What Does Organic Matter Do In Soil?

By Eddie Funderburg

Of all the components of soil, organic matter is probably the most important and most misunderstood. Organic matter serves as a reservoir of nutrients and water in the soil, aids in reducing compaction and surface crusting, and increases water infiltration into the soil. Yet it's often ignored and neglected. Let's examine the contributions of soil organic matter and talk about how to maintain or increase it.

What is Organic Matter?
Many times we think of organic matter as the plant and animal residues we incorporate into the soil. We see a pile of leaves, manure, or plant parts and think, "Wow! I'm adding a lot of organic matter to the soil." This stuff is actually organic material, not organic matter.

What's the difference between organic material and organic matter? Organic material is anything that was alive and is now in or on the soil. For it to become organic matter, it must be decomposed into humus. Humus is organic material that has been converted by microorganisms to a resistant state of decomposition. Organic material is unstable in the soil, changing form and mass readily as it decomposes. As much as 90 percent of it disappears quickly because of decomposition.

Organic matter is stable in the soil. It has been decomposed until it is resistant to further decomposition. Usually, only about 5 percent of it mineralizes yearly. That rate increases if temperature, oxygen, and moisture conditions become favorable for decomposition, which often occurs with excessive tillage. It is the stable organic matter that is analyzed in the soil test.

How Much Organic Matter Is in the Soil?
An acre of soil measured to a depth of 6 inches weighs approximately 2,000,000 pounds, which means that 1 percent organic matter in the soil would weigh about 20,000 pounds per acre. Remember that it takes at least 10 pounds of organic material to decompose to 1 pound of organic matter, so it takes at least 200,000 pounds (100 tons) of organic material applied or returned to the soil to add 1 percent stable organic matter under favorable conditions.

In soils that formed under prairie vegetation, organic-matter levels are generally comparatively high because organic material was supplied from both the top growth and the roots. We don't usually think of roots as supplying organic material, but a study in the Upper Great Plains showed that a mixed prairie had an above-ground (shoot) yield of 1.4 tons of organic material per acre, while the root yield was about 4 tons per acre. The plants were producing roots that were more than twice the weight of the shoots.

Soils that have developed under forest vegetation usually have comparably low organic-matter levels. There are at least two reasons for these levels:

1. trees produce a much smaller root mass per acre than grass plants, and
2. trees do not die back and decompose every year. Instead, much of the organic material in a forest is tied up in the tree instead of being returned to the soil.

Soils that formed under prairie vegetation usually have native organic matter levels at least twice as high as those formed under forest vegetation.

What Are the Benefits of Organic Matter?

• Nutrient Supply
  Organic matter is a reservoir of nutrients that can be released to the soil. Each percent of organic matter in the soil releases 20 to 30 pounds of nitrogen, 4.5 to 6.6 pounds of P₂O₅, and 2 to 3 pounds of sulfur per year. The nutrient release occurs predominantly in the spring and summer, so summer crops benefit more from organic-matter mineralization than winter crops.
• Water-Holding Capacity
  Organic matter behaves somewhat like a sponge, with the ability to absorb and hold up to 90 percent of its weight in water. A great advantage of the water-holding capacity of organic matter is that the matter will release most of the water that it absorbs to plants. In contrast, clay holds great quantities of water, but much of it is unavailable to plants.
• Soil Structure Aggregation
  Organic matter causes soil to clump and form soil aggregates, which improves soil structure. With better soil structure, permeability (infiltration of water through the soil) improves, in turn improving the soil's ability to take up and hold water.
• Erosion Prevention
  This property of organic matter is not widely known. Data used in the universal soil loss equation indicate that increasing soil organic matter from 1 to 3 percent can reduce erosion 20 to 33 percent because of increased water infiltration and stable soil aggregate formation caused by organic matter.

How Can I Maintain or Improve Soil Organic Matter Levels?
Building soil organic matter is a long-term process but can be beneficial. Here are a few ways to do it.

• Reduce or Eliminate Tillage
  Tillage improves the aeration of the soil and causes a flush of microbial action that speeds up the decomposition of organic matter. Tillage also often increases erosion. No-till practices can help build organic matter.
• Reduce Erosion
  Most soil organic matter is in the topsoil. When soil erodes, organic matter goes with it. Saving soil and soil organic matter go hand in hand.
• Soil-Test and Fertilize Properly
  You may not have considered this one. Proper fertilization encourages growth of plants, which increases root growth. Increased root growth can help build or maintain soil organic matter, even if you are removing much of the top growth.
• Cover Crops
  Growing cover crops can help build or maintain soil organic matter. However, best results are achieved if growing cover crops is combined with tillage reduction and erosion control measures.

A good supply of soil organic matter is beneficial in crop or forage production. Consider the benefits of this valuable resource and how you can manage your operation to build, or at least maintain, the organic matter in your soil.

References
Barber, S. A. Soil Nutrient Bioavailability: A Mechanistic Approach. New York: Wiley, 1984.
Brady, N. C. The Nature and Properties of Soils. New York: Macmillan Publishing Co., 1974.
Plaster, E. J. Soil Science and Management. 3rd ed. Albany: Delmar Publishers, 1996.
Tisdale, S. L. and W. L. Nelson. Soil Fertility and Fertilizers. 3rd ed. New York: Macmillan, 1975.
Source: Noble Foundation

Soil Testing: Give Your Ground a Surprise Pop Quiz

Written by  Annie Spiegelman

Having your yard landscaped can be expensive; so, before you or someone else starts digging, be sure to take the soil test so your money doesn’t go to waste…

If you’re thinking about here are some questions to first ask yourself (and anyone else who looks remotely interested) about your backyard soil:

• Is the soil worked easily?
• Is the soil full of living organisms?
• Are earthworms abundant in the soil?
• Is water and air available for plant growth?
• Does my garden make me look good?

“I’m really, really mystified by homeowners who will plop down $30,000 to a landscape designer who will come up with a plant palette without ever thinking to take a spoonful of soil to test it first,” says Professor Stephen Andrews, soil scientist at UC Berkeley. “One of the criteria for selecting a landscape architect is to give them a soil quiz! Ask them what kind of soil test they will be providing. Be an informed consumer.”

So, after you’re done hating your compacted soil and admiring yourself in front of the mirror in your new garden hat, it’s time to get scientific. Why? Because we compost- spinning tree huggers believe all home gardeners caring for a plot of land, large or small, can be become superb stewards of their gift from Mother Nature by learning a little soil science.

“If you’re going to do any type of landscaping project, make sure to test your soil first to understand what kind of a baseline you have,” says Andrews. “If you’re changing a large backyard area, doing drainage work or you’ve just purchased a new home, go get a ‘commercial’ soil test done. It may cost you a few hundred dollars, but you’ll have a thorough analysis and interpretation of your land. The soil scientists at the testing company will give you specific advice on how to proceed.”  

For the rest of us, who don’t have the green to spend on the brown, it’s perfectly fine to take the mom-and-pop route. Head down to your local plant nursery and purchase a home garden test kit. A good soil test will run about $20. Andrews recommends Mosser Lee’s Soil Master kit “because of the educational information included. It’s also a simple test. It’s color-coated and it’s idiot-proof, I promise. Do it with the kids or grandkids. Or, get the entire neighborhood and have a soil testing barbecue! One test kit will have enough tubes to do 10 soil tests. You may be the diva who does everything organic, but…you’re living next to Charlie Chevron who uses every petrochemical on the planet. Get together and literally talk dirt.”

With the home soil test, you’ll be testing your soil’s pH. The pH level will tell you if nutrients are actually available to your plants or if you’re just out fertilizing, polluting and wasting your hard-earned cash on garden products.

“The ideal pH of soil for many common plants is 6.5. The reason we want the soil to be slighty acidic is because the plant nutrients are carried in a solution. If it’s slightly acidic, the nutrients can dissolve and can be transported,” says Andrews. “If the pH is too alkaline, the nutrients will sit there like lead balls of pasta, not going anywhere. By having it slightly acidic you have the best pH for nutrient uptake. To lower the pH, use coffee grounds, tea bags, sulfur, aged animal manure or compost. To raise the pH, add limestone or oyster or egg shells.”

Home tests also check the availability of your soil’s macronutrients: nitrogen (N), phosphorus (P) and potassium (K). These are the main nutrients and minerals needed by your plants (which is why you’ll see the letters NPK on fertilizer containers). Once you know which nutrients are already hanging out in your soil, you won’t be wasting money on unnecessary products.

When collecting your home soil sample, choose a few different sections of your yard. For instance, your edible garden in raised beds would be one test area while your front lawn, a slope or a woody spot would each be a separate area to test. “For each chosen area, do a representative sampling. Pick ten to fifteen different spots in that area and dig down 6-8 in.,” recommends Andrews. “Remove critters, rocks, roots and plant material. You just want soil parts. Take all samples from that area and mix them into a plastic baggie. Label the bag and the area accordingly. For a lawn, dig down only 2-3 in..”

If you’ve decided to do the commercial test, you’ll want to decide just how comprehensive a test you need. Andrews suggests testing for pH nutrient availability, particle size analysis, bulk density, moisture content, organic matter content, macro- and micronutrients and soluble salts. If you live in an urban area and are growing edibles, or in an older home where lead contamination from paint is prevalent, heavy metals testing should be done as well.

As mentioned above, commercial soil testing should be done when you first move into a home. It should also be done every ten years or so, depending on your budget and your gardening success or utter failure. The home soil test, on the other hand, would be useful to do any time a considerable amount of plants in your yard look beaten down, chewed up or super sluggish. (Gardeners don’t have patience for lollygagging plants. Testing your soil twice a year—once in the spring and again in the fall—is especially helpful if you’re growing fruits and vegetables year round.

“Cold season crops have different needs than warm season crops. Like us, our underground soil friends slow down when it’s colder outside,” says Andrews. “The bacteria slow down; but, once the soil warms up, the disco lights come on and they’re ready to party!”

Source: maximum yield

Principles and Practice of Soil Science

Principles and Practice of Soil Science  is Copyright © 1979, 1987, 1997, 2006 by Blackwell Science Ltd,a Blackwell Publishing company. This book is posted only for Educational purpose; SALE/REPRINT of this book without permission from Publisher (Blackwell Publishing company) is unlawful and strongly prohibited.

Principles and Practice of Soil Science by

Soil Sampling

Soil testing is the single most important guide to the profitable use of fertilizer and lime. It is in the best interest of farmers, lawn care professionals, landscapers, gardeners, fertilizer suppliers, and consultants to promote the use of soil testing for several reasons like

• Grow Higher Crop Yields
• Produce Higher Quality Crops And Ornamentals
• Use Fertilizer Dollars More Efficiently

The purpose of soil testing is to identify the soil fertility that the plants or crop, in a given area will experience. The soil area and volume could be a large field, a small garden, or simply the root zone of a single tree or shrub. The most difficult step in soil testing is accurately representing the desired area of soil. A laboratory cannot improve the accuracy of a sample that does not represent the area.

In most soils, it takes more than one year to make significant changes to the soil test levels. As the soil improves with better fertility programs, subsequent crops or plant growth should show increasing rates of improvement. Soils are formed over thousands of years, and are not easily changed in a short time.

Sampling Tools

Tools that may be used to take a sod sample include a spade or shovel, soil sampling tube, or soil auger. Sample tubes or augers should either be stainless steel or chrome plated.

When sampling various soils at different times of the season it is important to use the proper equipment. A soil probe, either a hand tube or hydraulic probe, can be used under most conditions. A small wooden rod may be helpful in removing the soil core from the tube. The soil auger is especially useful when sampling frozen ground or heavily compacted soil that a soil tube can't penetrate. If a spade is used for sampling, dig a V-shaped hole to sample depth; then cut a thin slice of soil from one side of the hole. if using a pail to collect the soil, it should be plastic to avoid any contamination from trace metals. For instance, soil will pick up zinc from a galvanized pail. When sampling wet soils, vegetable oil or mineral oil may be used to lubricate the probe to minimize soil pushing ahead of the probe.

A Few Universal Basics

1. Soil samples can be taken with a professional soil probe, or simply using a shovel, spade, or garden trowel.

2. Each sample should be composed of from 10 to 15 cores.

3. As you take cores of soil, put them into the plastic bucket. Mix the soil thoroughly in the bucket (galvanized buckets will contaminate the sample with zinc), breaking up all cores. Then, fill the soil bag to the green line (about 1 cup of soil). Discard any extra soil.

Soil Sampling Procedure:

1. Samples are taken separately and away from the road side and heaps of the fertilizers or farm yard manure.

2. Take first sample of the soil with the Augar or shovel/spade at the depth of 0 to 15 cm.

3. Take second sample at the depth of 15 to 30 cm.

4. Similarly further samples will be taken from the selected are in the field.

5. Put the simples of soil in the buckets depth wise.

6. Note soil depth with the help of marker on polythene plastic bags.

7. Dry the samples at optimum sun shine.

8. Now store the sample for further analysis.