effect of preplant wheel traffic on soil compaction, water use, and growth of spring wheat1

Effect of Preplant Wheel Traffic on Soil Compaction, Water Use, and Growthof Spring Wheat1

W. B. VOORHEES, S. D. EVANS, AND D. D. WARNES2

ABSTRACTThe effects of wheel traffic on small grain emergence and early

growth is commonly observed in production fields. However, theplant response is not consistent, but appears dependent on soil andclimatic conditions. The objective of this study was to measure theeffects of preplanting wheel traffic on soil compaction and 'Era' springwheat (Triticum aestivum L.) growth in field plots in West CentralMinnesota under a range of growing season conditions. The 1975and 1977 growing season were slightly wetter than normal while the1976 growing season was significantly drier. Treatment comparisonswere wheat planted in soil compacted by wheel traffic during springfield operations and wheat planted in soil that had not been wheeltrafficked. Normal field-sized equipment (tractor weight ranged from4 000 to 7 000 kg) was used to perform spring fertilizer application,spring tillage, and seeding. The controlled wheel traffic concept wasused. In 1975, wheat emergence in the wheel-tracked soil was de-layed by about 10 d because of poor seed-soil contact, and grainyield was 27% lower than in the nontracked soil. Shortly after plant-ing in 1976, the nontracked soil lost excessive amounts of water byevaporation from the loose 0- to 0.15-m layer. As a result, wheatgrowth in the wheel-tracked soil was better than in the nontrackedsoil, and yield was increased by 53%. In both 1975 and 1976, therewas slightly more water used from the wheel-tracked treatment thanfrom the nontracked treatment, resulting in differences in water useefficiency. Effects of wheel traffic on wheat growth and yield wereclosely related to growing season precipitation and illustrate theneed to consider probable climatic conditions when developing man-agement systems for controlling field vehicular wheel traffic.

Additional Index Words: bulk density, penetrometer resistance,plant height, water use efficiency.

Voorhees, W. B., S. D. Evans, and D. D. Warnes. 1985. Effect ofpreplan! wheel traffic on soil compaction, water use, and growth ofspring wheat. Soil Sci. Soc. Am. J. 49:215-220.

THERE IS INCREASING CONCERN about Soil COm-paction due to the increasing weight of modern

agricultural equipment. In crops with widely spacedrows, some adverse effects of wheel traffic can be min-

1 Contribution from the North Central Soil Conservation Re-search Lab, Agricultural Research Service, USDA, Morris, MN, incooperation with the Minnesota Agricultural Expt. Sta., Sci. Jour.Series 13,901. Received 17 Apr. 1984. Approved 20 Sept. 1984.

2 Soil Scientist, ARS, USDA, Morris, MN 56267; Soil Scientistand Agronomist, Minnesota Agric. Expt. Sta., Morris, MN 56267.

imized by restricting all wheel traffic to only the areabetween the rows. But this is often not possible withcereal crops which are grown in rows with spacingsgenerally much narrower than the width of tractor orimplement tires. Thus, a considerable portion of theseedbed and early root growth zone is subjected to thecompactive force of a wheel either before or after seed-ing. This wheel traffic can significantly alter the phys-ical properties of soil (Voorhees et al., 1978), effectswhich may persist in spite of annual tillage, freezing,and thawing (Voorhees, 1983).

Rosenberg (1964), in his review of plant responseto soil compaction, showed the lack of a universalresponse to soil physical conditions. With respect towheat (Triticum aestivum L.) and other small grains,several researchers have reported decreased seedlinggrowth and reduced yields with increasing soil bulkdensity (Adams et al., 1960; Chaudhary and Prihar,1974; Cornish and Fettell, 1977; Kubota and Wil-liams, 1964; Pollard and Elliott, 1978). Others havereported a yield increase in response to increasing bulkdensity (Droese et al., 1975; Rashid and Sheikh, 1977;Stickler, 1962). Stoinev (1975) reported no significanteffect of pre-sowing compaction on wheat yields.

Explanations for the above yield responses vary, andlikely reflect differences in soil type, soil water content,and other environmental and cultural factors. Soilcompaction has contributed to decreased growth andyield via its mediatory influence on germination (Talhaet al., 1978), number of tillers (Pollard and Elliott,1978), uptake of nutrients (Nagpal et al., 1967), andmechanical resistance and oxygen diffusion (Rosen-berg and Willits, 1962). Improved soil water relation-ships brought about by compaction have contributedto wheat yield increases (Rosenberg and Willits, 1962;Wehrli, 1964). Feldman and Domier (1970) observedboth a positive and negative effect on wheat growthdepending on when the compactive forces were ap-plied with respect to planting. Similarly, Agrawal etal. (1975) measured both a positive and negative wheatyield response depending on the depth to the com-pacted layer.

When plant response is considered over a suffi-ciently wide range of soil compactness, a parabolic

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

relationship is generally observed for cereal crops (De-chnik et al., 1982; Eriksson et al., 1974; Kruger, 1970;and Rasmussen, 1976). Furthermore, the relation be-tween soil compaction and plant response depends ongrowing season climatic conditions (and possibly plantvariety).

The objective of this study was to ascertain the ef-fects of normal agricultural wheel traffic on soil phys-ical properties and subsequent spring wheat growthand yield under different but nevertheless frequentlyoccurring growing season climatic conditions. Thisknowledge is a necessary prelude to developing algo-rithms for modeling tillage and plant growth.

METHODS AND PROCEDURESField experiments were conducted on a Forman clay loam

(Udic Argiboroll) at the West Central Experiment Station,Morris, Minnesota. Prior to initiation of the experiment, thesite had been uniformly cropped to corn (Zea mays) for anumber of years. Beginning in May of 1975, wheat and po-tatoes (Solarium tuberosum) were grown in rotation, repli-cated four times. Each whole plot was 9.14m wide and 19.05m long. The sequence of field operations for wheat each yearwas fall moldboard plowing to a depth of about 25 cm, springbroadcast fertilizer application of 107 kg/ha of 34-0-0, springsecondary tillage with a tandem disk to a depth of about 20cm, and seeding 'Era' hard red spring wheat with a 4.57 mwide drill at the rate of 134.5 kg/ha in rows 0.17 m apart.The drill was equipped with press wheels to firm the soilaround the seed. Broadleaf weeds were controlled by a singleapplication of 3,5-Dibromo-4-hydroxybenzonitrite + [4-chloro-<9-totyl)oxy] acetic acid at the rate of 0.28 kg/ha (a.i.)using a bicycle sprayer. Harvesting was done by hand, butharvest wheel traffic was simulated with a large tractor. Thus,a total of five passes was mafle during each growing seasonwith tractor weight ranging from 4000 to 7000 kg dependingon the operation. Wheel spacing of any towed implementmatched that of the tractor. Specific compact! ve force actingon the soil surface was estimated to range from 100 to 300kPa. The above field operations, vehicular weights, andcompactive forces are typical for cereal crop production inthe northwest Corn Belt and the subhumid portion of north-ern Great Plains.

Traffic lanes were established by performing all field op-erations in the same direction and by using the controlledwheel traffic concept. In addition to the normal traffic lanes,one extra pass was made during each field operation withthe tractor shifted over to straddle the normal traffic lanesand thus establish a 3-m wide plot of wheel-tracked soiladjacent to the nontracked soil in each replicate. Further-more, the wheel-tracked area was always in the same loca-tion within the plot year after year. All plant and soil mea-surements were made in center of both the wheel-trackedand nontracked areas.

Total soil porosity was calculated from bulk density mea-surements taken after planting on soil core samples 0.035 min diameter. Twelve sets of cores were taken from each ofthe wheel-tracked and nontracked areas of the plots in 0.15-m increments to a depth of 1.5 m. These soil samples werealso used to determine the soil water characteristic curve.

Soil penetrometer resistance was measured in 0.15-m in-crements to a depth of 0.75 m with a hand held penetro-meter having a 30° cone, 0.019 m in diameter. Measure-ments were made in both the wheel-tracked and nontrackedareas shortly after the crop was planted.

Bulk soil samples (~ 15 kg) were collected from the 0- to0.15-m depth from both the wheel-tracked and nontrackedsoil. After air drying, the fraction < 0.05 m in diameter wassieved for aggregate size distribution from which the geo-

metric mean diameter was calculated. Individual clods about0.05 m in diameter were randomly selected for clod densitydetermination using the water displacement technique aftercoating the clods with paraffin.

Soil temperature was measured at a depth of 0.05 m usingcopper-constantan thermocouples. Six thermocouples in eachtreatment were read daily at 0800 and 1500 h. The monthlyaverage soil temperature was calculated from the daily meantemperatures. Soil water loss was determined from weeklymeasurements with a neutron moisture probe to a depth of1.5 m. In addition to these soil measurements, precipitation,air temperature and open pan evaporation were obtainedfrom an adjacent long-term weather station.

Depth of seed placement, emergence rate, plant height,and grain and straw yields were measured on both the wheeltracked and nontracked treatments in 1975 and 1976. In1977, only grain yield data was obtained. Yield was deter-mined by hand harvesting a sample of 0.46 m wide and 1.83m long from the center of each plot area.

Differences in soil environment created by wheel trafficwere established before the crop was planted, and there wasno additional wheel traffic on the plots after seeding of thecrop until harvest and fall tillage.

RESULTS AND DISCUSSIONThe 1975, 1976, and 1977 growing seasons repre-

sented distinctly different sets of climatic conditions,especially with respect to water supply. The 1975 and1977 seasons were slightly wetter than normal, whilethe 1976 growing season was extremely dry and av-eraged about 2 degrees warmer than normal (Table 1).Open pan evaporation was 36 and 126% higher in 1976than in 1975 and 1977, respectively. In 1975, Aprilwas wet and cool, and planting was delayed until 6May. By contrast April of 1976 was warm and dry,and planting was done on April 7. Planting was doneon 22 April in 1977.

In spite of the distinct differences during the grow-ing season, the gravimetric soil water concentration inthe upper 0.15 m at planting time was about 290 gkg"1 each year (near field capacity). The total porosityin the top 0.30 m of soil for 1975 and 1976, deter-mined about 30 d after planting is shown in Table 2.

Table 1. Growing season precipitation, open pan evaporation,and air temperature at Morris, MN.

Precipitation, mmdeparture!

Mean air temp., °Cdeparture!

Open pan evap., mm



Open pan evap., mm



Open pan evap., mm

April

70.14.81.8

-4.622

11.9-53.3

9.43.0

82

48.3-17.0

10.13.7

55

May

1975

38.9-39.9

14.61.3

208

1976

9.9-68.8

13.1-0.2

2551977139.260.518.95.6

164

June

173.775.718.3

-0.6204

41.4-56.6

21.12.0

311

69.1-29.0

19.30.4

140

July

51.6-35.8

22.71.0

282

27.2-64.5

22.91.2

303

89.42.0

22.10.4

132

August

111.535.619.9

-0.5208

44.7-31.2

22.42.0

313

81.35.3

17.6-2.868

Total

445.840.4

„924

135.1-274.4

..1264

427.321.8--

559

! Departure from 89-year norm.

VOORHEES ET AL.: EFFECT OF TRAFFIC ON SOIL COMPACTION, WATER USE, AND GROWTH OF WHEAT 217

Table 2. Total porosity and penetrometer resistance in surface0.3 m of soil as affected by wheel traffic.

Year

1975

1976

Depth, m

0-0.15

0.15-0.30

0-0.15

0.15-0.30

Treatment

No wheel trafficWheel trafficNo wheel trafficWheel trafficNo wheel trafficWheel trafficNo wheel trafficWheel traffic

Totalporosity

0.52 ± 0.04t0.44 ± 0.020.46 ± 0.010.45 ± 0.010.66 ± 0.030.57 ± 0.060.54 ± 0.030.46 ± 0.03

Penetrometerresistance, kPa

293 ± 130t1110 ± 246618 ± 204892 ± 182205 ± 74

1219 ± 155688 ± 108

1212 ± 228

f Mean and standard deviation.

Wheel traffic reduced the total porosity of the 0- to0.15-m layer by 8 to 9% both years. The tilled layertotal porosity in 1975 was lower than in 1976 andreflects consolidation from raindrop impact. Penetro-meter resistance in the 0- to 0.15-m layer was alsoincreased by wheel traffic both years (Table 2). Therewere no differences due to wheel traffic in either pe-netrometer resistance or total porosity below a depthof 0.30 m for either year.

In addition to differences in bulk soil properties,there were also differences in individual soil structuralunits. The geometric mean diameter of aggregates fromthe wheel-tracked soil was significantly larger than fromthe nontracked soil (7.5 mm vs. 1.6 mm), and theindividual soil clods from the wheel-tracked treatmenttended to be about 8 to 10% more dense. Thus, thephysical characteristics of the seedbed and the surfacelayers of soil in which early growth takes place werealtered by pre-seeding wheel traffic and consequentialcompaction.

Plant response to the different soil environmentsproduced by the presence or absence of wheel trafficdiffered for the 2 yr that plant data was collected, 1975and 1976. Intended depth of seed placement was thesame both years, approximately 40 mm, but the seedsplanted in the wheel-tracked treatment tended to beabout 10 to 20 mm shallower. The increased soilstrength and density in the wheel tracked treatmentoften prevented soil from completely filling in behindthe disk seed openers in 1975 and, as a result, someseeds were not satisfactorily covered with soil. Ger-mination and emergence in the wheel-tracked treat-ment lagged behind that in the nontracked area byabout 7 to 10 d, and subsequent vegetative growth, asindicated by plant height, was affected (Fig. 1). Plantheight in the wheel-tracked soil was statistically shorterthan in the nontracked soil throughout the growingseason. These differences in plant height were constantthroughout the growing season. Adequate precipita-tion and normal air temperatures in June did notovercome the early adverse effects of wheel traffic.

There were several important differences in plantresponse in 1976 (Fig. 1) compared to 1975. First, plantheight was shorter because of the drought conditions.Second, differences in germination and early growthwere not as obvious as in 1975. Even though April1976 precipitation was only 18% of normal, soil watercontent at planting was the same for both wheel-tracked and nontracked soil, due largely to adequatesoil water reserves from the previous year. However,total porosity of the 0-to 0.15-m layer was substan-

0.8

0.6

0.4

0.2

——— NO WHEEL TRACK f \ 1975

——— WHEEL TRACK

10 70 8020 30 40 50 60DAYS AFTER PLANTING

Fig. 1—Plant height with time as affected by wheel traffic, 1975 and1976. Data points with the same letter at a given date are notstatistically different at 0.05%.

tially higher in 1976 than in 1975 for both wheel-tracked and nontracked soil (Table 1). This allowedproper soil closure behind the disk opener and over-came the problem experienced in 1975 with poor seed-soil contact in the wheel-track treatment. The non-tracked treatment, however, was too porous for a dryyear and soil water evaporation was more rapid thanfrom the tracked treatment. Relative to 1975, germi-nation, emergence and early growth in 1976 was in-dicative of improved soil conditions brought about bymoderate wheel-induced consolidation of excessivelyporous soil under limited rainfall conditions.

A third difference in 1976 was better growththroughout the season in the wheel-tracked soil thanin the nontracked soil, indicated by taller plants (Fig.1), and observed increased tillering. Furthermore, therewas a gradual increase with time in plant height dif-ferences of the wheel-tracked over the nontrackedtreatment compared with a relatively constant differ-ence in 1975. The difference became statistically sig-nificant about 50 to 60 d after planting. Extremely dryconditions in 1976 forced the plants to rely heavilyon soil water reserves, and the plant height X timeinteraction is likely related to soil water supply.

Accumulative water use (evapotranspiration) withtime as affected by wheel traffic, along with accumu-lative precipitation, is shown in Fig. 2. Measurementsof soil water content were initiated when plants begantheir linear vegetative growth stage. Thus, the accu-mulative water use data in Fig. 2 begins with zero atabout 20 d after planting and ignores previous waterloss, essentially all by evaporation from the soil. Upto about 60 d after planting in 1975, precipitation ex-ceeded water use. Thus, there was a net gain in thesoil water content measured 35 to 63 d after planting(Fig. 3). These time periods were based on the changein seasonal precipitation pattern shown in Fig. 2. Thenontracked soil profile gained more water than did thewheel-tracked soil profile during the early period prob-ably because of higher infiltration rates (Lindstromand Voorhees, 1980). But the nontracked soil lost morewater during the second period than the wheel-trackedsoil, especially at a depth of about 1 m. This loss likelyreflects deeper and greater root growth where soil wasnot trafficked. Total seasonal water use was essentiallythe same for the two treatments (Fig. 2).

Evapotranspirational water loss always exceededprecipitation during the dry 1976 growing season (Fig.


zo

g.o

oBentoO-ja:uj

300

ZOO

100

1975

WHEEL TRACK/.

/?".'NO WHEEL TRACK

r—""PRECIPITATION

5 200-

>• NO WHEEL TRACK

30 11050 70 90DAYS AFTER PLANTING

Fig. 2— Precipitation and accumulative water loss as affected by wheeltraffic, 1975 and 1976.

2), and there was a cumulative water loss during boththe first and second period of the growing season (Fig.3). Excessive evaporative water loss from the loose,shallow layer of non tracked soil occurred shortly afterplanting. The surface 0. 1 5 m of the npntracked soilhad dried to below the permanent wilting percentagewhen data collection was initiated. This accounts forthe negligible loss of water from the surface 0. 1 5 m ofnontracked soil during the first part of the growingseason (Fig. 3). Higher soil temperature in the non-tracked soil in June (Table 3) is also indicative of adrier soil. Conversely, the wheel-tracked soil retainedwater for a longer period of time (because of lowerhydraulic conductivity, see Reicosky et al., 1981), pro-viding a source of water for evapotranspiration. Byabout 70 days after planting, there was essentially noplant available water in the upper 0.9 m of soil ineither treatment. By the end of the growing season,more water had been lost through transpiration bywheat growing in wheel-tracked soil than in non-tracked soil (Fig. 2) simply because the nontrackedsoil had lost substantial water by evaporation shortlyafter planting before the crop was sufficiently devel-oped to extract it.

Cumulative water use during the main vegetativegrowth period of 30 to 60 d after planting paralleled

CHANGE IN SOIL WATER CONTENT, mm30/.-50 -40 -30 -20 -10

1975

—— NO WHEEL TRACK -,-X —WHEEL TRACK /

1.5 • 35-63 DAYSAFTER PLANTING

63-94 DAYSAFTER PLANTING

Q.UJO -60 -50 -40 -30 -20 -10 0 ,.-30 -20 -10 0

01——————————————————————r/————————————

0.3

0.6

0.9

1.2

1.5

1976

—NO WHEEL TRACK— WHEEL TRACK



Fig. 3—Change in soil water content with depth as affected by wheeltraffic for two growth periods in 1975 and 1976.

•—NO WHEEL TRACK—— WHEEL TRACK

-—— NO WHEEL TRACK—— — WHEEL TRACK

}l975

}|976

-50 0 50 100 150 200

ACCUMULATIVE WATER USE,mmFig. 4—Relationship between plant height and water use as affected

by wheel traffic.

the height increase of the crop (compare Fig. 2 withFig. 1). A linear fit of these relationships was calcu-lated and is shown in Fig. 4, with the regression coef-ficients listed in Table 4. Vegetative water use effi-ciency (plant height per unit of water used) wasessentially constant throughout this growth period asindicated by the relatively high coefficient of deter-

Table 3. Soil temperature under wheat at the 0.05-m depth asaffected by wheel traffic, Morris, MN.

MonthTreatment April May June July

-average soil temperature, °C~

No wheel trackWheel track


1975

197611.011.7

17.818.1

16.615.8

18.718.9

25.021.1

22.222.0

Table 4. Linear regression coefficients for accumulative plantheight of wheat vs. accumulative water use over the period

from 30 to 60 d after planting, Morris, MN.Regression coefficients

Treatment



1975201.6

60.81976

66.039.6

2.943.07

3.232.32

0.560.87

0.920.98

VOORHEES ET AL.: EFFECT OF TRAFFIC ON SOIL COMPACTION, WATER USE, AND GROWTH OF WHEAT 219

Table 5. Wheat grain and straw yield, and water use efficiency.

Treatment

No wheel trafficWheel traffic

LSD (0.05)


LSD (0.05)


LSD (0.05)

Grain Strawyield yield

3.702.690.98

1.452.220.39

2.732.520.44

Mg/ha ——

19754.504.440.3119761.541.870.371977

••

Grain/strawratio

0.820.61

0.941.19

Water useefficiency

kg grain/mm HjO/ha

11.68.1

7.28.9

mination for a linear fit for a given treatment. In 1975,the rate at which plant height increased with increas-ing water consumption was not affected by wheel traffic(2.94 mm of height per mm of water used for the non-tracked compared with 3.07 for the wheel-trackedtreatment). This supports earlier discussion that wheeltraffic simply delayed germination and very earlygrowth during a relatively wet season. In 1976, how-ever, wheel traffic caused the crop to be about 30%less efficient in terms of using water to increase height(Table 4). This may have been offset by the observedgreater degree of tillering on plants growing in thewheel-tracked soil.

Grain and straw yield data, along with water useefficiency, are given in Table 5. In the wettest year(1975), wheel traffic caused a 27% reduction in grainyield while straw yields were the same in both treat-ments. Plants were less efficient in water use, and lessefficient in terms of partitioning total biomass intograin. Wheel traffic also reduced grain yield by 8% in1977, a year with almost normal precipitation. How-ever, during the dry growing season (1976), the op-posite results were observed. Grain yield was in-creased 53% by wheel traffic, and the plants were moreefficient in water use and partitioning of total biomassinto grain yield.

As expected, both grain and straw yields were lowerin 1976 than in 1975 because of the drought. Al-though, water use efficiency averaged slightly less in1976 compared with 1975, the crop was more efficientin terms of partitioning biomass into grain instead ofstraw.

The percent yield decrease as a result of wheel-trackcompaction for all three years is plotted against April-June precipitation in Fig. 5. April-June precipitationwas chosen as an arbitrary indicator of the "type" ofgrowing season encountered each year by spring wheat.Although not very definitive, the relationship shownin Fig. 5 does illustrate the scope of the problem andcan serve as a first approximation in developing al-gorithms and models relating crop response, soil phys-ical conditions and climatic variability. During rela-tively dry years (April-June precipitation < 200 mm),wheel traffic associated with normal pre-planting fieldoperations may not have any deterimental effect onspring wheat yield in this physiographic area, and mayeven significantly increase yield by reducing soil water

S i -600 100 200 300APRIL TO JUNE RAINFALL, mm

Fig. 5—Relation between wheel traffic effect on wheat yield andgrowing season precipitation.

evaporation. If the probability is high that April-Juneprecipitation or irrigation will exceed 200 mm, thenpreplanting field operations and associated wheel trafficshould be limited to only that necessary to producethe desired seedbed without causing excessive com-paction to the point of preventing proper seed depthplacement or seed-soil contact. This is supported by10 yr of similar data for soybeans under a similar rangeof climatic conditions (W. B. Voorhees, unpublisheddata).

These field data illustrate the difficulty in determin-ing the most desirable seedbed characteristics, and themethods to achieve them, due to the strong effects ofsubsequent climatic conditions. Under relatively dryconditions, wheel traffic compaction preceding plant-ing may not have detrimental consequences on wheatproduction, and can even significantly increase yieldsby reducing soil water evaporation. Under relativelywet climatic conditions, or irrigation, preplanting fieldoperations and associated wheel traffic should be lim-ited to produce proper seed depth placement or seed-soil contact without excessive soil compacting.


10. Kubpta, T., and R.J.B. Williams. 1964. Effect of artifically com-pacting seedbeds for barley and globe beet. p. 48-49. Ro-thamsted Exp. Sta. Report for 1964. Rothamsted, UK.

11. Lindstrom, M.J., and W.B. Voorhees. 1980. Planting wheel trafficeffects on interrow runoff and infiltration. Soil Sci. Soc. Am. J.44:84-88.

12. Nagpal, N.K., Y.V. Kathavate, and Abhiswar Sen. 1967. Effectof compaction of Delhi soil on the yield of wheat and its uptakeof common plant nutrients. Indian J. Agron. 12:375-378.

13. Pollard, F., and J.B. Elliott. 1978. The effect of soil compactionand method of fertilizer placement on the growth of barley us-ing a concrete track technique. J. Agric. Eng. Res. 23:203-216.

14. Rashid, Shadida, and Khalid Hamid Sheikh. 1977. Responseof wheat to different levels of soil compaction. Phyton (Austria)18:43-56.

15. Rasmussen, Karl J. 1976. Soil compaction by traffic in spring.I. Conditions of growth and yields of barley. Saertryk of Tidssk-rift for Planteavl. 80:821-834.

16. Reicosky, D.C., W.B. Voorhees, and J.K. Radke. 1981. Unsat-urated water flow through a simulated wheel track. Soil Sci.Soc. Am. J. 45:3-8.

17. Rosenberg, Norman J. 1964. Response of plants to the physicaleffects of soil compaction. Adv. Agron. 16:181-196.

18. Rosenberg, N.J., and N.A. Willits. 1962. Yield and physiolog-ical response of barley and beans grown in artificially com-pacted soils. Soil Sci. Soc. Am. Proc. 26:78-81.

19. Stickler, EC. 1962. Seeding depth and use of press wheels asfactors affecting winter barley and winter wheat yields in Kan-sas. Agron. J. 54:492-494.

20. Stoinev, K. 1975. Effect of tillage, fertilizer application and pre-sowing compaction of leached smolnitza on maize and winterwheat. Soil Sci. Agrochem. 10(6): 119-120.

21. Talha, M., S.Y. Metwally, and E. Abu-Gabal. 1978. Effect ofsoil compaction on germination and growth of cotton and wheatgrown in alluvial and calcareous soils. Egypt J. Soil Sci. 18(1):39-50.

22. Voorhees, W.B. 1983. Relative effectiveness of tillage and nat-ural forces in alleviating wheel-induced soil compaction. SoilSci. Soc. Am. J. 47:129-133.

23. Voorhees, W.B., C.G. Senst, and W.W. Nelson. 1978. Com-paction and soil structure modification by wheel traffic in thenorthern Corn Belt. Soil Sci. Soc. Am. J. 42:344-349.

24. Wehrli, A. 1964. The residual effect of tractor action on soilstructure and crop yield on a stand of winter wheat. Schweiz.London Forsch. 3:26-31.

effect of preplant wheel traffic on soil compaction, water use, and growth of spring wheat1

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