Zbl. Mikrobiol. 140, (1985) 277-282

[Department of Soil Microbiology, Academy of Agriculture, Poznan, Poland].

The Influence of Slurry on the Bacterial Biomass inIncubated Soil Samples

MARIA MUSZYNSKA and HENRYK KASZUBIAK

With 5 Figures

Summary

Attempts have been made to find the causes of the bacterial biomass decline in the soil, follow­ing a heavy slurry application. It was found that in well aerated soil samples, not covered withplants and incubated under laboratory conditions, this effect was weaker than that under fieldconditions. A decline in the biomass was a by-effect preceded by its increase; it was not a resultof overgrowth of fungi, release of significant amounts of free ammonia or changes in free phenolconcentration. It might be partially limited by moisture increase in soil.

Zusammenfassung

Es wurde den Ursachen der Verringerung der Bakterienbiomasse in inkubierten Bodenprobenals Folge intensiver Oulleanwendung nachgegangen. In gut belufteten, unbepflanzten Bodenprobentritt diese Erscheinung in geringerem Ausma/3e auf als unter Feldbedingungen. Faktoren wieUberhandnehmen der Pilzflora, Abgabe gro/3er Ammoniakmengen Bowie Verttuderungen im Ge­halt an freien Phenolen spielen keine Rolle. Erhohung der Bodenfeuchtigkeit begrenzt den Ein­flu/3 der Guile.

It was previously found (KASZUBIAK, DURSKA, KACZMAREK, and FILODA 1983)that meadow dressing with slurry in doses, corresponding to 375 or 500 kg N Iha,decreased the bacterial biomass in the soil throughout the vegetation season, despitesignificant concentration of nutrient for microorganisms in the slurry (KAS:lUBIAK1978).

Causes of that phenomenon might be theoretically different. In grasslands, thesoil bacteria are especially hardly influenced by plant roots (WOLDENDORP 1963) andslurry may modify this effect, it changes the meadow flora (BOROWIEC et al. 1977),as well as the mass and chemical composition of roots in particular grass species(COWAN 1976).

Moreover, heavy dressing of fields with slurry may limit oxygen diffusion in soil(McALLISTER 1977).

One cannot exclude that, even if slurry does not deteriorate aerobic conditions, itstimulates a competition between the fungi and the bacteria by overgrowth of theformer.

The presence of phenol compounds in the slurry (GISINGER 1966) should also betaken into consideration and the release of significant amounts of free ammonia aswell (KASZUBIAK and Mus:lYNSKA 1980).

This paper presents experiments, performed with incubated soil samples in orderto find whether a decline in bacterial biomass by slurry occurs independently of soilconditions, and which of the above-mentioned factors is an essential cause of thatphenomenon.

19 IIbl. Mikrobiol. Bd. 140

278 M. MUSZYNSKA and H. KASZUBIAK

Materials and Methods

Soil samples and their incubation

The experiments were carried out with a water-meadow soil from Miedzych6d, previouslystudied under field conditions (KASZUBIAK et al. 1983). It was loose, dusty loamy sand of pH 5.8,'containing 2.1 % organic C. For comparative purposes, soils from meadows in Brody (muck,pH 6.9,2.1 % organic C) and in Dlon (loose, loamy sand, pH 7.0, 2.1 % organic C) were additionallyused in one of the experiments. All the soils were collected from an object. not amended by anymanure or fertilizer for at least 2 years.

The soil was taken from the 30-cm deep surface layer, sieved and divided into two portions.The first of them was thoroughly mixed with dense cattle slurry (15 % dry wt.; C: N = 8.1), adose corresponding to 187 mg N/kg dry wt. of soil, which is adequate to about 800 kg N/ha. Thesecond portion was left without any additions as control.

The soil prepared in such a way was loosely put into jars, 1 kg of fresh mass each in three repli­cations, incubated for five teen weeks at 26 "C, maintaining field moisture (20-25 % of WHC).Microbiological and chemical determinations were made several dozens times, beginning from thefirst day of the experiment. In the studies on slurry action at different soil moisture the soil wasdried up, prior to incubation, at about 20°C for 3 days and then rewetted.

Microbiological determinations

The following values were determined in incubated soil samples: bacterial biomass - on thebasis of cell enumeration (KASZUBIAK et al. 1977) under a fluorescence microscope, using acridineorange as a fluorochrome (STRUGGER 1948); the number of soil bacteria, able to grow on laboratorymedia - using the plate-dilution method and a soil-extract agar; fungal biomass - on the basisof measurements of the length and width of hyphae, stained with aniline blue, according to JONESand MOLLISON (1948); the number of fungi, growing on laboratory media - by the method ofWarcup, modified by MANKA (1964), applying Martin's medium, modified by JOHNSON (1957).

Chemical determinations

Concentration of free NH3, according to KIM (1973), on the basis of sorption in 0.005 n H 2S04and concentrations of free phenols, ace. to GIEBEL (1970), differentiating mono- and polyphenols,were determined.

Results and Discussion

Contrary to field experiments (KASZUBIAK et al. 1983) the bacterial biomass in theslurry-treated soil samples, better aerated than the soil under field conditions and notovergrown by plant roots, show not only declines but also increases, depending on thetime of incubation (Fig. 1). Consequently, the average concentrations of the biomassin slurry treated and untreated samples were the same and for the soils from Mied­zychod, Brody, and Dlon amounted to 2.0, 1.7, and 1.0 mgjg dry wt., respectively.

The temporary increases became evident already at the moment while the experi­ment was set up - as a result of high bacterial number in the slurry. During the firstincubation days the bacterial biomass usually continued to increase, as in the soilsfrom Mi~dzych6dand Dlon was revealed. There were rather soil bacteria which multi­plied; no bacteria of the slurry adapted first of all to the alimentary tract (HRUBANT

1973). After these increases declines in the bacterial biomass occurred, and theirintensity depended on the soil under study. Generally, they lasted for several dozensday, i.e., much longer than biomass increases.

Decreases of the bacterial biomass in soil samples, incubated with slurry, could bypartially limited by adjusting their moisture to the optimum level for bacterial growth,as was revealed on the example of the soil from Miedzychod. At the water content,

The Influence of Slurry on the Bacterial Biomas, 279

,

1057122 35 57Days of analysis

,

850 L....,c--~-If--~-----:t::----:!-=------,=---=:,--------:~

Soil from;

o Mittdzychod

• Brody

!J. Dron

Fig. 1. Bacterial biomass in samples of various soils, incubated with slurry.

corresponding to 10 or 20 % WHO, declines in the biomass became evident betweenthe 5th and 25th day, whereas declines at a 50 %saturation of WHO were marked onlybetween the 8th and 40th day.

The dynamics of changes in the bacterial biomass suggested that the conditions,unfavourable to the bacterial growth, developed as a result of processes of slurry trans­formations in the soil.

o typica l bacter ia

• actinomycetes

300

c,~ 100o~

3 5 it. 24 38 50Days of analysis

55 85 105

Fig. 2. Numbers of bacteria growing in the laboratory media.

10'

280 M. MUSZYNSKA and H. KASZUBIAK

Declines in the bacterial biomass were probably not caused by deterioration ofaerobic conditions, as indicate changes in the number of aerobic bacteria, detectablein the soil by the method of culture (Fig. 2). The number of those forms of typicalbacteria and actinomycetes in slurry treated soil samples was never smaller than inthe control. The results obtained are in agreement with observations by other authors(CZEKALA and Dlj]BOSZ 1975, PIETE and ZUKOWSKA 1978, EILAND 1981), who alsostudied the reaction of soil bacteria on slurry-using methods of cultures.

Differences between changes in biomass and in the number of bacteria, detectableby the methods of cultures, were enlarged by a fact that increases in the number ofthose bacteria were considerably higher and were evident not only at the beginning,but also at the end of soil incubation with slurry. This phenomenon evidenced diffe­rent response of zymogenic and autochthonic bacteria to slurry. Soil bacteria, able togrow on the laboratory media, are according to KASZUBIAK et al. (1974) mainlyrepresented by zymogenic forms, constituting only a small portion of the total bac­terial biomass, which concentration depends first of all on more numerous autoch­thons, recognized in the soil while a microscope was used.

Decreases in the bacterial biomass were not caused by overgrowth of fungi. Thefungal biomass, irrespective of slurry addition, was about 5-fold smaller than thebacterial one, and when sometimes differences between the control and slurry­treated soil samples occurred, they were always within the experimental error.

While the number of fungi was estimated using the plate dilution method (Fig. 3),revealing only some groups of these microorganisms, no differences between the soilsamples with and without slurry addition were noted(28 X 103 cells/g dry wt.).Althoughduring incubation slurry caused increases in the number of fungi of the order 90 to340 %, as compared to the control, these increases occurred after 1-2 weeks, and there­fore, after a tendency towards a decline in the bacterial biomass, had become evident.

Also, a release of high amounts of free NH3 did not agree with the time of a declinein the bacterial biomass (Fig. 4). Free ammonia was mainly produced in the firstdays after slurry treatment while the biomass increased.

A relatively high concentration of free mono- and polyphenols (2.6 mg/g dry wt.each) was found in the slurry used. As a result of this the total concentration of these

eccu 200QJ

:l;;

co~ 100 --- ------------------

~

3 6 24 38 50Days of analysis

,

66,

85

Fig. 3. Number of fungi growing in the laboratory media in soil samples, incubated with slurry.

Tho Influence of Slu rry on the Bact erial Biom as s 281

• control

o + s lurry125

100

'>: 750VI

q,:l::

~'0

-6g. 25

~

~ a ~

4 8 T2 16 :iJ 36Days of measurement

F ig. 4. Rel ease of free a m mo nia in soil sa mples. incubated with slurry.

pheno ls initi ally increased nearl y 4-fold, t he concentration of monophenols 2-fold,and that of polyphenols 7-fold . However, during incubation of soil samples t he differ­ences in the concentrations of free phenol in the soil samples with and without slurryadded were so signifi cant that during a decline in t he bacterial biomass t hey were notgreater t han dur ing its increase (Fig . 5).

Generalizing, although our exp eriment s did not perm it to find a principal cause oftemporary declines in the bac terial biomass, occurring in the soil after heavy slurryapplication, the results obtained show which of th e supposed factors modify thi s phe­nomenon and which are without significance for its occurrence. They also suggestthat changes in the bact erial biomass, induced by slurry , are a product of action ofonly partially identified factors.

700 o monophenols

• polyphenols

'" mono + polyphenols

85386 I it.

___~ 1_01 3

.S:: 100

'$.

Days of analys is

Fig. 5. Content of free phenols in soi l sam ples. incubated with slu rry .

282 M. MUSZYNSKA and H. KASZUBIAK, The Influence of Slurry on the Bacterial Biomass

Acknowledgement

This work was partially supported by the Ministry of Agriculture within Project MR 2.11.

References

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CZEKALA, J., and D.Ij;BOSZ, K.: Dzialanie gnojowicy w glebie. 1. Przemiany wegla i azotu orazdynamika drobnoust.rojow. Roczniki Akademii Rolniczej w Poznaniu 82 (1975), 33~41.

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MANKA, K.: Proby dalszego udoskonalenia metody Warcupa izolowania grzybow z gleby. PraceKomisji Nauk Rolniczych i Komisji Nauk Lesnych 17/1 (1964), 1~23.

McALLISTER, J. S. V.: Spreading slurry on land. Soil Sci. 123 (1977), 338-343.PIETR, S. J., and ZUKOWSKA, Z.: Wplyw gnojowicy bydlecej na aktywnosc biologiczna gleb. In:

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Authors' address:

Dr. MARIA MUSZYNSKA and Prof. Dr. HENRYK KASZUBIAK, Department of Agricultural Micro­biology, Academy of Agriculture, Wolynska 35, 60-637 Poznan, Poland.