Appendix F SubsoilingTillage.docx

2020 CORP 2.0 Appendix F Subsoiling/Tillage

Subsoiling is defined as alleviating heavily compacted soils using an implement specifically designed to reduce soil strength, restore intrinsic bulk density (weight per unit volume), macropore space, permeability, infiltration, and tilth of soil layers to depth. An implement with two or fewer shanks will generally create less plowing/mixing. Treated areas shall span the total width of the compacted ground surface. In some instances, where machine capability allows, the full width of the skid trail may not warrant treatment (e.g., decompaction of the two-track surface may be preferable). Subsurface rocks should not be pulled to the surface and large supportive roots should not be severed. The distance between subsoiler shank passes within a compacted area shall typically not exceed 24 inches unless inspection by Soil Scientist determines greater distance between passes is effective at treating compaction. Scarification may also be necessary, in addition to subsoiling, where surface soil is puddled or crusted. Subsoiling shall be kept reasonably current and shall be done during optimal soil conditions unless otherwise agreed. Subsoiling should not occur when the ground is frozen, unless approved by the soil scientist, to prevent unwanted displacement and mixing. Subsoiling will not occur during excessively dry conditions (when soils are dusty and exhibit no adherence when squeezed in a ball) to prevent destruction of soil structure and unwanted mixing. Available slash (if available) should be placed in conjunction with subsoiling treatment.. Subsoiled areas must not be re-trafficked with machinery to place slash/surface cover.

Soil shall be decompacted to a minimum of 18 inches, except where the Government agrees to lesser depths. Disturbance of surface organics and remaining vegetation will be minimized.

Subsoiling results in soil that is decompacted, slightly lifted, and well-fractured both horizontally and vertically but is NOT plowed, mixed, or displaced. Subsurface rocks should not be pulled to the surface and large supportive roots should not be severed.

Subsoiling typically requires something with a winged shank or multiple winged shanks in order to create both horizontal and vertical fracture. Ripping with conventional dozer shanks is not acceptable. A drafting winged subsoiler mounted on a mid-size dozer is generally used by our force account crews on-Forest (see https://www.northstateauctions.com/auction/43/item/65082). A few contractors have built their own subsoiling shank to mount on an excavator brush rake head, which allows for the placement of surface cover during subsoiling operations (see attached photo). In some cases, particularly with road decommissioning, lifting and loosening with an excavator bucket may be acceptable (this would only apply on pumice soils on the Deschutes, would probably not be acceptable on clayey Ochoco soils).

Recommended Subsoiling Equipment Specifications: While drafting winged subsoilers are most commonly used to achieve this work, any subsoiling equipment/technique will be considered and evaluated as long as the definition of subsoiling can be met. Subsoiling is often performed with a fabricated mount on an excavator head/bucket or with a toolbar-mounted implement pulled behind a bulldozer. Equipment shanks must be capable of decompacting to a minimum soil depth of 18 inches. Implements shall be designed with adequate clearance to allow passage of smaller obstacles such as small rocks, brush, fine woody debris, and logging slash. Subsoiler design should also consider the ability to place slash to meet surface cover requirements specified below. Bulldozer-mounted implements are considered less desirable for this work due to their diminished maneuverability, greater likelihood of root system damage to the residual stand, and inability to place slash in the same pass.

General Description of a Drafting Winged Subsoiler Implement: Winged subsoilers generally consist of up to four, but ideally one to two, shanks/tines up to three feet long and spaced no more than two and a half feet apart. Shanks should be beveled or equipped with a coulter blade to cut through surface and subsurface organic materials, including roots. Wings attached to the tip of each shank are generally 7 to 10 inches wide, and angled approximately 15 to 20 degrees from horizontal with the lower edge pointing in the direction of travel. Subsoilers are usually controlled using hydraulic actuation so they can be drafted to maximum depth where the wing angle is maintained through the length of the pull. Hydraulic actuation also provides the capability to maneuver the implement up and down when obstacles (rocks, stumps, etc.) need to be avoided.

Tillage

Decompaction operations are conducted to counteract the cumlulative effect of ground based harvest operations on soil bulk density. The tillage decreases bulk density so that water and air can interact more effectively with roots and soild microflora/fauna. Infiltration rates are increased so that overland flow, peak flows and rates of subsequent surface, rill and channel erosions are reduced (long term versus short term).

Some sources/causes of compaction on forested lands are:

Roads Landings Skid Trails Machine Piling/Crushing Large Ungulates (both wild and domestic) Recreational Use especially along riparian areas Off Highway Vehicles

Methods used to decompact areas are:

Scarification with brushblades: (shallow tillage generally not deep enough to decompact adequately)

Tillage with Forest Cultivator: effective to 14 to 18 inches depending on slash, rock

Ripping with rippers on crawler type tractors: usually used for roads and landings

Discing or harrowing for surface decompaction such as with a large Towner disc..

Excavator tillage with a subsoiler excavator bucket which is a reinforced bucket with a tillage shank and winged subsoiler attached or alternatively just with the regular bucket alone. (Ochoco likes this method depending on where the work will be accomplished).

Rules of thumb on tillage are as follows: (tillage varies from shallow scarification via brush blade (4 to 12 inches deep) for seeding grass in skid trails to deep decompaction tillage to decompact roads and landings (up to 30 inches deep).

First the ground must be tillable: the chosen tillage implement and associated tractor must be able to traverse the area without hanging up on stones, boulders and rock outcrops. A minimum soil depth for effective tillage with a Forest Cultivator is viewed as being 12 inches for instance. Tolerable cobble, stone and boulder content varies for the Forest Cultivator, various winged subsoilers and standard crawler tractor rippers. Maximum slope percentage is viewed as 25 to 30 percent (for contour tillage) with standard equipment. (The key point to remember is that the overall utility of mechanical tillage is rather limited on the Ochoco NF due to the fact that 30 percent of the Ochoco NF is too steep and a large percentage of the 70 percent tractor ground is either too rocky or too shallow to allow for effective tillage. So the end result is that perhaps 10 percent of the tractor ground is suitable, largely on ash soils.)

Second, the objective of the tillage will vary. For timber harvest units the objective is to decompact ground in excess of what is viewed as a maximum harvest network. This harvest network (which includes roads, skid trails and landings.) is on the average roughly 20 to 30 percent of any given tractor unit. In tractor units with detrimentally compacted ground comprising 20 to 40 percent of the unit, the un-needed skid trails, landings and roads are tilled so that the 20 percent maximum level is met. For units with greater than 40 percent detrimental compaction, broadcast tillage is recommended due to the large cumulative extent of the compaction. Obviously, if the compacted unit has been re-forested with trees then broadcast tillage is no longer feasible.

Third, for compacted meadows and alluvial stream terraces, a buffer is recommended between a machine width wide ranging up to 25 feet between the active stream channel and tillage operations. These areas have been compacted by livestock, wildlife, machinery and recreation use. The best way to decompact these areas is to raise the water table through stream structures, vegetation (controlled grazing) and tillage operations to increase infiltration and rooting depth.

Fourth, for decommissioning/obliteration of roadbeds, tillage is used to re-establish infiltration by decompacting the roadbed and increasing roughness. Large tractors with large rippers or subsoilers are most effective on these jobs as compacted road soils can easily be 30 inches deep. Discontinuous and/or angled tillage is recommended on slopes over 10 percent.

Fifth, other reasons for tillage operations are to reduce competition for conifer seeding and provide a mineral soil seedbed. These types of tillage operations are usually not as deep and can be accomplished with harrows and large discs.