Effects of Tillage and Rainfall Simulation Date on Water and Soil Losses1

B. J. ANDRASKI, D. H. MUELLER, AND T. C. DANIEL2

ABSTRACTTime of data collection relative to recent tillage may influence

results of studies comparing water and soil losses among tillagesystems. In this study a rainfall simulator was used at various timesduring the growing season over a 4-yr period: (i) to compare waterand soil losses from conventional (moldboard plow; CN) and threeconservation tillage (CT) treatments: chisel plow (CH), (ill-plant(TP), and no-till (NT) and (ii) to observe major trends in runoffvolumes as a function of rainfall simulation date. Above-ground por-tions of corn (Zea mays L.) plants were removed prior to rainfallsimulation. Trials were conducted in September 1980, June and July1981, October 1982, and June and July 1983. Runoff volumes forCT treatments were consistently less than those observed for CN.For CT treatments, the volume of runoff (per unit rainfall) averaged11, 20, and 52% lower than that observed for CN for the June 1983,July 1981 and 1983, and October 1982 sampling periods, respec-.lively. Only the CH treatment significantly reduced runoff relativeto CN soon after planting. Among CT treatments, CH was signifi-cantly more effective in reducing runoff in September 1980. For theremaining sampling periods, differences among CT treatments werenot significant. An increase in residue cover consistently resulted ina decrease in sediment concentrations and, most often, a decreasein soil loss. Across all sampling periods, the NT treatment consist-ently decreased soil loss by 80 to 90% relative to CN, while soillosses for the CH and TP treatments varied, ranging from about 45to 90% less than those for CN. Only in September 1980 did lowrunoff for CH result in soil loss which was less than that observedfor NT.

Additional Index Words: chisel plow, till-plant, no-till, conser-vation tillage, runoff, erosion, sediment.

Andraski, B.J., D.H. Mueller, and T.C. Daniel. 1985. Effects of til-lage and rainfall simulation date on water and soil losses. Soil Sci.Soc. Am. J. 49:1512-1517.

CONSERVATION TILLAGE (CT) systems, which leavesome or all of the previous year's crop residue

on the soil surface, have become increasingly popularin the Midwest. In Wisconsin, approximately 20% ofcorn land is under some form of CT, and since 1976the use of such practices has increased at an averageannual rate of 80 000 ha. Three promising CT systemsinclude chisel plow (CH), till-plant (TP), and no-till(NT).

Studies on field plots under simulated and naturalrainfall and on small watersheds have shown that, al-most without exception, CT systems in general can behighly effective in reducing soil losses relative to thatfor the conventional (CN) system (Onstad, 1972;Romkens et al., 1973; Siemens and Oschwald, 1976;Laflen et al., 1978; Johnson and Moldenhauer, 1979;Laflen and Colvin, 1981; McGregor and Greer, 1982;Mueller et al., 1984). Past research by Wischmeier(1973) and Laflen et al. (1978) has indicated that the

' Research supported by the College of Agricultural and Life Sci-ences, Univ. of Wisconsin-Madison. Received 26 Oct. 1984. Ap-proved 16 June 1985.2 Research Assistant, Program Coordinator, and Professor, re-spectively, Dep. of Soil Science, Univ. of Wisconsin-Madison, Mad-ison, WI 53706.

percent of soil surface covered by residue is the bestmeasure for distinguishing between CT systems. How-ever, Cogo et al. (1984) have shown the importanceof factors other than residue cover, including soilroughness and placement of residues, when evaluatingsoil losses for CT systems.

Specifically, the often-reported effectiveness of NTin reducing sediment concentrations and soil losses,relative to other CT systems, has been mostly ascribedto increased residue cover (Laflen et al., 1978; Laflenand Colvin, 1981). However, the effectiveness of theNT system in reducing runoff volumes has been highlyvariable. Several studies have shown reduced runofffrom the NT system (Johnson et al., 1979; Langdaleet al., 1979; McGregor and Greer, 1982). Other studieshave reported little reduction or, in some cases, in-creased runoff from NT relative to the CN system(Siemens and Oschwald, 1976; Laflen and Colvin,1981; Lindstrom et al., 1981; Mueller et al., 1984).Increased runoff has been attributed to the interactioneffects of NT on surface residue and physical condi-tions of the soil. The effectiveness of surface residuein enhancing water infiltration through surface pro-tection is at least partially offset by higher NT bulkdensities which reduce plow layer porosity and satu-rated hydraulic conductivity (Lindstrom and Onstad,1984), which can promote rapid water runoff.

The CH and TP systems may also substantially re-duce soil losses compared to CN tillage (Onstad, 1972;Romkens et al., 1973; Wischmeier, 1973; Siemens andOschwald, 1976; Griffith et al., 1977; Johnson andMoldenhauer, 1979). Relative to CN, CH and TP havereduced both sediment concentrations and runoff vol-umes. Several studies, in which tillage was performedacross slope, have reported that soil loss reductionsfor the CH system were similar to those for NT, whileTP was somewhat less effective than either system(Romkens et al., 1973; Wischmeier, 1973; Griffith etal., 1977). Although sediment concentrations werelower for NT, CH was more effective in reducing run-off. Decreased runoff for the CH system has been at-tributed to increased surface roughness and macro-pore space and continuity (Romkens et al., 1973;Siemens and Oschwald, 1976; Johnson and Molden-hauer, 1979; Lindstrom et al., 1981; Mueller et al.,1984). In contrast, Laflen et al. (1978) found the CHand TP systems to be much less effective than NT inreducing soil loss. In their study, little difference inrunoff was observed among tillage systems. Conse-quently, the much lower sediment concentrations ob-served for NT resulted in much lower soil losses thanthose for CH and TP. Laflen et al. (1978) stated thatsoil loss from TP would likely be much less than thatfrom CN if field operations had been contoured. Re-search by Onstad (1972) supported this contention inthat runoff and soil losses were observed to be twoand four times less, respectively, from contoured TPplots compared to up- and down-slope TP plots. Thus,differences in a tillage system's ability to reduce runoffvolumes can, at times, have major effects on soil losses.

1512

ANDRASKI ET AL.: EFFECTS OF TILLAGE AND RAINFALL SIMULATION DATE ON WATER AND SOIL LOSSES 1513

Differing surface conditions among treatments at thetime of data collection may contribute to inconsistentresults among tillage studies, particularly in terms ofrunoff. These conditions may include differences insoil roughness and porosity, surface storage, and thedegree of surface crusting. Increased surface roughnessand porosity have resulted in decreased runoff (Bur-well et al., 1968; Burwell and Larson, 1969). Depres-sion storage resulting from a roughened and/or con-tour-ridged or furrowed surface also improvesinfiltration by increasing surface water detention (On-stad, 1972). However, the effectiveness of an initiallyrough and porous surface has been observed to de-crease due to rainfall and/or fall-to-spring weatheringwhich broke down clods, causing surface crust devel-opment (Burwell et al., 1968; Burwell and Larson,1969). Thus, time of data collection relative to recenttillage may influence results of studies comparing waterand soil losses among tillage systems.

Little data are available showing the relative effec-tiveness of CT systems under simulated rainfall con-ditions over the growing season or from year-to-yearfollowing initial implementation of a given system.Because of this, simulated rainfall was applied at var-ious times during the growing season over a 4-yr pe-riod: (i) to evaluate the comparative effectiveness ofCH, TP, and NT systems in reducing runoff and soillosses relative to those of CN, and (ii) to observe ma-jor trends in runoff volumes as a function of rainfallsimulation date.

MATERIALS AND METHODSThe study site was located on the Arlington Experimental

Farm near Arlington, WI on a Griswold silt loam (fine-loamy,mixed, mesic Typic Argiudoll) with a 6% slope. Particle-sizedistribution for the top 18 cm of this soil is 22.0% clay,63.8% silt, and 14.2% sand with 3.9% being very fine sand(SCS, 1967). A soil erodibility K value of 0.046 t ha h (haMJ mm)"1 was estimated from the soil erodibility nomo-graph of Wischmeier and Smith (1978). Four tillage treat-ments replicated four times were randomly assigned to 10.6-by 22.1-m plots. The plots were established so that all tillageand planting operations were performed 2% off-contour withborder areas of approximately 9 m at each end and 5 mabove and below each plot.

Prior to initiating this study, the site was cropped to con-tinuous corn (Zea mays L.) for 5 yr using a conventionaltillage system, and residues had been removed each year. Inthe spring of 1980, corn residue was distributed by hand onall plots prior to spring tillage and/or planting operations.Thereafter, stalks were chopped in late November and allresidues were left. Tillage treatments investigated were con-ventional (CN), chisel plow (CH), till-plant (TP), and no-till(NT). Conventional was moldboard plowed to a depth of20 cm, and CH plots were chiseled with a twisted-shankplow (38-cm spaced shanks) to a depth of 24 cm. Plowingof the CN and CH treatments was done in the spring of1980 and in the fall preceding each subsequent growing sea-son. The CN treatment was disked twice, and the CH treat-ment once, to a depth of approximately 10 cm, prior toplanting. Till-plant was planted in a 25-cm wide seedbedusing a sweep on 15-cm ridges which were formed with cul-tivation operations in early November of the precedinggrowing season. No-till received no tillage and was plantedin a 10-cm wide seedbed using a double-disk opener. Cornwas planted on all plots in rows 91 cm apart. Planting dates

were 15 May 1980, 6 May 1981, 12 May 1982, and 25 May1983. Fertilizer, herbicides, and pesticides were applied withthe planting operation. Bulk densities, 0 to 7.6-cm depthimmediately after planting, for the CN, CH, TP, and NTtreatments were 1.17, 1.27, 1.31, and 1.39 Mg m "3, respec-tively, and water contents at saturation were 0.46, 0.42, 0.39,and 0.36 kg kg"1, respectively (Johnson et al., 1984).

Simulated rainfall was applied to each of the 1.35 m2 testareas using a modified Purdue sprinkling infiltrometer (Dixpnand Peterson, 1965) that included a rotating shutter (Rawitzet al., 1972) which provided flexibility with respect to rain-fall intensity selection. Each test area contained a single cornrow. Rainfall simulation was performed in late September1980, early June and early July 1981, mid-October 1982,and mid-June and mid-July 1983. In 1980 and 1982, onetest area within each plot was used. Duplicate test areaswithin each plot were used in 1981 and 1983, with June andJuly simulations being conducted in the same area. Prior torainfall simulation corn plants were cut from within testareas. Test areas were covered when natural rainfall eventswere expected prior to and during a given sampling period,thus allowing for consistent antecedent rainfall conditionsamong all test areas. In 1980 and 1982, this involved ap-proximately 7 d prior to and during the set of simulationruns. In 1981 and 1983, this involved the time from plantingthrough completion of the July sampling periods. Moderateintensity simulated rainfall was applied in 1980, 1981, 1982,and July 1983. The average application rate and energy, re-spectively, was 73 ± 9 mm h"1 and 0.098 MJ (ha mm)"1

except for the October 1982 simulation, where mechanicalproblems caused a somewhat higher application rate andenergy of 90 ± 6 mm h~' and 0.121 MJ (ha mm),"1, re-spectively. In June 1983, a high intensity of 136 ± 8 mmh"1 [0.182 MJ (ha mm)"1] was applied. Runoff generated bythe simulator and test conditions used in this study haveshown relative trends among treatments to be similar to thatgenerated by natural rainfall (Andraski et al., 1985).

Total runoff during each 1-h simulated rainfall event wascollected by a vacuum system (Dixon and Peterson, 1968)and the volume measured. A 1-L subsample of the totalrunoff suspension was obtained for analyses. Sediment con-tent was determined by drying an aliquot of runoff suspen-sion at 105°C and weighing the residue. Results were cor-rected for dissolved solids content (296 mg L"1). Soil losswas estimated as the product of the measured runoff volumeand the sediment concentration in the total runoff collected(Wendt and Corey, 1980).

Surface residue cover after planting was estimated by themeterstick method (Hartwig and Laflen, 1978) in 1980 andby projecting photographs of the soil surface onto a grid(Laflen et al., 1981) in subsequent years.

Antecedent soil moisture samples were taken in adjacentareas treated similarly to test areas. Samples for the TP treat-ment were obtained at the midpoint between the existingvalley and ridge-top. In 1980, June 1981, and 1983 moisturewas determined gravimetrically on soil collected to a depthof 7.6 cm and in 1982 by tensiometers placed at a depth of15 cm. Tensiometer readings were converted to percent waterby weight from moisture retention curves (Johnson et al.,1984) and bulk density measurements (R. Hilfiker, unpub-lished data) made at the study site.

Data were analyzed using a one-way analysis of varianceprocedure in 1980 and 1982, and a one-way analysis of var-iance with subsampling in 1981 and 1983 (Steel and Torrie,1980). Data for each sampling period were analyzed sepa-rately. Logarithmic transformations of sediment concentra-tions and soil losses were made prior to analyses to obtaingreater homogeneity among sample variances. Treatmentmeans were compared using Fisher's least significant differ-ence test (Steel and Torrie, 1980).

1514 SOIL SCI. SOC. AM. J., VOL. 49, 1985

Table 1. Corn residue cover after planting for each yearby tillage method.

Tillage method 1980 1981 1982 1983 Avg

Table 2. Surface runoff losses for each measurement periodby tillage method.

ConventionalChiselTill-plantNo-till

6at57b33c69d

2a32b23c62d

—— % ——4a

32b29b55c

la25b29b78c

3372966

t Values within each year that are followed by the same letter are not sig-nificantly different atp = 0.1, as determined by Fisher's least significantdifference test.

RESULTS AND DISCUSSIONAlthough the data were collected at various sam-

pling times during a 4-yr period, they are presented inchronological order. This is done to aid interpretationof major trends which were apparent from year to yearor within a given year.

Residue coyer values (Table 1) were typical of thosereported for similar treatments (Romkens et al., 1973;Wischmeier, 1973; Laflen et al., 1978), with the ex-ception of the high residue cover value for CH in 1980.This high value was attributed to hand spreadinggreater amounts of corn residue on CH plots prior totillage than is typically left after normal stalk choppingoperations.

Runoff VolumesTotal runoff volumes (Table 2) were affected by til-

lage treatments. The CT treatments consistently hadlower average runoff volumes than did the CN treat-ments at all sampling periods. Runoff volumes for allthree CT treatments were significantly lower in all buttwo cases, both of which occurred at the early sam-pling periods, June 1981 and June 1983 (Table 2). Lowantecedent soil moisture in June 1981, caused by dryspring conditions, resulted in very low total runoff forall tillage treatments. Antecedent soil moisture for thissampling period decreased in the order: NT (10.8 kgkg-1) > TP (7.9 kg kg-') > CH (7.2 kg kg~')> CN(5.7 kg kg"1), with NT significantly higher than alltreatments and TP significantly higher than CN. How-ever, antecedent soil moisture showed no apparent af-fect on runoff volumes among treatments. A high in-tensity storm was used in June 1983. Only the CHtreatment produced runoff volumes that were signifi-cantly lower than CN. Antecedent soil moisture con-tents in June 1983 were not significantly differentamong treatments, avg 22.0 ± 1.3 kg kg"1. Johnsonet al. (1984) reported that the soil for the CN treat-ment at this site was more porous (immediately afterplanting and before crusting) than that for CT treat-ments, which had soil porosities decreasing in the or-der CH, TP, NT. Although initial porosity was highestfor the CN treatment, total accumulative infiltrationwas apparently limited by a greater degree of surfacesealing caused by simulated rainfall, relative to the CTtreatments. Even under this high intensity storm, itappears that partially incorporating surface residueswith the chisel plow allowed for maintenance of in-filtration rates which resulted in lower runoff losses.In contrast, lower initial porosity of TP and NT ap-parently limited total infiltration for these treatments.In June 1983, CH, NT, and TP reduced runoff by 37,

Tillage method

ConventionalChiselTill-plantNo-till

1980

Sept.

61atlie37b40b

1981 1982t

June

2atr§ala

tr a

July

26a5b9b4b

Oct.

68a22b22b21b

1983T

June

60a38b48ab47ab

July

20a12b12b9b

t Simulated rainfall intensity of 90 ± 6 mm h'1 for October and 136 ± 8mm h~' for June, remaining intensities were 73 ± 9 mm h"1.

t Values for each measurement period that are followed by the same letterare not significantly different at p = 0.1, as determined by Fisher'sleast significant difference test.

§ tr = trace (< 1 mm).

22, and 20%, respectively, relative to CN. Similar orincreased effectiveness of these CT systems at earlysampling periods has been reported by Romkens etal. (1973).

Within each of the July sampling periods, the CTtreatments were found to be equally effective in sig-nificantly reducing runoff relative to CN (Table 2). InJuly 1981, antecedent soil moisture was not measured,arid in July 1983 moisture contents were not signifi-cantly different among treatments, averaging 21.1 ±1.3 kg kg"1. Runoff volumes for the CT treatmentsavg 77 and 45% less than that for CN in July 1981and July 1983, respectively.

In October 1982, the CT treatments were also equallyeffective in controlling runoff, resulting in a 68% avgreduction relative to CN (Table 2). Antecedent soilmoisture for this sampling period decreased in the or-der: NT (29.3 kg kg-1) > CH (28.6 kg kg-1) > TP(21.1 kg kg-1) > CN (20.5 kg kg"1), and NT and CHwere significantly greater than TP and CN. Once againantecedent moisture showed no apparent effect onrunoff volumes among treatments. The other late sam-pling period (September 1980) resulted in the only in-stance where runoff volumes were significantly differ-ent among CT treatments. In September 1980, TP andNT runoff volumes were significantly greater than thatof CH (Table 2). Antecedent soil moisture contentsfor this sampling period were not significantly differ-ent among treatments, avg 18.6 ± 0.9 kg kg"1. Thereason for the significant difference in runoff volumesamong CT treatments was apparently due to the sur-face conditions of the CH, TP, and NT plots. First,spring plowing and relatively high surface residue (Ta-ble 1) appear to have effectively increased infiltrationrates for the CH treatment. In addition, a soil crustwhich would have developed prior to hand distribu-tion of residue was not broken up by tillage on the TPand NT plots. Borst and Woodburn (1942) demon-strated that the effectiveness of surface mulch in con-trolling runoff was reduced when mulch was placedon a crusted soil. Although residue cover values weretypical for the NT and TP treatments (Table 1), theunderlying soil surface conditions probably caused therelatively high runoff losses from these treatments inSeptember 1980.

The effect of rainfall simulation date on runoff vol-umes among treatments was evident in our study. Dueto varying simulated rainfall intensities among sam-

ANDRASKI ET AL.: EFFECTS OF TILLAGE AND RAINFALL SIMUALTION DATE ON WATER AND SOIL LOSSES 1515

pling periods, these relative trends may best be viewedin terms of runoff per unit rainfall. For the CT treat-ments, the volume of runoff (per unit rainfall) avg 11,20, and 52% lower than that observed for CN for theJune 1983, July 1981 and 1983, and October 1982sampling periods, respectively. Relative to the CTtreatments, the lack of surface residue for CN allowedfor greater development of a surface seal caused byredistribution of soil particles during rainstorms anda surface crust caused by drying of the soil surfacelayer. This greater degree of surface sealing and/orcrusting on the CN plots apparently resulted in anincrease in the magnitude of runoff differences be-tween CN and CT treatments later in the season. Sim-ilar results were reported by Burwell and Larson (1969).Surface sealing prior to the July sampling periods re-sulted from the preceding simulated storm in June.Surface sealing and crust development prior to the latesampling periods (September 1980 and October 1982)occurred under natural rainfall and canopy develop-ment. In September 1980, a very strong surface crusthad developed on the CN plots following naturalstorms (recurrence intervals of 1, 1, and 25 yr) whichoccurred within 14 d preceding plot covering. Relativeto the other sampling periods, this crust formationresulted in the highest (84%) runoff volume per unitrainfall for CN.

The influence of time of data collection on runoffvolumes was also indicated by improved runoff re-ductions for TP and NT following the 1980 study year.This may be attributed to normal soil amelioratoryprocesses (freezing and thawing, wetting and drying,or earthworm activity) which would improve infiltra-tion and thus decrease runoff. In addition, the surfacecrust which would have developed on TP plots wasbroken up by ridging/cultivation operations at the endof each growing season. In contrast, Lindstrom et al.(1981) observed a consolidated NT soil surface, whichpersisted for 10 yr after converting from a conven-tional tillage system, resulted in high runoff losses.These results indicate that it may be advisable to per-form some type of tillage prior to initial implemen-tation of a no-till system.

Different soil surface factors appeared to have vary-ing importance in reducing runoff for each of the CTtreatments under the site and soil conditions of thisstudy. The CH treatment combined residue cover,partial incorporation of residue, and across-slope ridgeswhich persisted with time. Till-plant had residue covervalues which were, in most cases, similar to CH, butmore substantial and stable ridges (across-slope). TheNT treatment had a relatively smooth surface but highamounts of residue cover. The interaction effects ofthese factors on soil porosity at the time of samplingappear to explain the runoff-reducing effectiveness ofeach CT treatment within a given sampling period.

The CN treatment was never effective in reducingrunoff. Differences in runoff volumes between CN andthe CT treatments increased with time over the grow-ing season. Among the CT treatments, differences inrunoff volumes decreased later in the growing seasonfollowing the first year of this study. These runoff re-sults indicate that relative relationships among treat-ments may change from one time to another within

Table 3. Sediment concentrations and soil losses for eachmeasurement period by tillage method.

Tillage method

1980

Sept.

1981T

June July

1982J

Oct.

1983J

June July

Sediment concentration, g L~'ConventionalChiselTill-plantNo-till

3.79a§2.81a3.62a1.17b

18.431

8.55

53.51a11.25b15.57b10.95b

7.48a2.92b3.28b2.04b

4.89a2.92b2.32b0.77c

2.59a2.40a2.06a0.88b

Soil loss, g nr2

ConventionalChiselTill-plantNo-till

242a§27b

135a48b

19atr#blOatr b

1414a64c

151b40c

508a65b66b44b

294a117b115b32c

53a29ab21b

7c

t Field sampling problems possibly resulted in high sediment concentra-tions and soil losses for all treatments.

t Simulated rainfall intensity of 90 ± 6 mm h~' for October and 136 ± 8mm h'1 for June, remaining intensities were 73 ± 9 mm h"1.

§ Values for each measurement period that are followed by the same letterare not significantly different atp = 0.1, as determined by Fisher's leastsignificant difference test.

1 Value is average of seven and three observations for CN and TP, re-spectively, where measurable runoff occurred. No value for CH and NTbecause of insufficient sample for analysis.

# tr = trace.

the cropping year. Applying simulated rainfall onlyearly in the year would have underestimated the run-off-reducing effectiveness of the CT treatments, par-ticularly TP and NT, relative to CN. Such changes inrunoff relationships within the cropping year could alsohave major implications in terms of evaluating therelative relationships of soil and chemical losses amongtillage systems.

Soil LossesSediment concentration and soil loss data are pre-

sented in Table 3. Statistical analysis was not per-formed on June 1981 sediment concentration data be-cause of low runoff which resulted in insufficientsample volumes. In addition, field sampling problemsin 1981 possibly resulted in the high sediment con-centrations and soil losses reported for June and July.As a result, data for 1981 are presented without furtherdiscussion, with detailed discussion being centered onthe remaining four sampling periods.

Sediment concentrations were consistently highestfor CN, intermediate for CH and TP, and lowest forNT (Table 3). Soil losses generally followed this sametrend. In June and July 1983, the NT treatment wassignificantly more effective in reducing soil loss thanCH and TP due to significantly lower sediment con-centrations (Table 3). For these sampling periods, CHand TP also reduced soil loss relative to CN. However,in July 1983, the difference between CH and CN wasnot significant as a result of similar sediment concen-trations.

In October 1982, all CT treatments significantly re-duced sediment concentrations and soil losses relativeto CN. For this sampling period, differences in soilloss among CT treatments were not significant due tocomparable runoff volumes and sediment concentra-tions. Sediment concentrations for CN and NT wererelatively low in September 1980 compared to thosemeasured in October 1982, while sediment concen-trations for CH and TP were similar between the mea-

1516 SOIL SCI. SOC. AM. J., VOL. 49, 1985

surement periods (Table 3). The strong surface crustwhich had developed on CN plots prior to the Sep-tember 1980 sampling period apparently limited thedetachment capacity of the raindrops delivered by thesimulator. Similarly, presence of a surface crust priorto residue distribution may have led to the relativelylow sediment concentration for NT. As a result, sed-iment concentrations among the CN, CH, and TPtreatments were not significantly different, and therunoff reduction afforded by the TP treatment was notsubstantial enough to significantly reduce soil loss rel-ative to CN (Table 3). In contrast, significantly lowerrunoff for CH resulted in soil loss which was less thanthat for NT.

Across all sampling periods, the NT treatment con-sistently decreased soil loss by 80 to 90% relative toCN, while soil losses for the CH and TP treatmentsvaried, ranging from about 45 to 90% less than thosefor CN. Thus, rainfall simulation date had little influ-ence on NT soil loss reductions relative to CN. Al-though relative soil loss reductions for CH and TP didvary, no consistent trends were observed to explainthis variability as a function of rainfall simulation date.With the exception of the 1st yr of this study, trendsin soil losses among treatments generally followedthose for sediment concentrations more closely thanthose observed for runoff volumes.

The importance of surface residue cover in reducingsoil loss has been demonstrated by Wischmeier (1973)and Laflen et al. (1978). Sediment concentration andsoil loss results from this study also show that residuecover influenced the relative ranking of these two pa-rarneters. Within each sampling period an increase inresidue cover consistently resulted in a decrease insediment concentrations and, most often, a decreasein soil loss. Although NT generally provided the great-est decrease in soil loss relative to CN, soil losses forthe CH and TP systems, on the average, were about65% less than those for CN. These results imply thatCH and TP systems, which leave approximately 25 to30% residue cover and are implemented across-slope,may also provide substantial soil loss reductions rel-ative to CN. Such findings are important in cases wherefarmers are reluctant to adopt a tillage system such asNT, which leaves larger amounts of residue on thesoil surface.

SUMMARYResults of this study show that runoff volumes for

the CT treatments were consistently less than thosefor CN. The magnitude of the difference between theCN and CT treatments increased at later sampling pe-riods relative to those measured soon after planting,being attributed to an increasing degree of surfacecrusting with time on CN plots. Relative to CN, onlythe CH treatment significantly reduced runoff soonafter planting. Among CT treatments, differences inrunoff volumes were generally not significant. Therunoff-reducing effectiveness of TP and NT was ob-served to improve following the 1st yr of our study.This was attributed to natural soil amelioratory pro-cesses and, in addition, the surface crust that wouldhave developed on TP plots was broken up by ridging/

cultivation operations at the end of each growing sea-son.

At all sampling periods, sediment concentrationswere highest for CN, intermediate for CH and TP, andlowest for NT. Soil losses generally followed this sametrend. The NT system provided consistent soil lossreductions across all sampling periods, relative to CN,while CH and TP provided more variable erosion con-trol.

Although surface residue cover appears to be a dom-inant factor in determining soil losses among tillagesystems, the effect of residue cover on runoff losseshas been inconsistent. Additional research is neededto identify and quantify the soil characteristics underindividual tillage systems that affect runoff losses andto evaluate how these factors change over time.

PIKUL, JR., & ALLMARAS: HEAT FLUX AND WATER DISTRIBUTION IN SUMMER-FALLOWED HAPLOXEROLLS 1517

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Romkens, M.J.M., D.W. Nelson, and J.V. Mannering. 1973. Nitro-gen and phosphorus composition of surface runoff as affected bytillage method. J. Environ. Qual. 2:292-295.

Siemens, J.C., and W.R. Oschwald. 1976. Erosion for corn tillagesystems. Trans. ASAE 19:69-72.

Soil Conservation Service (SCS). 1967. Soil survey laboratory dataand descriptions for some soils of Wisconsin. Soil Survey Inves-tigations Rep. no. 17. U.S. Government Printing Office, Wash-ington, DC.

Steel, R.G., and J.H. Torrie. 1980. Principles and procedures of

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face runoff from agricultural lands as a function of land use. J.Environ. Qual. 9:130-136.

Wischmeier, W.H. 1973. Conservation tillage to control water ero-sion, p. 133-141. In Conservation tillage. Proc. Natl. Conserv.Tillage Conf., Des Moines, IA. 28-30 March. Soil ConservationSociety of America, Ankeny, IA.

Wischmeier, W.H., and D.D. Smith. 1978. Predicting rainfall ero-sion losses—a guide to conservation planning. Agric. Handb. no.537, USDA-SEA. U.S. Government Printing Office, Washington,DC.