THE ASH CONTENT OF THE PLOUGH LAYER OF
PEAT LANDS CULTIVATED BY DIFFERENT METHODS

Yrjö Pessi

Society of Peat Cultivation, Experimental Station Leteensuo

Received June 15, 1961

The ash content of the peat in Finnish bogs in their natural condition is rarely
higher than 10 %. The lowest ash content is encountered in Sphagnum bogs (3).
In the course of cultivation the ash content of the peat increases owing to the effects
of fertilizers and soil improvement. As peat has an inherently low ash content, the
increase caused by the cultivation measures has a favourable effect on the physical
properties of the soil as regards the thriving of cultivated plants. Fertilizing and
liming are not applied with this result in mind, but mineral soil is frequently added
as a soil improving agent to peat soils with the express purpose of changing the physi-
cal properties of the peat. This measure is often repeated after a few decades on the
assumption that the mineral soil has disappeared from the plough layer for one reason
or another.

The purpose of the present investigation is to report on the ash content of the
plough layer of cultivated peat lands today as the outcome of agricultural use
during several decades and according to different cultivation techniques. The
investigation material was collected in 1960.

Objects of investigation

A number of long-term soil improvement tests at the Experimental Station of
Northern Pohjanmaa at Ruukki (A = 25.1°E, <p = 64.6°N), the Experimental Sta-
tion of the Peat Cultivation Society at Leteensuo (A = 24.3°E, <p = 61.6°N) and the
Experimental Station of the same Society at Tohmajärvi (A = 30.2°E, cp = 62.1°N)
were chosen as objects of the investigation. Several tests now in progress at these
stations have been carried on through many decades. Attention was paid to ash
content conditions in fen land as well as Sphagnum bogs. The peats concerned in
the following tests were studied in this investigation.

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216

Leteensuo

Claying and sand addition test on fen land. The peat on the test area consists
of forest sedge peat. The experiment was started in 1910, in which year claying
and sand addition was performed for the first time. Mineral soil additions of 100,
200, 300 and 400 m 3 per hectare were used. Claying and sand addition were repeated
according to the same experimental plan in 1928. The results of the investigation
are stated as referring to the soil improving agent additions of 200, 400, 600 and
800 m 3 per hectare, respectively, and it should be noted that these quantities have
been applied in two instalments. Several different fertilizations have also been
included in the test. In this connection the completely unfertilized test plot and the
treatments with annually recurring phosphate and potassium fertilization (100 kg
P 20 5 and 100 kg K2O per hectare) have been subjected to study. The experimental
plants were spring cereals, hay, and root crops. The fertilizers were mostly super-
phosphate and potassium salt. Vesikivi (7) has given an account of this experiment
and in part of its results from the first decades of its duration.

At the time when the area was brought into cultivation, the following contents
of its peat w'ere recorded: N 3.19, Si02 3.66, S0 3 0.88, P 20 5 0.23, Al2Os + Fe203
2.97, MnO 0.02, CaO 2.01, MgO 0.28, K 2O 0.13, 0.07 % (6). The kind of mineral

Table 1. Chemical composition of the mineral soil used in the soil improving tests at Leteensuo (7).

Constituents soluble in 4 % HCI, %

Clay Sand

Si0 2 0.49 0.20
SO, 0.07 0.03
P 805 0.10 0.06
A12 0, + Fe2 0, 5.14 1.01
MnO < 0.01 0.01
CaO 0.47 0.08
MgO 0.47 0.05
K aO 0.22 0.06
NajO 0.11 0.05

Table 2. Mechanical composition and pH value of the mineral soil used in the soil improving tests at
Leteensuo (7).

Grain size, mm 0 Clay, % Sand, %

2 0.0 0.0
2 -0.2 0.0 21.5
0.2 -0.02 5.0 76.5
0.02 -0.002 17.5 2.0
0.002 77.5
Total 100 100
pH 5.9 4.4



217

soil used for soil improvement can be seen from the results of th analysis preseneted
in Table 1 (7, p. 34), while Table 2 gives its mechanical composition (7, p. 34).

Claying test on fen land. The peat on the test area is forest sedge peat. Cultiva-
tion of the area was started in 1921 and the experiment proper was commenced
in 1923. One half of the experimental strip was clayed (at 200 m 3 per hectare) in
1923; repeated claying at the same rate was done in 1941. A potassium fertilizing
test has been combined with this experiment. The potassium fertilizer quantities
were initially equivalent to 0, 20, 40, 60 and 80 kg K 2O per hectare, but since 1930
the annual quantities of 0, 30, 60, 90 and 120 kg per hectare have been applied.
The notation of the treatments used in this work refers to the latter fertilizing plan.
The fertilizing test plots were 50 m 2 in size each. Their location has been described
in detail in a previous publication (5, p. 4). As base fertilization, the entire test
area received an annual phosphate fertilization equivalent to about 300 kg super-
phosphate per hectare. No nitrogen fertilizer was given. The experimental plants
cultivated on this area and the test results have been presented on a previous
occasion (5).

The test is immediately adjacent to the above-mentioned claying and sand
addition test and the peat quality is therefore largely identical in both tests. The
same clay was also used for soil improvement in both instances.

Liming and claying test on Sphagnum bog. The peat on the test area is Sphagnum
peat, mainly composed of Sph. fuscum moss. The area was cleared for cultivation in
1921 and the test was started in 1923. One half of the test strip was clayed at 300 m;!

per hectare. Of the lime quantities provided by the experimental plan (0, 1,2, 3
and 4 t ons CaO per hectare) one half was given in the spring of 1923and the otherhalf
in the spring of 1924. The annual fertilization varied in the range equivalent to
100—300 kg superphosphate, 200 kg 40 % potassium salt and 100—300 kg calcium
nitrate per hectare. Stable manure was given altogether 51 tons per hectare in 1923
and 1931. The results of the experiment up to 1957 have been presented in a previous
publication (4), which also gives an account of the location of the test plots. The
properties of the clay used for soil improvement can be seen from Tables 1 and 2. The
ash content of uncultivated peat near the test was 1.0 %.

Claying, sand addition and liming test on Sphagnum bog. The peat on the test
area is similar to that in the preceding test. The area was cleared for cultivation in
1930 and the mineral soil additions were spread in 1932. One half of the test strip
had been limed (with 4 000 kg slaked lime per hectare), and this was also done in
the spring of 1932. The liming was repeated (at 2 000 kg per hectare) in 1937. Stable
manure was given in 1932 and 1935, altogether 70 tons per hectare. The annual
administration of artificial fertilizers was equivalent to 200—250kg superphosphate,
200—300 kg 40 % potassium salt and 200—300 kg calcium nitrate per hectare.
The test results up to 1957 have been reported in a previous publication (4), which
also gives a detailed account of the location of the test plots. The properties of the
mineral soil used for soil improvement can be seen from Tables 1 and 2.



Table
3.
Ash
content
of
the
peat
in
the
tests
at

Leteensuo,
referred
to
the
dry
peat.

Test
No.
1

Test
No.
2

Test
No.
3

Test
No.
4

Mineral
Ash

percentage
Ferti-
Ash

percentage
Liming,
Ash

percentage
Mineral
Ash

percentage

soil

Un-

Fertü"
lization

'

"urT
Clayed

tons
Ca
°

Un-

Clayed
SOÜ

Unlimed
Limed

addition,
ferti

.
Uzed

kgK2
0

per

daye(J

addition,

m'
per

..

,

per

hectare

m3per

hectare

hectare

hectare

0

25.2

28.2

0

19.5±
16

46.8±8.5
0

13.1±8.3
53.1±5.6
0

34.1
±3.4
30.1
±

4.0

200
Clay
32.6

41.3

30

18.9±2.1
47.4±6.4
1

10.8±3.6
55.3±1.8
200
S

57.0
±2.6
55.6
±

4.7

200
Sand
44.8

45.4

60

20.6±
1.9

50.0±2.2
2

8.4±1.8
55.4±2.1
200
Hk
53.3±6.0

56.3±11.5

400
Clay
45.3

48.7

90

20.1
±

4.7
52.3
±4.7
3

11.5±2.2
55.1±2.9
400
S

63.3
±B.O
60.1
±

5.8

400
Sand
54.4
60.3

120
24.3±10.2
50.2±4.5
4

13.2±3.8
53.2±9.0
400
Hk
75.6±4.1
72.5
±

7.5

600
Clay
51.6
61.0

600
Sand
66.4

68.9

800
Clay
64.7

65.9

800
Sand
68.9

75.3

218



219

Tohmajärvi

Claying and sand addition test on fen land. The peat on the test area consists
of forest sedge peat. The area was cleared for cultivation in 1932; prior to this it
had served as undrained meadow land. The experiment was established in 1935,
at which time the soil improving agents were applied. Various fertilizing tests were
combined with the experiment. The following combinations of soil improvement
and fertilization were chosen as subjects of the present investigation: Completely
unfertilized plots and phosphate and potassium-fertilized (50 kg P 2O ä and 80 kg K2 O
per hectare) plots without soil improving agents and with addition of 200 m 3 clay,
200 m 3 fine sand, 200 m 3 gravel and 200 m 3 fine sand of another quality per hectare,
respectively. The unfertilized and fertilized samples were lumped together.

Table 4. Ash content of the peat in the tests at Ruukki and Tohmajärvi, referred to the dry peat.

Test No. 5 Test No. 6 Test No. 7

Clay addi- Ash P« Soil Ash percentage Mineral soil Ash
tion, m 3 Unferti- Ferti- improving Unferti- Ferti- addition, percentage

per hectare lized lized treatment lized lized m* per hectare

O 17.2- 2.1 16.7 0.6 None 20.5 • 6.4 18.8 12.6 0 42.8±11.0
100 31.5 j_ 0.7 32.6i2.3 Clayed 60.7 i 5.0 69.6±1.6 Fine sand 200 66.1± 2.2
200 45.2 1.8 43.7 ' 1.5 Limed 26.7+4.0 Clay 200 66.2± 2.9

Clayed and
300 43.1 16.2 47.8 5.2 limed 57.9±9.9 Fine sand 200 71.5: 3.0

Gravel 200 54.8± 6.3
0 42.5± 7.2

Ruukki

Claying test on fen land. The peat on the test area consists of sedge peat. The
area was worked over with the mattock and drained in the 1910’s but was not
brought into cultivation. It was ploughed in 1932 and the soil improvement test
was established in 1933. Clay was added as soil improving agent at 0, 100, 200
and 300 m 3 per hectare. Various fertilizing tests were combined with the experiment.
The plots with soil improving treatment, without fertilization and with annual
nitrogen, phosphate and potassium fertilization (100 kg calcium nitrate, 300 kg
Kotka phosphate and 150 kg 40 % potassium salt per hectare) were chosen as
subjects of the present investigation. This experiment and its results have been
described by Anttinen (2), and the location of the plots has been given in detail
in his publication.

Claying and liming test on Sphagnum bog. The peat on the test area is Sphagnum
peat. The area was worked over with the mattock and drained in the 1910’s but it
was not taken into actual cultivation until about ten years later. The thickness
of the peat layer is only about 30—50 cm. The properties of the peat on the test
area are illustrated by the following compilation (1, p. 7):



Ignition losses, referred to the dry matter
Volume weight
Electrolytes, mg per 1 litre of soil
pH
N (in the dry matter)
CaO (soluble in 0.2-n HCI)
P a06 ( » » 0.2-n » )

KjO ( » » 0.2-n » )

94.2 %

0.28
188

4.13
14.5 »/00

3.29 »/„„

0,24 o/00

0 54 »/oo

Different fertilizing tests were also combined with this experiment. The plots
with soil improvement by 0 and 200 m 3 clay per hectare (applied twice, in 1929 and
1935), by liming (3 000 kg ground limestone per hectare in 1929, 4 000 kg per hect-

are in 1935 and 4 000 kg per hectare in 1947) and by combined claying and liming
were considered in the present investigation. In the last-mentioned treatment the
claying and liming was done as in the treatments with one or the other treatment
alone. Test samples were taken from the soil improvement test plots without fer-
tilization and from plots that had been given nitrogen, phosphate and potassium
fertilization (200 kg calcium nitrate, 400 kg Kotka phosphate and 200 kg 40%
potassium salt per hectare). Anttinen (1 a) has described this test and its results
and given an account of the location of the test plots.

Methods of investigation

The peat samples were taken in the following way. About 20—30 samples ex-
tending to 10 cm depth from the soil surface were taken with the aid of a sampling
cylinder 7.14 cm in diameter from each test plot, at equal distances along two
parallel lines. The samples of the different replicates were not combined but were
separately investigated. The samples were immediately spread out in a thin layer
and air-dried. The moisture content of the peat was determined by keeping the peat
samples 24 hours at + 110°C. The ignition residue, in per cent, of the dry matter,
was taken to represent the ash percentage of the peat.

Results

The results of the present investigation are compiled in Tables 3 and 4, where
the figures after each value show the dispersion. It can be noted that the ash content
of the peat in the plough layer has consistently increased as a consequence of culti-
vation through several decades. Addition of mineral soil as a soil improving agent
on peat land has caused a remarkable increase in the ash content and it can be said
that its effect on the properties of the soil seems to be very prolonged since the most
recent addition in the present tests was made 25—27 years ago. It can be assumed
that in the tests Nos. 4 and 6 transportation of soil from one soil improvement
plot to another has occurred because the mineral soil was spread separately on each
plot in these tests. The ash content established for the plot without treatment may
be too high for this reason.

220



221

Various substances are added to the soil as effects of cultivation, such as plant
residues and root substance, which alter the original properties of the peat in the
course of time. The increase of the ash content of the plough layer as a consequence
of cultivation is thought to be one of the factors responsible for the phenomenon
that cultivated peat land gradually loses its original character.

Conclusions

The results of this investigation justify the conclusion that the ash content of
peat increases under cultivation through the effects of the administered fertilizers
and soil improving agents. The ash content is increased in a particularly remarkable
degree by addition of mineral soil as a soil improving agent. The ash content in the
plough layer of cultivated peat lands which had received an addition of mineral soil
as long as 37 years ago was found to be quite high. This would seem to indicate a
prolonged effect of mineral soil on the properties of the plough layer. The increase
of the ash content in the plough layer of cultivated peat land is obviously one of
the factors responsible for the phenomenon that long-term cultivation of peat land
slowly deprives the peat of its original character.

REFERENCES

(1) Anttinen, O. 1957. Rahkasuon lannoitus- ja maanparannuskokeen tuloksia. Referat: Ergebnisse
eines Düngungs- und Bodenverbesserungsversuchs auf Sphagnum-Moor. Valt. maatal.
koetoim. julk. 155: 1 29.

(2) —»— 1957. Saraturvesuon saveus- ja lannoituskokeen tuloksia. Referat: Ergebnisse eines
Lehmzufuhr- und Düngungsversuchs auf Seggentorfmoor. Ibid. 163: 1 20.

(3) Kivinen, E. 1948. Suotiede. Porvoo. 219 p.
(4) Pessi, Y. 1959. Kivennäismaan vaikutuksesta rahkasuon maanparannusaineena Leteensuon koe-

aseman pitkäaikaisten kenttäkokeiden perusteella. Summary: On the effect of mineral
soil as a soil improving agent on Sphagnum bogs on the basis of prolonged field tests at
Leteensuo Experimental Station. Acta agr. fenn. 94, 14: 241 268.

(5) —» 1960. Kivennäismaan merkityksestä mutasuon maanparannusaineena Leteensuon koe-
aseman pitkäaikaisten kenttäkokeiden perusteella. Summary: On the significance of mi-
neral soil as a soil improving agent on fens on the basis of prolonged field tests at Leteensuo
Experimental Station. Ibid. 95, 3.

(6) Simola, E. F. 1916. Über die durch Kali- und Phosphorsäuredüngung auf einem Niedermoore be-
wirkten Schwankungen der Eigenschaften und Ernteerträge des Hafers. Helsinki. 32 p.

(7) Vesikivi, A. 1929. Suonsavetuksen ja -hiekoituksen taloudellisesta kannatta vaisuudesta. Referat.
Über die Rentabilität der Lehm- und Sandmischkultur auf Moorboden. Suomen suovilj.
yhd. tiet. julk. 12: 1 131.



222

SELOSTUS:

VILJELTYJEN TURVEMAIDEN MUOKKAUSKERROKSEN TUHKAPITOISUUDESTA

Yrjö Pessi

Suoviljelysyhdistys, Leteensuon koeasema

Viljeltyjen turvemaiden muokkauskerroksen tuhkapitoisuutta on tutkittu Leteensuon, Tohma
järven ja Pohjois-Pohjanmaan koeaseman pitkäaikaisista maanparannus- ja lannoituskokeista. Tulok
sista voidaan päätellä, että turpeen tuhkapitoisuus lisääntyy viljelyn yhteydessä käytettyjen lannoit
teiden ja maanparannusaineiden vaikutuksesta. Erityisen huomattavasti tuhkapitoisuutta lisää kiven
näismaan käyttö maanparannusaineena. Kun kivennäismaata oli lisätty 37 vuotta aikaisemmin, osoit
tautui muokkauskerroksen tuhkapitoisuus yhä edelleen suureksi. Tämä viittaisi kivennäismaan pitkä
aikaiseen vaikutukseen suoviljelyksen maanparannusaineena. Viljeltyjen turvemaiden muokkaus
kerroksen tuhkapitoisuuden lisääntyminen on ilmeisesti eräs syy siihen, että kauan viljellyt suovilje
lykset menettävät aikaa myöten alkuperäisen luonteensa ja muuttuvat vähitellen multamaita muis
tuttaviksi.