WATER RESEARCH AND MANAGEMENT IN SEMIARID ENVIRONMENTS

  Water infiltration control at the soil surface: Theory and practice

An International Symposium
November 1-3, 1994
Tucson, Arizona

Robert M. Dixon, Ph.D

This paper traces the course of research conducted by the author and several coworkers beginning in 1960 and continuing to the present time. The vast amount of literature on infiltration reveals that field studies often stress the importance of surface conditions whereas laboratory studies using soil columns indicate that profile properties largely determine infiltration rates. Our field research concluded that two physical properties of the soil surface--microroughness and macroporosity--interact to control the infiltration rates of an initially dry soil. This finding led to the formulation of the Air Earth Interface (AEI) Concept of infiltration which states that the microroughness and macroporosity of the AEI regulate the exchange of surface water and displaced soil air across the AEI with the rough, open interface having very high fluid exchange rates and with the smooth, closed interface having very low rates. A series of studies conducted under widely ranging climatic, edaphic, and vegetal conditions showed that manipulation of AEI roughness and openness can easily provide an order-of-magnitude control of water infiltration into dry soils. The last study site in this series was located in the lower reaches of Walnut Gulch Experimental watershed which surrounds Tombstone , Arizona.

 

While the author was at the Reno Field Station, a number of new infiltrometers were invented--a border irrigation infiltrometer and several types of closed-top (tension) infiltrometers-- to elucidate the effects of soil-air pressure and soil-air counterflow on infiltration. Data from these infiltrometers showed that just a few millibars of soil air pressure could greatly reduce infiltration and that macropores connected to the crests in a microrough surface served to relieve this pressure. Thus, these results were consistent with the AEI concept of infiltration.

 

To realize the many potential benefits of wide-range infiltration control through field application of the AEI concept, a new land treatment method called land imprinting was conceived and devices called land imprinters were invented and USDA patented. The prototypic land imprinter was fabricated at the machine shop of the Walnut Gulch Experimental Watershed. In July 1976, this imprinter was successfully tested on some desert shrubland just east of the machine shop. This rolling rangeland imprinter, with a front-mounted drop seeder, was compared to the USDA-developed rangeland drill for establishing forage species at several overgrazed sites in the Sonoran Desert near Tucson , Arizona . A series of studies found that the imprinting practice was greatly superior because of much better surface control of rainwater along with other resources important.

November 1- 3, 1994, Tucson, Arizona

in seed germination and seedling establishment. The V-shaped imprinted pockets or indentations, formed by angle-iron imprinter teeth efficiently funneled rainwater, seed, plant litter, and splash-eroded topsoil together at the bottom of the V where these resources could work in concert to germinate seeds and establish seedlings. In contrast, the continuous furrows created by the rangeland drill tended to bleed resources downslope until encountering a flow obstruction, at which place infiltration, sedimentation, and deposition occurred. The end result was a sparse and spotty stand as compared with uniform stand of seedlings in the geometrically closed V-shaped imprints.

Early rolling imprinters, designed from 1976 to 1985, were massive machines having large-diameter rollers with complex patterns of imprinting teeth welded to their circumferences. Imprinters designed after 1985 were smaller in diameter, lighter in weight, cheaper to fabricate, and easier to transport. They also have simpler and more efficient imprinting patterns. A drop seeder was mounted above the imprinting roller so that the seeder agitator could be directly driven by the tips of the imprinting teeth.

The AEI Concept for wide-range control of infiltration gradually evolved into the AEI Model for reversing global land desertification through imprintation and revegetation. This model verbally and diagrammatically describes the four interrelated and interacting processes: Desertification, Infiltration, Imprintation, and Revegetation.

Desertification smoothes and seals the normally rough open interface, thereby greatly decreasing infiltration with resultant increases in water runoff, erosion, flash flooding, and sedimentation. Imprintation efficiently converts the smooth, sealed, desertified AEI back into the rough, open condition, thereby restoring infiltration to high levels.

Imprints greatly accelerate the revegetation process by funneling and concentrating resources to, in turn, germinate seeds and establish seedlings. Seedling establishment is enhanced by the favorable microclimate created by imprints. The AEI model can help develop and guide the cultural practices for sustainable agriculture and ecological restoration of non-agricultural land areas. Imprinter seeding has already restored perennial grasses on 50,000 acres of degraded land in the Sonoran Desert of southern Arizona and is currently being used to restore native vegetation at several degraded land sites in the Mojave Desert of southern California where annual precipitation is only about half that of the Sonoran Desert.

WATER INFILTRATION CONTROL AT THE SOIL SURFACE: THEORY AND PRACTICE

This paper traces the course of research conducted by the author and several coworkers beginning in 1960 and continuing to the present time. The vast amount of literature on infiltration reveals that field studies often stress the importance of surface conditions whereas laboratory studies using soil columns indicate that profile properties largely determine infiltration rates. Our field research concluded that two physical properties of the soil surface--microroughness and macroporosity--interact to control the infiltration rates of an initially dry soil. This finding led to the formulation of the Air-Earth Interface (AEI) Concept of infiltration which states that the microroughness and macroporosity of the AEI regulate the exchange of surface water and displaced soil air across the AEI with the rough, open interface having very high fluid exchange rates and with the smooth, closed interface having very low rates. A series of studies conducted under widely ranging climatic, edaphic, and vegetal conditions showed that manipulation of AEI roughness and openness can easily provide an order-of-magnitude control of water infiltration into dry soils. The last study site in this series was located in the lower reaches of Walnut Gulch Experimental Watershed which surrounds Tombstone , Arizona .

While the author was at the Reno Field Station, a number of new infiltrometers were invented--a border irrigation infiltrometer and several types of closed-top (tension) infiltrometers--to elucidate the effects of soil-air pressure and soil-air counterflow on infiltration. Data from these infiltrometers showed that just a few millibars of soil air pressure could greatly reduce infiltration and that macropores connected to the crests in a microrough surface served to relieve this pressure. Thus, these results were consistent with the AEI concept of infiltration.

To realize the many potential benefits of wide-range infiltration control through field application of the AEI concept, a new land treatment method called land imprinting was conceived and devices called land imprinters were invented and USDA patented. The prototypic land imprinter was fabricated at the machine shop of the Walnut Gulch Experimental Watershed. In July 1976, this imprinter was successfully tested on some desert shrubland just east of machine shop. This rolling rangeland imprinter, with a front-mounted drop seeder, was compared to the USDA- developed rangeland drill for establishing forage species at several overgrazed sites in the Sonoran Desert near Tucson , Arizona . A series of studies found that the imprinting practice was greatly superior because of much better surface control of rainwater along with other resources important in seed germination and seedling establishment. The V-shaped imprinted pockets or indentations, formed by angle-iron imprinter teeth efficiently funneled rainwater, seed, plant litter, and splash-eroded topsoil together at the bottom of the V where these resources could work in concert to germinate seeds and establish seedlings. In contrast, the continuous furrows created by the rangeland drill tended to bleed resources downslope until encountering a flow obstruction, at which place infiltration, sedimentation and deposition occurred. The end result was a sparse and spotty stand as compared with uniform stands of seedlings in the geometrically closed, V-shaped imprints.

Early rolling imprinters, designed from 1976 to 1985, were massive machines having large-diameter rollers with complex patterns of imprinting teeth welded to their circumferences. Imprinters designed after 1985 were smaller in diameter, lighter in weight, cheaper to fabricate, and easier to transport. They also have simpler and more efficient imprinting patterns. A drop seeder was mounted above the imprinting roller so that the seeder agitator could be directly driven by the tips of the imprinting teeth.

The AEI Concept for wide-range control of infiltration gradually evolved into the AEI Model for reversing global land desertification through imprintation and revegetation. This model verbally and diagrammatically describes the four interrelated and interacting processes: Desertification, Infiltration, Imprintation, and Revegetation. Desertification smoothes and seals the normally rough open interface, thereby greatly decreasing infiltration with resultant increases in water runoff, erosion, flash flooding, and sedimentation. Imprintation efficiently converts the smooth sealed desertified AEI back into the rough open condition, thereby restoring infiltration to high levels. Imprints greatly accelerate the revegetation process by funneling and concentrating resources to, in turn, germinate seeds and establish seedlings. Seedling establishment is enhanced by the favorable microclimate created by imprints. The AEI model can help develop and guide the cultural practices for sustainable agriculture and ecological restoration of non-agricultural land areas. Imprinter seeding has already restored perennial grasses on 50,000 acres of degraded land in the Sonoran Desert of southern Arizona and is currently being used to restore native vegetation at several degraded land sites in the Mojave Desert of southern California where annual precipitation is only about half that of the Sonoran Desert.

 

 

Imprints made by the imprinter at a sand and gravel mine near Pearblossom, CA

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