#1. Control soil erosion.

#2. Control dust (avoid dust storms).

#5. Conserve water.

#7. Enhance water-use efficiency.

#12. Aid in transplanting trees.

#16. Stop loss of soil, soil organic matter, fertilizers and pesticides from erosion.

PM-10 refers to atmospheric particles with an aerodynamic diameter less than or equal to 10 microns. Clay particles are smaller than 2 microns. PM-10 particles can settle in the lungs and impair respiratory function. Actually PM-4 particles are respirable and can be emitted in soils and manipulated (Clausnitzer and Singer 1997). Recent studies indicate that ambient PM-10 levels exceed federal standards in large areas of Central and Southern California (Brookhart 1991, Calif. Ag. 1994). Dust in at least eight counties in the San Joaquin Valley of California exceed acceptable standards (Brookhart 1991 ). Levels in virtually the entire state of California exceed even stricter standards. The new proposal for decreasing the acceptable size of particulate matter in air to 2.5 microns with low permissible maximum daily and annual concentrations (Raber, 1997a & b) could influence farm practices. Particles that small may originate more from industrial pollution than from farms (Kaiser 1997, Odum et al. 1997, Raber 1997b ). Such common agricultural practices as plowing and harvesting create PM-10; large agricultural areas such as the San Joaquin Valley, the Imperial Valley and the Coachella Valley have been asked to submit control plans and show attainment of federal standards by deadlines which range to December 2001 (Flocchini, 1994). Soil debris on hard-surfaced roads is a major source of particulate dust. The question being asked is: To what extent do farming practices contribute to health problems associated with PM-10 or to PM-2.5?

In order to get accurate, scientific data on the size and scope of the PM-10 problem, a research effort called the California Regional PM-10 Air Quality Study was initiated. The $23 million project represents a joint public-private partnership that is strongly supported by several agricultural Interests. It is managed under the umbrella of the San Joaquin Valley wide Air Pollution Study for Ozone which is experienced with the methodologies required for this undertaking (Calif. Ariz. Farm Press, 1995). The status of the program has been updated (Beach 1997).

The objectives of that study were to provide an understanding of PM-10 emissions, composition and dynamic atmosphere processes; establish a strong scientific foundation for informed decision-making; and to develop methods to identify the most efficient and cost-effective emission control strategies to achieve the PM-10 standards that will be required within the air basin.

Completion of the multi-year study is essential because regulatory actions to reduce PM-10 are inevitable. Given agriculture's pre-eminence in the region, the industry should be better served by hard science than empirical assumptions. The studies of Clausnitzer and Singer (1997) are part of the effort. They conclude that respirable dust arises from many land operations with land planing and plowing highest and discing operation next. Roads also emit considerable dust.

In California the San Joaquin Valley Unified Air Pollution Control District has a series of rules affecting the dust resulting from wind erosion. They also enforce California's visible emission rule. "Every air district has such a rule or else they use the state rule. The state rule requires that visible emissions are emitted with a plume density of greater than 40% opacity, meaning that the density of whatever it is can't obscure more than 40% of the light or view behind the plume. Most districts use what’s known as EPA’s Method 9 Test to read the opacity" (Merrill 1996).

The district also has a nuisance rule that applies to any source emitting contaminants or other materials that harm or annoy citizens. Some cities are coming to the realization that they do not want to put up with the repercussions that come from wind erosion, such as damage to homes, health and safety risks, and decreased property values (Merrill 1996).

Anytime the wind velocity gets above 4.5 meters per second (10 mph), it is close to the threshold at which many soils will begin to erode. Another concern is the condition of the soil surface itself. "Any kind of traffic – vehicular, animal, or human— is likely to disturb or destroy the soil structure of that surface. By breaking down a nonerodible surface you are going to increase its susceptibility to wind erosion" (Merrill 1996).

PM-10 dust can be a hindrance to successful biological control of insect pests (Phillips, 1996). It is well known that excessive road dust adjacent to orchard and other agricultural crops aggravates pest problems (DeBach, 1974). Dry-dust deposits on plant surfaces are a serious hindrance to effective biological control and may even be lethal to certain of the more delicate parasites that farmers depend on for an ever increasing proportion of pest control. Clean plants promote biological control.

Another potential dust problem in need of better control is that from cattle-feed yards (Carroll et el. 1974).

A large potential exists for control of fugitive dusts on farm lands and roads with water-soluble polyacrylamide (Wallace and Wallace 1995 a, b, c, d, e). Farms treated with these polymers have less soil moving to highways on the wheels of equipment. Farm roads can be protected with special treatment. Less dust can arise with cultivation when PAM is used.

Even though the EPA is working toward legislation of PM-2.5 particles it is the PM-10 currently where enforcement is required. Plans for attainment in California need to be functioning by December 31, 2001 (This has been postponed). Considerable farm effort is involved (Beach 1997). The use of water-soluble polyacrylamide has not been factored into the plans and its use could be extremely important. Unfortunately it has been ignored as a possible solution (Bader 1997) and even up to 2001.

Bader, C.D. 1997. Controlling dust. Erosion Control 4(5):20-32.

Beach, G. 1997. PM-10 draft attainment plan. Nut Grower 17(5):17, 31.

Brookhart, B. 1991. Dusting off the valley. California Farmer Jan. 19, 1991:50-52.

California Agri. 1994. Research Update: Researchers try to arrest fugitive dust. Calif. Agri. 48(4):5-8.

California Ariz. Farm Press. 1995. PM-10 air pollution level standard to be difficult. Calif. Agri. Farm Press 17(13):4.

Carroll, J.J., J.R. Dunbar, R.L. Givens, and W.B. Goddard. 1974. Sprinkling for dust suppression in a cattle feedlot. Calif. Agri. 28(3):12-14.

Clausnitzer, H. and M.J. Singer. 1997. Intensive land preparation emits respirable dust. Calif. Agric. 51(2):23-30.

Daly, S. 1995. Chemicals, fertilizers, and polymers. Erosion Control 2(5):44-53.

DeBach, P. 1974. Biological control by natural enemies. Cambridge Univ. Press. 323 pp.

Flocchini, R.G. 1994. PM-10 -The unknown compound. Calif. Agric. 48(4):2.

Kaiser, J. 1997. Getting a handle on air pollution's tiny killers. Science 276:33.

Merrill, L. 1996. Blowing in the wind: Controlling fugitive dust. Erosion Control 3(1):56-58, 62.

Odum, J.R., T.P.W. Jungkamp, R.J. Griffin, R.C. Flagan and J.H. Sienfeld. The atmospheric aerosol-forming potential of whole gasoline vapor. Science 276:96-99

Phillips, P .A. 1996. Revisiting dust: A real threat to successful biological control. Citrograph. 81(7):7, 9-10.

Raber, L.R. 1997a. Clean air: Dollars versus lives. Chem. Eng. Ne 75(5):28-30.

Raber, L.R. 1997b. EPA's air standards: Pushing too far, too fast? Chem. Eng. News 75(15):10-18.

Sullivan, R. 1991. From dirt to toxic dust. Environmental Protection 8(5):12-13.

Wallace, A., and G.A. Wallace. 1995a. Water-soluble polymer soil conditioners on physical properties of soils and some benefits. Soil Conditioner and Amendment Technologies Vol. I. pp. 99-111 Wallace Laboratories, El Segundo, CA, USA.

Wallace, A., and G.A. Wallace. 1995b. Water-soluble polymers gaining momentum in erosion control. Soil Conditioner and Amendment Technologies Vol. 1. pp. 153-158. Wallace Laboratories, Segundo, CA, USA.

Wallace, A., and G.A. Wallace. 1995c. How much future for conditionerigation? Soil Conditioner and Amendment Technology Vol. 1. pp. 159-165. Wallace Laboratories, El Segundo, CA, USA

Wallace, A., and G.A. Wallace. 1995d. Promises of new water-soluble polymer soil conditioners: Looking for growers willing to try new ideas. Soil Conditioner and Amendment Technologies Vol. 1. pp. 173-186. Wallace Laboratories, El Segundo, CA, USA.

Wallace, A., and G.A. Wallace. 1995e. Over 40 years of literature concerning synthetic polymer soil conditioners for land improvement. Soil Conditioner and Amendment Technologies Vol. 1. pp.217-276. Wallace Laboratories, El Segundo, CA, USA.

This note is adapted from Soil Conditioner and Amendment Technologies, Vol. 2, pg. 141 (1997).

PAM can be an important means for controlling dust. Where water is used in sprinkler trucks to control dust, the inclusion of two or three pounds of PAM (15 pounds of 20% "MP" (Micronized PAM) in gypsum is better) per each 1000 gallons of water will more effectively control the dust and also make it possible to need fewer sprinkling passes to save both time and water. For dust control the inclusion of 5 to 20 pounds of sodium bicarbonate or sodium chloride per 1000 gallons will aid to the control. It increases cementing action of the PAM and soil. Highway edges that emit dust may be treated this way. Treatments will last until disturbance of soil requires repeat application. In addition to decreasing dust, precious water will be saved. In some cases, one gallon of Soil Sement (a latex polymer) or equivalent may be added per 1000 gallons.

Dust control of vineyards and orchards may be achieved by sprinkling the above rates over bare soil as often as necessary. An alternative procedure is to add good compost containing gypsum and "MP" over the surface that emits dust. One to 2½ percent "MP" is sufficient in one ton per acre. For construction sites using compost, 5 or more percent "MP" may be used to give more longevity.

Abandoned farms may also be sprinkled with PAM with sprinkler trucks to inhibit dust. Again 15 pounds of 20% "MP" in gypsum for 1000 gallons water is suggested. One thousand gallons will do roughly ½ acre. If necessary an aerial drop of dry "MP" (Micronized PAM) under ideal wind conditions to be followed up by a rain could be useful. Farms where PAM has been used are less subject to wind erosion (see figure 2).

Scene of November 1991 accident that resulted from a dust windstrom coming across farmland at midday. Dust did not blow off a farm that had been treated with PAM.

(Fiery 164 vehicle pileup in 1991 killed 17 people and injured 151, unleashing a flood of lawsuits. Source: LA Times Nov. 1991)

Dust control on farms around homes and landscape areas can be obtained as described in appropriate sections above.

Copious amounts of biosolids have been used on the per acre basis in restoration projects. Some safety issues have not been 100% resolved but success has been good. The price is right. From 200 to 500 tons per acre are often used. Some places however prefer not to use biosolids for various reasons. PAM can be extremely useful where less biosolids or other compost are used. PAM use will result in fewer problems than the very high levels of biosolids.

Gypsum is commonly used in renovation where soils are sodic. For extreme sodicity, calcium chloride is often used with gypsum because calcium chloride is very soluble. Co-use with MP can be very useful.

Other renovation problems exist. Lime or lime substitutes like fly ash are used when soils are acid. Considerable of the mine operations especially those drilling for iron, copper, and lead are often acidic because of oxidation of pyrites that are a source of the metals. Acidic water drainage from some mines pose a large problem. Neutralizing the acid is often more difficult than reclaiming the soil.

Phenomenal success has been reported with use of mycorrhizae for establishing of trees and shrubs on lands being renovated. On old mined land and borrow pits, plantings flourished with use of mycorrhizae but failed without, even on very acid soil. Again, MP can help. Some references to these matters follow.

1. Garbaye, J. and J.L. Curin. 1996. Effects of ectomycorrhizal inoculation at planting on growth and foliage quality of Tilia tomentosa. J. Arboric. 22:29-33.

2. Geist, S. 1998. Mycorrhizal inoculation and fertilizer effects on roots of newly planted trees. Tree Leaves (ISA RM Chapter) 24 (2): 4 pg.

3. Marrs, L.F., D.H. Marx and C.E. Cordell. 1999. Establishment of vegetation on mined sites by management of mycorrhizae. Proc. Nat. Meet. Amer. Soc. for Surface Mining and Reclamation. Scottsdale, AZ. Aug. 1999.

4. Marx, D.H. 1991. The practical significance of ectomycorrhizae in forest establishment. pp. 54-90. In Ecophysiology of ectomycorrhizae of forest trees. The Marcus Wallenberg Foundation Symposium Proc. 7, Stockholm, Sweden .

5. Marx, D.H., M.D., Pettway, and R.D. Mellick. 1995. Study focuses on ectomycorrhizal fungi. Tree Care Industry (August): 29-32.

6. Marx, D.H., M. Murphy, T. Parrish, S. Marx, D. Haigler and D. Eckard. 1997. Root response of mature live oaks in coastal South Carolina to root zone inoculations with ectomycorrhizal fungal inoculants. J. Arboric 23:257-263.

7. Marx, D.H. and R. McCartney. 1997. Tree roots and their microbial partners. Arbor Age. 17:8-10.

8. Quarles, W. 1999. Plant disease biocontrol and VAM fungi. The IPM Practitioner. 21 : 1-9 (April) .

9. Rao, B. and B. Jeffers. 1999. Effects of mycorrhizal inoculates and fertilizer on newly planted trees. Poster, ISA Annual Conference, Stamford, CT. Aug. 1999.

10. Smiley, E.T., D.H. Marx, and B.R. Fraedrich. 1997. Ectomycorrhizal fungus inoculation of established residential trees. J. Arboric. 23:113-115.

11. Smith, S.E. and.D.J. Read. 1997. Mycorrhizal Symbiosis. Academic Press, Harcourt Brace and Company, Publishers, New York, 605 pg.

Standard usage of soil amendments including "MP" (Micronized PAM) should always be used as possible. Soil conditioning with PAM, following landscape procedures, will improve soils containing clay provided that attention has been given to correction of salinity and of very acid soils. If crops are to be grown, PAM use as for farms or landscape is advised. Mycorrhizae and PAM may be co-used to great advantage. PAM can help restore severely damaged soils to their natural condition with landscape procedures.

Settling ponds are commonly used especially at construction sites. Rainwater moves considerable soil from the site that is collected in ponds so that the soil can settle out and clean water can then be discharged as necessary. Contractors like for the sediments to settle out as rapidly as possible partly because the possibility of more rain to move more soil. Gypsum has been used as a flocculating agent but its action is too slow.

A small amount of PAM can flocculate a large amount of soil especially if some soluble calcium (gypsum for example) is present. One pound of PAM can flocculate up to 20,000 pounds of soil depending upon its clay content.

A very special problem in clay-settling ponds is the case of the phosphate mining industry in Florida and elsewhere. The raw phosphate rock is in association with clay that has very finely divided particles. The clay is washed from the rock and flowed into large ponds for the clay to settle out. Settling to the point where the surface may be used for native vegetation and wildlife takes months of time. There has been an accident where a man-made pond has broken to result in a muddy flood. The industry has done many studies in effort to hasten the time of flocculation with little success. Polymers used for soil conditioners have helped little. It is possible however to flocculate the clay with PAM solutions in soluble calcium chloride. Such solutions are easy to prepare from "MP" (Micronized PAM).

One way to reduce the amounts of silt and clay going off farms is the use of sediment basins, which are large on-farm reservoirs where drainage water is held for two hours or more to give suspended clay particles time to settle out. The basins clean 90% of the silt from the water going into rivers or elsewhere. However, they require periodic maintenance and can take up a substantial amount of land. PAM is more effective and somewhat easier to use.

Clay or soil containing clay in settling ponds is best flocculated and rapidly with addition of either solutions of "MP" (Micronized PAM) with calcium salts or granular finely divided "MP" (Micronized PAM) with gypsum. An ounce of PAM can flocculate clay in as many as 10,000 gallons of water especially if some gypsum is also used; 10,000 gallons of water with 60 parts per million calcium would require about 25 pounds of gypsum. One gallon of one per cent or so PAM in calcium chloride or calcium nitrate solution could very efficiently flocculate the clay in 10,000 gallons of water.

Wherever water-soluble polyacrylamide (PAM) has been used as a component in hydroseeding, results have been outstanding. Hydroseeding without PAM (water- soluble PAM as in Micronized PAM) in the same general location has often resulted in failure or in the need for returning to redo patches. The usual rate for using PAM in hydroseeding is about two to four pounds per 1000 gallons water mix. When applied at this concentration, the PAM stabilizes the soil aggregates for as deep as the hydroseeding mixture penetrates into the soil. It is assumed that the soil surface is tilled in some way and not previously rained on or irrigated after the tillage but before the treatment. The benefits are multiple: decreased soil erosion, better soil aeration, better seed emergence, less time to when the new plant cover itself can protect the soil.

When shrubs and trees are transplanted with use of PAM in the backfill, more rapid growth is further protection against erosion. Rooting can be more extensive to hold soil in place. This is extremely worthwhile on slopes.

Many experts on transplanting of trees and shrubs say that organic matter should not be used in backfill mixes for transplanting. When used, a good chance is made to create some soil in which roots can proliferate and grow rapidly. Sometimes when used, however, at least two problems can arise. One problem is the creation of soil interfaces between two types of soil with the result that neither roots nor water will cross the boundary. The other problem is related and concerns having too much water accumulating in the transplant hole due to the high water-holding capacity of the organics and also to possible boundaries that keep water trapped (bathtub effect). The use of solutions of PAM usually with some gypsum in the backfill mix can do much to solve both problems. The transplant hole needs to be much wider than the transplant ball or container. Better aeration due to the effect of the PAM prevents water-logging and anaerobic decomposition of the organic matter. It is the by-products of anaerobic decomposition of organic matter that causes severe problems with transplanted shrubs and trees. Proper use of PAM can avoid the problem and obtain needed value from the organic matter.

Soil preparation with PAM generally uses from 5 to 20 pounds per 1000 square feet and preferably with some gypsum. Alternatively, much less PAM will suffice if applied in solution from a tank truck. In backfill use, solutions of 200 to 400 parts per million (mg per kg) of PAM are used.

Much publicity has been given to the procedures used for controlling erosion in furrow-irrigated agriculture. Several locations have reported good success; Idaho, California, Washington, Oregon are among them. From 1 to 10 parts per million of PAM are applied to all or part of the irrigation stream to control over 90 per cent of the soil loss from erosion. Although the cost is small, about $10 to $25 per acre usually, it is thought by some that, for the procedure to be economically viable, additional benefits must be obtained. Sometimes more PAM is needed but workers are finding increased yields and considerable water-savings. In one preliminary study tomato yields were increased to result in $295 per acre gain for the yield. Several similar experiences have been seen. Associated water savings and erosion control were then obtained at no real cost.

Erosion control on farms is not confined to furrow irrigation. Erosion is also controlled when PAM is used in sprinkler irrigation. There may be no runoff from the sprinklers but rain may be superimposed upon PAM-treated land which will be protected from erosion with any water runoff.

Methodology is being developed for use of PAM to control erosion on rain-fed agricultural land. To accomplish such is easy. To do it in an economical way is possible. Control of erosion is possible with use of PAM in connection with other inputs. It is also important to spread the cost over as many benefits as possible.

As a non-toxic easy to use product, PAM is beneficial in many other types of erosion control. Applied in sprinkler trucks, it can control PM-10 and 25 dust emissions from roads and bare land. Control of erosion from both wind and water can be obtained for use of PAM at construction sites or partially built roadways. Treatment procedures are outlined in previous sections.

This note was adapted from Soil Conditioner and Amendment Technologies, Vol. 2 pg 146 (1997).

During the post WWII era, the country looked inward to build the infrastructure needed to service the rapid growth of the nation. Residential and commercial building was growing at an unprecedented pace and the urban sprawl was born. Government investment to develop a transportation system to support the growth became a top priority among legislatures.

As highway systems were being built across the nation, the need for more effective methods for revegetating the scarred landscape became essential. Then, in 1953, Charles Finn of the Finn Equipment Company, developed the first commercially successful HydroSeeder. It mechanically mixed seed, fertilizer, and lime with water, producing a slurry mixture, which was then applied to the seedbed. As the market grew, companies such as Reinco, Inc., and Bowie Industries, Inc. developed equipment that could effectively pump, spray and distribute large volumes of water and seed on disturbed landscapes. In the late 1950's, International Paper introduced a mulching material made from natural cellulose fibers to provide a one-step mulching process that worked better than the water-only system. The custom blend of hydraulic mulch, seed and fertilizer was called a "homogeneous slurry" and could be applied by hydraulic seeding equipment to a wide range of project types. International Paper soon withdrew from the market so Weyerhaeuser and Conwed Corporation stepped in to fill the void.

Conwed Corporation and Weyerhaeuser commercialized the process of Thermo-mechanical defibration of wood fiber, in the early 1960s. Both companies became the dominant manufacturers in the industry, providing the seeding contractor with a top performing wood fiber mulching material that not only assisted plant establishment, but helped control erosion. The popularity of hydromulching grew at a rapid pace in the 1970s and 1980s when equipment manufacturers developed smaller machines targeting contractors that focused on residential, commercial and fine turf projects. The flexible technology allowed the seeding contractor to custom blend seed, fertilizer and mulch to establish a wide range of plant material at an economical cost.

As the industry grew so did the number of suppliers of hydraulic seeding equipment and hydraulic mulch. Advancements were made both with materials and equipment to insure contractor success. In the later 1970s, Conwed Corporation received a process patent for incorporating guar tackifier with wood fiber that significantly improved the fiber's ability to control erosion. Other manufacturers also blended and marketed a host of tacking agents, which improved seeding success. During the same time period, warm season grass sprigs were incorporated with wood fiber mulch to produce a vegetative planting system called hydro-sprigging. Today, Hydro-Sprigging has been used on hundreds of golf courses as an effective way to quickly establish premium hybrid Bermuda grasses on expansive fairways. Today's hydraulic seeding equipment can pump a broader range of materials reliably and cost effectively.

Due to the proliferation of hydromulching projects nationwide, awareness of the process has trickled down to the consumer level. Most homeowners, when asked, are aware of the technology by referring to hydromulching as "that green stuff that they spray along the roadside". International awareness has also increased and US based machine and hydraulic mulch manufacturers export multiple seeding units and thousands of tons of fiber all over the world. One of the largest international projects using wood fiber mulch was at the Hong Kong Airport project in 1997 and 1998, which consumed multiple containers of virgin wood fiber with guar tackifier. The hydromulching project was effective, completed on time and within budget.

Other vegetative methods that compete with hydromulching include direct seeding, sodding, and manual or mechanical sprigging. Each of these methods has always been somewhat easy for the hydromulching contractor to compete with because hydromulching is a cost-effective way to control erosion, custom vegetate an area and can usually save developers time and money. Shortfalls of this seeding method are due to the use of substandard seeds, mulching material and/or application rates that fall short of manufacturers recommendations. Other factors that can effect success is the amount of available water and soil preparation which is always a factor when establishing plant material.

Today's hydromulching contractor has distinct advantages over the pioneers of the industry. Advances in seed research, equipment and mulching materials help contractors better meet the demands of their client. New product technologies like bonded fiber matrix products gives the hydromulching contractors a broader arsenal of tools to combat erosion. Chemically bonded fiber matrix products have the potential to revolutionize the seeding industry by bridging the gap between current hydraulic mulching products and other temporary erosion products. Introduced in 1994, bonded fiber matrix products can be hydraulically applied saving both time and labor while successfully securing some of the most challenging erosion sites. This niche product is ideal for areas where vegetation is the primary long-term erosion medium. Chemically bonded fiber matrix product must be applied in dry conditions to be effective and is now available from leading hydraulic mulch manufactures.

Hydraulic seeding is a proven technology that has met the needs of contractors and developers for over forty years. The wide range of equipment, materials and contractors, warrants the consumer to ask key questions prior to accepting a seeding bid.

Make sure that the seeding contractor is a reputable established company that can provide you with references.

Ask your contractor to bid the job using different grades of seed and hydraulic mulch. The quality of materials used can make a huge difference on the final result of the project so don't focus only on price.

Insist on a disclosure on materials used on the project and make sure the materials used are at the rates recommended by the manufacturer.

Since hydraulic mulch materials are not all the same, request performance data on material used and options like including tackifiing agents. (Leading manufactures and contractors will be more than happy to provide that information upon request.)

The hydromulching industry continues to thrive as hundreds of new machines are purchased every year by innovative contractors. This forty-year-old technology, which is still considered new, is sure to evolve and thrive well into the new millennium. From Land and Water, March/April, 1999. p. 24

PAM should be used as possible in all soil erosion control endeavors for both water and air erosion. Methodology for use of "MP" (Micronized PAM) as given for farms, landscapes, and gardens (Parts 2, 3, and 4) will be very useful. Lower concentrations than 10 parts per million PAM can be possible with "MP" especially when used in calcium solutions or other solutions. In hydroseeding, 10-15 pounds per 1000 gallon of 20% "MP" (Micronized PAM) and 80% solution grade gypsum may be used very effectively as the tackifier. PAM should be better than guar because it is less biologically degraded and because it more strongly binds clay. The gypsum aids the ability of the PAM to bind with clay. Both "MP" and gypsum make better soil.

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Use of PAM on farms according to directions can also conserve organic matter—that available can be spread over more land when used with PAM. Crop residues can then also be more efficient as soil conditioners.