spatial and temporal influence of soil frost on infiltration and erosion of sagebrush rangelands

7
WATER RESOURCES BULLETIN VOL 26, NO.6 AMERICAN WATER RESOURCES ASSOCIATION DECEMBER 1990 SPATIAL AND TEMPORAL INFLUENCE OF SOIL FROST ON INFILTRATION AND EROSION OF SAGEBRUSH RANGELANDS' Wilbert H. Blackburn, Frederick B. Pierson, and Mark S. Seyfried2 ABSTRACT: Soil infiltration capacity and interrill erosion are sig- nificantly influenced by soil frost on western rangelands which are characterized by cold winters and numerous freeze-thaw cycles. However, little is known about the variable influence of this phe- nomenon. Infiltration and interrill erosion were measured within a sagebrush-grass plant community during the winter, spring, and summer of 1989. Significant spatial and temporal differences in infiltration capacity and interrill erosion were found for shrub cop- pice dune and dune interspace soils. Infiltration was generally higher for coppice dune soils compared to interspace soils through- out the year. Infiltration capacity for both soils was lowest early in the year when the soil was frozen or saturated, then increased as the soil dried in the spring and summer. Interrill erosion was con- sistently lower for coppice dune soils compared to interspace soils. Erosion from interspace soils was greatest during a 19-day period in late winter characterized by diurnal freeze-thaw cycles, saturat- ed surface soil conditions, and soil slaking. (KEY TERMS: runoff; bare ground; plant cover; soil water; bulk density; soil frost.) INTRODUCTION Soil erosion and water infiltration are strongly influenced by soil frost in parts of the Northwest and Intermountain West (Haupt, 1967; Papendick et al., 1983; Zuzel and Pikul, 1987; Wilcox et al., 1989). These regions are characterized by cold winters, tran- sient snow cover, and soils that may freeze and thaw several times each year for periods ranging from one day to several weeks (Pikul and Allmaras, 1986; Zuzel et al., 1982). Soil erosion in the Pacific Northwest is most severe during periods of rain and rapid snowmelt on partially thawed, weakly structured soils (Zuzel et aL, 1982; Papendick et al., 1983). The cohesional strength of these soils is reduced by freeze- thaw cycles (Fonnanek et al., 1984; Bullock et al., 1988); however, the influence of freeze-thaw cycles on aggregate stability is dependent on many factors such as the water content at the time of freezing (Mostaghimi et al., 1988). Infiltration capacity of frozen soil is strongly influenced by the structure of the soil frost which is also determined in part by the soil water content at the time of freezing. Concrete non-porous frost which is characterized by many thin ice lenses, small crystals, and high density has been identified as having the greatest impact on reducing infiltration capacity (Haupt, 1967; Story, 1955). The spatial influence of shrub coppice dune (cop- pice) and dune interspace (interspace) soils on infil- tration of unfrozen soil was originally established by Blackburn (1975) and verified by numerous other investigators (Johnson and Gordon, 1988; Swanson and Buckhouse, 1984; Thurow et al., 1986; Wood and Blackburn, 1981; Wood et al., 1987). Blackburn and Wood (1990) hypothesized that coppice and interspace soils would respond differently to soil freezing and thawing due to differences in vegetation cover and surface soil characteristics, thus imposing a spatial and temporal response in infiltration and soil erosion. Achouri and Gifford (1984) also found significant sea- sonal trends in infiltration capacity on a rangeland site in Utah and indicated the need to improve the understanding of freezing and thawing on hydrologic processes. The objective of this study was to quantifr and compare the temporal variability in infiltration capacity and interrill erosion of frozen and unfrozen coppice and interspace soils. METHODS The study area was located at the Quonset site on the Reynolds Creek Experimental Watershed in 'Paper No. 90051 of the Water Resources Bulletin. Discussions are open until October 1, 1991 2Respectively, Supervisory Research Hydrologist, Research Hydrologist, and Soil Scientist, USDA-Agricultural Research Service, 800 Park Blvd., Plaza W, Suite 105, Boise, Idaho 83712-7716. 991 WATER RESOURCES BULLETIN

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WATER RESOURCES BULLETINVOL 26, NO.6 AMERICAN WATER RESOURCES ASSOCIATION DECEMBER 1990

SPATIAL AND TEMPORAL INFLUENCE OF SOIL FROST ON INFILTRATIONAND EROSION OF SAGEBRUSH RANGELANDS'

Wilbert H. Blackburn, Frederick B. Pierson, and Mark S. Seyfried2

ABSTRACT: Soil infiltration capacity and interrill erosion are sig-nificantly influenced by soil frost on western rangelands which arecharacterized by cold winters and numerous freeze-thaw cycles.However, little is known about the variable influence of this phe-nomenon. Infiltration and interrill erosion were measured within asagebrush-grass plant community during the winter, spring, andsummer of 1989. Significant spatial and temporal differences ininfiltration capacity and interrill erosion were found for shrub cop-pice dune and dune interspace soils. Infiltration was generallyhigher for coppice dune soils compared to interspace soils through-out the year. Infiltration capacity for both soils was lowest early inthe year when the soil was frozen or saturated, then increased asthe soil dried in the spring and summer. Interrill erosion was con-sistently lower for coppice dune soils compared to interspace soils.Erosion from interspace soils was greatest during a 19-day periodin late winter characterized by diurnal freeze-thaw cycles, saturat-ed surface soil conditions, and soil slaking.(KEY TERMS: runoff; bare ground; plant cover; soil water; bulkdensity; soil frost.)

INTRODUCTION

Soil erosion and water infiltration are stronglyinfluenced by soil frost in parts of the Northwest andIntermountain West (Haupt, 1967; Papendick et al.,1983; Zuzel and Pikul, 1987; Wilcox et al., 1989).These regions are characterized by cold winters, tran-sient snow cover, and soils that may freeze and thawseveral times each year for periods ranging from oneday to several weeks (Pikul and Allmaras, 1986; Zuzelet al., 1982). Soil erosion in the Pacific Northwest ismost severe during periods of rain and rapidsnowmelt on partially thawed, weakly structuredsoils (Zuzel et aL, 1982; Papendick et al., 1983). Thecohesional strength of these soils is reduced by freeze-thaw cycles (Fonnanek et al., 1984; Bullock et al.,1988); however, the influence of freeze-thaw cycles onaggregate stability is dependent on many factors such

as the water content at the time of freezing(Mostaghimi et al., 1988). Infiltration capacity offrozen soil is strongly influenced by the structure ofthe soil frost which is also determined in part by thesoil water content at the time of freezing. Concretenon-porous frost which is characterized by many thinice lenses, small crystals, and high density has beenidentified as having the greatest impact on reducinginfiltration capacity (Haupt, 1967; Story, 1955).

The spatial influence of shrub coppice dune (cop-pice) and dune interspace (interspace) soils on infil-tration of unfrozen soil was originally established byBlackburn (1975) and verified by numerous otherinvestigators (Johnson and Gordon, 1988; Swansonand Buckhouse, 1984; Thurow et al., 1986; Wood andBlackburn, 1981; Wood et al., 1987). Blackburn andWood (1990) hypothesized that coppice and interspacesoils would respond differently to soil freezing andthawing due to differences in vegetation cover andsurface soil characteristics, thus imposing a spatialand temporal response in infiltration and soil erosion.Achouri and Gifford (1984) also found significant sea-sonal trends in infiltration capacity on a rangelandsite in Utah and indicated the need to improve theunderstanding of freezing and thawing on hydrologicprocesses. The objective of this study was to quantifrand compare the temporal variability in infiltrationcapacity and interrill erosion of frozen and unfrozencoppice and interspace soils.

METHODS

The study area was located at the Quonset site onthe Reynolds Creek Experimental Watershed in

'Paper No. 90051 of the Water Resources Bulletin. Discussions are open until October 1, 19912Respectively, Supervisory Research Hydrologist, Research Hydrologist, and Soil Scientist, USDA-Agricultural Research Service, 800 Park

Blvd., Plaza W, Suite 105, Boise, Idaho 83712-7716.

991 WATER RESOURCES BULLETIN

Blackburn, Pierson, and Seyfried

southwest Idaho about 80 km southwest of Boise. Theaverage annual precipitation is 281 mm, with approx-imately 70 percent rain and 30 percent snow, the ele-vation is 1,193 m, and the average slope is about 6percent to the northeast. Years are characterized bynumerous freeze-thaw cycles of one day to severalweeks in length.

Wyoming big sagebrush (Artemisia tridentata ssp.wyomingensis) is the dominant shrub with 30 percentcrown cover and rubber rabbitbrush (Chiysothamnusnauseosus) is an associated species with less than 2percent crown cover. Sandberg bluegrass (Poasand-bergii) is the dominant grass with 8 percent crowncover. Cryptogams (mosses and algae) found predomi-nately beneath and on the north side of shrubs coverabout 52 percent of the soil surface.

The soil is a member of the Larimer series withinthe fine, loamy, mixed, mesic family of XeraliicHaplargids. Two major types of surface soils are foundon the study site: the coppice soil under shrubs andthe interspace soil between shrubs. The coppice soilcovers 39 percent of the surface while interspace soilcovers 61 percent. The A horizon (the upper-mostmineral soil layer) of the coppice soil is densely cov-ered with cryptogams and characterized by weaklygranular structure, loam texture, and is classified assoil surface Type I (Eckert et at., 1986). The inter-space soil is sparsely covered with gravel and cryp-togams with a loam textured A horizon characterizedby a 15 mm thick crust with platy structure andvesicular pores (small spherical cavities formed bybubbles of trapped air). The surface is broken into 80-150 mm diameter polygons when dry, and is classifiedas soil surface Type III (Eckert et at., 1986).

Simulated rainfall was applied using a modifica-tion of the drip-type rainfall simulator described byBlackburn et al. (1974). Raindrop size is correlated torainfall intensity with larger drops being morenumerous as rainfall intensity increases (Hess, 1974).The simulated 2.5 mm diameter raindrops are similarto the mean drop size of natural rainfall of the inten-sity used in this study (Carter et at., 1974;Wischmeier and Smith, 1958). Drops falling 2.1 mreach 5.25 m sec1 or 71 percent of the terminalvelocity achieved by raindrops in an unlimited fail(Laws, 1941). Simulated rainfall was applied at a rateof 88.2 mm hr1 for 30 mm to assure runoff from eachstudy plot. Rainfall was simulated six times(February 15 and 16; February 22; March 1 and 3;March 15 and 16; April 13 and 14; June 20 and 21) onsoil that was continuously frozen, diurnally frozen orunfrozen. The March 1 and 3 sampling was spreadover three days due to extreme weather conditions onMarch 2. Soil frost conditions remained constant overthis three day period, therefore no adjustment ofresults was necessary. Mean water temperatures used

for rainfall simulation were 5.8C in February and the1st of March, 10°C on March 15 and 16, 19.TC onApril 13 and 14, and 37°C on June 20 and 21. Runoffplots (254 x 254 mm) were randomly placed on sixcoppice, and six interspace soils for all sample datesexcept February 22 and March 1 and 3 when four andfive plots were placed on coppice soils and three andfive plots on interspace soils, respectively. This sam-pie size is considered adequate for rangeland condi-tions (Wood, 1987). Shrubs were cut at ground leveland removed from the coppice dunes to reduce rainfallinterception losses.

Infiltration rates were determined as the differencebetween simulated rainfall and runoff volumes at 2-minute intervals for 30 minutes. Thirty-minute infil-tration rates were calculated over the 28- to 30-minute time period and were assumed to representsteady state infiltration capacity. Samples of suspend-ed sediment were collected every 4 minutes for 30minutes, filtered through a 0.45 j.i filter, dried at105°C for 24 hours, weighed and converted to sedi-ment loss (kg ha—1-) as an index of interrill erosion.

Percent ground covered by cryptogams, grasses, lit-ter, and rock (> 0.50 mm diam.) was estimated foreach plot. Grasses, forbs, and cryptogams wereclipped at ground level, dried for 48 hours at 60°C,and weighed to determine above ground biomass. Soilbulk density of the 0 to 50 mm depth and antecedentsoil water of the 0 to 50 mm and 50 to 100 mm depthswere determined adjacent to each plot using a Troxiersurface density gage and gravimetric method, respec-tively (Gardner, 1986). Also, a soil sample from the 0to 50 mm depth immediately adjacent to each runoffplot was used for determination of soil texture by thehydrometer method (Bouyoucos, 1962), and aggregatestability by the vapor wetting, wet-sieve method(Kemper and Rosenau, 1986).

Soil frost at the 10, 50, and 100 mm depths wascharacterized as continuously frozen, diurnallyfrozen, or unfrozen using cyclindrical gypsum blocks(Gardner, 1986) and type E thermocouples (Taylorand Jackson, 1986) connected to data loggers. Sensorswere replicated four times in coppice and interspacesoils adjacent to the study site. Soil temperature wastaken adjacent to each plot immediately prior to therainfall simulation using a portable digital probethermometer (accurate to ± 0.3°C) and used to verif'the continuously recorded temperature data. Concretefrost was the only structural form of soil frostobserved on the plots and was subjectively classifiedaccording to criteria by Hale (1951) and Haupt (1967).The frost was characterized by dense thin ice lensesand ice crystals.

Analysis of variance and least significant differencemean separation tests (Steel and Torrie, 1980)were used to test for differences between infiltration

WATER RESOURCES BULLETIN 992

Spatial and Temporal Influence of Soil Frost on Infiltration and Erosion of Sagebrush Rangelands

capacity and interrill erosion of the coppice and inter-space soils for the different sample dates. Correlationanalysis (Draper and Smith, 1981) was used to assessmagnitude of linear association among variables.

RESULTS AND DISCUSSION

Surface soil texture was similar for coppice andinterspace soils (sand 50 percent, silt 41 percent, andclay 9 percent). Soil water content was significantlygreater in the coppice surface soil than in the inter-space soils for all sample dates except March 15 and16 (Table 1). Significant temporal trends in surfacesoil water were also found for both soils. All surfacesoils were at or near saturation during the first threesample dates, then progressively dried during theremaining sample dates.

Due to the saturated and unstable surface soil con-ditions that existed during the second and third sam-ple dates, bulk density samples were unable to betaken. The surface soils were in an expanded stateand would immediately collapse when disturbed. Bulkdensity was significantly greater for interspace soilsthan for coppice soils on all but the first sample date,and tended to increase with time for both soils (Table1). Aggregate stability was significantly greater incoppice soils than in interspace soils for all sampledates except February 22.

Cryptogams accounted for most of the surface coverand biomass (Table 2) on both coppice and interspacesoils. Biomass and cryptogam cover was significantlygreater on coppice than on interspace soils for allsample dates, but grass and litter cover were similarfor the two soils. Interspace cryptogam, litter, androck cover were similar for all sample dates.Percentage of the interspace areas covered by bare

ground was greatest the first three sample dates withthe third sample date being significantly greater thanthe fourth, fifth, or sixth sample dates (Table 3). thegreater bare ground cover and a nonsignificant trendfor lower cryptogam cover during the first three sam-ple dates may be explained in part by plant dormancy,but more importantly the interspace soils were satu-rated and dispersed from slaking. The slaked soilprobably covered part of the dormant cryptogams,thus increasing the percentage of bare ground (Eckertet at., 1989).

Coppice soils were frozen to 100 mm during thefirst three sample dates, then were unfrozen through-out the remainder of the study (Table 4). The inter-space soils were frozen on the first sample date withonly slight diurnal thawing occurring to a depth of 10mm in some locations. On the second sample date, theinterspace soils were still frozen but with diurnalthawing to a depth of 50 mm occurring more uniform-ly across the landscape. By the third sample date, theinterspace soils had thawed but were still experienc-ing diurnal freeze-thaw cycles to a depth of 50 mm.On the fourth sample date the interspace soils wereagain thawed with diurnal freezing to a depth of 10mm. The soils remained thawed for the fifth and sixthsample dates.

Infiltration capacity was significantly greater incoppice soils than in interspace soils for all sampledates except March 1 and 3 (Figure 1). Similar resultshave been reported for unfrozen soils by Blackburn(1975), Swanson and Buckhouse (1984), Johnson andGordon (1988), Thurow et al. (1986), and Wood et al.(1987), and for frozen soils by Blackburn and Wood(1990). Infiltration capacities for both coppice andinterspace soils were greater when unfrozen and welldrained in April and June than in February andMarch when the soils were frozen or recently thawed.In particular, infiltration capacities for interspace

TABLE 1. Surface Soil Water Content (percent), Bulk Density (Mg rn3) and Aggregate Stability (percent)for Coppice Dune (Cop) and Dune Interspace (Int) Soils at Each Sample Date, Reynolds, Idaho.

Sample Date

VariableSoil Water Bulk Density Aggregate Stability

Cop mt Cop mt Cop mt

February 15, 16 76.8a1 28.7a 0.97bt 1.O5bt 76.2a 58.4aFebruary 22 76.7a 28.Oa - - - - 54.4b 41.ObcMarch 1,3 71;4a 29.3a - - - 77.la 54.5abMarch 15, 16 23.Sbt 21.2bt 1.26a 1.40a 58.5b 38.lcApril 13, 14 17.9b 11.8c 1.25a 1.35a 73.3a 56.5aJune 20, 21 3.4b 1.8d 1.34a 1.41a 86.4a 54.6ab

- - No sample collected due to unstable saturated soils.Means followed by the same letter within columns for coppice dune or dune interspace are not significantly different (p <0.05).

* Coppice dune and dune interspace means for each variable and sample date followed byt are not significantly different (p < 0.05).

993 WATER RESOURCES BULLETIN

Blackburn, Pierson, and Seyfried

TABLE 2. Mean Above Ground Plant Biomass (kg nc-2) and Surface Cover (percent) of Grass, Cryptogam, Litter, andRock Cover for Coppice Dune (Cop) and Dune Interspace (Int) Soils at Each Sample Date, Reynolds, Idaho.

Surface Cover1Biomass Grass Cryptogam Litter Rock

Sample Date Cop mt Cop mt Cop mt Cop mt Cop mt

February 15, 16 1.4d2 O.2ab 3b* 7bc* 91a 22a 5ab* lla* la 12aFebruary 22 2.labc -. lbS 8abc5 94a 12a 5ab5 7a Oa 17aMarch 1, 3 1.8bcd - - 6b5 2c 92a 18a 2b5 12a5 On 8aMarch 15, 16 2.5a 0.4a 5b5 13ab 87a 30a 8ab5 ha5 Oa 17aApril 13, 14 1.8bcd O.lb 12a5 iSa5 77b 30a ha5 8a On 16aJune 20, 21 2.2ab O.2ab 7ab5 Sc5 88a 39a 5ab ha5 On 12a

- -1

2

No sample collected due to unstable saturated soils.Surface cover estimates do not include estimates of percent bare ground.Means followed by the same letter within columns for coppice dune or dune interspace are not significantly different (p <0.05).Coppice dune and dune interspace means for each variable and sample date followed are not significantly different (p <0.05).

TABLE 3. Mean, Range, and Coefficient of Determination (R2) for Interspace Interrill Erosion (kg ha—1)and Bare Ground (percent) for Each Sample Date, Reynolds, Idaho.

Interrili Erosion Bare GroundSample Date Mean Range Mean Range R2

February 15, 16 698b1 273-1130 48ab 20-80 0.34February 22 3996a 1765-5972 57ab 35-70 0.92March 1, 3 3464a 1082-7778 60a 23-94 0.61March 15, 16 644b 259-884 29b 10-45 0.78April 13, 14 688b 445-1017 31b 5-60 0.07June 20, 21 718b 239-1365 33b 23-48 0.40

1 Means followed by the same letter within columns are not significantly different (p <0.05).

soils were initially low due to the presence of soilfrost, then remained low after the surface soil hadthawed due to saturated surface soil conditions main-tained by diurnal freeze-thaw cycles. In soils withhigh water contents, diurnal freeze-thaw cycles canmove significant amounts of water from lower depthsupward toward the soil surface due to soil watermovement toward the freezing front (Cary et al.,1979). If the soil water content is low, then the freez-ing front moves more rapidly down through the soilprofile and very little water is transported upward.Pikul and Alimaras (1985) working on a Walla Wallasilt loam soil in Oregon found that one six-hour freez-ing period was enough to raise the volumetric watercontent of the 2.5 mm soil surface layer from 0.31 to0.57 m3 m3. They also found that as the soil dried,water movement toward the surface became negligi-ble.

Interrill erosion was significantly greater frominterspace soils than from coppice soils for all sampledates (Figure 2). Erosion from interspace soils wassimilar for all sample dates characterized by either

continuous frost (February 15 and 16) or by thawedand well drained surface soil conditions (March 15,April 13, and June 20). Erosion from the interspaceswas greatly accelerated during the second and thirdsample dates (February 22 and March 1 and 3) whichcorresponded with the period of strong diurnal freeze-thaw cycles, high surface soil water contents (Figure3), and high bare ground (Table 3). The recurrent sat.-urations of the surface soil during this period (Figure3) and the resultant slaking, created a surface soilthat; was very susceptible to water erosion. This con-dition has been reported by Eckert et al. (1989), forinterspace Type III soils. This period was probablyalso characterized by low bulk density and aggregatestability; however, methods are not currently avail-able which accurately measure these variables in thefield during such periods.

In addition, the interspace surface soil varied bysample date in the degree of surface crusting, vesicu-lar porosity, and bare ground. Commonly a greaterpercentage of bare ground is accompanied by agreater degree of crusting, vesicular porosity, and

WATER RESOURCES BULLETIN 994

Spatial and Temporal Influence of Soil Frost on Inifitration and Erosion of Sagebrush Rangelands

erosion (Eckert et al., 1989). Bare ground was poorlycorrelated with interrill erosion when the soil wasfrozen (sample date one) and when the surface soilwas dry, consulated, and crusted (sample dates fiveand six) (Tables 3 and 4). Percent bare ground, how-ever, was highly correlated with interrill erosion dur-ing periods of diurnal freeze-thaw and high surfacesoil water content (sample dates two and three) aswell as the following period (sample date four) whenthe soil was moist and experiencing some diurnalfreeze-thaw cycles, but was not consulated and crust-ed.

Sample Date

Copplce Dune Duna Interspace10

mm50

mm100mm

10mm

50mm

100mm

Februaryl516

FF

FF

FF

DFDF

FF

FF

February22 F F F DF DF F

Marchi3

FF

FF

FF

DFDF

TDF

TT

March1516

TT

TT

TT

DFDF

TT

TT

April1314

TT

TT

TT

TT

TT

TT

June2021

TT

TT

TT

TT

TT

TT

Interrill erosion from coppice soils was relativelylow for each sample date, but was significantly higheron the fourth sample date (March 15 and 16, Tables 1and 3, Figure 2) after the surface soil had thawed andwas at a high water content. Thus, the coppice soilsalso showed a slight increase in susceptibility to ero-sion under similar surface soil conditions as thosefound in the interspace soils during the February 22and March 1 and 3 sample dates.

The freeze-thaw period when these soils are partic-ularly susceptible to erosion can vary in lengthdepending on yearly climatic conditions. For the win-ter of 1989, this period occurred over 19 days fromFebruary 17 through March 7 (Figure 3). Diurnalfreezing was observed beyond March 7 (March 15through 18), but the surface soil water content had

been reduced enough to prevent any appreciable soilwater movement upward to the surface, thus prevent-ing saturated and slaked surface soil conditions.

EE

0z0

ILz

995 WATER RESOURCES BULLETIN

TABLE 4. Frost Condition of the Coppice Dune and DuneInterspace Surface Soil at 10,50, and 100 mm Depths

for Each Sample Date, Reynolds, Idaho.

2/15 2/22 3/1 3/15 4/13 6/20DATE (1989)

Figure 1. Mean Infiltration Capacity by Sample Date for ShrubCoppice Dune and Dune Interspace Soils. Means with the sameletter for coppice dune or interspace across sample dates are notsignificantly different (p < 0.05). Means with an for the samesample date arenot significantly different (p <0.05).

= continuously frozen, DF = diurnally frozen, T = unfrozen. Allfrozen soils were classified as concrete frost.

ro 4000-Ca 3500

3000z22500(no 2000

Wi500

100050o

— — COPPICEa — INTERSPACE

0

b b b

aflb cb !j1 ;fl2/15 2/22 3/1 3/15 4/13 6/20

DATE (1989)

Figure 2. Cumulative Interrill Erosion Over a 30.Minute Intervalby Sample Date for Shrub Coppice Dune and Dune InterspaceSoils. Means with the same letter for coppice dune or dune inter.space soils across sample dates are not significantly different (p <0.05). Interrill erosion values between coppice dune and dune inter-space were significantly different (p < 0.05) for each sample date.

Blackburn, Pierson, and Seyfried

DAY OF YEAR (1989)

Figure 3. Hourly Soil Temperature at the 1-cm Depth (—) onEach Day and Surface Soil Water Contents (.—.) for Each ofthe First Four Sample Dates U) Within the Interspace Soil. Theperiod of high erosional susceptibility is also outlined.

LITERATURE CITED

Achouri, M. and G. F. Gifford, 1984. Spatial and Seasonal Variabil-ity of Field Measured Infiltration Rates on a Rangeland Site inUtah. Journal of Range Management 37:451-455.

Blackburn, W. H. and M. K. Wood, 1990. Influence of Soil Frost onInfiltration of Shrub Coppice Dune and Dune Interspace inSoutheastern Nevada. Great Basin Naturalist 50:41-46.

Blackburn, W. H., 1975. Factors Influencing Infiltration andSediment Production of Semi-Arid Rangelands in Nevada.Water Resources Research 11:929-937.

Blackburn, W. H., R. 0. Meeuwig, and C. M. Skau, 1974. A MobileInifitrometer for Use on Rangeland. Journal of Range Manage.ment 27:322-323.

Bouyoucos, G. J., 1962. Hydrometer Method Improved for MakingParticle Size Analysis of Soil. Agronomy Journal 54:464-465.

Bullock, M. S., W. D. Kemper, and S. D. Nelson, 1988. Soil Cohesionas Affected by Freezing, Water Content, Time and Tillage. SoilScience Society of America Journal 52:770-776.

Carter, C. E., J. E. Greer, H. J. Braud, and J. M. Flogy 1974.Raindrop Characteristics in South Central United States.Transactions of American Society of Agricultural Engineers17:1033-1037.

Cary, J. W., R. I. Papendick, and C. S. Campbell, 1979. Water andSalt Movement in Unsaturated Frozen Soil: Principles and FieldObservations. Soil Science Society of America Journal 43:3-8.

Draper, N. R. and H. Smith, 1981. Applied Regression Analysis.John Wiley and Sons, Inc., New York, New York.

Eckert, R. E., Jr., F. F. Peterson, and J. T. Belton, 1986. RelationBetween Ecological Range Condition and Proportion of SoilSurface Types. Journal of Range Management 39:409-414.

Eckert, R. E., Jr., F. F. Peterson, M. K. Wood, W. H. Blackburn, andJ. L. Stephens, 1989. The Role of Soil-Surface Morphology in theFunction of Semiarid Rangelands. Nevada AgriculturalExperiment Station Technical Bulletin (TB-89-01), University ofNevada, Reno.

Formanek, G. E., D. K. McCool, and R. I. Papendick, 1984. Freeze-Thaw and Consolidation Effects on Strength of a Wet Silt Loam.Transactions of the American Society of Agricultural Engineers27:1749-1752.

Gardner, W. H., 1986. Water Content. In: Methods of Soil Analysis:Physical and Mineralogical Methods, A. Kiute (Editor).Agronomy Series Number 9 (Part 1), Soil Science Society ofAmerica, Madison, Wisconsin, pp.493-544.

Hale, C. E., 1951. Further Observations on Soil Freezing in thePacific Northwest. Pacific Northwest Forest and RangeExperiment Station Research Note No. 74, Portland, Oregon.

Haupt, H. F., 1967. Infiltration, Overland Flow and Soil Movementon Frozen and Snow-Covered Plot. Water Resources Research3:145-161.

Hess, W. N., 1974. Weather and Climate Modification. John Wileyand Sons, New York, New York.

Johnson, C. W. and N. E. Gordon, 1988. Runoff and Erosion FromRainfall Simulator Plots on Sagebrush Rangeland. Transactionsof the American Society of Agricultural Engineers 31:421-427.

Kemper, W. D. and R. C. Rosenau, 1986. Aggregate Stability andSize Distribution. In: Methods of Soil Analysis: Physical andMineralogical Methods, A. Klute (Editor). Agronomy SeriesNumber 9 (Part 1), Soil Science Society of America, Madison,Wisconsin, pp. 425-442.

Laws, J. D., 1941. Measurements of the Fall-Velocity of Water-Drops and Raindrops. Transactions of the American GeophysicalUnion 22:709-721.

Mostaghimi, S., R. A. Young, A. R. Wilts, and A. L. Kenimer, 1988.Effects of Frost Action on Soil Aggregate Stability. Transactionsof the American Society of Agricultural Engineers 31:435-439.

Papendick, R. I., D. K. McCool, and H. A. Krauss, 1983. SoilConservation: Pacific Northwest. In: Dryland Agriculture,

WATER RESOURCES BULLETIN 996

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SUMMARY AND CONCLUSIONS

Significant spatial and temporal differences ininfiltration capacity and interrill erosion were foundfor coppice and interspace soils within a sagebrush-grass plant community. Infiltration was generallyhigher for coppice soils compared to interspace soilsthroughout the year. Infiltration capacities for bothsoils were lowest early in the year when the soil wasfrozen or saturated, then increased as the soil dried inthe spring and summer.

Interrill erosion was consistently lower for coppicesoils compared to interspace soils. Erosion from inter-space soils was highest (3500 to 4000 kg ha) duringthe period in late winter characterized by diurnalfreeze-thaw cycles. The surface soil during this timeremained in a saturated or super-saturated state dueto water being drawn up to the soil surface from sub-surface layers during each recurrent freeze-thawcycle. Freeze-thaw processes also caused slaking ofsurface soil aggregates, thus increasing the soilsusceptibility to erosion. This period lasted for a pro-longed 19-day period from February 17 throughMarch 7, 1989. If an intense storm or rapid snowmeltwere to occur during a period of high erosional sus-ceptibility, an extreme erosional event could occur.

Spatial and Temporal Influence of Soil Frost on Inifitration and Erosion of Sagebrush Rangelands

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