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No-till know-how with Dr. John Bradley

Con-till's Role in Eliminating Soil Compaction Dr. John F. Bradley Conservation Tillage Specialist Monsanto Company Dr. John Bradley is widely recognized by farmers across the Cotton Belt as one of the top experts in the science of conservation tillage. For 14 years, Dr. Bradley was the leader of the University of Tennessee's Milan Experiment Station, where he conducted research on conservation- and no-till cropping systems. He also directed the Milan No-Till Field Day, which became-under his leadership-the preeminent reduced tillage field event for farmers in the United States. Currently, Dr. Bradley is working with farmers across the Cotton Belt to encourage and ease the switch to crop production systems that utilize conservation tillage practices.

The reduction or elimination of soil compaction is one very good reason to consider using a con-till system on your farm in 2001. Soil compaction occurs when soil particles are pressed together and the pore space between the soil particles is decreased. This causes an increase in the bulk density or weight of the solids per unit volume of soil. Soil compaction occurs as a response to pressure or weight per unit area exerted by field machinery, tillage equipment or animals. The risk for compaction is greatest when soils are wet. If you have noticed soil compaction in your fields, it's a good idea to assess the situation immediately and try to resolve the problem as early as possible after harvest of the 2000 crop.

Soil compaction is a problem because it restricts rooting depth, which dramatically reduces the uptake of water and nutrients into the crop. It also decreases pore size and increases the proportion of water-filled pore space - factors that can decrease soil temperature. This affects the activity of soil organisms by decreasing the rate of decomposition of soil organic matter and the subsequent release of nutrients. Compaction also decreases water infiltration, which leads to an increase in runoff and water erosion.

The major cause of soil compaction is tilling, harvesting or grazing when soils are wet. A dry soil is much more resistant to compaction than moist or wet soil. Compaction has also become more of a concern in recent years due to the development of larger field equipment for tillage and harvesting, a reduction in organic matter due to less rotation and use of cover crops, and tilling of soil when it is still wet due to the demands of larger farming operations and the need for timeliness.

Other factors that influence compaction include soil texture, the amount of pressure exerted on the soil, the composition of the soil and the number of trips or passes made over the field by machinery during the year. Sandy loam soils, loam, and sandy clay loam soils compact more easily than silt, silt loam, silty clay loam, silty clay or clay soils.

To check for soil compaction, probe the soil when it is saturated and pull up plants to observe possible root restrictions. If compaction exists, determine the depth and thickness. Probing should be performed in or near the existing row, bed or drill. By examining the root system of existing plants, you may be able to determine whether or not soil compaction is a problem in your fields. Plants with flattened, turned or stubby roots usually indicate compaction. Soils that are difficult to penetrate and have high bulk density provide another good indicator of soil compaction. Coarse, medium and fine sand and loamy sands have a higher bulk density than silty clay or clay soils.

There are several instruments that can also be used to identify soil compaction. Some are more sophisticated than others, but they are all accurate. One of these tools is a soil penetration probe. This is a device that measures the soil's resistance in pounds per square inch with a gauge or dial. A "sharp shooter" spade or shovel also works for measuring soil compaction, as does a wire or surveyor's flag. Compaction can occur at almost any depth, from the soil surface to a depth of 20 inches or more.

It is also a good idea to have someone from your National Resource Conservation Service, an extension agent, soil specialist, ag retailer or Monsanto field representative assist you when checking fields. They can help you determine whether or not soil compaction is really a problem in your situation. Many fields do not currently have problems with soil compaction due to modern farming practices, such as conservation tillage and use of crop biotechnology. Many growers have significantly reduced tillage and have still been able to control weeds and pests with Roundup Ready(r) technology and Roundup Ultra MAX(tm) herbicide. Spray booms can cover 60-90 feet swaths with only one set of tracks, and most growers use controlled traffic patterns. Fewer spray trips for insects have been made by growers in recent years as the result of good scouting procedures and the in-plant protection provided by biotech crops such as Bollgard(r) cotton and YieldGard(r) corn. All of these practices decrease the likelihood that soil compaction exists.

If soil compaction does exist, it should be addressed as soon as possible after harvest of the 2000 crop. There are several implements that may be used to remedy existing soil compaction. I prefer and recommend the parabolic plow. This piece of equipment has elbow- shaped shanks that run between existing rows, lifting and fracturing the soil under the row with the "hand", which runs under the row. A roller is often added to roll behind the parabolic subsoiler in order to level the lifting effect of the shanks. Another type of soil compaction "buster" is a rip-strip-till rig that can be run in the fall, early spring or at planting. These are very popular on Coastal Plains soils, which are composed of a sandy surface layer over a layer of clay found 8-18 inches below the soil surface. I would discourage the use of rippers or subsoilers that leave large chunks of compacted soil on the soil surface. This will require multiple tillage trips to break the chunks into clods and eventually into pulverized soil. This method of eliminating soil compaction often nullifies the fracturing of the compacted layer. All parabolic, ripping or subsoiling should be performed when the soil is low in moisture, not wet.

Once any soil compaction is determined, addressed and corrected, no-till and conservation-tillage will decrease the probability of any future compaction. The number of trips across the field, as well as the size and weight of the equipment, are reduced in a no-till or con-till situation. In a con-till program, the fields are not worked or tilled when the soil is wet. Since the equipment is usually smaller, there is less pressure on the soil.

By not inverting the soil with traditional tillage tools, plant roots are left in the soil. The root system makes up 40-50% of the total mass of most plants. As these roots die and decay, they become organic matter that reduces the bulk density and increases the water holding capacity and porosity of the soil. Rather than plowing up roots so they are exposed to the sun and burned up as carbon, the carbon can remain in the soil to build organic matter. High soil organic matter promotes aggregation of soil particles. By leaving the previous crop reside, old root systems and/or cover crop intact, soil structure is improved. As they decay, the roots provide "bio-holes" for water, oxygen, and nutrients to translocate in the soil. The layers of residue and mulch also reduce the impact of machinery, thus reducing compaction by providing a "cushioning" effect.

If you have had problems with soil compaction, consider reducing tillage trips. With conservation tillage systems such as no-till, strip-till and stale seed bed, along with the use of Roundup Ready technology, soil compaction can be decreased or eliminated completely. Don't settle for less than desirable soil conditions in your fields. The right tools, technology and expertise are available to increase organic matter in your soil, decrease compaction and improve yields.

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