Posted 25 June 2007. Crop Management.
Does Organic Matter Really Matter?
University of Minnesota. www.cfans.umn.edu
St. Paul, Minnesota (June 18, 2007)--Ask any farmer which field he would choose if two are similar, except one had a higher soil organic matter content. Chances are he would choose the one with the higher organic matter.
Most farmers know that these fields seem to produce better with fewer inputs. But why do those fields perform better?
Organic matter (OM) is composed of dead animal and plant material in various stages of decomposition. The composition of OM is very complex and is different, based on where it is formed. However, all organic matter consists of multiple nutrients (nitrogen, phosphorus and sulfur) and about 50 percent carbon.
Organic matter promotes soil binding into aggregates. Aggregation gives soil its structure, and structure is the soil's number one defense against soil compaction. Soil structure is instrumental in increasing water infiltration and decreasing crusting.
Due to the multiple holding sites, organic matter maintains nutrients longer in the soil so they don't leach through the soil profile. One percent of organic matter contains about 900 pounds of nitrogen per acre. It mineralizes a small percent each year for the plant, especially in the spring. About 10 to 40 pounds per acre per year is mineralized based on temperature, precipitation and percent organic matter.
Have you ever wondered why a corn field yielded 50 bushels per acre over what you fertilized for that year? It was due to good climatic conditions that enhanced mineralization. Fields with low organic matter need higher levels of nitrogen fertilizer and may be prone to sulfur deficiencies.
Organic matter acts as a sponge in the soil, soaking up rainfall, helping it infiltrate into the soil, and maintaining the moisture longer. This is more apparent in a dry summer. Watch the corn curl up on the low organic matter hilltops before it curls in low lying areas. This is due to the organic matter-rich topsoil eroding over time to the lower areas, leaving the less productive subsoil on the hillsides to support plant growth.
Scientists at the USDA Agricultural Research Service in Morris, Minn., conducted research on the slopes north of Cyrus, Minn. They found that wheat yields varied across the landscape based on the amount of topsoil present. In the low lying areas the yield was as high as 90 bushels per acre. But on the side slopes where the topsoil had eroded downhill, the yield was 46 bushels per acre.
How can you maintain or build the organic matter content of your soil?
• Reduce tillage by using no-till, strip-till or ridge till and leaving as much residue as possible on the soil surface. This is one of the best ways to maintain OM levels.
• Use livestock manure or cover crops as a way to build the carbon levels in the soil.
• Add perennial and companion crops to increase OM content.
Within a few years, you'll see less ponding, better water holding capacity and a more productive field. And economic benefits will include lower fertilizer costs and fuel savings from fewer trips across the fields.
Jodi DeJong-Hughes is a crops educator with University of Minnesota Extension.