Tag Archives | humus

Book of the Week: How to Grow Top Quality Corn, by Dr. Harold Willis

Editor’s Note: This is an excerpt from Acres U.S.A. original book, How to Grow Top Quality Corn, written by Dr. Harold Willis. Copyright 1984, 2009, softcover, 58 pages. BOTW price: $8.00 ($12.00 regularly priced.)

By Dr. Harold Willis

So you want to grow top quality corn. Where do you begin?

Soil. The very most basic thing for growing really good crops is good soil. Soil that is not only high in fertility, but is alive with beneficial organisms. The ideal soil for growing corn is deep (six or more feet), medium-textured and loose, well-drained, high in water-holding capacity and organic matter, and able to supply all the nutrients the plant needs. Of course, not everyone has the perfect soil, and corn isn’t so fussy that it can’t do well on less than ideal soil. But I will show you how to build up your soil so that you can grow much better corn.

How to Grow Top Quality Corn

How to Grow Top Quality Corn, by Dr. Harold Willis

Climate. Corn does best with warm, sunny growing weather (75–86° F), well-distributed intermittent moderate rains, or irrigation (15 or more inches during the growing season), and 130 or more frost-free days. The U.S. corn belt has these soil and climatic conditions.

Humus. Even if the weather isn’t ideal, a good, living soil with high humus content will often make the difference between a good crop and disaster, for humus allows soil to soak up considerable moisture and hold it for dry periods. It is often the case that one farmer who has been building up his soil will have lush, green crops in a drought year, while his neighbor’s crops have burned up.

Soil parts. An average, good soil should contain nearly one-half mineral particles, one-fourth water, one-fourth air, and a few percent organic matter. The minerals supply and hold some nutrients and give bulk to the soil. Water is necessary for plant growth and for the soil organisms, but not too much or too little. Air (oxygen) is needed by roots and beneficial soil organisms. Organic matter (humus and the living organisms that produce it) is a storehouse of certain nutrients, holds water, gives soil a loose crumbly texture, reduces erosion, buffers and detoxifies soil, and even helps protect plants from diseases and pests because of antibiotics and inhibitors produced by beneficial bacteria and fungi. Some of these friendly microbes also produce plant growth stimulators, others help feed nutrients directly to roots, and others trap (fix) nitrogen from the air—free fertilizer. Continue Reading →

Supplying Nitrogen: Tap into Nature

Human activity is affecting planet Earth to such an extent that natural scientists are naming this time the beginning of a new geological age/epoch called Anthropocene (the recent age of man) and ending what was the Holocene epoch (about 17,000 years ago to present).

We are no longer observers of nature, but significant influencers of what is happening to nature. The sheer weight of humans and their livestock is now bigger than the Earth’s wild animal population. Our activities are rapidly increasing the amount of CO2 in the air. That is an established fact, the effect of which is the only thing in dispute, i.e. will it get warmer or cooler and will we be wetter or dryer?

The temporary warmth is obvious in the Arctic. Although growers usually help to absorb CO2 by growing crops, their improper handling of crop residue or improper feeding of livestock can add the CO2 back into the air. However, farming’s bigger polluting effect concerns nitrogen.

Plants have always used N from the air by a variety of natural methods. Now the rate we are taking N out of the air is 50 percent higher than what nature has done for millions of years. Most of this industrially created N is now used for fertilizer. This industrial process was originally used to make munitions prior to World War I.

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Soil Testing: The Need for Total Testing

What many farmers probably don’t know about soil testing is that most soil tests only tell us what is soluble in the soil. They do not tell us what is actually there in the soil, no matter what fertilizer salesmen might like to imply. To find out what is actually there requires a total acid digest similar to what is used for plant tissue analysis. Mining labs run these total acid di­gests on ore samples which are crushed, ground and extracted with concentrated nitric and hydrochloric acid solutions, but a mining assay does not determine total carbon, nitrogen and sulfur as a plant tissue analysis would. These ele­ments need a separate procedure essen­tial for evaluating soil humic reserves.

Total soil testing is key to understanding your soils’ needs.

Most soil tests measure total carbon, which then is multiplied by 1.72 to calcu­late soil organic matter. This assumes that most of the carbon in the soil is humus of one form or another. While this may or may not be true, determining the car­bon to nitrogen, nitrogen to sulfur, and nitrogen to phosphorus ratios is a good guide for evaluating organic matter, and this requires testing total nitrogen, sulfur and phosphorus as well as carbon.

While carbon in almost any form is a benefit to the soil, it helps enormously if it is accompanied by the right ratios of ni­trogen, sulfur and phosphorus. Though these ratios are not set in stone, a target for carbon to nitrogen is 10:1, for nitro­gen to sulfur is 5.5:1 and for nitrogen to phosphorus is 4:1. This works out to an ideal carbon to sulfur ratio of 55:1, and a carbon to phosphorus ratio of 40:1. Because soil biology is very adjustable these targets are not exact, but achieving them in soil total tests is a good indica­tion of humus reserves that will supply the required amounts of amino acids, sulfates and phosphates whenever the soil food web draws on them. Continue Reading →

Soil Organic Matter: Tips for Responsible Nitrogen Management

For soil organic matter to work the way it should, it depends on a careful balance of nutrients and minerals, including one of

Healthy, homegrown carrots in rich soil.

the most important elements — nitrogen. One of the great paradoxes of farming is that lack of nitrogen is regarded as one of the great limitations on plant growth, and yet plants are bathed in it because the atmosphere is 78 percent nitrogen.

Most plants cannot use nitrogen in this form (N2) as it is regarded as inert. It has to be converted into other forms — nitrate, ammonia, ammonium and amino acids for plants to utilize it.

In conventional agriculture most of these plant-available forms of nitrogen are obtained through synthetic nitrogen fertilizers that have been produced by the Haber-Bosch process.

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Humic Acid: The Science of Humus and How it Benefits Soil

Humic acid is a group of molecules that bind to, and help plant roots receive, water and nutrients. High humic acid levels can dramatically increase yields. Humic acid deficiency can prevent farmers and gardeners from growing crops with optimum nutrition. Conventional wisdom today ignores humic acids, though, holding that it is impossible to grow and maintain an urban landscape such as a park, golf course, or lawn without high-analysis NPK fertilizers.

This article will drill down into the details on humus. We can adjust our soil biology and chemistry and achieve better yields if we understand its characteristics.

Humus vs. Organic Matter

We must begin by understanding that there is a difference between soil organic matter and humus. “Humus” is a general term that describes a group of separate but distinct humic substances. “Soil organic matter” is material that is decomposing at various rates in the ground.

Some of the most common substances we collectively refer to as “humus” include:

  • Fulvic acid: a yellow to yellow-brown humic substance that is soluble in water under all pH conditions and is of low molecular weight.
  • Humic acid: a dark-brown humic substance that is soluble in water only at higher soil pH values and is of greater molecular weight than fulvic acid. Humic acid may remain for centuries in undisturbed soil.
  • Humin: a black humic substance that is not soluble in water at any pH, has a high molecular weight, and is never found in base-extracted liquid humic acid products.
Humic acid

Adding a small amount of humus to an acre of soil can achieve positive results.

Applying organic matter is certainly an excellent way to remineralize a soil that has been leached or has no chemical reactions, such as with some sands. Sand with a low cation exchange capacity (CEC) has difficulty holding onto the cations of nutrients, and these cations can easily leach deep into the soil and become unavailable for plant uptake.

Sandy soils are also unable to hold onto water when arid conditions prevail and humus is lacking. Sands reside in a condition of “feast or famine,” since water and nutrients are only available for a short time after they are applied. Biomolecules of humus can help retain water and the ionized nutrients that are produced by the natural cycling of organic biomass, compost, or other sources of fertilizer.

The electronegativity factor of humic acids is key in developing and maintaining a healthy and sustainable soil. The source of these humic acids in a sustainable agricultural program, organic certified farm, or urban landscape can be decaying organic matter such as compost. In essence, this is fertilizer in an organic form. It is therefore important to know the ingredient source and the nutrient analysis of your compost.

Humus is powerful stuff, and a tiny amount can produce a huge measurable result. We have seen as little as 40 total pounds on an acre of farmland increase the yield of a crop dramatically.

The Physics of Humic Acid

Humic acids are extremely important as a medium for transporting nutrients from the soil to the plant because they can hold onto ionized nutrients, preventing them from leaching away. Humic acids are also attracted to the depletion zone of the plant root. When they arrive at the roots, they bring along water and nutrients the plant needs.

Humic acid and grass root system

Humic acid brings nutrients directly to plant roots.

The depletion zone is the area close to the root of a plant from which the root draws (depletes) nutrients. This zone can become particularly depleted if there is a lack of either humic acid or mycorrhizal fungus. When plants are mycorrhizal, the depletion zone is of less importance. Mycorrhizae have hyphae micro-tubes that can extend much further into the soil than the host plant can reach. They can gather mineral nutrition for the benefit of the host plant from outside the depletion zone. Humus is even more critical for plant nutrient availability and uptake if there aren’t healthy mycorrhizal relationships in the soil.

Positive ions are more easily absorbed by a plant’s root because the root has a negative charge. In other words, the positive (cation) is attracted to negative (the living root). Humic acids hold cations (positive ions) in a way they can be more easily absorbed by a plant’s root, improving micronutrient transfer to the plant’s circulation system. This works because humic acids (ulmic, humic, and fulvic) pick up positive ions and are then attracted to the root depletion zone and to the hyphae micro-tubes of mycorrhizae.

Since the root’s negative charge is greater than humic acid biomolecules’ negative charge, scientists theorize that the micronutrients are taken up by the plant’s root and are absorbed by the plant’s circulation system. Some of the micronutrients are released from the humic acid molecule as they enter the root membrane, but we are now realizing that the plant will also uptake some of the lighter molecular-weight humic acids as well. In essence, the humic substances are chelating such cations as magnesium (Mg2+), calcium (Ca2+), and iron (Fe2+). Through chelation, humic substances increase the availability of these cations to plants.

How to Build Humic Acid Levels

Compost and other sources of decomposing organic matter are not an efficient way to build soil humus levels. Compost rapidly decomposes and leaves its minerals behind, releasing carbon into the atmosphere as CO2. Humic substances, on the other hand, are stable, long-lasting biomolecules. Components of humus have a mean residence time (based on radiocarbon dating, using extracts from non-disturbed soils) of 1,140 to 1,235 years, depending on the molecular weight of the humic acid.

If you really want to fix or rehabilitate a soil, increase its CEC, improve its tilth and porosity, improve water availability for conservation, and therefore make a soil a healthier terrestrial biosphere for all plants, roots, microorganisms, you must depend on humus. Humus is a product of soil chemistry, and is dependent upon a source of its precursor chemicals: amino acids.

Amino acids are the building blocks of protein. The best source of the amino acids in a natural ecotone are produced by the Glomus species of mycorrhizae. These are associated with any grass in a natural, undisturbed site. The tallgrass prairies of the Midwest exemplify this soil-building process better than any ecotone on earth, because grasses utilize a Glomus-mycorrhizal relationship. This is why there is was so much humus-rich topsoil in the Tall Grass Prairies. Glomus makes a soil protein called glomalin, a substance that is rich in amino acids. Combined with humus, they create a huge carbon sequestering and banking factor.

Scientists can measure the percentage of calories in compost that come from proteins (the amino acids), carbohydrates, and fats. This enables them to measure the lack of humus-making potential of compost. Even in supreme-quality compost, the percentage of calories coming from amino acids (protein) is less than 5 percent. Since it is difficult to rely on the perfect amino acid ratio in compost because of differing manufacturing quality controls and ingredient consistency, we cannot predict a 100 percent efficient conversion of all these amino acids into humic substances. Compost or other soil amendments of organic matter are therefore not a reliable way of increasing soil humic substances.

Attempting to add adequate amounts of humic acid through application of compost would require such a huge amount that it could lead to overdosing the site with nutrients. In fact, the better the quality of the compost, the more concentrated the nutrients will be, and the less you should use. In the case of our TTP Supreme Compost, for example, we recommend using it sparingly – never more than 60 pounds per 1,000 square feet or 2,600 pounds per acre. And this is assuming no other fertilizer is being used at the same time.

Humus supplementation is necessary if you want humus. You can measure the quantity of humic acid in a compost product at a qualified lab. A good quality compost will measure around 5 to 8 percent humic acids.

Benefits of High Humic Acid Levels

One obvious benefit of humus we have seen at our Arboretum in Los Lunas, New Mexico, has been the aggregation of clay. This aggregation has made the clay more porous, soft, and aerobic, with better drainage, resulting in deeper root growth of all plants. The site was purchased in 1986 with clay soil 12 feet deep and a pH ranging from 8.3 to 9.2 – so alkaline that in the winter the site would turn white.

Today we have one of the largest oak species collections of the Quercus genus in the United States, and the largest collection of native oaks of the Chihuahuan Desert Region in North America. Also on the site are several types of redwoods, maples, dogwoods and giant timber bamboo. None of these plants should be able to grow on soils with the conditions we started with, but with the power (or magic) of humic acids we have rehabilitated the soils to a productive and healthy level.

Finally, “Humic Acids: Marvelous Products of Soil Chemistry” (The Journal of Chemical Education, December 2001) states, “Humic acids are remarkable brown to black products of soil chemistry that are essential for healthy and productive soils. They are functionalized molecules that can act as photosensitizers, retain water, bind to clays, act as plant growth stimulants, and scavenge toxic pollutants. No synthetic material can match humic acid’s physical and chemical versatility.”

By Michael Martin Meléndrez. This story was first published in the August 2009 issue of Acres U.S.A. magazine.

Organic Nitrogen: When are Nitrogen Units Not Nitrogen Units?

Organic nitrogen and inorganic nitrogen: what’s the difference?

A farmer gives a plant organic humus fertilizer to plant.

Organic growers frequently attempt to quantify the amount of organic nitrogen they add to their soil ecosystems in the same manner that conventional growers use inorganic nitrogen units to calculate their nitrogen requirements. Logically, they reason that a ton of organic material with 4 percent nitrogen content as verified by a laboratory test will provide 80 pounds, or units by some determinations, of nitrogen.

The truth is that organic nitrogen sources vary in their efficiency of transformation into soil components over a much broader range of response than do inorganic synthetics, which offer precision measurement and a repeatable predictability of release. Use of inorganic nitrogen units to determine nitrogen needs for organic growers is therefore problematic. A popularly available and reliable conversion algorithm between tested inorganic nitrogen and untested organic nitrogen in organic soils does not exist, however. Without such an algorithm there can be no scientific basis of comparison. Continue Reading →