AG News and Views Originally published February 2016

SOILS Organic matter serves important role in health by Eddie Funderburg, Ed.D. / [email protected]

Of all the compo- ily as it decomposes. As much as 90 nents of soil, organic percent disappears quickly because matter is probably of decomposition. the most important Organic matter is stable in the and most misunder­ soil. It has been decomposed until it stood. Organic is resistant to further decomposition. matter serves as a Usually, only about 5 percent of it reservoir of nutrients mineralizes yearly. That rate increases and in the soil, aids in reduc- if temperature, oxygen and moisture ing compaction and surface crusting, conditions become favorable for and increases water into decomposition. This often occurs with the soil. Yet, it’s often ignored and excessive tillage. Stable organic mat- neglected. Let’s examine the contri- ter is analyzed in a . butions of and talk about how to maintain or increase it. How much organic matter is in the soil? An acre of soil measured to a depth What is organic matter? of 6.67 inches weighs approximately Many times we think of organic matter 2 million pounds, which means that 1 as the and animal residues we percent organic matter in soil weighs incorporate into the soil. We see a pile about 20,000 pounds. Remember, it of leaves, manure or plant parts and takes at least 10 pounds of organic think, “Wow! I’m adding a lot of organic material to decompose to 1 pound matter to the soil.” This stuff is actually of organic matter, so it takes at least organic material, not organic matter. 200,000 pounds (100 tons) of organic What’s the difference between material applied or returned to the a mixed prairie had an above-ground organic material and organic mat- soil to add 1 percent stable organic (shoot) yield of 1.4 tons of organic ter? Organic material is anything that matter under favorable conditions. material per acre, while the root yield was alive and is now in or on the soil. In formed under prairie was about 4 tons per acre. The For it to become organic matter, it , organic matter levels are were producing roots that were more must be decomposed into . generally comparatively high because than twice the weight of the shoots. Humus is organic material that has organic material was supplied from Soils that have developed under been converted by both the top growth and roots. We vegetation usually have compa- to a resistant state of decomposition. don’t usually think of roots as supply- rably low organic matter levels. There Organic material is unstable in the ing organic material, but a study in are at least two reasons for these soil, changing form and mass read- the Upper Great Plains showed that levels:4

Ag News and Views SOILS

1. Trees produce a much smaller root 16,500 gallons of plant-available Proper fertilization encourages mass per acre than grass plants. water per acre. growth of plants, which increases 2. Trees do not die back and decom- • aggregation root growth. Increased root growth pose every year. Instead, much Organic matter causes soil to clump can help build or maintain soil of the organic material in a forest and form soil aggregates, which organic matter, even if you are is tied up in the trees instead of improves soil structure. With better removing much of the top growth. being returned to the soil. soil structure, permeability (infil- • Grow cover crops. Soils formed under prairie veg- tration of water through the soil) Growing cover crops can help build etation usually have native organic improves, in turn improving the soil’s or maintain soil organic matter. matter levels at least twice as high as ability to take up and hold water. However, best results are achieved those formed under forest vegetation. • prevention when cover crops are combined This property of organic matter is with tillage reduction and erosion What are the benefits of organic not widely known. Data used in the control measures. matter? universal soil loss equation indicate A good supply of soil organic • Nutrient supply that increasing soil organic mat- matter is beneficial in crop or forage Organic matter is a reservoir of ter from 1 to 3 percent can reduce production. Consider the benefits of nutrients released to the soil. Each erosion 20 to 33 percent because this valuable and how you 1 percent of soil organic matter of increased water infiltration and can manage your operation to build releases 20 to 30 pounds of nitro- stable soil aggregate formation or at least maintain the organic mat- < gen, 4.5 to 6.6 pounds of P2O5, and caused by organic matter. ter in your soil. 2 to 3 pounds of sulfur per year. The nutrient release occurs predomi- How can I maintain or improve soil References nantly in the spring and summer, so organic matter levels? Barber, S. A. Soil Nutrient Bio­ summer crops benefit more from Building soil organic matter is a long- availability: A Mechanistic Approach. organic matter mineralization than term process but can be beneficial. New York: Wiley, 1984. winter crops. Here are a few ways to do it: Brady, N. C. The Nature and Properties • Water-holding capacity • Reduce or eliminate tillage. of Soils. New York: Macmillan Pub- Organic matter behaves somewhat Tillage increases the aeration of the lishing Co., 1974. like a sponge, with the ability to soil and causes a flush of microbial Gould, S.M. Compost Increases the absorb and hold up to 90 percent of action that speeds up the decom- Water Holding Capacity of Droughty its weight in water. A great advan- position of organic matter. Tillage Soils. Michigan State University tage of the water-holding capacity also often increases erosion. No-till Extension online article October 16, of organic matter is that the mat- practices help build organic matter. 2015. ter will release most of the water it • Reduce erosion. Plaster, E. J. and Manage­ absorbs to plants. In contrast, Most soil organic matter is in the ment. 3rd ed. Albany: Delmar Pub- holds great quantities of water but . When soil erodes, organic lishers, 1996. much of it is unavailable to plants. matter goes with it. Saving soil and Tisdale, S. L. and W. L. Nelson. Soil An increase of 1 percent soil organic soil organic matter go hand-in-hand. Fertility and Fertilizers. 3rd ed. New matter can result in an increase of • Soil test and fertilize properly. York: Macmillan, 1975.

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