F o l i a Microbiol. 24, 478--482 (1979)

Effect of Soil Microstructure on the Relationship between the Intensity of Nitrification and Soil Moisture I . STUDNI'~KOV/~ Libsreckd 36, 466 01 Jablonec n. N . , Czechoslovakia

Received J u l y 12, 1978

ABSTRACT. The relationship between the logarithm of nitrification intensity and moisture (expressed as pF) did n o t h a v e a n ideal l i n e a r c o u r s e in structural soils in which pores of a certain size predominated. W h e n i n c r e a s i n g t h e i n c u b a t i o n m o i s t u r e it c o u l d be observed t h a t the intensity of nitrification decreases at p F 3.5--4.4 and increases again on further increasing the incubation moisture. The detected anomaly was observed when applying moistures corresponding to peaks of derivation pF-curves. :It can be assumed t h a t the relationship between the intensity of nitrification and moisture is modified by soil m i c r o s t ~ c t u r e ; t h e r e f o r e , this relationship was studied in more detail in the present communication.

The relationship between nitrification and moisture has so far been studied in detail b y Seifert (1960, 1962, 1968, 1969a, b, 1970, 1972, 1973; Seifert and Mrhzkov~ 1966). F u r t h e r papers along this way were published b y Parker and Larson (1962), Miller and Johnson (1964) and b y Dubey (1968). I t was found t h a t the increasing soil moisture brings about an increasing intensity of nitrification. A pronounced wetting of the soil leads finally to a permanently decreased aeration and hence to a decreased intensity of nitrification. The increase of nitrates during the incubation (intensity of nitrification) depends not only on the incubation moisture but also on the initial moisture, i.e. the soil moisture prior to wetting up to the incubation moisture value (Seifert 1969a, b, 1970). When the incubation moisture of various samples is the same it holds true t h a t the drier the soil prior to wetting the higher the increase of nitrates (Bolotina and Abramova 1964; Seifert and Mr~zkov~ 1966; Seifert 1969a, b, 1970, 1973). A mathematical model of the relationship between the intensity of nitrificatiou and soil moisture makes it possible to determine the intensity of nitrification under various conditions with the use of a small n u m b e r of determinations of nitrates in the soil. Seifert (1973) found t h a t the logarithmic relationship between the intensity of nitrification and moisture expressed as pF is linear at a given initial moisture. The intensity of nitrification is also influenced by soil structure which regulates aeration and soil water relations (Seifert 1963a, b 1964a, b, 1968). Thu:s for instance, it was found t h a t the degree of nitrification in soil samples is directly proportional to the size of specific surface of soil particles (Seifert 1962). The effect of soil microstructure on the overall course of the relationship between the intensity of nitrification and moisture has not yet been thoroughly investigated.

1979

NITRIFICATION

AND SOIL MOISTURE

4?9

TABLE I. C h a r a c t e r i s t i c s o f localities w h e r e soil s a m p l e s were t a k e n on t h e Oblik hill

Soil

Stand

Soil t y p e

Depth of A-horizon mm

A B C D

south-west foot south-east slope below t h e p e a k north-west hill-side peak plateau

e h e r n o z e m o n loess r a n k e r on b a s a l t

g r a y forest soil b on b a s a l t mul ranker on e basalt

Moisture conditions

600 50

good a extreme aridity a

500

good

200

good

a C f. R y d l o (1973).

b Peli~ek (1964). e High content of nutrients.

MATERIALS AND METHODS

Soil samples were taken on the Obiik hill in the Bohemian Central Mountains, a prominent locality of xerothermic vegetation. Samplings were performed in J u l y 1972 from the depth of 0--100 mm in four ecologically and pedologically different stands (Table I). The relationship between the intensity of nitrification and moisture was determined using the incubation method of Seifert (1973). The content of nitrates in the samples was determined colorimetrically using 2,4-phenoldisulphonic acid. The increase of nitrates originating during the incubation was recalculated as ppm N--N03. The soil water potential for construction of pF-curves was determined by the cryoscopic method for pF 3.1--4.2 and by the desiccator method for pF higher than 4.2 (Kutilek 1966; Klika et al. 1954). Predominant soil pores were determined according to peaks of curves of the function f ~ dw/dpF, where w is soil moisture (Kutilek 1966).

R E S U L T S A N D DISCUSSION

The relationship between the intensity of nitrification and moisture, or the logarithmic relationship between the intensity of nitrification and soil water potential is usually illustrated by straight lines. Each of them corresponds to a certain initial moisture. Each point on a given straight line corresponds to a different incubation moisture (Seifert 1973). In the studied soils an unexpected decrease of the intensity of nitrification takes place at a certain moisture. The decrease is not permanent, as compared with the situation when moisture is higher than optimum. The intensity of nitrification increases again when further increasing the incubation moisture (Fig. 1). The observed phenomenon may be associated with structural properties of the soils. Therefore, the relationship between the intensity of nitrification and moisture was supplemented by derivation pF-curves. It follows from the pronounced peaks of these curves that pores corresponding to certain pF values predominate in the soils. The intensity of nitrification decreases just at these values.

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1979

NITRIFICATION

AND SOIL MOISTURE

45|

The relationship between nitrification and mierostructure of the soil referred to here is usually most pronounced in the case of curves corresponding to the lowest initial moisture. The observed effect was least significant in soil ]3 at higher initia moistures (Fig. 1). This is apparently due to the fact that the derivation pF-curve of this soil has no sharp peak and, hence, predominant pores do not form a narrow size-characterized group. Aeration conditions m a y v a r y during wetting of such a soil in a much more complex w a y due to complex phenomena at the interface of the soil and liquid with as compared with soils, a simpler derivation pF-curve. The effect illustr"~ted in Fig. 1 might be explained b y assuming t h a t a rapid saturation of predominant pores occurs at a certain moisture. Certain soil interspaces are than not aerated and bacteria exist in an anaerobic environment. Due to this the intensity of nitrification m a y decrease. On further wetting of the soil the intensity of nitrification increases again as the wetted active surface of the soil and hence the life environment of bacteria, extends, similarly te t h e situation prior to the decrease of the intensity of nitrification. I f the above hypothesis is correct an ideal straight-line relationship between nitrification and moisture m a y be expected in soil, the derivation pF-curves of which do not have significant peaks. Soils with a different structure would then deviate from the straight line course of the relationship between the logarithm of the intensity of nitrification and pF. L7 h e a u t h o r ~ i s h e s to thank[:Frof. Dr. J. h'eiftJt. I~iEc. for i n t r o d u e i r g h e r to s t u d i e s of nitrification

REFERENCES

BOLOTINA N. I., A]31~AMOVAE. A.: A m e t h o d of d e t e r m i n a t i o n of t h e nitrification ability o f soils. Agrokhimyia 3, 110 (1964). DUBEu H . D.: Effect of soil m o i s t u r e on nitrification. Can.J.Microbiol. 14, 1348 (1968). I{LI:KA J . , NOV~K V . , GI~EGOR A. : Laboratory ]Flannual of Phytocoenology, Ecology, Clin~atolcgy and Pedology. P u b l . H o u s e Czech. A c a d . Sci., P r a g u e 1954. I~IYTilJEI~ M.: Water-economic Pedology. S t a t e P u b l . :House Tech. Liter., P r a g u e 1966. MILLER R . D., JO~l~SO~ D . : T h e effect of soil m o i s t u r e t e n s i o n on c a r b o n dioxide e v o l u t i o n , nitrification a n d n i t r o g e n Ininera]ization. Soil Sci.Soc.Amer.Proc. 28, 644 (1964). PAI~:KEP, D. T., LARSOI< W . E.: Nitrification as affected b y t e m p e r a t u r e a n d m o i s t u r e c o n t e n t of m u l c h e d soils. Soil Sci.Soc.An*er., Prec. 26, 238 (1962). I)ELI~EK J.: Forest Pedology, p. 446. S t a t e A g r i c u l t u r a l P u b l . :House, P r a g u e 1964. RYDLO J . : A c o n t r i b u t i o n to u n d e r s t a n d i n g o f soil m o i s t u r e relations o n t h e Oblik hill in Czech C e n t r a l M o u n t a i n s . MsC. Thesis, F a c u l t y of N a t u r a l Sciences, Charles U n i v e r s i t y , P r a g u e 1973. SEIFERT J . : T h e influence o f m o i s t u r e a n d t e m p e r a t u r e o n t h e n u m b e r of n~icroorganisms in t h e soil. Felts ~licrobiol. 5, 176 (1960). SEI~ERT J.: T h e influence of t h e soil s t r u c t u r e a n d m o i s t u r e coulenfG on t h e n u m b e r of b a c t e r i a a n d t h e degree of nitrification. F e l t s ~licrobiol. 7, 234 (1962). SEIFEI~T J . : T h e effect o f soil s t r u c t u r a l a g g r e g a t e s o n t h e i n t e n s i t y o f nitrification. Plclnt Production 9, 832 (1963a). S~.IFELT J . : T h e influence of c r u s h i n g s t r u c t u r a l soil a g g r e g a t e s on nitrification i n t e n s i t y . Acta Unto.Carol., Biol., 1963, 271 (1963b). SEIJFERT J . : I n f l u e n c e of t h e size of soil s t r u c t u r a l a g g r e g a t e s on t h e degree of nitrification, ffolia Microbiol. 9, 115 (1964a). SEIFEI~T J . : T h e effect o f t h e size o f soil s t r u c t u r a l a g g r e g a t e s on t h e degree of nitrification. II. T h e role of aeration. Folia Microbiol. 9, 347 (1964b). SEI]~ERT J. : Effect of p r e d r y i n g soil on n i t r a t e p r o d u c t i o n . Acre Unto.Carol., Biol., 1968, 237 (1968).

Fig. 1. D e r i v a t i o n p F - c u r v e s a n d t h e r e l a t i o n s h i p b e t w e e n t h e logaritl~m of tLe nitrification i n t e n s i t y (log :N--:NOs) a n d m o i s t u r e (p:F) for softs A - - D ; p:F of t h e initial n o i s t u i e is g i v e n s t i n d i v i d u a l curves.

482

I. S T U D N I ~ K O V A

Vol. 24

SEIFERT J . : W a t e r p o t e n t i a l o f t h e soil as a basis of t h e influence of m o i s t u r e on n u m b e r of b a c t e r i a in t h e soil. Fotia Microbiol. 14, 89 (1969a). S~.IFERT J . : Nitrification in t h e a i r - d r i e d a n d w e t t e d soil. Plant Production 18, 181 (1969b). S~.rFERT J. : T h e influence o f m o i s t u r e o n t h e degree of nitrification in soil. I. Acta Univ.Garol., Biol., 1969, 352 (1970). S~.IFERT J . : T h e influence of m o i s t u r e o n t h e degree of nitrification in soil. I I . Acta Univ.Carol., Biol., 1970, 467 (1972). SEIFERT g . : Effect o f p r e d r y i n g soil o n n i t r a t e p r o d u c t i o n . Acta Univ.Carol., Biol., 1968, 237 (1968). SEIFERT g . : W a t e r p o t e n t i a l of t h e soil as a basis of t h e influence o f m o i s t u r e on n u m b e r of b a c t e r i a in t h e soil. Folia Microbiol. 14, 89 (1969a). S~.IPERT J . : Nitrification in t h e air-dried a n d w e t t e d soil. Plant Production 15, 181 (1969b). SEIFERT g.: C a l c u l a t i o n of t h e nitrification i n t e n s i t y on t h e b a s i s o f its relation w i t h p F of t h e soil. Plant Production 19, 159 (1973). SEIFERT J . , I~RXZKOVX Z.: Effect o f soil d r y i n g o n t h e b i o g e n i c i t y a n d i n t e n s i t y o f nitrification. Plant Production 12, 29 (1966).

Effect of soil microstructure on the relationship between the intensity of nitrification and soil moisture.

F o l i a Microbiol. 24, 478--482 (1979) Effect of Soil Microstructure on the Relationship between the Intensity of Nitrification and Soil Moisture I...
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