Contour Tilling/Ripping

Mechanical turning of the soil with a plow or ripping device. Often used to promote soil infiltration by breaking up water repellent soil layers. 

Purpose: Tilling and ripping are mechanical soil treatments aimed at improving infiltration rates in ma-chine- compacted or water repellent soils. Both treatments may increase the amount of macropore space in soils by physical breakup of dense or water repellent soils, and thus increase the amount of rainfall that infiltrates into the soil.

Relative Effectiveness: Excellent-33% Good-33% Fair-33% Poor-0% (Replies = 3).   Tilling and ripping was judged to be an “excellent” treatment for roads, firebreaks, and trails but less effective on hillslopes. These techniques may add roughness to the soil and promote infiltration. They may be successful for site-specific circum-stances like compacted or water repellent areas, but not economically feasible on large areas or safe to do on slopes greater than 30 to 45 percent. Size of the equipment and crawler tractor operator skill are also important effectiveness factors. Up- and down-hill tilling/ripping needs to be avoided because it can diminish the effectiveness of the treatment in reducing soil erosion by promoting rilling in the furrows. According to some personnel, this type of treatment was the most effective when done in combination with broadcast seeding. Others indicated that tilling/rip-ping can be successful accomplished at a high production rate on non-timbered areas without seeding.

Implementation and Environmental Factors: Shallow soils, rock outcrops, steep slopes, incised drainages, fine-textured soils, and high tree density create significant problems for tilling and ripping. These treatments work best where there is a good soil depth, the soils are coarse textured, slopes are less than 30 percent, and woody vegetation density is low. This type of treatment has a high logistics support requirement (fuel, transport carriers, access, and drainage crossing).

Other Factors: Since tilling and ripping are ground-disturbing activities, cultural clearances are required. Obtaining proper cultural clearances may significantly slow accomplishment of tilling/ripping projects.

Contour Tilling/Ripping Implementation

OBJECTIVE

The objectives of contour tilling is to:

Maintain on site soil productivity and reduce the potential of accelerated erosion.

Increase infiltration.

Reduce overland runoff.

Store sediments on the slope. 

Maintain water control and prevent deterioration of water quality.

Break up the hydrophobic (water repellent) soil layer.

SITE SELECTION

Contour tilling has been used in several fires but it does have some constraints in its application. Conditions which are important for contour tilling include the following:

Slopes less than 35% (in some areas you may only want to go to 30%)

Slopes that are fairly open so that a piece of machinery can work on the contour. Dense timbered stands are not recommended.

Areas where there may be an abrupt slope change.

Hydrophobic soils are prevalent.

Brush fields that have strong a strong hydrophobic layer.

CONSTRUCTION AND EQUIPMENT

Contour tilling has been successfully implemented. The equipment utilized was a D-6 cat with a tool bar. On the tool bar there were three winged rippers mounted.  The equipment is usually easily attainable from contractors.  Winged rippers can be fairly easily constructed with out much cost or time.

Initially the prescription is to till one eight foot wide swath on the contour and then skip approximately 24 feet and till another swath. This enables a fairly high production rate. The operator does not have much difficulty staying on the contour in areas that are open. In other areas that are more heavily timbered there is a greater hazard created by tops of trees breaking out and hitting the equipment and operator.

Tilling depth and distribution of contour strips can be modified on site by the inspector. Tilled depths can range from 8 inches to 20 inches, and distance between contours is modified as the slope becomes steeper.

It is important to note that since this is a ground disturbing activity it does require archeology surveys. If a fire has burned in an area where the unit does not have any archeological surveys then the time for this work must be factored in.

COST AND COST FACTORS

The cost for this type of work tends to vary but can range between $25.00 per acre up to $60.00 per acre (1995). It is important to remember that the treatment cost applies to per acre but the actual number of contour strips placed and depth will depend on the following:

Depth and persistence of hydrophobic layer

Vegetation type and density

Slope

Other Burned Area Emergency Stabilization and Rehabilitation (ESR) treatments being implemented

CASE STUDY

The Ruby Fire of 1991 burned almost entirely within the headwaters of the Rose Creek watershed. The fire although only 3460 acres in size had 2357 acres burned with a high fire intensity and creating 2930 acres of hydrophobic (water repellant) soils.

The Emergency defined was a potential high soil loss at the rate of 19 tons per acre from the 2930 acres. In addition, a loss of water control and deterioration of water quality due to the increased efficiency of the watershed as a result of the fire. Lack of soil cover and the extent of hydrophobic soils increased the risk of flash floods, floods, and stream bulking.

Treatment objectives were twofold:

Maintain on site soil productivity and reduce the potential of accelerated erosion.

Maintain control of water on hillslopes by increasing infiltration.

Other resource objectives which the ESR survey team discussed with unit personnel was the presence of several unsuccessful plantations within the burn area. Although these areas did not have a high threat of accelerated erosion, the unit was concerned with seeding near some of these areas and questioned if some of the burn area could be tilled to accomplish the above objectives.

As a result contour tilling was recommended on 480 acres. Tilling was to be on the contour and the soil would be tilled to a depth of 6 inches to increase infiltration. Tilling would occur with one pass of 8 feet in width with 25 feet in between passes. In addition there were several slopes that were burned with a high burn intensity that were less than 35%. This factor plus the openness of some of these areas greatly facilitated our belief that this treatment could be highly effective.

Treatment Implementation

The area where crews started first had a slope of approximately 25% and could be worked from the ridge down to a road which had been an old railroad grade. The area was fairly open and areas with brush (manzanita) and wanted it knocked down and incorporated with the soil. Tillage was done to depths deeper than the original 6 inches and ended up placing the tillers to a depth of 16-18 inches. Wings were used on the-ripper shanks to provide more uplift and fracture, and three winged tillers were used.

ADVANTAGES OF CONTOUR TILLING

Can be implemented shortly after the fire is controlled. We started within 16 days after the fire had started.

Knocking over material and crushing brush helps to maintain soil productivity by incorporating some of the standing dead on the soil surface.

The treatment is immediately effective by increasing infiltration.

If Force accounts are familiar with this type of work, there is less supervision involved because they are familiar with the limitations and capabilities of the equipment. We used a D-6 tractor with great success.

The treatment can be fast, efficient, and economical. our unit cost was less than $25.00 per acre for the treatment.

It is easy to modify widths between contour strips as you see the results and as slopes increase.

Contour strips act like mini catchment areas by trapping any soil that moves from the untiled portion.

Grass seeding in contour tilled strips has an excellent catch and survival rate.

DISADVANTAGES OF CONTOUR TILLING

Not applicable on steep slopes over 35%.

This is a hazardous activity especially since there is still much material coming down from the effect of the fire. Not all tractor equipment has the operator well protected from tree tops.

In dense stands it is difficult to maneuver equipment and still stay on the contour.

Areas with heavy brush tend to ball up in the rippers which slows the process considerable.

Areas have to be surveyed ahead of time for heritage resources.  Unsurveyed areas will slow your progress.

SUMMARY

Contour tilling can be an effective tool which helps to improve infiltration and reduce accelerated erosion.  It is important to monitor the work being performed to ensure that spacing is correct for that particular soil, slope, and location. 

By having different treatment options to reduce the effects of a fire on an area, provides ESR team members increased flexibility. This flexibility is important when fires strike late in the summer and our ability to implement treatments is limited.