temporal effects of subsoil compaction on soil strength and plant growth

Temporal Effects of Subsoil Compaction on Soil Strength and Plant GrowthB. Lowery* and R. T. Schuler

ABSTRACTIn recent years, scientists have become concerned that heavy farm

equipment is causing soil compaction below the nominal depth oftillage. Compaction this deep may not be ameliorated after one sea-son's freeze-thaw and wet-dry cycles. Experiments were conductedon a Kewaunee (fine, mixed, mesic Typic Hapludalf) and Rozetta(fine-silty, mixed, mesic Typic Hapludalf) soil to determine the du-ration and effect of subsoil compaction on soil strength and corn(Zea mays L.) growth. Soil at two sites was compacted with 8 and12.5 Mg axle loads in the spring of 1983. Cone-penetration resist-ance of compacted soil was significantly higher than that of uncom-pacted soil below the plow zone. Plant heights, at physiologicalmaturity averaged across both sites, were reduced 13 and 26% onthe 8- and 12.5-Mg compaction treatments, respectively, comparedwith the control in 1983. In 1984, average mature plant heights were2.4, 2.3, and 2.3 m for the control, 8-, and 12.5-Mg compaction,respectively. Three years after the compaction was applied (1986),the average mature plant height for the 8- and 12.5-Mg compactedsites were reduced 3.1 and 4.3% compared with the control. Nitrogenand K uptake was reduced by compaction. Iron, Al, and Mn uptakeincreased with increasing levels of compaction on the Kewaunee soilin 1983. In 1983, yields for the 8- and 12.5-Mg treatments on theRozetta soil were reduced 4 and 14%, respectively, relative to thecontrol. Similarly, yields for the Kewaunee soil were reduced 14 and43%. Yields for the Kewaunee soil were not reduced by compactionin 1984, although 5 and 9% reductions were observed at the Rozettasite. Yields were not affected the following 2 yr (1985 and 1986),whereas the resistance to cone penetration was significantly higherin the compacted plots compared with the control.

THE EFFECT OF SOIL COMPACTION on soil physicalproperties and crop yields has been researched

extensively throughout the agricultural revolution inthe USA (Barnes et al., 1971). Until recently, however,little attention has been given to compaction of thesubsoil by wheel traffic from massive farm equipment.The concern with subsoil compaction is: how long dothe effects remain? In fact, as previously noted bySchuler and Lowery (1986), much of the early workon soil compaction was directed toward genetic or til-lage-induced and topsoil compaction. The bulk of thiswork was conducted in areas where freezing did notreach the subsoil. Deep frost conditions were believedto ameliorate compaction effects (McKibben, 1971).

Reaves and Cooper (1960) showed that surface soilcompaction was reduced by spreading a given loadover a larger area. They found soil stress twice as greatunder a tire (33-cm tread width, 97-cm rim diam.)compared with that under a crawler tractor track (30cm wide and 1.5 m long) with the same total weight.This does not mean that, if the contact pressure is keptconstant while the overall weight is increased (i.e., in-creasing tire size as the machine weight is increased),B. Lowery, Dep. of Soil Science and R.T. Schuler, Dep. of Agri-cultural Engineering, Univ. of Wisconsin, Madison, WI 53706. Re-search supported by the College of Agricultural and Life Sciences,Univ. of Wisconsin, Madison. Received 27 Nov. 1989. *Corre-sponding author.

Published in Soil Sci. Soc. Am. J. 55:216-223 (1991).

there is less potential for causing soil compaction.With a constant contact pressure, Soehne (1958) madecalculations showing that, when the total weight andtire size were increased, the depth to which compac-tion penetrated also increased. Similar results were ob-tained from experiments conducted by Cooper et al.(1957).

In recent years, studies have been conducted show-ing the effect of subsoil compaction on soil physicalproperties and crop growth. Heavy farm equipmenthas been found to cause considerable subsoil com-paction, which persists five or more years, dependingon soil clay content (Hakansson et al., 1987). Voorhees(1983) reported that natural forces such as wet-dry andfreeze-thaw cycles have limited effects on alleviatingwheel-induced soil compaction in the plow layer of aclayey soil. Voorhees et al. (1986) indicated that sub-soil compaction effects persisted after four seasons offreezing and thawing. Blake et al. (1976) found thatbulk density and cone penetration resistance werehigher in the subsoil of compacted land compared withuncompacted land after ten seasons of natural forces.During the first season after the soil was compacted,Gaultney et al. (1982) and Gameda et al. (1985) re-ported increased soil bulk density and cone index dueto compaction. In laboratory studies, Gaultney et al.(1982) found that freezing and thawing cycles did notcompletely ameliorate the compaction effects.

The effects of subsoil compaction on crop yield havebeen documented by Raghavan et al. (1976), Gaultneyet al. (1982), Gameda et al. (1985), Hakansson et al.(1987), and Voorhees et al. (1989).

The objective of this study was to evaluate the lon-gevity of subsoil compaction on soil strength, plantgrowth, and corn yield.

MATERIALS AND METHODSThis study was conducted for 4 yr (1983-1986) on a Roz-

etta silt loam at the University of Wisconsin Research Sta-tion in Lancaster, and on a Kewaunee silty clay at a privatefarm in Valders, WI. Selected data were collected at the Ke-waunee site in 1987. The Kewaunee soil has about 10 cmof loess overlying a dense clayey residuum, and Rozetta iscomposed of deep, silty soils that are moderately welldrained.

At each location, three levels of soil compaction were uti-lized in a randomized complete-block design; there were fourblocks, thus 12 plots. The plots were 7.28 and 7.76 m wide(eight rows) at the Rozetta and Kewaunee sites, respectively,and 15.24 m long at both sites. Four passes of the compactiveload were made in May 1983, covering the entire plot areawith wheel tracks with each pass. The four passes simulatedtypical field operations for a growing season. The controltreatment received no compaction except normal field op-erations with axle loads less than 4.5 Mg per axle. The firstlevel of compaction per axle was imposed with an 8-Mgtractor; the second level (12.5 Mg axle"1) was imposed witha six-row combine at the Rozetta site and with a liquid man-ure tank at the Kewaunee site. Tire inflation pressures were100, 150, and 220 kPa for the tractor (rear wheels), manuretank, and combine (front wheels), respectively. Average soil

216

LOWERY & SCHULER: SUBSOIL COMPACTION EFFECTS 217

water content (from the surface to 30-cm depth) at the timeof compaction was 16 and 20 kg kg-' for the Kewaunee andRozetta sites, respectively.

Corn (Zea mays L.) was planted in all plots with rowspacing of 0.91 m on the Rozetta and 0.97 m on the Ke-waunee soil (four-row planter). Prior to this study, both fieldswere in alfalfa (Medicago saliva L.). Corn hybrid Pioneer3732 was planted on 12, 9, 1, and 2 May 1983, 1984, 1985,and 1986, respectively, at the Rozetta site. Corn hybridJacques 4700 (1984), Cenex 2096 (1985), and Jacques 4100(1983 and 1986) were planted on 18, 20, 9, and 6 May 1983,1984, 1985, and 1986, respectively, at the Kewaunee site. Asingle variety was not used due to availability and privateoperator selection. Fertilizer was added according to soil-testrecommendations for 13.4 Mg ha-' yield. In each year of the4 yr of this study, 6-24-24 fertilizer was applied to the Rozettasite at planting at a rate of 112 kg ha-'; 224 kg ha~' of an-hydrous N was injected (22 cm deep) prior to planting. Atthe Kewaunee site, 224 kg ha-' of 9-23-30 fertilizer and 112kg ha"1 of anhydrous N were used each year.

The Kewaunee site was moldboard plowed prior to com-

paction in the fall of 1982. After the compaction was applied(spring 1983), the Kewaunee soil was tilled with a field cul-tivator prior to planting. It was moldboard plowed (20-cmdepth) and field cultivated in the fall and spring, respectively,the following 4 yr (an additional year of penetration datawas collected at this site). The Rozetta soil was chisel plowedafter compaction and chisel plowed in the fall and disked inthe spring of the following 3 yr. With respect to corn rows,the planting and harvesting traffic was controlled; tillage traff-ic was not controlled.

Plant emergence was determined by counting the numberof seedlings emerged within a 7.62-m segment of the twocenter rows of each plot. Percentage corn emerged was de-termined by dividing the number of seedlings emerged bythe final plant population (the final population was taken asthe total number of plants emerged for this 7.62-m segment).Plant height (leaf extended) was determined on ten plantswithin a 3.04-m segment of the center two rows of each plotevery 7 to 10 d from complete emergence to mature height.Ear-leaf samples were collected at silking each year for tissueanalysis. A 7.62-m segment of the two center rows of each

x-10-

Eo

-20-Q.0)Q

O00-30-

-40-

Kewaunee Soil-1983

~cfl5~——

Efb

* ooooo 4.5 Mg* MBM 8.0 Mg

*-+.*-+-* 12.5 MI

Vf*

g

Rozetta Soil-1983

ooooo 4.5 MgDQ&cm 8.0 Mg*.*•*•*-* 12.5 Mi

60001000 2000 3000 4000 5000 6000 0 1000 2000 3000 4000 5000Cone Index (kPa) Cone Index (kPa)

Fig. 1. Penetration-resistance profile for two soils with three levels of compaction (4.5-, 8-, and 12.5-Mg compaction), 1983. Data points fora given depth followed by the same letter and those with no letters are not significantly different at the 0.05 level.

-10-

Eo

-20-

Q.(DQ-30-

OCO

-40-

-50

Rozetta Soil-1984

ooooo 4.5 MgMB-M 8.0 Mg*•*•*•*•* 12.5 Mi

Kewaunee Soil—1984

ooooo 4.5 MgDBB-DQ 8.0 Mg*-*-*.*-* 12.5 Mg

0 500 1000 1500 2000 25)0 0Cone Index (kPa)

500 1000 1500 2000Cone Index (kPa)

2500


218 SOIL SCI. SOC. AM. J., VOL. 55, JANUARY-FEBRUARY 1991

-10-

-30

— -40-O

CO

-50-

-60-

Rozetta Soil-1985

ooooo 4.5 MgMB-DB 8.0 Mg*•*•*•*•* 12.5 M

1000 2000 3000 4000 5000Cone Index (kPa)

Kewaunee Soil-1985

ooooo 4.5 MgDQBDB 8.0 Mg*•*-*-*•* 12.5 Mg

6000 0 1000 2000 3000Cone Index (kPa)


plot was harvested by hand for grain yield and moisturecontent.

Cone-penetrometer measurements were made each yearduring the middle of the growing season with a constant-rate penetrometer (Lowery, 1986). Three measurementswere made within the center two rows of each plot. Thepenetrometer had a standard 30° cone with a base diameterof 1.28 cm (ASAE, 1989). The penetrating force was contin-uously recorded across the depth of measurement; however,the maximum penetration resistances at 2-cm intervals arepresented here. Soil water content was measured gravimet-rically at the time penetrometer measurements were made.A push probe (1.9-cm diam.) was used to collect soil samplesfor gravimetric soil water content determination.

Data were analyzed using analysis of variance (ANOVA)for each year. Means comparisons were made with the leastsignificant differences (LSD) procedures (Steel and Torrie,1980).

RESULTS AND DISCUSSIONSoil Physical Properties

Soil compaction by heavy farm equipment extendedto the subsoil and persisted for more than 3 yr. Theeffect of compaction on the soil was measured with acone penetrometer. Figures 1 through 4 show cone-penetration-resistance profiles for the Rozetta and Ke-waunee soil for 1983 through 1986, and Fig. 5 theKewaunee for 1987. As previously described, the soilswere compacted only in the first year (May 1983) ofthe study; however, as shown in Fig. 1 through 5, theeffect of this compaction remained at both sitesthrough the study period. The effect of compaction isclearly shown in the penetration-resistance data for1983, 1984, and 1986. It is not clear why the effect of

-10

.— -40O

CO

-50

-60-

Kewaunee Soil-1986

oeeeo4.58.0 Mg

***** 12.5 Mg

Rozetta Soil-1986

oeeee4.5s.o Mg

***** 12.5 Mg

46

500 1000 1500 2000 2500 0 500 1000 1500 2000 2500Cone Index (kPa) Cone Index (kPa)

Fig. 4. Penetration-resistance profile for two soils with three levels of compaction (4.5-, 8-, and 12.5-Mg compaction), 1986. Positions (depths)where cone penetration resistances are not significantly different at the 0.05 level are indicated with the same letter; those with no significanceare not listed.


o -20

CL<uO— -40O

-60-

Kewaunee Soil-1987

ooooo 4.5 tM&DQ 8.0 t*.*.*-*-* 12.5 t

"«x

,*'

500 1000 1500 2000 2500Cone Index (kPa)

Fig. 5. Penetration-resistance profile for two soils with three levelsof compaction (4.5-, 8-, and 12.5-Mg compaction), 1987. Datapoints for a given depth followed by the same letter and thosewith no letters are not significantly different at the 0.05 level.

compaction was not more evident in 1985 (Fig. 3),particularly at the Kewaunee site, given the strong ef-fect in 1986 (Fig. 4). This difference was not due tosoil-water-content differences. Soil water content wasnot significantly different between treatments in anyyears (Table 1). To minimize differences due to soilwater content, penetration-resistance measurementswere taken at least 2 d following a large rainfall event.

In 1983, compaction effects were noted down toabout 40 cm at both sites (Fig. 1), but were significantfrom 2 to 24 cm and 6 to 24 cm for Rozetta andKewaunee soils, respectively. On Kewaunee, a signif-icant compaction effect was present at 34 cm. Althoughthe soil was tilled after compaction was applied, theeffect of compaction was apparent near the soil surface.In 1984, following one season of freeze-thaw and wet-

Table 1. Soil water content for 0- to 30-cm depth at the time of cone-penetration measurements.

CompactionlevelMg

4.58

12.5Significance!

4.58

12.5Significance

1983

0.190.200.19NS

0.190.190.19NS

1984

Rozetta0.130.110.13NS

Kewaunee0.120.110.09NS

1985

^e fce

0.210.220.20NS

0.180.180.19NS

1986

0.250.230.24NS

0.230.200.22NS

1987

0.200.190.20NS

t There was no significant (NS) difference in soil water content at the 0.05level between compaction treatments.

dry cycles and tillage, the effect of compaction was notapparent near the soil surface, but was apparent at 16and 18 cm and 16 to 36 cm for the Rozetta and Ke-waunee sites (Fig. 2). In 1984, significant differenceswere noted in the lower profile of the Kewaunee soiland only at two depths in the center profile of theRozetta soil'(Fig. 2).

Amelioration of compaction was extended to greaterdepths the following years, and by the end of the studyit extended to about 18 cm (Fig. 4 and 5). Significantdifferences occurred only at one to three positions inthe center of the profile in 1985 and 1987 (Fig. 3 and5). In 1986, significant differences were noted in muchof the lower profile below the depth of tillage (Fig. 4).

Plant GrowthPlant emergence rates were taken the first and sec-

ond year of the study. The time for 100% emergencewas delayed 4 and 8 d for the 8- and 12.5-Mg com-paction, respectively, for the Rozetta site. These datawere not collected for the other site. Although theemergence was delayed, the population was not af-

250

200-

Eo

150-_cCT

m•jftc_DCL

100-

50-

Rozetta Soil-1983ooooo 4.5 Mgaaano 8.0 Mg

12.5 Mg

25

Kewaunee Soil-1983

50 60 70 80After Planting

90 10035 45 55 65 75 85 95 20 30 40Days After Planting Days

Fig. 6. Plant height for corn grown on Kewaunee and Rozetta soils with three levels of compaction (4.5-, 8-, and 12.5-Mg compaction), 1983.Data points for a given day followed by the same letter are not significantly different at the 0.05 level.


fected by compaction and the emergence was not af-fected the second year. Delayed emergence wasattributed to poor seed bed caused by large clods.

Other phenological parameters affected by compactioninclude plant height, nutrient uptake, and yield.

In general, plant height was decreased at both sitesTable 2. Ear-leaf analysis for corn grown on compacted Kewaunee and Rozetta soils at Lancaster and Valders, WI, 1983.

AverageCompaction level N Ca Mg Zn Mn Fe Cu Al

Mg

4.58

12.5Significance

- mg kg-'

2.902.912.83NS

0.320.320.31NS

2.161.881.83NS

0.740.700.62NS

0.470.510.46NS


Kewaunee

19.623.420.8NS

11.614.313.0NS

65.153.650.5NS

177158133NS

11.012.712.0NS

73.878.666.1NS

4.58

12.5Significance

2.872.762.60

*

0.310.330.31NS

2.061.992.04NS

0.290.430.45NS

0.230.230.24NS

0.190.190.18NS

23.927.726.2NS

8.68.68.8

NS

23.536.549.8**

98.1112118NS

12.812.510.7NS

60.190.6

100**

' Significant at 0.05 and 0.01 levels, respectively; NS — not significant.

250

200-

Eo,150-

100-c

Q. 50-

Kewaunee Soil-1984

ooooo 4.5 MgOODDD 8.0 Mg

12.5 Mg

20 30 40 50 60 70Days After Planting

Rozetta Soil-1984

OOOOO 4.5 MgDoaoa 8.0 Mg

12.5 Mg

8015 25 35 45 55 65 75 85Days After Planting

Fig. 7. Plant height for corn grown on Kewaunee and Rozetta soils with three levels of compaction (4.5-, 8-, and 12.5-Mg compaction), 1984.Days when plant heights are not significantly different at the 0.05 level are listed with the same letter; those with no significance are notlisted.

250-

200-

EO

150-

100-

cJ2D_ 50-

20

Rozetta Soil-1985

oeeeo 4.5 MgI 8.0 Mg

12.5 Mi

30 40 50 60

Kewaunee Soil—1985

oeeee 4.5 Mg————I 8.0 Mg

• 12.5 Mg

Days After Planting7 3 0 10 20 30 40 50 60 70 80 90 100 V O

Days After PlantingFig. 8. Plant height for corn grown on Kewaunee and Rozetta soils with three levels of compaction (4.5-, 8-, and 12.5-Mg compaction), 1985.

Days when plant heights are not significantly different at the 0.05 level are listed with the same letter; those with no significance are notlisted.


with increasing levels of compaction (Fig. 6-9). Thisdifference decreased in each succeeding season. Themost dramatic effects occurred at both sites in 1983,the first year after compaction (Fig. 6). In the first year,there were significant differences among all treatmentsthroughout the growing season at both sites. Althoughthere were significant differences in plant height 27 d

after planting (DAP) at the Rozetta site in 1984, themost noticeable differences were observed midwaythrough the growing season starting at 52 DAP (Fig.7). This delayed response to compaction is believedto be due to some alleviation of compaction, whichincludes breakup of dense soil clods by natural forcesand tillage in the upper soil layers. During the initial

Table 3. Ear-leaf analysis for corn grown on compacted Kewaunee and Rozetta soils at Lancaster and Valders, WI, 1984.Average

Compaction levelMg

4.58

12.5Significance

4.58

12.5Significance

N

2.532.552.77NS

3.293.303.18NS

P

0.270.290.29NS

0.280.270.27NS

K————— c)

1.831.831.75NS

2.312.212.20NS

Ca'o —————

0.580.620.63NS

0.610.610.60NS

Mg

0.440.460.47NS

0.300.340.32NS

S



Zn

23.923.826.2NS

31.028.125.4NS

B

7.99.7

10.1NS

7.98.18.1NS

Mn

65.351.054.9NS

47.050.546.1NS

Fe

130155143NS

94.089.291.5

NS

Cu

52.011.011.8NS

11.611.310.6NS

Al

51.762.862.1NS

34.035.434.5NS

Na

59.959.359.4NS

59.361.860.2NS

*,** Significant at 0.05 and 0.01 levels, respectively; NS = not significant.

Table 4. Ear-leaf analysis for corn grown on compacted Kewaunee and Rozetta soils at Lancaster and Valders, WI, 1985.

AverageCompaction levelMg

4.58

12.5Significance

4.58

12.5Significance

N

2.382.372.50NS

3.053.112.95NS

P

0.280.300.29NS

0.320.330.32NS

K

1.781.931.74NS

2.081.901.93NS

Ca

0.780.750.72NS

0.410.490.43NS

Mg

0.460.480.50NS

0.240.260.24NS

S



Zn

18.121.722.8NS

30.730.024.0NS

B

17.617.717.6NS

10.010.69.4

NS

Mn

55.456.057.1NS

60.159.045.8NS

Fe- mg kg-' -

181187167NS

96.410796.0

NS

Cu

11.512.012.1NS

15.717.816.6NS

Al

157147147NS

133138127NS

Na

276271277NS

273272267NS

' Significant at 0.05 and 0.01 levels, respectively; NS = not significant.

300

250

^200•*->SI.ETiso

cS3

CL

100

50

Rozetta Soil-1986

oeeeo4.5 MgHBBHa 8.0 Mg***** 12.5 Mg

Day o D *55 ab a b67 a a b83 ab a b

25 35 45 55 65Days After Planting

75

Kewaunee Soil-1986

oeeeo4.5 Mg——— 8.0 Mg

12.5 Mg

Day O D *62 a b b77 a b b93 a b b

8530 40 50 60 70 80Days After Planting

go 100

Fig. 9. Plant height for corn grown on Kewaunee and Rozetta soils with three levels of compaction (4.5-, 8-, and 12.5-Mg compaction), 1986,Days when plant heights are not significantly diflerent at the 0.05 level are listed with the same letter; those with no significance are notlisted.


Table 5. Ear-leaf analysis for corn grown on compacted Kewaunee and Rozetta soils at Lancaster and Valders, WI, 1986.

AverageCompaction level N Ca Mg Zn Mn Fe Cu Al NaMg - mg kg~' -

Rozetta4.58

12.5Significance

4.58

12.5Significance

2.622.552.61NS

2.062.022.21NS

0.320.320.33NS

0.270.260.27NS

2.142.142.05NS

2.162.102.08NS

0.830.830.83NS

0.490.500.50NS

0.540.540.54NS

0.270.280.29NS

0.210.210.23NS


14.514.815.2NS

16.015.915.5NS

9.19.99.7NS

5.35.45.4NS

62.158.058.8NS

38.237.340.7NS

217219223NS

74.875.984.4

NS

7.57.68.1NS

6.06.37.0NS

106106110NS

35.737.941.0

NS

266267277NS

176187199NS

*,** Significant at 0.05 and 0.01 levels, respectively; NS = not significant.

Table 6. Grain yield at 15.5% moisture content.

Compactionlevel

Year1983 1984 1985 1986

Mg - Mg ha"1

Rozetta4.58

12.5

6.7a6.4a5.7a

lO.Oa*9.6ab9.2b

7.6a8.0a7.5a

10.5a11. la10.8a

Kewaunee4.58

12.5

7.5a6.5ab4.3b

10.9a10.8a10.9a

5.3a4.7a5.1a

7.8a7.1a6.8a

* Grain yields at a given site for a particular year with the same letter are notsignificantly different at the 0.05 level.

growth stages (25 DAP for the Kewaunee and 41 forRozetta soils; Fig. 7), corn roots were growing in rel-atively uncompacted soil, thus plant height was notaffected. In the latter growth stages, corn roots ap-peared to encounter the compacted zone and growth-rate differences occurred.

Similar trends in plant growth were noted for 1985at the Kewaunee site and for 1986 at both sites (Fig.8 and 9). Reductions in plant height with increasinglevels of compaction at the latter growth stages in 1984to 1986 were significantly different at the P = 0.05level at both sites, except at the Rozetta site in 1985(Fig. 7-9). Plant height at physiological maturity wassignificantly different each year of the study. At ma-turity, plant height for the three levels of compactiongenerally ranked 4.5 > 8 > 12.5 Mg, except 1985 and1986. The 8-Mg compaction had the tallest corn atmaturity in 1985 and 1986 at the Rozetta site, and theshortest corn at the Kewaunee site in 1986.

Ear-leaf analyses were done to determine if reduc-tions in plant growth were related to nutrient uptake.Leaf-tissue analyses showed that compaction affectedplant nutrient uptake (Tables 2-5) only at the Ke-waunee site in 1983. Nitrogen in leaf tissue was sig-nificantly decreased, and Mn and Al were significantlyincreased by compaction (Table 2). Iron concentrationin leaves was also increased by compaction, but theincrease was not significant. In general, leaf K con-centration at the Rozetta site was reduced with com-paction, but the reduction was not significant.Although these differences were not statistically sig-nificant, this apparently affected yield. Subsequentwork has shown that corn yield on soils with low initial

K tests can be increased with row-applied K (Wol-kowski, 1989).

Corn yield was reduced significantly with increasinglevels of compaction the second year at the Rozettasite and the first year at the Kewaunee site (Table 6).Reduced yields at the Kewaunee site the fourth yearwere unexpected, and are attributed to very wet soilconditions. This was a year with higher than normalrainfall. This suggests that the effect of prior compac-tion may reappear under adverse weather conditions.Although cone-penetration resistance and plant-heightmeasurements suggested that the effect of compactionexisted several years after it was applied, grain yieldwas not continually affected.

SUMMARYPenetration-resistance measurements showed that

compaction existed in the subsoil and persisted formore than 4 yr. Corn emergence rate was slowed dur-ing the first growing season after compaction, but plantpopulation was not affected. Plant height was lower inthe compacted plots in all years. Corn grain yields werereduced in the compaction treatments the first yearafter compaction at both sites and the second andfourth years at the silt loam and silty clay loam site,respectively.

RADCLIFFE ET AL.: SURFACE SEALING 223

temporal effects of subsoil compaction on soil strength and plant growth

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