Soil & Tillage Research, 19 ( 199 i ) 307-317 Elsevier Science Publishers B.V., Amsterdam

307

Soil physical prope~ies and growth of" spring barley as related to the degree of compactness of

two soils

J. Lipiec ~, I. Hhkansson 2, S. Tarkiewicz ~ and J. KossowskP ;Polish Academy of Sciences, Institute of Agrophysics, u!. Doiwiadczalna 4, 20-236 Lublin (Poland) 2Swedish University of AgriculturaI Sciences, Deparlment of Soil Sciences, 750 07 Uppsala (Sweden)

(Accepted for publication 21 March 1990)

ABSTRACT

Lipiec, J., H~ikansson, I., Tarkiewicz, S. and Kossowski, J., 1991. Soil physical properties and growth of spring barley as related to the degree of compactness of two soils. Soil Tillage l~.es., 19:307-3 ! 7.

The relationships between the degree of compactness of soil and soil penetration resistance, air- filled porosity, temperature and root development, leaf area index (LAI) and yield of spring barley were studied. The data were oLtained from field experiments on a silty loam and a loamy sand, with five wheel-compaction treatments prior to sowing in 1986-1989.

An increase in the degree of compactness resulted in higher penetration resistance, lower air-filled porosity and smaller daily temperature fluctuations, a greater accumulation of roots in the topsoil and shallower rooting depth. The LAI and grain yields decreased sharply when the degree of compactness exceeded ~ 88%.

INTRODUCTION

Paramete r s such as dry bulk density, total porosity, air-filled porosi ty and soil s trength have f requent ly been used to character ize the state o f soil com- partness . However , these pa ramete r s have a l imi ted value for compar i son o f the state o f compac t ion be tween soil types. A par t icular bulk densi ty m a y indicate an ex t remely compac t state in one soil, but a very loose state in an- o ther (Bowen, 1981; Hfikansson, 1990). To facili tate the compar i son o f the state o f soil compactness be tween sites, the concept "degree o f compac tness" was suggested, in which the actual bulk dens i ty is expressed as a percentage o f a reference bulk densi ty for the par t icular soil (Eriksson et al., 1974; Hfik- ansson, 1990).

The concept has been widely used in Swedish agricultural research on the crop yield response to plough layer compac t ion and appears to have biologi- cal significance (Hfikansson, 1990). Studies in Norway (Riley, 1988) showed that the degree o f compactness describes the condi t ions for plant growth bet- ter than bulk density,

0167-1987/91/$03.50 © 1991 - - Elsevier Science Publishers B.V.

308 J. LIPIEC ET AL.

The purpose of this study was to investigate the relationship between the soil compaction in the plough layer, as expressed by the degree of compact- ness, and some physical properties of two soils, rooting patterns and crop yields of spring barley, and also to study whether the optimum degree of compact- ness was the same in a region with conditions different from those where this approach was originally used.

MATERIALS AND METHODS

Field experiments ( 1986-1989 ) were carried out at two sites in the Lublin region, Poland, on an Orthic Luvisol developed from ~ilt formations, ncn- unilbrm, over limestone (Felin, Swidnicki Plateau) and on a Leptic Podzol developed from hydroglacial sands (Sobieszyn, South-Podlasie Lowland). Some characteristics of the soils are given in Table 1. The silt formations, corapared to loess, are characterized by a higher content of sand and clay fractions, and are referred to as "loess-like".

The various degrees of compactness were obtained by five wheel traffic treatments: (a) unwheeled; (b) one pass of a light tractor (weight 2.7 t, rear axle load 17.0 kN, inflation pressure 60 kPa ); (c) one pass of a heavy tractor (weight 4.8 t and rear axle load 31.8 kN on the silty loam soil, and 4.0 t ~nd 25.6 kN on the loamy sand soil, inflation pressure 160 kPa for both reactors); (d) three passes as in Treatment c; (e) eight passes as io %eatment c. The traffic treatments were applied uniformly over the whole plot area (46.5 m e ) before sowing spring barley. An approximately uniform seedbed for all treat- ments was prepared by a variable number ofharrowings. To avoid secondary compaction, horse-draw.,., harrows were used.

The bulk density for the whole plough layer was measured by four times replicated sampling with a 0.5-m 2 frame sampler in i 986 and core samples of 28 cm diameter and 10 cm height in 1987-1989.

The degree of compactness, D, was calculated according to the equation

"IABLE I

Some properties of the soils

,~,oil Particle size (ram) distribution (%, w/w) Organic Water content matter (%, w/w) at

1-0.1 0.1-0.05 0.05-0.02 0.02-0.006 0.006-0.002 <0.002 content -1 .5 MPa water (%, w/w) potential

Silty 20 loam

Loamy 66 sand

6 42 23 3 6 1.48 8.8

12 10 3 2 7 1.21 4.3

COMPACTNESS EFFECTS ON SOIL PROPERTIES AND BARLEY G R O W T H 3 0 9

D= 100pd/pdr

where pd is the actual dry bulk density and parr is the dry density of the ~ame soil in a reference state. This state is the most compact state that can be ob- tained by a static pressure of 200 kPa (H~kansson, 1990). The reference bulk densities were 1.621 and 1.788 Mg m -3 for silty loam and loanly sand, respectively.

Penetration resistance was measured in the field at vaiic, as ~oil moisture contents (six replications) by means of a penetrometer with a cone angle of 30 ° and an area of I cm 2 (Walczack et al., 1973).

Air-filled porosity was calculated on the basis of the moisture content at various matric potentials, the bulk density of the soil (in core samples of 100 cm 3 volume, 12 replications) and the particle density.

The temperature of the silty loam soil was measured at depths of 1, 2.5, 4, 6, 8, 10, 12.5, 15, 17.5, 20, 23, 26.5 and 30 cm by means of multisenzor ther- moelectrical thermometers (Kossowski, 1987) on Treatments a and d under both spring barley and bare soil. The variation in soil moisture content and bulk density within the plough layer was determined simultaneously.

The response of spring barley to compaction was characterized by leaf area index (LAI), root length and grain yield.

Root length ( 10 replications) was determined by the line-intersect method (Newman, 1966). Root length density, defined as total length per unit vol- ume of soil, was obtained by dividing the total root length per sample by the sample volume (200 cm 3). The leaf area was measured by means of the Delta- T Area Meter and was expressed in m 2 of leaf area per m 2 of ground area

| - T x (~A~). Both root length and LAI were determined at the heading growth phase.

RESULTS AND DISCUSSION

Weather

Some meteorological data which characterize the weather cond~itions dur- ing the spring barley growing seasons are given in Table 2 (data from the Meteorological Station, Agricultural Univers!tty of Lublin). Precipitation, air temperature and insolation during the main growth phases showed a large variation among years.

Soil physical properties

Soil compaction, as characterized by the degree of compactness, increased witll the number of wheelings and varied greatly among years (Fig. 1 ). These differences can be attributed mainly to the soil matric water potential at

310

TABLE 2

Weather conditions after sowing during the 1986-1989 growing seasons

J. LIPIEC ET AL.

Year t Growth phase 2

S-E E-Sh Sh-H H-MR MR-FR S-FR

1986

1987

1988

1989

Fcriod (days) 15 !7 26 18 21 97 Mean insolation (h day -~ ) 7.5 8.6 7.1 8.5 7.8 7.8 Mean air temperature (°C) 12.6 13.1 14.7 17.9 17.8 15.4 Frecipitation (mn,) 6.4 27.5 57.7 10.5 29.6 131.7

Period (days) 15 23 22 15 27 102 Mean insolation (h day-t ) 6.5 5.3 6.8 8.7 6.8 6.7 Mean air temperature (°C) 11.2 11.7 16.0 18.6 17.3 15.0 Precipitation (mm) 11.3 39.9 40.9 3.0 62.2 157.3

Period (days) 19 23 18 19 20 99 Mean insolation (h day -~ ) 8.4 7.1 6.2 6.2 7.6 7.1 Mean air temperature (°C) 9.3 15.0 15.7 18.4 18.7 15.5 Precipitation (ram) 4.5 43.8 62.4 55.5 25.7 191.9

Period (days) 18 28 24 22 22 114 Mean insolation (h day- ~ ) 4.1 5.3 8.6 6.6 8.3 6.6 Mean air temperz ture (°C) 8.0 11.3 15.3 15.9 17.8 12.8 Precipitation (ram) 26.0 45.1 24.8 45.9 40.1 181.9

~Date of sowing: 15 April ( 1986); 24 April ( 1987); 21 April ( 1988); 3i March (1989). 2S, sowing; E, emergence; Sh, shooting; H, heading; MR, milk ripeness, FR, full ripeness.

wheeling and to the initial degree of-ompactness. In both soils, the highest degree cfcompactness occurred in 1986 when the soil matric water potential at wheelin:=, was extremely high.

The r., ~ponse of penetration resistance and air-filled porosity to the degree of compa,.tness was related to the matric water potential (Fig. 2). For the majority of plants, the critical penetration resistance is 3 MPa (Ehlers, 1982; Boone et al., 1986; Willatt, 1986; Glifiski and Lipiec, ! 990) and the critical air-filled porosity 10%, v /v (Glinski and Stc~pniewski, 1985 ). Figure 2 shows that the range of matric water potentials in which these factors are not restric- tive for plant growth becomes narrower as the degree of compactness in- creases. For example, in silty loam for degrees of compactness o~'88 and 95%, the ranges are from - 8 0 0 to - 10 kPa, and from - 2 4 8 to - 3 0 kPa, respec- tively. These data agree with the findings of earlier experiments in which the soil water status was related to ODR (oxygen diffusion rate) and mechanical impedance (St,pniewski, 1981; Letey, 1985 ), as well as to the oxygen diffu- sion coefficient and mechanical impedance (Boone et al., 1986).

Measurements in bare silty loam soil showed that on sunny days the rate of

COMPACTNESS EFFECTS ON SOIL PROPERTIES AND BARLEY GROWTH 311

105/" ~ SILTY LOAM

I . . . . . LOAMY SAND e. ,,1986

c • 1988 t , . . '> , , -" , -~. ; " . . . ,~.~ " , , . ~ . . . ; , -.. \

~ 9 5 x xx ' x ~l " ,

~ Q4

' , . . . . , . - - - ' ~ \ c ",. t.1989 \ ~ b rr 85 ,, ~ .

", / ~""~19a8 \ 80 v1987 \

\o - I0 -20 -30 -ZO -50 - 60

MATRIC WATER POTENTIAL ( k P o )

Fig. 1. Degree of compacmess in the plough layer for Treatments a-e in relation to the matric water potential at wheeling.

o_ 100.

_

~ -100

rr ua

~ -10

S~LTY LOAM

"~-C ,.'>.._ ~ , . . ' ; : > - ~ _ ~ , 7":~-ZRAT'O" -I00~

-1(

" 7o I~'A[R_FILLED POROSITY s7%

8b 8g 9b 9g 1oo ~os -} ['JEGREE OF COMPACTNESS. %

OAMY SAND

g; . 15og_ - -

- ~ AIR-FILLED PORUSI r(

8'5 90 95 100 DEOREE OF COMPACTNESS. %

Fig. 2. Different levels of penetration resistance a~d air-filled porosity of soil in relation to the degree of compactness and matric water potential.

warming and cooling, the daily temperature fluctuations and the values efthe noon temperature in the topsoil were greater in loose soil than in compacted soil. At greater depths, however, a higher temperature was noted in com- pacted soil (Fig. 3A). The differences may be due to greater volumetric heat capacit) and thermal conductivity in the compacted soil than in the control soil at similar gravimetric soil moisture content. This is discussed in more detail elsewhere (Sikora et al., 1990). Bare soil may be regarded as being

312 J. LIPIEC ET AL.

2C

3O

-6 DIFFERENCES OF TEMPERATURE (T,.~,,p- TL==~ e ) , C"

- 4 -2 0 2 -2 0 '.. .

. . . . \ " 1 "%=

' I ~ : ' " "11"' '1 'V: "It" '1 T" 1)"

• • .I. • i I ~ . I~

• . i ~." mean. " ~.

• ! • :8 iI : l ! Fig. 3. Example of temperature differences between compacted (Treatment d) and loose (Treatment a) silty loam soil without plants (A) and with plants (B). Data from 10 sunny days at 13:00 h, in the period from shooting to the milk ripeness growth phase of spring barley in 1987.

similar to cropped soil early in the growing season. However, after the plant cover is well developed, the effect of soil compaction on the temperature is much smaller (Fig. 3B).

Crop response

An increase in the degree of compactness resulted in a concentration of the roots in the top layer (0-10 cm) and in decreased rooting depth (Table 3; Fig. 4). Field observations showed that this higher concentration of roots in the upper layer of compacted soil can be attributed to more horizontal growth. In a heavily compacted soil, such root distribution can be partly due to a hor- izontal orientation of pores, as found by Stowifiska-Jurkiewicz and Dom~at ( 1991 ). Roots grown in a severely compacted soil were characterized by a greater diameter, a higher degree of flattening, an irregular surface with dis- torted epidermal cells which had been penetrated by soil particles, and by tortuous growth (Fig. 5B). The thickening of roots indicates that, in com- pacted soil, pores with a diameter equal to or larger than the roots were ab-

C O M P A C T N E S S E F F E C T S O N S O I L P R O P E R T I E S A N D B A R L E Y G R O W T H 313

TABLE 3

Mean ( ! 986-1988 ) root length density ( cm c m - 3 ) at the heading growth phase of spring barley in various layers and treatments

Layer Silty loam Loamy sand (era)

a b c d e LSD a b c d e LSD ( P < 0.05 ) ( P < 0.05 )

0 - 1 0 4.7 5.2 5.3 5.9 7.1 0.65 4.9 4.6 4.8 5.7 7.3 1.18 10-20 2.0 1.9 1.3 1.0 0.5 0.38 2.5 2.1 1.8 1.4 0.7 0.41 20-30 i.1 1.0 0.6 0.6 0.1 0.21 1.7 1.3 I .I 0.2 0.1 0,36 30-40 0.6 0.2 0.1 - - 0.22 0.4 0.3 0.2 - - 0.18 40 -50 0.4 . . . . . 0.1 . . . . . 50-60 0.2 . . . . . 0.1 . . . . .

6° I 50

1 -

E

~-o

sitty loomy loom sand

v o - 1 9 8 6 - • o a - 1 9 8 7 - •

x , ~ o r ' , __ 1988 - •

~ . v - - 1989 - •

• v

v

~' a o •

• ¢

D • o

• • o o o

• • v

0 75 80 85 90 95 100 105

DEGREE OF COMPACTNESS ( % )

Fig. 4. Rooting depth of spring barley at heading time in relation to the degree of compactness.

sent. It was suggested (Sutton, 1969) that the tortuous root growth can be due to the root conforming to structural ped surfaces. Figure 5 also shows that the cortex cells of roots grown in compacted soil were radially enlarged. Pe- terson and Barber (1981 ) suggested that the wider cortex cells, with their greater absorptive surface area, will aid in overcoming nutrient stress.

The above findings imply that the main factor limiting root growth in the compacted soil was soil strength. In the experiments, values of penetration resistance critical for root growth frequently occurred t:~uring the growing sea- son. However, both ODR (in the silty loam; St~pniewska et al., 1990) and

314 J. LIPIEC ET AL.

A

C ~

Fig. 5. Root system and cross-section of roots grown in loose (A) and compacted (B) (Treat- mere e) silty loam soil ( X 150).

air-filled porosity (in both soils; Fig. 2) were found to be critically low in compacted treatments when soil moisture content was at or above field ca- pacity. However, during the spring barley growing season such wet conditions were rare and of short duration. They occurred within l-3-day periods, only once in 1986 and 1987, twice in 1988 and three times in 1989 (mostly at tillering and at the shooting growth phase). The better rooting in a loose soil might also have been partly due to the warmer top layer compared to that in a wheeled soil early in the growing season.

The LAI at heading and grain yields (Figs. 6 and 7 ) sharply decreased when the degree of compactness in the plough layer of both soils exceeded values of ~ 88 and 91%, respectively. The crop yield response to the degree of com- pactness proved to be very similar to that obtained in Swedish (Hfikansson, 1973, 1983, 1990) and Norwegian (Riley, 1983, 1988) experiments. The lowest LAI and grain yields correspond with the most reduced rooting depth (Fig. 4). Shallow rooting may result in decreased water and nutrient uptake. In addition, in the deepest layers of severely compacted soil (Table 3) the root length density is much below that considered as being capable of extract- ing most of the available water (Jordan and Miller, 1980; Barraclough, 1984; De Willigen and Van Noordwijk, 1987).

The response of LAI and grain yield to the degree of compactness varied

COMPACTNESS EFFECTS ON SOIL PRC PERTIES AND BARLEY GROWTH 315

!iii i r

t 50~, 5

• ~',,, o o v e

a

o

a

• eV

o • oe

o

g

o

e

O

80 85 90 93 100 DEGREE OF COMPACTNESS , °/o

Fig. 6. Relative leaf area index at heading (LAI; control plots = ! 00) in relation to the degree of compactness (symbols used as in Fig. 4).

~110

a

>.

o_ 9C o

u 80

~ 7c

60

I A • ~.oo.!,& 0% oa ~

o • o v

a •

[3o

8(3 8L5 90 9~5 100

DEGREE OF COMPACTNESS ,%

Fig. 7. Relative crop yield (control plots = 100) in relation to the degree of compactness (sym- bols used as in Fig. 4).

from year to year, which indicates interactions between meteorological con- ditions and the degree o f compactness.

The grain yield could also be affected by the plant population and resis- tance to lodging. The mean plant population at harvest on silty loam was lower than the sowing density by 17.6, 17.7, 1&1, 18.9 and 20.8% in Treatments a, b, c, d and e, respectively. The lowest values o f the degree o f resistance to lodging (on a scale from 1 to 9; 9 being the max imum resistance to lodging) were found for Treatments a, b and c ( 4 . 4 - 4 . 7 ) , and they increased up to 5.8

316 ~. LIPIEC El" AL.

and 8,6 i r "~'re.~tments d and e, respectively (B. Styk, Agdct~!*.ural University, Lublin, Poland, personal communicat ion, 1989).

CONCLUSIONS

( 1 ) The penetration resistance and air-filled porosity of soil are well cor- related with the degree of compactness.

(2) The daily temperature fluctuations and the noon temperature in the sub-surface layer of bare soil were lower in wheeled than in unwheeled soil. On soil with a plant cover, the effect of soil compact ion on temperature was much lower.

(3) An increase in the degree of compactness resulted in a ~ "eater concen- tration of roots in the surface layer and in a lower rooting depth. The roots grown in severely compacted plots were characterized by a higher degree of flattening, tortuous growth, distorted epidermal cells and radially enlarged cortex cells.

(4) Under Polish climatic conditions, excessive soil penetration resistance seems to be the main factor limiting root growth of spring barley in severely compacted soil.

(5) Crop yield and LA; decreased sharply when the degree of compactness exceeded values of ~ 91 and 88%, respectively.

(6) The correlations obtained between the degree of compactness and some soil properties of direct biological significance, as well as the consistency be- tween the crop yield results in Poland and in other countries, demonstrate the usefulness of this parameter for characterizing the compactness of a tilled soil layer from the point of view of soil physical condit ions for crop production.

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