he Manhattan, Kans., area with average rainfall of 32 inches per year. `he mulches are bulky and therefore are practical only where they are vailable locally. They appear to be about equally effective on sandy nd fine-textured soils.

Cost.-Costs are $15 per ton for hay or straw, delivered, in the Manhattan, Kans., area; cost of applying the mulch is $30 to $40 per cre. Total cost of mulch packed with disk packer is $89.49 per acre. If asphalt is used to anchor the mulch the cutback asphalt costs 12 cents per gallon and the asphalt emulsion, 25 cents per gallon, carload ots, f.o.b. Manhattan, Kans. Total estimated cost of mulch plus 400 gallons per acre of asphalt treatment is $200 per acre.

Wood cellulose fiber

2. Wood cellulose fiber for mulching is manufactured in such a manner that after agitation in a slurry tank with fertilizer, grass seeds, water, and an additive that might be needed to anchor the fibers on the ground surface, the fibers in the slurry become uniformly suspended. When the slurry is sprayed on the ground, it forms a blotterlike ground cover impregnated uniformly with grass seed. The manufacturer claims that the cover allows percolation of rainwater to underlying soil, facilitates seed germination, and reduces runoff and erosion. Additive used was a resinous material of unknown origin and chemical composition.

Preliminary tests with this material on level ground were encouraging for controlling wind erosion, but on sloping around with 3:1 slope and 20-foot length the results were not encouraging. The cover, composed of 1,000 pounds of the fiber per acre with 18 gallons per acre of resin (Resyn) mixed with fiber, washed readily down the slope under heavy rains amounting to 2.51, 7.28, and 4.19 inches during April, May, and June, respectively, at Manhattan, Kans.

A suitable method of anchoring the fiber to the ground surface has not been found. Resinous materials, if applied in sufficient quantities, may give sufficient anchorage but will raise the cost of the treatment and may tend to seal the surface and restrict percolation of water through the fibrous cover.

Cost. The cost is $120 per ton, delivered. Cost of suitable cementing (anchoring) agent, if it could be found, is unknown.

Asphalt emulsion and cutback asphalt

3. Asphalt emulsion and cutback asphalt sprayed on the surface as thin films stabilize the soil against erosion by wind and water and facilitate germination and growth of grass. The asphalts are natural bituminous materials in liquid form, products of the oil industry, and either positively or negatively charged (cationic or anionic). Slow, medium, and rapid curing (SC, MC, and RC) materials are available for cutbacks. The emulsions are usually fast curing (setting hard rapidly).

The asphalt emulsion, diluted 1:1 with water and sprayed at the minimum rate of one-fourth gallon per square yard of concentrate (1,200 gallons per acre), was just barely sufficient to give reasonably effective control of rill erosion on 3:1 slopes of silty clay soil (table 7). Grass was seeded before the surface was sprayed with asphalt. Ground cover by grass 3 months after treatment was 72 percent on the average as compared with 90 to 100 percent with 4,000 pounds per acre of straw and hay mulch anchored with a disk packer. The as

phalt film was virtually nonporous and almost all the water that fell as rain ran off. Therefore, it is important that seeds be placed on or in moist soil before the asphalt is sprayed on the surface.

Results in another test with cutback asphalt sprayed at the minimum rate of one-fourth gallon of concentrate per square yard were about the same as with asphalt emulsion, provided the cutback was heated to facilitate spraying. Dilution of cutback with kerosene to facilitate spraying resulted in some killing of grass seedlings.

The materials facilitated runoff and did not reduce it. Therefore, they are more suited for purposes of concentrating runoff water into channels or reservoirs where the water may be used for whatever purpose is intended. On sandy soils, the asphalt films from the abovementioned rate of application last from 6 months to 1 year, but on silty clay and clay they disintegrate within 2 or 3 months due to swelling and contraction of the soil.

Cost.-Asphalt emulsion costs about 25 cents per gallon in 55-gallon drums in carload lots, f.o.b. Manhattan, Kans. Cutback asphalts cost about 12 cents on the same basis. Total cost of the abovementioned treatments was $247 per acre for cutback asphalt and $335 per acre for asphalt emulsion.

Cutbacks are byproducts of the petroleum industry and their cost. in Kansas includes principally the cost of handling. They are readily available in large volumes. Asphalt emulsions are somewhat less readily available, since their source is principally from Venezuela. Resin-in-water emulsion

4. Resin-in-water emulsion (when sprayed on the surface) has been tested to stabilize the soil against erosion by wind and water without inhibiting penetration of rainwater into the soil and to facilitate germination and growth of grass. It is also proposed that dilution with water and spraying in sufficient quantity for the material to penetrate the soil surface 1 to 2 inches in depth will keep down dust that otherwise would arise from foot or vehicle traffic.

TABLE 7.-Surface films to stabilize silty clay soil on 3:1 slope against erosion by Treated Mar. 27 to Apr. 7, 1961. Treatments are listed in order of

water.

highest to lowest effectiveness.

It is a liquid emulsion of water and natural petroleum resins. The esins have high resistance to weathering and soil bacteria. When liluted 1:1 with water and sprayed on the surface at a rate of oneeighth gallon of concentrate per square yard (600 gallons of concentrate per acre), the material was completely effective in stabilizing a highly rodible sandy loam soil against 85-mile-per-hour winds for at least 3 months after treatment. The material penetrated the soil surface. and left the surface highly permeable to water. Water from heavy rains (7 inches) penetrated the treated surface readily and left it virtually intact. The untreated surface, on the other hand, slaked smooth, and much of the water apparently ran off.

On silty clay with a 3:1 slope 20 feet long, the results were entirely different. The clay apparently absorbed the material and a few weeks after treatment caused the formation of loose granules, which were readily eroded down. the slope by runoff water. Germination and growth of grass and alfalfa were generally better than on the untreated, bare areas. The material apparently binds sands, loamy sands, and sandy loams and makes them resistant to erosion by wind and water and, at the same time, facilitates penetration of rainwater; but on fine-textured soils it has failed to produce these effects and has caused the soil surface to loosen and be readily eroded by runoff water.

Cost. The cost of resins is 301⁄2 cents per gallon in 55-gallon drums, carload lots, f.o.b. Manhattan, Kans. Total cost of treatment was about $200 and $400 with a - and 4-gallon per square yard rate, respectively.

Latex emulsion

5. Latex emulsion has been proposed to stabilize the soil surface against erosion by wind and water and to facilitate germination and growth of grass when sprayed as a thin film on a seeded ground surface. It has an elastomatic polymer (synthetic rubber latex) base. Its chemical composition is not known to us. When sprayed lightly it forms a thin, weblike film through which grass seeds emerge readily. The porous film is supposed to be receptive to percolation of water into the soil.

The emulsion diluted 1:8 with water and sprayed on silty clay with a 3:1 slope at rates up to three sixty-fourths gallon per square yard of concentrate failed to control rill erosion adequately (table 7). Also, apparently a considerable proportion of the seeds were washed away. The emulsion broke as soon as it hit the surface and produced a pliable, porous latex film on the surface. However, the amounts of emulsion were too small to produce a film that would cover the surface adequately. On the other hand, adequate cover to control erosion might have reduced percolation of water into the soil and increased runoff. Costs. The cost of the emulsion is $1.60 per gallon in 50-gallon drums. Cost of the treatment with amount of latex sufficient to control rill erosion is estimated to be about $1,000 per acre.

Water dispersible starch compounds

6. Water-dispersible starch compounds when sprayed on a seeded soil surface were proposed to control wind erosion until such time as seedlings covered the surface of the ground. This is a hydrolyzed starch compound from cereal crops. The material remains water dispersible after application and readily disappears with rain.

Starch compounds were found unsatisfactory to control wind or water erosion, because the film disappeared with the first moderate rain. Rates up to one-fortieth pound in one-fourth gallon of water per square yard were used.

Cost. The cost is from 3 to 10 cents per pound. Total cost of application is $60 to $150 per acre.

Effectiveness of various covers

None of the materials (2) through (6) excels the well-anchored vegetative mulch from the standpoint of cost and effectiveness in decreasing runoff and controlling wind and water erosion of denuded land until such time as permanent vegetation can be established. All the materials tested, except starch, if applied in sufficient quantity and concentration and if sufficiently anchored would control erosion by wind or water on flat or sloping land, but at a cost substantially higher than that for the well-anchored vegetative mulch.

It is apparent from these investigations that an ideal type of organic film to decrease runoff and control wind and water erosion should be insoluble or indispersible in water, durable, and yet porous enough to allow percolation of water and adequate seedling penetration. Apart from the vegetative mulches, the resin emulsion appears to be the only one that meets all these requirements, but only on sandy soils.

Jute thatching

CHANNEL STABILIZATION

1. Jute thatching has been used with success to protect formed channels or waterways where flash runoff cannot be diverted. Specifications for the material are as follows:

Cloth shall be of uniform open plain weave of undyed unbleached single jute yarn average 190 pounds per spindle of 14,400 yards. The yarn shall be of a loosely twisted construction having an average twist of not less than 1.6 turns per inch and shall not vary in thickness by more than one-half its normal diameter.

The cloth shall be woven as follows: Width, 45 inches plus or minus 1 inch; 78 warp ends per width of cloth; 41 weft ends per yard.

In any one shipment of approximately 50 linear yards, weight of cloth to average 1.8 pounds per linear yard with a tolerance of plus or minus 5 percent.

Tests at the Stillwater Outdoor Hydraulic Laboratory, Stillwater, Okla., and extensive field trials in the Northeast have shown that this material can do an outstanding job of stabilizing soil (fig. 15).

Cost. Newly shaped and seeded waterways and ditches can be protected immediately by jute thatching applied over smoothed areas and anchored in place with pins. Properly laid jute forms a close bond with the soil and has a permissible velocity of about 3.6 feet per second. The material can be left in place and seems to aid the growth of grass, owing to its mulching effect. The use of this material eliminates the need for sodding, which costs about $194 per acre.

Jute thatching must be properly applied to give good results. Its effectiveness is limited where waterflow exceeds 3.6 feet per second. The cost of material is less than 20 cents per square yard, so material for 1 acre would cost around $968.

Cellular concrete blocks

2. Cellular concrete blocks are placed in shaped bank slopes to protect streambanks from erosion during floodflows. The cellular units are of a size convenient to handle (weight 75 pounds) and are joined together by keyed tongue-and-groove joints so as to form a protective cover for an eroding stream. The cells are placed perpendicular to the slope of the bank and to the stream's edge.

The cellular blocks make hand placement easier by keeping the weight down; make possible shrub plantings in the openings, which help to hold blocks in place against high stream velocities; and produce a block with greater roughness than that of a smooth block. The depth of the block must be sufficiently great so the block will be able to resist the boundary shear stress. In a field test during an extreme flood, the cellular blocks were practically unharmed while nearby stone revetments upstream and downstream of the cellular block installation were severely damaged. A high-quality concrete is required, so that the blocks can withstand the forces of disintegration.

In order for cellular concrete blocks to be effective as a streambank revetment measure, they must be placed flush with the bank and firmly anchored at the toe of the slope. The depth of the block must be based on the boundary shear stress expected from the stream velocities. Cellular concrete blocks can be produced in commercial block machines. Costs of the blocks usually run slightly higher than that for quarried stone.