Deep Tillage

Deep tillage is defined by NRCS as performing tillage operations below the normal tillage depth to modify adverse physical or chemical properties of a soil. This practice does not apply to normal tillage practices to prepare a seedbed.

Deep tillage, commonly referred to as deep plowing, in-row subsoiling, strip-tillage, paratilling, subsoiling, ripping, or row-till, is not performed as a part of the normal tillage. This practice applies to land having adverse soil conditions which inhibit plant growth, such as compacted layers formed by field operations, restrictive layers such as cemented hardpans (duripan), in the root zone, overwash or deposits from wind and water erosion or flooding, or contaminants in the root zone.

Deep tillage is an important practice in Southeastern Arkansas where soil in the plant root zone has been contaminated with chloride where irrigation-well-water containing greater than 100 ppm of chloride has been used. Deep tillage allows downward movement of water and chloride below the root zone which provides relief from chloride toxicity, especially in soybean. However, this is a corrective action and it is recommended to have well water tested for chlorides and other soluble salts before using for irrigation to prevent chloride build-up in soils.
Deep tillage operations should be performed when soil moisture is less than 30 percent of field capacity, at the maximum depth the tillage will be done.

Deep tillage for fracturing restrictive soil layers should be performed at least 1 inch below the restrictive layer with equipment such as chisels, subsoilers, bent-leg subsoilers, or rippers capable of reaching the required depth.

Burying soil deposits left from flood overwash or erosion deposits is performed with large moldboard or disk plows capable of reaching sufficient depths. Mixing soil deposits from flood overwash or erosion deposits is performed with a large twisted point chisel, moldboard plow, or disk plow. Mixing requires the affected area to be plowed at least twice the depth of the surface soil deposits being mixed.

Deep Tillage to reduce plant growth inhibiting soil contaminates uses large twisted point chisel, moldboard plow, or disk plow capable of reaching the required depth to mix uncontaminated soil with the contaminated, to evenly distribute the contaminate, reducing its concentration to a level the crop can tolerate.

Deep Tillage offers many conservation benefits as well, including

• Bury or mix soil deposits from wind or water erosion or flood overwash.

• Reduce concentration of soil contaminants, such as chloride which inhibit plant growth.

• Fracture restrictive soil layers.

• Reduce transport of sediment borne pollutant(s) offsite

John Deere Tractors tilling soil

These benefits will vary with soils, crops, climate, severity of conditions necessitating remediation, and other factors. However, these benefits are important to increasing long-term profitability and sustainability of areas with adverse physical and chemical soil properties. The USDA-NRCS provides financial incentives for deep tillage (Practice 324) through programs such as the Environmental Quality Incentives Program (EQIP).

Some considerations should be made when considering deep tillage for hard pan layers. There are other preventative measures that can be taken to limit the need of deep tillage. Access control (practice 472) such as reducing traffic, especially heavy loads (greater than 6 tons/axle), the use of radial tires with a larger contact patch on equipment instead of bias-ply tires, and conducting normal tillage when soil moisture is less than 50% of field capacity have all been shown to help reduce compaction. Deep rooted plants that can be worked into a crop rotation (practice 328) or used as a cover crop (practice 327) can also aid in penetrating soil hardpan layers. Deep soil tillage, excessively deeper than the hardpan does not promote increased yields, requires excessive amounts of tillage energy, and increases the potential of future compaction from nearby vehicle traffic.

Other considerations should be taken into account when using deep tillage to mix flood overwash, especially when the overwash layer is too thick to effectively mix with the original soil profile. Some instances require physical removal of the overwash and/or land smoothing (practice 466) to redistribute the overwash over a larger area in which it can be incorporated. Common equipment used for mixing the overwash into the soil profile generally cannot uniformly mix more than 6 inches of overwash. Situations in which infertile overwash is mixing with the original soil profile, the infertile overwash can be amended with the addition of organic matter such as cover crops (practice 327), manure, other nutrient management practices (practice 590), as well as maintaining high crop residue levels from conservation practices such as no-till (practice 329) to enhance the soil rebuilding process.

Deep tillage can result in some unfavorable soil conditions as well. While deep tillage can distribute unfavorable contaminates in the root zone to a plant tolerable levels, other sometimes unfavorable soil materials such as calcium, gypsum, and excessive sodium can be brought to the surface. Deep tillage should not be preformed if these unwanted materials are within the range of the deep tillage depth. Additionally, the equipment used in deep tillage is also very destructive to the physical characteristics of the soil and can create a soil condition more susceptible to compaction.

Deep tillage is not necessarily performed with each planting season, and should only be performed when attempting to mitigate issues/concerns similar to those listed above. If conditions requiring deep tillage exist, there are financial incentive programs which may cost-share the expenses of the additional tillage requirements. Implementation of deep tillage can be worked into an EQIP application package and may complement other conservation practices such as 472-Access Control, 328-Crop rotation, 327-Cover crops, 466-Land smoothing, 590-Nutrient Management, 329-No till

In summary, deep tillage is an important conservation and production practice
in Arkansas and can be utilized in conservation programs. Deep tillage is crucial to maintain a healthy root zone in compacted soils, and key to incorporating surface soil deposits into the root zone. For more information contact your local County Extension Office or your local USDA Service Center.

— Lee Riley