tions, improved crop residue management, and new tillage methods have been very effective throughout the country in improving infiltration and reducing erosion and sedimentation from periods of revege.tation without chemical or mechanical stabilizers.

INFILTRATION CONTROL THROUGH USE OF SOIL STABILIZERS

Plastic films, asphalt mulches, straw mulches, and vegetative covers Several experiments in Iowa were conducted, to compare plastic. films, asphalt mulches, straw mulches, and various vegetative covers as soil stabilizers. From these comparisons the effectiveness of the covers in controlling infiltration while vegetation was being established in exposed subsoil areas was determined. A complete cover of plastic film will obviously cause all precipitation to run off. Partial coverings of plastic films and perforated plastic films have given partial reduction in infiltration. A covering of water-emulsion asphalt has given near complete runoff if the surface is completely covered. Wateremulsion asphalt at the rate applied (0.2 gallon per square yard) soon cracked and checked, resulting in somewhat less runoff than where the surface was completely covered. Crop residue mulches applied at rates of several tons per acre have given almost complete infiltration of precipitation water on the soil materials studied in Iowa. Organic cationic chemicals

Evaluation studies of a number of organic cationic chemicals as stabilizing agents for Iowa loess soils have been conducted for the Iowa Highway Commission by the Iowa Engineering Experiment Station.

A quaternary ammonium chloride known commercially as ARQUAD-2HT was considered especially promising from the standpoints of economic feasibility and improvement of immersed compressive strength, moisture absorption, and swelling. It reduced the plasticity index of soils and resulted in flocculation of the clays in silty soil, a substantial increase in soaked bearing strength, a decreased cohesion in air-dry soil, and an increased resistance to physical weathering.

The immersed strength and the air-dry strength of silty loam treated with large cationic materials are increased by the addition of various polyacids and can be further increased by the addition of small amounts of ferrous carbonate. In the Iowa investigations, highest strengths were obtained by combinations of polyacrylic acid and ferrous carbonate with two large organic cationic materials, ARMAC-T and ARQUAD-2HT.

Soil stabilizers and conditioners

Infiltration improvement through use of soil stabilizers or soil conditioners mixed with the soil has received limited attention in the Eastern United States.

Soil-aggregating chemicals such as vinyl acetate, malic acid, and hydrolyzed polyacrylonitrile have been mixed with soil to make water-stable aggregates. When used on single-grained, poorly structured soils, infiltration, permeability, and aeration of the treated soil are improved. Results from laboratory and field tests show positive benefits for application of this type material on many soils. The effects are not marked on soils that are well aggregated to begin with,

but the aggregation produced by conditioners causes extensive physical changes in poorly structured soil. Soil conditioners do not work with some soils, and their effects with other soils are only temporary.

Cost.-Materials need to be applied at the rate of 1 pound per 100 square feet, which means a rate of application in excess of 400 pounds per acre. With the material costing $1 per pound or more, the cost per acre would be $400. Because of expense of material and because cost of manufacture could not be reduced, these materials are no longer available.

RUNOFF MANAGEMENT THROUGH USE OF POROUS COVERS

Considerable research has been conducted and is being continued at several locations on runoff management to reduce rate of water movement to facilitate revegetation. Various methods and materials. are under study.

Heavy jute mesh

The jute matting is used to stabilize soil surfaces during the establishment of grass seedlings (fig. 13). The matting serves as a mulch to keep the soil from drying rapidly and crusting. The matting protects the soil surface from the energy of raindrops and from wind erosion, and serves to reduce the velocity of runoff waters over the

cover.

soil surface. The matting may be used on slopes, ditches, and waterways where such protection is required.

The matting or mesh is woven from jute yarn, approximately inch in diameter, spaced on 4-inch centers to form the mesh. Jute is an organic material. Physical, not chemical, action is responsible for the desired effects. The effects are obtained solely from the protection offered by the low-density, inert material. The jute decays and adds organic material to the surface. It is nontoxic and does not

have to be removed.

Jute mesh was used by the Soil Conservation Service in the grade stabilization program on the Farwell irrigation project in Nebraska. Approximately 1,100 square yards were installed on the Farwell project in the summer of 1960 and additional amounts were installed in 1961. This material has also been used on Public Law 46 installations in Nebraska by the Soil Conservation Service. It has been used on channel stabilization where it was necessary to take runoff flows immediately and where velocities were expected to be relatively high. The Soil Conservation Service reports:

It has been installed approximately in accordance with supplier's recommendations and although some minor erosion under the mat has occurred, it has not been serious. Good stands of grass are now in all of the locations where this jute was used.

The jute mesh will decay sometime after the first season. It would not be effective over a long period of time if a vegetative cover were not established. It must be installed over a prepared, smooth soil surface. No problems of toxicity have been reported.

Cost. The cost is about 20 cents per square yard. This is a commonly used, imported material, and reduced cost would result principally from the shipments of large amounts to a single location. Twisted-paper fabric mesh

The twisted-paper mesh is used to stabilize soil surfaces during the establishment of grass seedlings (fig. 14). The mesh serves both as a mulch and as a means of holding mulches of straw or hay in place. This protects the soil surface from the energy of raindrops and from erosion by wind and runoff water. It also reduces the rate of soil drying and protects grass seedlings from the wind.

This mesh is woven from a twisted-paper fabric manufactured from natural kraft paper. It retains about 75 percent of its tensile strength when wet. It is available in varying mesh sizes. Like jute, it is an organic material. Physical, not chemical, effects are obtained solely from the physical protection offered by the low-density, inert material. The paper decays, adds organic material to the soil, and does not have to be removed. The twisted-paper mesh has been utilized by the Soil Conservation Service on watershed projects in Nebraska. It has been most successfully used as a restraining material for straw or hay mulches. It has a particular value where equipment cannot be used to anchor mulches.

The paper mesh will decay sometime after the first season and would not be effective over a long period if vegetative cover were not established. It must be installed over a prepared, smooth seedbed and preferably over a mulch of straw or hay.

Cost. The material costs from 4 to 8 cents per square yard, depending upon the weight and size of mesh. It is a domestically available product. Great reductions in price are probably not possible.

FIGURE 14.-Berm of floodway seeded to native grass and mulched with hay. The mulch is held in place with paper netting, which is never removed.

Plastic covers

Plastic covers have been used with limited success to protect newly shaped and seeded areas. Polyethylene with 2- or 4-mil thickness has been used to cover new seedlings on steep areas during establishment. White or yellow plastic gives best results. This allows light for plant growth, yet ground temperatures beneath these colors are not raised to a point where plants are damaged.

Field tests show that plastic covers give good erosion control during the grass establishment period on newly formed roadbanks, water spillways, or similar critical areas. Under some conditions this method of protection for seedlings can be substituted for sodding. Usual costs for sodding are around 4 cents a square yard, or $194 per acre. Covers are only used for a short time and are removed as soon as grass is established.

While these plastics are satisfactory under some conditions, the problem of anchoring plastic covers in place without damaging the grass still needs to be worked out. There does not seem to be any satisfactory answer to this problem.

Cost.-Cost of plastic material is around 5 cents per square yard, so material to cover an acre will be about $250.

VEGETABLE FIBERS, ASPHALT MULCHES, PLASTIC OR OTHER CHEMICAL SOIL STABILIZERS

The following materials have been tested as soil stabilizers to facilitate revegetation.

Mulches of wheat straw

1. Mulches of wheat straw that had gone through a combine and any kind of dried and baled prairie hay were used. The mulches were spread uniformly on the surface, using a mulch spreader. The mulches were anchored with rapid-curing and hard-setting liquid asphalt sprayed directly into the mulch blower, or they were applied and then anchored with a suitable packer.

Five thousand pounds per acre of wheat straw or 4,000 pounds per acre of prairie hay uniformly anchored with a colter disk packer were found completely effective in holding runoff water, preventing erosion, and facilitating germination of grass and alfalfa seeds on sloping land. Of the five types of packers tested, the disk packer proved best. The disk packer was best running across the slope. The best depth of penetration of disks was about 2 to 21⁄2 inches. The mulch that was punched into the soil surface acted as little check dams against running water and facilitated penetration of the water into the soil. Much of the mulch was left standing. This orientation of the mulch was most effective against erosion by wind, and facilitated germination of grass seeds best. Flattened mulch caused some smothering of seedlings, especially if the quantity exceeded 4,000 pounds per acre. The mulch held from 85 to 100 percent against erosion by water. Straw was slightly poorer than hay for this purpose. Coverage of ground surface with grass 7 weeks after seeding was 100 percent under hay mulch and 90 percent under straw mulch.

If a construction slope exceeds 3:1 but does not exceed 20 to 30 feet in length, 400 gallons per acre of rapid curing cutback asphalt (RC-3) or asphalt emulsion mixed with the above-mentioned quantities of straw or hay gave adequate protection against runoff and erosion in