Soil & Tillage Research, 10 (1987) 123-130 123 Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands

Subsoil Compaction in a Clay Soil. II. Natural Al leviat ion

S. GAMEDA, G.S.V. RAGHAVAN, E. McKYES and R. THERIAULT 1

Agricultural Engineering Department, Macdonald College of McGill University, Ste. Anne de Bellevue, Quebec H9X 1C0 (Canada) 1Agriculture Canada Research Station, St.-Jean-sur-Richelieu, Quebec J3B 6Z8 (Canada)

(Accepted for publication 10 February 1987)

ABSTRACT

Gameda, S., Raghavan, G.S.V., McKyes, E. and Theriault, R., 1987. Subsoil compaction in a clay soil. II. Natural alleviation. Soil Tillage Res., 10: 123-130.

The recovery of clay soil from a single incidence of heavy axle load compaction was investigated. Loads of 10 and 20 t axle- 1 were applied before and after a rainfall event in May, 1982. Grain corn (Zea mays L.) was then grown for three consecutive seasons and changes in bulk density to a depth of 0.6 m and crop yields were monitored. Differences between the effects of loading treat- ments on soil bulk density decreased with time, but 3 years after compaction application there were still significantly higher densities caused by both loading levels at depths between 0.3 and 0.4 m. In the third year of studies, crop growth and yields were still significantly lower owing to heavy axle loading.

INTRODUCTION

T h e effect of soil compac t ion on p l an t growth and yield has been the subject of num e r ous s tudies (Wi t t se l l and Hobbs , 1965; Bi lanski and Varma, 1976; Raghavan et al., 1978; G a u l t n e y et al., 1980; Negi e t al., 1980; Tay lo r et al., 1981; S t ibbe and Te rps t r a , 1982 ). T h e r e has been associa ted wi th th is an inter- est in reduc ing compact ion . W h e r e a s the use of conven t iona l til lage in alle- v ia t ing topsoil compac t ion is genera l ly accepted, the ef fec t iveness of me thods and processes t ha t reduce subsoil compac t ion is not well defined. Some researchers have observed t h a t subsoi l ing reduces soil compac t ion and resul ts in h igher yields ( D u m a s et al., 1975; Negi et al., 1980). However , a subsoiled field can easily be r ecompac t ed by t raff ic and s imilar ex te rna l forces (H a r tg e and Sommer , 1980).

T h e r e are also conf l ic t ing repor t s as to the effect of win te r f r eez ing / thawing cycles on a l levia t ion of compac t ion . K r u m b a c h and W h i t e (1964) r epor t t ha t to ta l pore space in the uppe r 0.30 m of two soils was h igher and bulk dens i ty

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124

lower after a freezing/thawing cycle than prior to freezing. In laboratory exper- iments, Gaultney et al. (1980) found that bulk density was significantly reduced by freezing/thawing cycles. The extent of natural alleviation under field con- ditions depended on the amount of precipitation prior to winter freezing, with higher soil moisture contents leading to greater reductions in soil bulk density and strength (Voorhees, 1983). However, Akram and Kemper (1979) observed that wetting/drying as well as freezing/thawing cycles did not restore infiltra- tion rates to precompacted levels. Other studies have shown that bulk density and penetration resistance in compacted subsoils did not decrease over several years of observations (Blake et al., 1976; Voorhees et al., 1978; H~kansson, 1982).

Some researchers have shown that crop yields improve with time, in spite of compaction which persists in the soil profile. Wittsell and Hobbs (1965) showed that, although compaction reduced wheat yields in the first year of application, it had no residual effects in subsequent years. H~kansson (1982) observed that, despite persistently higher soil bulk densities and strength, crop yields improved with time, probably owing to the creation of a network of cracks, earthworm holes and similar large holes, or to the interaction between subsoil compaction and weather conditions. In view of this, the present investigation seeks to determine soil bulk density reductions and crop responses in a clay soil subjected to 1 incidence of high axle load compaction prior to 3 crop grow- ing seasons in southern Quebec.

MATERIALS AND METHODS

Loads of 10 and 20 t axle- 1 were applied before and after a rainfall event in a clay soil (35% clay, 22% silt, 43% sand) at Macdonald College of McGill University, Quebec, Canada, in May 1982. After this set of compactive treat- ments, field traffic was never greater than 6 t axle- 1 during 3 crop production seasons. The experimental design, manner of t reatment application and field operations in the first year have been described elsewhere (Gameda et al., 1987 ). Discussions in this paper will concentrate on findings during the third season of crop production following compaction. Soil bulk density changes and crop yield responses over the 3 years of study will also be indicated. A schedule of the field events that were carried out is given in Fig. 1.

RESULTS AND DISCUSSION

Soil bulk density and moisture

Statistical analyses showed that there was no significant difference between the effects of the 2 soil moisture contents during compaction. As a result only loading effects are considered.

125

PLOT LAYOUT (MAY 1982)

COMPACTION and TILLAGE (MAY 1982)

FIRST YEAR CROP PRODUCTION (MAY-OCT 1982)

TILLAGE (OCT 1982)

SECOND YEAR CROP PRODUCTION (MAY-OCT 198])

TILLAGE (NOV 1983)

CULTIVATION and HERBICIDE APPLICATION (MAY 1984)

SEEDING and SIDE DRESSING (MAY 1984)

SOIL DENSITY and MOISTURE MEASUREMENTS (JUNE-AUG 1984)

HARVEST FOR EAR AND GRAIN YIELDS (OCT 1984)

HARVEST FOR TOTAL PLANT YIELDS (OCT 1984)

Fig. 1. Schedule of field events.

Soil bulk densities to a depth of 0.6 m were determined 3 times during the 1984 crop growing season. The mean of their distribution under loading treat- ments is shown in Fig. 2. At depths between 0.3 and 0.4 m there were significant differences between compacted and uncompacted plots (Table I ). In fact, the soil density profiles for each treatment show the persistence of higher bulk densities at depths below 0.25 m under the 20 t ax le - 1 treatment, and at depths below 0.30 m under the 10 t axle-1 loading. The fact that the persistence of

0.0 ..-~P= 0.2 ~~ 0 4 ; = CONTROL

10 TONNE

0.6 : ; 20 TONNE

I'.1 112 1'3 I i.4 1'.5 116 ti't DRY BULK DENSITY (Mg/m 3)

Fig. 2. Mean dry bulk density distributions during the 1984 season.

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TABLE I

Mean values of soil bulk density, 1984

Depth Compaction t reatment Dry bulk density (m) (t axle- ' ) (Mg m -3)

0-0.1 control 1.44 a 1 10 1.44 a 20 1.46 a

0.1-0.2

0.2-0.3

0.3-0.4

0.4-0.5

0.5-0.6

control 1.57 a 10 1.56 a 20 1.58 a

control 1.58 a 10 1.58 a 20 1.60 a

control 1.56 a 10 1.59 b 20 1.61 b

control 1.53 a 10 1.56 a 20 1.56 a

control 1.52 ab 10 1.55 b 20 1.51 a

1Means with the same letter are not significantly different at the 0.05 level.

higher bulk densities was evident at shallower depths under the 20 t axle-1 loading suggests that soil structural changes that had occurred under the 10 t axle- 1 loading may have been more responsive to wetting/drying and freezing/ thawing cycles than were changes due to the 20 t axle-1 load. The relieving effect of these cycles, however, was limited to a depth of about 0.35 m.

Observations of soil density profiles over the 3 years of study indicate several trends ( Fig. 3 ). Compared with profiles in 1982, following the initiation of the experiment, density distributions in 1983 and 1984 were higher. This increase indicates the change that occurred when the land was shifted from forage to corn production, thereby being subjected to traffic and implements associated with tillage, fertilizer and pesticide applications and to harvesting equipment. Apart from this initial shift there have been no notable changes in soil bulk density profiles. This suggests that there were only minimal reductions in soil bulk density as a result of wetting/drying and freezing/thawing cycles, and it indicates that whatever changes take place do so very slowly.

127

0.0

E 0 2 v

z I.- a. ~ 0.4

0.6

0.0

A E 0 .2

z I.-

0 . 4

0 .6

0 . 0 '

0 . 2

,.r p- o.

0.4

0.6

CONTROL

= = 1982

1983

-" ; 1984

; I I I t

I0 TONNE

= = 1982

1~83

; : 1984

I I I I i I

20 TONNE

= = 1982

~ 1983

: 1984

I:1 112 1'3 "I ',4 ".5 It.6

DRY BULK DENSITY ( M g / m 3)

,17

Fig. 3. Dry bulk density distributions from 1982 to 1984 following loading treatments applied in 1982.

There were no differences in soil volumetric moisture content due to com- pactive t rea tments over the whole growing season. However, air-filled porosi- ties to a depth of 0.3 m were limiting during most of the season (Table II ), and below depths of 0.3 m the soil was saturated throughout the same period.

Crop yields

In contrast to the small observed differences in soil bulk densities, corn (Zea mays L.) yield responses caused by high axle loading applied before 3 crop growing seasons were substantial (Table III) . For example, total plant dry matter yields due to the 10 and 20 t ax le- 1 t rea tments were, respectively, 23.3 and 24.7% lower than values observed in control plots. Corresponding grain yield reductions were 23.9 and 23.4%. Total plant and grain moisture contents in compacted plots were higher than those in uncompacted plots, indicating

128

T A B L E II

Mean values of air filled porosity to a dep th of 0.3 m, 1984

T r e a t m e n t No. of days after seeding ( t axle -1)

32 45 58 76 86 101

control - 7.2 7.2 11.0 8.1 0.4 10 4.0 8.2 6.8 10.5 6.8 - 20 1.8 7.3 7.1 11.2 9.0

the need for a prolonged crop dry-down period prior to harvest or for more energy during grain drying after harvest.

Comparisons of relative yields under loading treatments are presented in Fig. 4. Total plant and grain yield responses in the first year of studies (1982) reflect the poor conditions that existed for plant establishment in compacted plots. In the first year, compaction, plowing and disc harrowing of plots were carried out in the spring. As a result, the seedbed was not ideal for crop estab- lishment and germination was delayed by over 1 month, resulting in a shorter season for plant growth and leading to reduced yields. Relative crop yields were higher in 1983 than in 1984. Since weather conditions during the 1983 growing season were very dry, the compaction in the previous year may have relieved some of the moisture deficiency stress on crops by decreasing hydraulic con- ductivity and increasing water holding capacity. However, the higher than average precipitation in 1984 contributed to excess moisture availability and reduced aeration, as was seen from volumetric moisture content and air-filled porosity observations. This is probably the main reason for the large difference in overall yields between areas that were compacted annually and those that were compacted only in the first year of studies. The latter area was in a lower portion of the field and was susceptible to high water-table levels.

T A B L E III

Mean values for total p lan t and grain yields and moisture contents , 1984

Compact ion t r ea tmen t ( t axle- 1 )

Total p lan t Grain

Yield Moisture Yield Moisture (kg con ten t (kg conten t ha 1) (%) ha 1) (%)

control 7362.6 a 1 43.8 a 3884.6 a 36.9 a 10 5646.2 b 45.7 ab 2957.5 b 39.4 b 20 5545.5 b 46.4 b 2976.5 b 40.0 b

1Means wi th the same letter are no t significantly different at the 0.05 level.

I00

_1

>.- 8O

6o

40

TOTAL PLANT

19183 I 1982 1984

129

v I00

w m

>" 80

-~ 60

40

i i

G R A I N

i 19'8:3 ' 1982 1984

Fig. 4. Relative yields from 1982 to 1984 (control = 100%).

SUMMARY AND CONCLUSIONS

Owing to the marginal difference between them, the soil moisture levels at which compaction treatments had been applied showed no significant effect on soil bulk density. There were, however, significantly higher subsoil bulk densities caused by the 10 and 20 t axle- 1 loads. The extent and trend of recov- ery in the shallow subsoil suggests that wetting/drying and freezing/thawing were more effective in reducing bulk density increases which had resulted from the 10 rather than the 20 t axle-1 loading.

Crop yields in 1984 were significantly reduced by heavy axle loading, with both levels of loading equally contributing to the reductions. Comparisons of relative yields in 1984 with values in previous years indicate that, although the levels of compaction which persist in the soil may be conducive to higher mois- ture availability in dry years, they may lead to excess moisture stresses in years with greater than average precipitation. For the soil and weather conditions studied, soil bulk density reductions by wetting/drying and freezing/thawing, and improvements in crop yields following a single incidence of high axle load- ing, will take substantially longer than 3 years.

130

REFERENCES

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