certain balance of nutrients, not just the nitrogen (N), phosphate (P) and potassium (K) that we typically associate with plant foods. And like animals, plants need different amounts of the various nutrients at different life stages. How does the soil supply these nutrients in the right balance, and how can we improve soil properties to maximize plant health and vigor?

Table 1. Typical Elemental Plant Composition (%)

Carbon (from air)


In the real world of crop and pasture management, two things are very important to maintaining soil health, and therefore plant vitality: the decay cycle (by which organic matter is recycled to recover critical elements), and supplemental provision of nutrients, usually via some kind of fertilizer.

Decay of organic matter that enriches the soil is a cycle – there must be organic matter present to decay, and there must be microbes present to cause the decay. Organic matter, plants and microbes have a symbiotic relationship; organic matter enriches the physical attributes of the soil by holding water, warming appropriately but not baking in the sun as barren soil would, and providing a food source for the soil microbes. The microbes breakdown the organic matter and make elemental nutrients available to the plants. And the plants provide shade to prevent excessive soil warming (which would be detrimental to the microbes) and provide a continuous supply of organic matter through fallen leaves, dead grass blades, seed husks, etc. The addition of complex chemical and biological compounds to the soil via decay substantially enriches the physical, chemical and biochemical complexity of the soil and helps to maintain the proper pH (6.0 to 6.8) that allows for a healthy balance of microbial life. Use of a natural fertilizer such as the Bradfield products contributes to this provision of organic matter and nutrients.

This symbiotic development of a nutrient cycle results in healthy plants with deep, extensive root systems that are better able to absorb nutrients and water from the surrounding soil. Use of a straight chemical fertilizer interrupts this symbiotic cycle by 1) not contributing organic matter; 2) depressing natural fixation of nutrients by bacteria living in the soil and in nodules found on the roots of plants; 3) disrupting the balance of nutrients available to the plant (much as oversupply of one nutrient may disrupt absorption of another in animals); and 4) interrupting the normal progress of the decay cycle. Over time, this results in plants suffering from malnutrition and inadequate root development, thus increasing the need for extraneous provision of fertilizers.

Nutrient needs are relatively small at the beginning of a crop’s or pasture’s growth, then increase dramatically during peak vegetative growth and during seed production. If soil is healthy and the decay cycle is progressing normally, last year’s residues will be digested and their nutrients released and available to the plant at about the time the plant is approaching its peak needs. Anything that interrupts or slows the cycle can result in inadequate nutrition when the plant most needs it.

Healthy soils have far larger amounts of nutrient elements than crops need, but most of this total soil nutrient supply is unavailable to plants. Most of the nutrients in soil are initially “tied up”, their molecules chemically bound in mineral particles, or in the complex organic molecules in humus or the bodies of soil organisms.

These nutrients can be made available through natural processes: weathering, the action of precipitation and temperature changes; plant root release of acidic substances (hydrogen ions and organic acids); microbe release of acids and chelating substances; and microbial decay of organic matter. In a healthy, biologically active soil, these natural release mechanisms can often meet much of a plant’s nutrient needs. Indeed, natural nutrient release is one reason that biological farmers can reduce their fertilizer inputs after several years. Farmers using inorganic sources of fertilizer typically find that they must increase application rates year after year in order to sustain reasonable crop growth.

For optimal plant health and production, your soil needs sufficient organic matter (2 to 3% minimum), adequate moisture, a proper balance of all nutrients (not just N, P and K), and high biological activity in order to provide an appropriate balance of nutrients and encourage plants to have strong root systems by which to absorb these nutrients. Bradfield products act as a part of the symbiotic cycle to provide natural sources of nutrients in a base of organic matter to feed the soil, not just the plants!

Zimmer, Gary. 2006. Soil Basics: How It Works. Acres U.S.A.

Harrison, John Arthur. The Nitrogen Cycle: Of Microbes and Men.

Soil Basics - How it Works

1. The Symbiotic Decay-Nutrition Cycle

2. Water Uptake

3. Ions, Nutrition and all that “Scary” Chemistry

4. Who are these Microbes, and what are they doing in my Soil?

Download Soil Basics - How it Works from Bradfield Organics® (Adobe Acrobat Required)"

I am posting this for my reviews and yours and as a reference for the future.

Have a great day,

Ed Winkle

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