Próba wyznaczania w warunkach laboratoryjnych granicznych wartości spulchniania i samozagęszczania się warstw ornych i podornych gleb uprawnych

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R O C Z N IK I G L E B O Z N A W C Z E T. X X V , D O D A T E K , W A R S Z A W A 1974

S T A N IS Ł A W T R Z E C K I

A T T E M P T OF D E T E R M IN IN G IN L A B O R A T O R Y C O N D IT IO N S

B O U N D A R Y V A L U E S O F L O O S E N IN G A N D S E L F -C O N D E N S A T IO N

O F A R A B L E A N D S U B A R A B L E L A Y E R S OF C U L T IV A T E D SO ILS

Institute of Crop Production, Agricu ltu re U niversity of W arsaw

IN T R O D U C T IO N A N D B IB L IO G R A P H IC S U R V E Y

The soil compactness constitutes more and more significant problem

in crop cultivation [2, 3, 4, 5, 6, 7, 8, 13]. It acquires particular importance

in view of the general tendency to the tillage simplification (minimum

tillage) as w ell as application of heavier and heavier tractors and farm

implements [4, 9, 13].

M any publications appeared recently concerning plant response to

soil compactness degree [3, 5, 6, 7, 8, 9, 11]. These investigations prove

that particular crop species show a different response to the soil com

pactness and the best growth and yields can be secured at medium com

pactness degree, and not in conditions of loose and very loose or

excessively compact soils.

On the other hand, there are only few investigations on the phenomen

on of loosening and self-condensation of soils as w ell as on the measure

ment methods of their dynamics in growing season. The hitherto works

concerning this question and own observations prove that the most im

portant factors of soil condensation are mechanical pressure (of tractor

and machine wheels, rollers etc.) and self-condensation of soil in the

shrinkage process occurring in natural conditions during drying up of

humid soil. Of a minimal effect on self-condensation process is soil

gravity (at the depth of 20 cm it does not exceed 0.04 kG/cm2 and at the

depth of 40 cm— 0.08 kG/cm2) and flattening effect of rain drops. Rain

irrespective of its intensity washes out soil aggregates, analogically to

any other form of soil moistening. Simultaneously there decreases the

friction between soil aggregates, w hat results in a closer contiguity of

elementary soil particles and aggregates. A further self-condensation

process consists in soil shrinkage during its drying up.

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290 S. Trzecki

It m ay be supposed that the mutual attraction of soil particles would

vary from several to several ten atmospheres, depending on soil moisture,

thus considerably exceeding the pressure of wheels of even heavy tractors

and farm implements, not exceeding normally 1 kG/cm2.

A certain corroboration of this presumption can constitute the fact

that in some soils the self-condensation occurring in the course of sum

mer period (expressed in terms of bulk density) is often much higher

than that formed at passage of even the heaviest tractor over newly

loosened soil. It is to stress, however, that any soil condensation stimula

tes its self-condensation ability in the shrinkage process.

Below an attempt of preliminary laboratory investigations on bound

ary values of loosening and self-condensation of arable and subarable

layers of various soils is presented.

O W N IN V E S T IG A T IO N S

For investigation 384 soil samples w ere used, delivered b y the Station

of Agricultural Chemistry in W arsaw, taken from arable and subarable

layers of adequately selected soils. W e tried to have by 12 samples

representative for particular groups of the mechanical composition of

soil. W e w ere successful in it only partly, since w e could obtain in such

a w ay a complete number of samples only for 14 mechanical composition

groups of arable and 16 groups of subarable layers.

In these samples actual moisture content, specific gravity, and bulk

density w ere determined for particular condensation states, viz. : for loose,

weakly compact and compact state of soils. Here only the data hased

on means for 12 samples representative for the given mechanical com

position group are presented. Every determination was made in three

replications. Thus the given data constitute means for 36 determinations,

what considerably enhances their reliability.

The samples for investigations, apart from using their certain number

for mechanical composition determination (Tables 1 and 2, Fig. 1), were

adequately prepared for further determinations, viz. :

— by means of a rubber pestle larger aggregates and lumps were

crushed at obtaining partly powdered soil,

— the samples were stored for a longer time in the laboratory room

to approximate their moisture content to the air-dry state.

Thus w e tried to secure for all the samples equal starting conditions.

If the samples w ere left in aggregated state, it w ould certainly give

much greater differences in bulk density of particular soils, making at

the same time impossible drawing general conclusions.

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Mechanical composition of arable layer samples taken for determination of mechanical composition groups /means for 12 soil samples/

T a b l e 1 No. of mecha nical compo sition group Mechanical composition group Nos of soil samples forming

the given mean

Percentage of mechanical fraction sizes in mm _{of particular sizes in mm}Total percentage

1.0-0.10 о о о H чл о 0.05-0.02 0.02-0.006 .0.006-0.002 < 0 . 0 0 2 1.0-0.1 0.10-0.02 < 0.02

I Loose sand la-12a 87 7 3 3 0 0 87 10 3

II Silty sand 193a-204a 69 21 6 4 0 0 69 27 4

III Weakly loamy sand 13a-24a 74 11 8 4 2 1 74 19 7

IV Weakly loamy silty sand 121a-132a 61 19 12 5 2 1 61 31 8

V Light loamy sand 25a-26a 66 12 10 6 3 3 66 22 12

VI Light loamy silty sand 133a-144a 54 16 17 7 3 3 54 33 13

VII Heavy loamy sand 37a-48a 63 10 10 8 4 5 63 20 17

VIII Heavy loamy silty sand 145a-156a 50 13 19 10 4 : 4 50 32 18

IX Light loam 49a-60a 54 10 10 9 7 10 54 20 26

X Light silty loam 157a-168a 41 12 21 13 6 7 41 33 26

XI Medium loam 61a-72a 41 8 11 15 10 15 41 19 40

XII Medium silty loam 169a-180a 27 8 23 19 11 12 27 31 42

XIII Common silt 73a-84a 22 18 36 12 5 7 22 54 24

XIV Clayey silt 109a-120a 13 10 38 20 7 12 13 48 39

to

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, T а Ъ 1 e 2 Mechanical composition of subarable layer samples taken for determination of mechanical composition groups

/means for 12 soil samples/

Ko.cf mecha nical compo sition group Mechanical 1 composition group Nos.of soil samples forming the given mean

Percentage of mechanical fraction sizes in mm

Total percentage of particular sizes in mm 1 .0-0,10 0.10-O.O5 0.05-0.02 0.02-0.006 0.006-0.002 < 0.002 1 .0-0 .1 0. io- о. 02 < 0.02 I Loose sand 1-12 90 5 2 3 0 0 90 7 3 II Silty sand 193-204 66 26 5 3 0 0 66 31 3

' III Weakly loamy sand 13-24 78 9 5 4 2 2 78 14 8

IV Weakly loamy silty sand 121-1J2 63 17 12 5 1 2 63 29 8

V Light loamy sand 25-36 68 12 8 7 3 2 68 20 12

VI Light loamy silty sand 133-144 58 16 13 7 3 3 58 29 13

VII Heavy loamy sand 37-48 62 13 7 8 3 7 62 20 18

VIII Heavy loamy silty sand 145-156 55 15 13

- 8 , 4 5 55 28 17

IX Light loam 49-60 51 14 8 8 5 14 51 22 27

X Light silty loam 157-168 44 15 14 10 5 12 44 29 27

XI Medium loam 61-72 39 10 9 15 10 17 ' 39 19 42

XII Medium silty loam 169-180 28 11 20 17 8 16 28 31 41

XIII Heavy loam 97-108 22 7 11 22 13 25 22 18 60

XIV Common silt 73-84 28 25 26 11 4 6 28 51 21

XV Clayey silt 109-120 14 12 35 18 8 13 14 47 39 XVI Clay 85-96 13 4 6 20 42 13 10 77

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Fig. 1. A vera ge mechanical composition of various arable layers of cultivated

m ineral soils

1 — loose sand, 2 — loose silty sand, 3 — w e a k ly loam y sand, 4 — w e a k ly loam y silty sand, 5 — light loam y sand, 6 — light loam y silty sand, 7 — h eavy loam y sand, 8 — h eavy loam y silty sand, 9 — light loam , 10 — light silty loam, 11 — m edium loam , 12 — m edium silty loam,

13 — com m on silt, 14 — clayey silt

It must be reminded here that the overdried soils, at so-called free

pouring, settle down rather closely. The highest loosening degree, as

it is exemplified by Fig. 2, is reached by them, with exception of sand,

at the moisture content equal to the field water capacity. Thus a further

increase of loosening degree of the soils investigated could take place

only at their clodding or lumping.

A s it follows from the above, in the investigations, at free pouring

. 1 y-0.006831xz-0.08295x * 1.761

)2

y=0.003626x z-0.08308+1.637

^ 3

y=0.00Z056xz-0.05608x+1.548 ,¥ y =0.004294X z-0.Q9Z21x+14

0)5

, y~0.001xz-0.05191 + 1.Z75 - 20 weight % o f water

Fig. 2. Changes of condensation state of arable layers at fre e pouring depending

on soil moisture expressed in w eigh t % (after S. Trzecki)

2 — san dy podzolic soil (loose san d), 2 — b la c k earth (light lo a m ), 3 — blac k earth (light silty loam ), 4 — silty pseudopodzolic soil (h eavy silty sand), 5 — river alluvial soil (common silt), 6 — m oisture at the perm anent w ilting pointof plants (pF = 4.2), 7 — m oisture of plant grow th inhibition start (pF = 3.0), 8 — m oisture equal to field w a ter acpacity (pF = 2.4)

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294

S. Trzecki

of air-dry soil, the state was reached by us, called conventionally

a loose state.

W hile comparing it with natural conditions it is as compact that

even at its loosening in most unfavourable conditions it could not be

more compact. Hence it is as if a boundary minimal loosening possible

in field conditions (Tables 3 and 4).

It seems, however, that in natural conditions is would be somewhat

higher.

The intermediate state, called weakly compact, was estimated as

follows: from the soil sample a thick pulp was made (to enable closer

contiguity of elementary soil particles) and with in the 100 cm3 cylinders

were filled up. The cylinders were placed on a dry blotting paper and

the moisture content decreasing gradually in them was supplemented

so as to secure a w ell filling-UD cylinders after flowing off the water

surplus. The soil excess protruding from top was cut with the knife,

the surface being appropriately levelled.

Such weakly compact condensation state should correspond with such

state in field conditions, attainable b y very loose arable or subarable

layer after abundant rainfalls when the first self-condensation takes

place due to a decrease of friction between elementary soil particles.

It is to stress that such state is to a certain extent characteristic for any

soil. It constitutes a maximal compactness degree attainable by soil after

moistening, although in natural conditions such compactness usually

cannot be reached due to the cloddy structure and other factors.

Further self-condensation occurs due to a natural shrinkage of soil

during drying up. Such self-condensation state called compact was deter

mined in the following w ay: moistened soil sample was brought into the

drier at the temperature of 105°C. A fter drying up the earth lump was

weighed and then its valume was determined by the paraffin method.

Having these two values: bulk and volume, the bulk density was calcula

ted. In natural conditions still higher condensation can be reached, called

very compact state. However, for its occurrence two factors must overlap:

first— mechanical condensation (e. g. passage of a heavy machine) and

then soil shrinkage process during its drying up.

It seems that in the self-condensation process the soil could not reach

in natural conditions higher condensation state than that determined

in our investigations. However, the compact state is usually not attainable,

as the arable layer or loosened subarable layer does not dry up so far.

It may be confirmed to a certain extent by the measurements o f the

arable layer compactness, carried out in a sugar beet field in 1971. The

measurements have proved, namely, that in the applied variants (five

various soil tillage kinds) irrigated soil (i.e. not drying up as strongly

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Boundary values of loosening and self-condensation of arable layers of various cultivated soils T a b l e 3 No. of mecha nical 1 Mechanical No. of soil sample forming the given mean Initial moist ening of Specific z Bulk density in g/cnr in the state Dif ference in bulk density between compact and loose state Total porosity in the state compo

sition group

composition group sample,

in weight

%

gravity

loose weakly

compact compact loose

weakly

compact compact

I Loose sand la-12a 0.40 2.67 1.55 1.59 П.О.* П.О.* 41.9 40.4 П.О.*

II Silty sand 193a-204a 0.66 2.64 1.45 1.55 1.82 0.37 45.1 41.3 31.1

III Weakly loamy sand 13a-24a 0.55 2.65 1.51 1.68 1.82 0.31 42.0 36.6 31.2

IV Weakly loamy silty sand 121a-l?2a 0.44 2.63 1.50 1.72 1.83 .0.33 43.0 34.6 30.4

V Light loamy sand 1 25a-26a 0.68 2.65 1.51 1.67 1.78 0.27 43.0 37.0 32.8

VI Light loamy silty sand 133a-144a 0.54 2.65 1.49 1.65 1.79 0.30 43.8 37.7 32.4

VII Heavy loamy sand 37a-48a 1.10 2.63 1.37 1.51 1.66 0.29 47.9 42.6 36.9

VIII Heavy loamy silty sand 145a-156a 0.90 2.65 1.41 1.52 1.72 0.31 46.8 42.6 35.1

IX Light loam 49a-60a 2.37 2.65 1.38 1.32 1.64 0.26 47.9 50.2 38.1

X Light silty loam 157a-168a 1 . 1 1 2.65 1.35 1.48 1.76 0.41 49.0 44.2 '33.6

XI Medium loam 61a-72a 2.23 2.65 1.34 1.25 1.57 . 0.23 49.4 52.8 40.8

211

Medium silty loam 169a-180a lo20 2.66 1 .2 1 1.36 1.61 0.40 54.5 48.9 39.5

XIII Common silt 73a-84a 0.99 2.65 1.36 1.34 1.56 0.20 48.7 49.4 41.1

XIV Clayey silt 109a-120a 2 .1 1 2.63 1.25 1.32 1.54 0.29 52.5 49.8 41.4

* Sand broke up when dried up, hence its bulk density could not be determined by the paraffin method

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Boundary values of loosening and self-condensation of subarable layers of various cultivated soils T a b l e 4 No. of mecha nical compo sition group Mechanical composition group No. of soil sample forming the given mean Initial moist ening of sample, in weight % Specific gravity Bulk density in g/cnr in the state Dif ference in bulk density between compact and loose state Total porosity in the state

loose weakly

compact compact loose

weakly

compact compact

I Loose sand 1-12 0.20 2.65 1.61 1.72 1.77 0.16 39.2 35.1 33.2

II Silty sand 193-204 0.30 2.63 1.54 1.57 1.71 0.17 41.4 40.3 35.0

III Weakly loamy sand 13-24 0.32 2.64 1.59 1.78 1.88 0.29 39.8 32.6 28.8

IV Weakly loamy silty sand 121-132 0.34 2.63 1.56 1.64 1.82 0.26 40.7 37.6 30.8

V Light loamy sand 25-36 0.39 2.63 1.56 1.80 1.94 0.38 40.7 3 1.6 26.2

VI Light loamy silty sand 133-144 0.55 2.61 1.51 1.72 1.87 0.36 42.1 38.3 28.4

VII Heavy loamy sand 37-48 0.95 2.63 1.43 1.63 1.83 0.40 45.6 38.0 30.4

VIII Heavy loamy silty sand 145-156 0.72 2.67 1.44 1.67 1.83 0.39 46.1 37.4 31.5

IX Light loam 49-60 1.78 2.63 1.37 1.51 1.82 0.45 47.9 42.6 30.8

X Light silty loam 157-168 1.27 2.67 1.35 1.58 1.82 0.47 49.4 40.8 31.8

XI Medium loam 61-72 1.91 2.68 1.35 1.40 1.80 0.45 49.6 47.8 32.8

XII Medium silty loam 169-180 1.44 2.75 1.29 1.43 1.70 0.41 53.1 48.0 38.2

XIII Heavy loam 97-108 2.60 2.64 1.30 1.22 1.74 0.44 50.8 53.8 34.1

XIV Common silt 73-84 0.98 2.63 1.38 1.49 1.70 0.32 47.5 43.4 35.4

XV' Clayey silt 109-120 1.67 2.65 1.25 1.29 1.65 0.40 52.8 50.9 37.7 XVI Clay 85-96 4.48 2.69 : 1.22 1.08 1.76 0.54 54.6 59.8 30.9

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as non-irrigated one) showed in the second half of growing season the

bulk density by 0.08-0.12 g/cm3 lower than non-irrigated soils.

It is to note that both arable and subarable layer does not reach any

constant compactness degree. Additional condensation factors are: devel

oping root system on the one hand and moisture changes resulting in

alternate shrinkage and swelling of soil on the other.

C O N C LU S IO N S

1. On the basis of the results obtained it can be concluded that sandy

soils reach a relatively high bulk density in the loosened state and also

a very high bulk density in the campact state. These features show much

less values in clayey and silty soils. A n intermediate place take loamy

soils. A n increase of the sand and silt content increases and an increase

of the clay content decreases the bulk density of soil.

2. The analogic mechanical composition group shows in the same con

ditions different compactness degree depending on its origin from arable

or subarable layer. The arable layer, richer in organic compounds showed

in three compactness states investigated lower bulk density, i.e., settled

down more loosely than the analogic soil from subarable layers (Tables

3 and 4).

REFERENCES

[1] A t a m a n i u k A. K.: К m ietodikie opredielenija płotnosti poczw y P oczw o-

w edien 4, 1970, 120-124.

[2] B i r e c k i М., T r z e c k i S., Z i m n a J.: W p ły w zbitości w arstw y ornej na

zdolność zatrzym yw ania w od y (pF). Rocz. glebozn. 18, 1967, 1, 133-142.

[3] K a i s e r

M.: Optim ale Bodendichte zur Getreideaussaat. Feldwirtsch. 10,

1969, 3, 124.

[4] K o w a c z e w D., S t o j n e w K., T o d o r o w F.: Izuczenije płotnosti poczw y

w sw yazi z woprosam i obrabotki poczw y v Bolgarii. International Scientific

Conference „Contem poraty Trends in Soil T illa g e ” , IU N G P u ław y R (38),

1972, 23-38.

[5] L i t y ń s k i A., T r z e c k i

S.: Badania nad w p ływ em rodzaju i zbitości

w arstw y podornej oraz zmiennych w arunków wilgotnościow ych na plony bu

raków cukrowych. Zesz. probl. Post. Nauk roi. 112, 1971, 209-221.

[

6 ] S i e n k i e w i c z J., G o n e t I.: W p ły w ciężaru objętościowego gleby na p lo

nowanie zbóż

jarych.

International Scientific

Conference

’’Contemporary

Trends in Soil T illa g e ” , IU N G Pu ław y R (38), 1972, 39-48.

[7] S t r a n a k A .: К niekterym otazkam teorie zapracowanii pudy. P. III. Rost-

linna w yroba 13, 1967,

6 , 621-636.

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298 S. Trzecki

roślin zbożowych i okopowych. International Scientific Conference ’’Contem-

poraty Trends in Soil T illa g e ” , IU N G P u ław y R (38), 1972, 23-38.

[9] T r z e c k i S.: Próba wyznaczenia granicznych oporów gleby i zawartości po

w ietrza dla początkowego wzrostu korzeni niektórych roślin uprawnych (ba

dania wazonowe). Post. Nauk roi.

6 , 1969, 71-78.

[10] T r z e c k i S.: Zależność stopnia spulchnienia gleby od jej rodzaju i w ilg o t

ności. N ow e Roi. 23, 1970, 9-10.

[11] T r z e c k i S., K a s z t e l a n J.: Próba wyznaczenia granicznych oporów gleby

dla wschodów niektórych gatunków roślin uprawnych. International Scientific

Conference ’’Contem porary Trends in Soil T illa g e ” , IU N G P u ław y R(38),

1972, 69-80.

[12] T r z e c k i S., Z d u n K.: Próba opracowania prostej polow ej m etody pomiaru

oporów gleby stawianym grubiejącym korzeniom spichrzowym roślin upraw

nych. Zesz. nauk. S G G W — Roi. (in print).

[13] W e r e s S.: W p ły w ugniatającego działania kół ciągników na glebę. Masz.

i Ciągn. roi. 11, 1965.

с . Т Ш Е Ц К И

П О П Ы Т К И О П РЕ Д Е Л Е Н И Я В Л А Б О Р А Т О Р Н Ы Х У С Л О В И Я Х

П Р Е Д Е Л Ь Н Ы Х В Е Л И Ч И Н Р Ы Х Л Е Н И Я И С А М О У П Л О Т Н Е Н И Я

П А Х О Т Н Ы Х И П О Д П А Х О Т Н Ы Х СЛО ЕВ К У Л Ь Т У Р Н Ы Х П О Ч В

Институт растениеводства Варшавской сельскохозяйственной академии

Р е з ю м е

В период 1971-1972 гг. в Институте растениеводства Варшавксой сельско

хозяйственной академии проводились исследования по определению в лабора

торных услови ях предельны х величин ры хлен ия и самоуплотнения пахотны х

и подпахотны х слоев разны х к ульту р н ы х почв.

Исследования проводились на 384 вы бранных образцах представительны х

д ля возможно всех групп механического состава почв примерно

12 образцов

для каждой группы — таблицы

1 и

2 , рис.

1 ).

В исследованиях определяли д ля каж дого из исследуем ы х пахотны х и под

пахотны х слоев три состояния плотности, в частности:

— р ы хлое (при свободном пересыпывании почвы),

— слабо уплотненное (полученное путем смачивания),

— уплотненное (путем определения максимальной сжимаемости).

Р езульта ты как средние д ля групп механического состава почв представ

лены в таблицах 3 и 4.

Н аиболее компактным состоянием уплотнения характеризовались песчаные

почвы, в меньшей степени — суглинисты е почвы, а в наименьшей — п ы лева

тые и илисты е почвы.

В исследованиях оказались гораздо более р ы хлы м и в таких ж е самых

услови я х пахотны е чем подпахотные слои аналогичны х групп механического

состава почв. Это свидетельствует о благоприятном воздействии органического

вещества на повышение степени ры хлости почвы.

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S. T R Z E C K I

E S S A IS DE L A D E S IG N A T IO N D A N S DES C O N D IT IO N S DE L A B O R A T O IR E

DES V A L E U R S L IM IT É E S DE L A S C A R IF IC A T IO N

E T DE L ’A U T O C O N D E N S A T IO N DES COUCHES L A B O U R A B L E S

E T S O U S -L A B O U R A B L E S DES SO LS C U L T IV A B L E S

Institut de la Production Végétale, Université Agronom ique de V arsovie

R é s u m é

Au cours les années 1971 et 1972 à l ’Institut de la Production V égétale

à Varsovie on a étudié dans les conditions de laboratoire la désignation des valeurs

lim itées de la scarification et de l ’autocondensation des couches labourables et

sous-labourables des sols cultivables.

On a exam iné 384 échantillons choisis, représentant autant que possible tous

les groupes mécaniques de sols (approxim ativem ent

12 échantillons pour chaque

groupe — tab.

1 et

2 , dess.

1 ).

Dans ces recherches on a désigné trois états de concentration pour chaque

couche labourable et sous-labourable, à savoir:

— scarifié (obtenu par une libre élévation du sol),

— faiblem ent compact (obtenu par humectation),

— compact (par la désignation de la contraction au maximum).

Les tableux 3 et 4 présentent des résultats moyens pour des groupes

mécaniques.

Ce sont des sols sablonneux qui se caractérisent d’un état d’agglom ération le

plus serré, les sols argileux sont moins serrés et les sols poussiereux — les moins

serrés.

Dans les mêmes conditions les couches labourables se sont, montées moins

serrées que les sous-labourables des groupes mécaniques analogiques.

Cela confirm e l ’action avantageuse du m atériel organique sur l ’augmentation

du degré de la scarification du sol.

S. T R Z E C K I

VE R SU C H DER E R M IT T L U N G IN DEN L A B O R B E D IN G U N G E N

V O N G R E N Z W E R T E N DER L O C K E R U N G UND S E L B S T V E R D IC H T U N G

DER A C K E R - UND U N T E R A C K E R S C H IC H T E N DER BÖDEN

Institut fü r Pflanzenproduktion

der Landw irtschaftlichen U niversität in W arszawa

Z u s a m m e n f a s s u n g

In den Jahren 1971-1972 wurden im Institut für Pflanzenproduktion der L a n d

w irtschaftlichen U niversität in W arszawa die Untersuchungen über die Erm ittlung

in den Laborbedingungen von G renzw erten der Lockerung und Selbstverdichtung

der A ck er- und Unterackerschichten verschiedener Kulturboden durchgeführt.

Die Untersuchungen umfassten 384 Bodenproben vertretbar für, möglichst alle

Gruppen der mechanischen Zusammensetzung der Böden (etw a 12 Bodenproben je

Gruppe) (Tab. 1 und 2, Abb. 1).

(12)

300 S. Trzecki

In den Untersuchungen wurden fü r jede der untersuchten A ck etr- und Unter -

ackterschichten drei Dichtezustände erm ittelt, und zw ar:

— locker (bei freier Bodenschüttung),

— schwach verdichtet (erhalten bei Benetzung),

— kom pakt (erm ittelt durch die Bestimmung des m axim alen Zusammen

schrumpfens).

Die Ergebnisse als M ittlere fü r die Gruppen der mechanischen Zusammenset

zung w erden in den Tabellen 3 und 4 dargestellt.

M it höchst kompakten Dichtezustand charakterisierten sich sandige Böden, m it

dem w en iger kompakten — lehm ige Böden und m it dem wenigsten kompakten —

staubige und Tonböden.

In den Untersuchungen erwiesen sich in gleichen Bedingungen die A c k e r

schichten v ie l lockerer als die Unterackerschichten analogischer Gruppen der

mechanischen Zusammensetzung. Dies zeugt über eine günstige W irkung des

organischen Stoffes auf die Erhöhung des Bodenlockerungsgrades.

s.

T R Z E C K I