Substancje humusowe a struktura gleby

Vol. 63 No 3/2012: 31–36

INTRODUCTION

Organic matter is considered an essential element in the formation of aggregates [Šimanský 2011; Zey-tin and Baran 2003], and contrast formation of ag-gregates contributes to the stabilization of soil orga-nic matter through physical protection within aggre-gates [Balabane and Plante 2004]. Relation between soil structure and organic matter is dynamic. The de-gree of organic matter decomposition affects the for-mation of soil aggregates and their stability [Bonde et al. 1988. The stability of soil aggregates thus de-pends not only on quantity, but also quality of orga-nic matter inputs [Tisdall and Oades 1982]. Soil struc-ture of natural ecosystems is different from the soil structure of agro-ecosystems [Šimanský and Zaujec 2009; Zaujec and Šimanský 2003]. Natural ecosys-tems accumulate in the surface layer of soil more particulate organic matter in soil aggregates and also organic matter in the much more stabile fractions [Fre-ixo et al., 2002]. Higher concentration of organic car-bon and higher intensity of mineralization is often associated with fractions of macro-aggregates. By contrast, organic carbon in micro-aggregates is more physically protected and therefore a higher content of biochemical recalcitrant fraction leads to the for-mation of stabile micro-aggregates and lower inten-sity of decay inside the aggregates [Six et al. 2000]. Stabile organic compounds in soil are represented by

humus substances and other macromolecules, which are naturally resistant against microorganisms activi-ty or are physically protected inside the aggregates [Theng et al. 1989]. The subjects of this study are: i) assessment of the impact of humus substances on the formation of soil aggregates; ii) comparison of soil structure in ecosystems on Haplic Chernozems and Eutric Fluvisols.

MATERIALS AND METHODS

Localities of soil sampling are situated in Danube Lowland. Geological substrates of this area are Neo-gene clays, sands and gravels, which are in most are-as covered with loess and loess loam. Along the river Váh and Nitra are fluvial sediments. The average annual temperature in the studied localities is 9.8°C and average sum of rainfall per year is 570 mm. In drier areas of the Danube Lowland oak forests are preserved and along the river Váh floodplain forests. In vegetation of agro-ecosystems cereals, especially Zea mays, Triticum aestivum, Hordeum vulgare are dominated; there are also Beta vulgaris, Helianthus annuus and Brassica napus var. napus. The experi-ment included two soil types – Haplic Chernozems and Eutric Fluvisols and four ecosystems – forest, meadow, urban and agro-ecosystem. The soil sam-ples for determination of the quantity and quality of soil organic matter and soil structure were taken from ERIKA TOBIAŠOVÁ, JURAJ MIŠKOLCZI

Slovak University of Agriculture, Department of Soil Science

HUMUS SUBSTANCES AND SOIL STRUCTURE

Abstract: In this study, the soil structure of two soil types (Haplic Chernozems and Eutric Fluvisols) in four ecosystems (forest,

meadow, urban and agro-ecosystem) with dependence on humus substances were compared. The stability of dry-sieved and water-resistant macro-aggregates and micro-aggregates with a dependence on the proportion of humus substance fractions was determined. Quantity of humus substances influenced mainly water-resistant aggregates. A positive correlation was recorded between size frac-tion of 2–3 mm and contents of humus substances (P < 0.01; r = +0.710) and fulvic acids (P < 0.05; r = +0.634), and negative correlation between size fraction of 0.5–1 mm and contents of humus substances (P < 0.05; r = -0.613) and fulvic acids (P < 0.01; r = -0.711). Humic acids influenced mainly the formation of dry-sieved aggregates and fulvic acids played an important role in micro-aggregate formation. The quality of humus substances influenced more intensively the formation of dry-sieved aggregates. There were positive correlations between optical parameters of humus substances and humic acids and larger dry-sieved aggregates (3–7 mm) and negative correlations with smaller (0.5–3 mm). The highest proportions of larger size of water-resistant aggregates (1– 20 mm) were in forest ecosystem, but smaller (0.25–1 mm) agreggates were dominated in agro-ecosystem.

Keywords: Humus substances, Soil aggregates, Ecosystems, Haplic Chernozems, Eutric Fluvisols DOI 12.2478/v10239-012-0030-3

the humus horizon in three replications. From the chemical properties, organic carbon by wet combu-stion according to the Tyurin method [Orlov and Grišina 1981], fractional composition of humus sub-stances according to the Ponomarevova and Plotni-kova method [1975], the optical properties of humus substances [Orlov and Grišina 1981] were determi-ned. From the physical properties, soil structure – dry-sieved macro-aggregates, water-resistant macro-ag-gregates according to the Baksejev method and mi-cro-aggregates according to the Kaèinský method [Hraško 1962], index of aggregate stability [Henin et al. 1969], the coefficient of vulnerability [Valla et al. 2000], index of crusting and critical contents of soil organic matter according to Pieri [Lal and Shukla 2004] were determined. The obtained results were analyzed using statistical software Statgraphic Plus. In addition to basic descriptive statistical indicators for the evaluation of the relevance of various factors on the observed parameters, multi-factorial analysis of variance (ANOVA) was used. Differences betwe-en variants were assessed by Tukey test for signifi-cance level P<0.05. To determine interdependencies, correlation analysis was used. Minimum significant correlation coefficient was determined on the level of significance P<0.05 and P<0.01.

RESULTS AND DISCUSSION

Higher content of total carbon and nitrogen and narrower C:N ratio was in Eutric Fluvisols than in Haplic Chernozems (Table 1). In soil profile of Eu-tric Fluvisols higher soil moisture was, due to the carbon contents were also higher here compared with dry Haplic Chernozems. The close relationship be-tween soil organic carbon content and soil moisture were also recorded by Alvarez and Lavado [1998], Meersmans et al. [2008] and Tobiašová [2010]. Co-nversely quality of organic substances assessed on the basis of the carbon of humic acids carbon to car-bon of fulvic acids ratio (C_HA:C_FA) and colour coeffi-cients of humus substances (Q_HS) and humic acids (Q_HA) were higher in Haplic Chernozems than in Eutric Fluvisols. Dry conditions in Haplic Cherno-zems contributed to higher stabilization of organic matter, which confirmed the results of Denef et al. [2002]. Higher proportion of humic acids was in Ha-plic Chernozem, especially of fraction of humic acids bound with divalent cations. In the case of dry-sie-ved aggregates (Table 2) in Haplic Chernozems gre-ater proportion of smaller aggregates from 0.25 to 5 mm was, while in the Eutric Fluvisols there were lar-ger 5–20 mm aggregates. This may be caused just by a different quality of organic matter inputs in soil.

In Haplic Chernozem more stabilized organic substan-ces dominated, as reflected in a higher proportion of smaller aggregates, which include more stabile com-ponent and vice versa in Eutric Fluvisols less stabile, so we also recorded a higher proportion of larger ag-gregates. According to Roberson et al. [1991] diffe-rent fractions of organic matter participate on the for-mation and stabilization of aggregates. As organic matter is gradually stabilizing some binds break down and new create, thus larger aggregates may be by time to break down into smaller, in which organic matter is more stabilized. Therefore, higher content of smaller aggregates was recorded in Haplic Chernozem and lar-ger in Eutric Fluvisols. In the case of water-resistant aggregates significantly higher proportion of fractions from 0.25 to 0.5 mm was in Haplic Chernozems.

From the ecosystems (Table 1) the highest con-tent of organic matter was in forest ecosystem, but its quality was the highest in the agro-ecosystem, which is mainly the result of the impact of tillage on orga-nic substances stabilization and application of manu-re, which also contains humus substances with a high degree of polycondensation [Nannipieri 1993]. Lar-ger fractions of dry-sieved aggregates (3–20 mm) had the higher proportion in the urban ecosystem and vice versa smaller fractions (0.25 to 3 mm) dominated in the forest ecosystem. These are aggregates, whose stability have been changing over the change of soil moisture; due to this situation can be evaluated as positive. According to Tisdall and Oades [1982] in ca-se of temporary and unstable aggregates mainly po-lysaccharides, roots and fungal hyphae are binding agents. Larger aggregates had higher proportion in the meadow ecosystem. In an urban and also meadow ecosystems grass vegetation was, so the formation of larger aggregates was conditional mechanically by plant roots. The greater stabilization of aggregates is in the natural ecosystem, due to this reason a higher content of smaller aggregates was here compared to urban ecosystem, which is confirmed by the study Barreto et al. [2009]. They also showed on a higher degree of aggregation under natural vegetation.

The forest ecosystem had the highest proportion of the fraction of humic acids bound with divalent ca-tions, and also the fractions of dry-sieved aggregates of size from 0.25 to 3 mm was dominated here and from the water-resistant conversely the larger ones.

Formation of aggregates is influenced by the sta-bility of soil organic matter. In the case of dry-sieved aggregates fractions larger than 3 mm were in nega-tive correlation with the stability of organic matter and vice versa aggregates smaller than 3 mm was in positive (Table 3). Less stabilized organic matter supported production of larger aggregates, while more

TABLE 1. Average values of soil organic mater parameters in soil types and ecosystems s r o t c a F TOC NT C:N CHA:CFAQHS QHA HA1 HA2 HA3 S AH FA1a FA1 FA2 FA3 S AF g m [ × gk –1_{] [%]} e p y t li o S C H F E 2221033700 22527032 98..8476 00..6892 34..7617 34..5042 54..4306 193..5763 1111..4801 2305..7494 44..6200 77..9961 23..5744 77..0358 2213..7635 m e t s y s o c E L A E F E M E U 0 8 0 8 1 0 3 9 5 2 0 2 6 1 2 0 8 1 1 2 5 0 9 1 9 4 5 2 5 1 6 2 4 8 4 2 7 4 . 9 1 4 . 0 1 7 2 . 8 1 5 . 8 1 1 . 1 4 8 . 0 2 6 . 0 7 4 . 0 6 2 . 3 9 3 . 4 8 0 . 4 5 0 . 5 7 3 . 3 7 6 . 3 9 8 . 3 8 1 . 4 4 5 . 5 1 8 . 4 2 9 . 4 5 2 . 4 8 7 . 1 1 6 0 . 5 1 3 9 . 6 1 8 . 2 1 9 6 . 2 1 6 1 . 9 6 3 . 4 1 1 2 . 0 1 5 9 . 9 2 4 0 . 9 2 0 2 . 6 2 7 2 . 7 2 4 4 . 4 8 5 . 4 8 2 . 4 1 3 . 4 1 8 . 9 4 4 . 9 8 3 . 6 2 1 . 6 3 3 . 1 6 9 . 2 7 8 . 1 2 4 . 6 6 1 . 8 6 4 . 8 1 6 . 6 4 6 . 5 2 7 . 3 2 3 4 . 5 2 3 1 . 9 1 8 4 . 2 2

Explanations: HC – Haplic Chernozems, EF – Eutric Fluvisols, FE – forest ecosystem, AL – agro-ecosystem, ME – meadow ecosystem, UE – urban ecosystem, TOC – total organic carbon, NT – total nitrogen, C:N – carbon and nitrogen ratio, CHA:CFA – humic acids carbon and fulvic acids carbon

ratio, QHS – colour coefficient of humus substances, QHA – colour coefficient of humic acids, HA 1 – fraction of humic acids free and bound with

mobile R2O3, HA 2 – fraction of humic acids bound with Ca2+, HA 3 – fraction of humic acids bound with mineral particles of soil and with stabile

R2O3, SHA – sum of humic acids, FA 1a – free aggressive fulvic acids, FA 1 – fraction of fulvic acids free and bound with mobile R2O3,

FA 2 – fraction of fulvic acids bound with Ca2+_{, FA 3 – fraction of fulvic acids bound with mineral particles of soil and with stabile R}

2O3, SFA – sum

of fulvic acids.

TABLE 2. Average contents of air dry and water-stable macro-aggregates in soil types and ecosystems

s r o t c a F 2–7mm D 7D–5mm 5D–3mm3D–1mm1D–0.5mm0D.5–0.25mm 3W–2mm 2W–1mm1W–0.5mm0W.5–0.25mm<W0.25mm ] % [ e p y t li o S C H F E 172..9830 2250..4668 2268..1736 2236..3151 79..8184 23..2449 1111..6360 1123..6904 1110..9796 170..5477 166..7389 m e t s y s o c E L A E F E M E U 1 4 . 1 1 3 2 . 6 4 7 . 9 9 0 . 4 1 9 2 . 1 2 6 0 . 8 1 9 2 . 4 2 4 6 . 8 2 8 2 . 5 2 7 8 . 5 2 8 0 . 9 2 5 5 . 9 2 5 9 . 6 2 6 3 . 9 2 3 2 . 2 2 8 3 . 0 2 8 0 . 0 1 5 1 . 2 1 2 3 . 7 9 4 . 4 5 8 . 2 9 5 . 4 2 5 . 2 1 5 . 1 8 1 . 2 2 7 . 9 1 8 0 . 0 1 4 9 . 3 1 6 2 . 2 1 2 3 . 7 1 8 8 . 4 1 2 6 . 8 8 7 . 0 2 6 9 . 9 6 5 . 8 8 1 . 6 8 9 . 2 2 2 5 . 4 0 6 . 7 8 9 . 0 9 2 . 4 1 0 9 . 5 6 6 . 8 1 0 5 . 7

Explanations: HC – Haplic Chernozems, EF – Eutric Fluvisols, FE – forest ecosystem, AL – agro-ecosystem, ME – meadow ecosystem, UE – urban ecosystem, D – dry-sieved macro-aggregates, W – water-resistant macro-aggregates.

TABLE 3. Correlations between soil organic mater parameters and dry-sieved and water-resistant macro-aggregates

Explanations: * P < 0.05, ** P< 0.01; TOC – total organic carbon, NT – total nitrogen, C:N – carbon and nitrogen ratio, C_HA:C_FA – humic acids carbon and fulvic acids carbon ratio, QHS – colour coefficient of humus substances, QHA – colour coefficient of humic acids, HA 1 – fraction of

humic acids free and bound with mobile R₂O₃, HA 2 – fraction of humic acids bound with Ca2+_{, HA 3 – fraction of humic acids bound with mineral}

particles of soil and with stabile R2O3, SHA – sum of humic acids, FA 1a – free aggressive fulvic acids, FA 1 – fraction of fulvic acids free and

bonded with mobile R₂O₃, FA 2 – fraction of fulvic acids bound with Ca2+_{, FA 3 – fraction of fulvic acids bound with mineral particles of soil and}

with stabile R2O3, SFA – sum of fulvic acids.

s e t a g e r g g a -o r c a m d e v e i s -y r D Water-ressitantmacro-aggregates m m 7 – 2 7–5mm 5–3mm 3–1mm 1–0.5mm 0.5–0.25mm3–2mm 2–1mm 1–0.5mm 0.5–0.25 m m C O T T N N : C 5 5 2 . 0 -6 7 0 . 0 -3 5 2 . 0 -8 7 0 . 0 -8 0 4 . 0 + -0.708** 8 2 0 . 0 -1 6 3 . 0 + * 9 7 5 . 0 -5 1 1 . 0 -7 9 4 . 0 -8 1 5 . 0 + 2 7 1 . 0 + 7 4 3 . 0 -* * 8 7 7 . 0 + 9 9 4 . 0 + 1 1 0 . 0 + * * 4 5 7 . 0 + 9 3 2 . 0 + 2 1 2 . 0 + 2 5 0 . 0 + 9 0 2 . 0 -3 1 5 . 0 -3 4 4 . 0 + 1 4 3 . 0 -* 5 3 5 . 0 -1 1 2 . 0 + 4 8 3 . 0 -* 2 0 6 . 0 -9 6 2 . 0 + C_HA:C_FA S H Q A H Q 4 9 0 . 0 -0 6 2 . 0 + 0 2 2 . 0 + 3 2 5 . 0 -* 5 7 5 . 0 + * 1 9 5 . 0 + 5 6 3 . 0 -5 9 3 . 0 + 2 3 5 . 0 + 5 8 4 . 0 + * 6 9 5 . 0 -* 5 6 5 . 0 -2 5 4 . 0 + * 8 6 5 . 0 -* * 8 7 6 . 0 -8 7 2 . 0 + 7 3 3 . 0 -1 1 5 . 0 -9 1 1 . 0 + 5 5 2 . 0 + 4 7 0 . 0 + * * 9 1 7 . 0 + * 5 6 5 . 0 -* 4 9 5 . 0 -2 2 2 . 0 + * 7 5 6 . 0 -9 4 4 . 0 -7 9 3 . 0 + * * 9 3 7 . 0 -1 7 4 . 0 -1 A H 2 A H 3 A H S AH 9 1 0 . 0 + * 3 0 6 . 0 -7 3 0 . 0 + * 7 5 6 . 0 -9 6 4 . 0 -* 6 1 6 . 0 -3 5 2 . 0 + * * 6 2 7 . 0 -6 4 4 . 0 -1 3 1 . 0 -7 9 1 . 0 + 4 9 1 . 0 -8 5 1 . 0 + * * 2 2 8 . 0 + 1 6 4 . 0 -* * 1 6 6 . 0 + 2 1 5 . 0 + * 6 0 6 . 0 + 0 0 3 . 0 -* * 8 9 6 . 0 + 9 4 4 . 0 + 8 9 3 . 0 + 8 6 0 . 0 -* 6 0 6 . 0 + 2 9 1 . 0 -9 4 0 . 0 + 1 0 0 . 0 + 4 1 0 . 0 -0 7 4 . 0 + 0 7 1 . 0 + 3 8 0 . 0 -7 4 3 . 0 + 3 7 1 . 0 + 2 3 4 . 0 + 2 4 2 . 0 -3 7 3 . 0 + 4 0 4 . 0 + 9 9 1 . 0 + 4 5 0 . 0 + 3 4 4 . 0 + a 1 A F 1 A F 2 A F 3 A F S AF 7 7 2 . 0 -9 7 1 . 0 -6 6 1 . 0 -1 9 3 . 0 -* 9 5 5 . 0 -4 8 0 . 0 + 0 2 5 . 0 -8 4 0 . 0 -6 0 0 . 0 -9 0 3 . 0 + 8 8 2 . 0 + 5 9 4 . 0 -4 1 2 . 0 + 1 9 2 . 0 + 1 0 2 . 0 + 5 0 1 . 0 -2 7 3 . 0 + 2 9 2 . 0 + 2 5 0 . 0 -4 5 4 . 0 + 8 9 0 . 0 -* 6 3 5 . 0 + 8 7 0 . 0 -1 0 0 . 0 + 8 7 1 . 0 + 1 5 1 . 0 + * 1 1 6 . 0 + 1 6 2 . 0 -8 1 3 . 0 + 1 6 2 . 0 + 9 8 3 . 0 + 7 8 1 . 0 -3 1 1 . 0 + 1 7 1 . 0 + 7 9 1 . 0 + 7 9 2 . 0 -7 0 3 . 0 + 7 4 1 . 0 + 9 9 4 . 0 -4 4 0 . 0 -6 2 3 . 0 -2 0 3 . 0 + 7 9 1 . 0 + 3 6 4 . 0 -4 2 0 . 0 + * 2 3 5 . 0 -1 9 2 . 0 + 8 2 0 . 0 + * 3 2 6 . 0 -7 9 2 . 0

-stabilized, especially humus substances supported the formation of aggregates of smaller fractions, which is consistent with the theory of Six et al. [2000].

From the humus substances there were humic acids, which were in a positive correlation with the aggregates of size 0.5–3 mm, in particular, a fraction of humic acids bound with divalent cations (Ca2+_,

Mg2+_{), with whose they form humates, which are}

small water soluble. Therefore they have importance in the aggregation process, when they create a thin layer on the surfaces of mineral particles, which act as binding agents in case of smaller aggregates. The stabilization of organic substances in the case of smal-ler aggregates also occurs through their bonds with the clay fraction [Jastrow 1996]. Such a bond is more stabile and more resistant against decomposition ac-tivity of soil organisms. Organic matter in smaller aggregates is protected through the inhibition of car-bon oxidation [Hernanz et al. 2002]. In larger tions of aggregates a greater proportion has sand frac-tion and in smaller aggregates fracfrac-tion of clay. Orga-nic matter, which is part of larger aggregates, is lar-gely composed of particulate organic matter and the-re athe-re also structural substances, which subject ra-ther the process of mineralization than the stabiliza-tion. In the case of aggregate fraction of 0.25–1 mm a positive correlation with the fraction of fulvic acids bound with monovalent cations was found.

Formation of aggregates was strongly influenced not only by the quantity of humic acids, but also their quality (Table 3). From the individual fractions posi-tive influence on their stability, fraction of humic acids bound with divalent cations had. The more sta-bilized humic acids were, the higher proportion of aggregates from 0.5 to 3 mm was.

In case of narrower C:N ratio in soil organic mat-ter, higher proportion of 3–7 mm aggregates was and in case of wider C:N ratio larger proportion of smal-ler 0.25–1 mm aggregates was. Rate of nitrogen mi-neralization is higher, thus over time the ratio of C:N extends to what also the results of Gregorich et al. [2003] showed. This also indicates the presence of fresh organic matter in the larger aggregates.

In the case of water-resistant aggregates (Table 1) correlation between the quality of humus substances and water-resistant aggregates of size <2 mm was observed. In case of the C_HA:C_FA ratio this correla-tion was positive and in the case of colour coeffi-cients was negative. The higher the contents of nitro-gen, fulvic acids fractions of free and bound with R₂O₃ were, the smaller the content of water-resi-stant 0.25-0.5 mm aggregates was. Tisdall and Oades [1982] describe as permanent aggregates these, on

whose formation degraded aromatic humus substan-ces in connection with polyvalent metal ions, which are strongly bound to clay particles participate.

Micro-aggregates (Table 4) had a higher propor-tion in Haplic Chernozems (16.39%) than in Eutric Fluvisols (6.78%). It also shows on a higher propor-tion of stabile organic substances in the formapropor-tion of smaller aggregates. According to Bedrna et al. [1968] in this case it can be the formation of micro-aggrega-tes not only by adsorption on the surfaces, but also by diffusion of humus substances into interlayer spa-ces of clay minerals lattice. Aggregate fraction of 0.01-0.05 mm had higher proportion in Haplic Cherno-zems and all other fractions had higher contents in Eutric Fluvisols. The higher the total organic carbon and wider C:N ratio were, the higher proportion of micro-aggregates of fraction 0.01–0.05 mm was (Ta-ble 5). This fraction was also in negative correlation with fraction of fulvic acids bound with divalent ca-tions (r =-0.691, P>0.01). From the ecosystems this fraction of micro-aggregates had the highest propor-tion in the forest ecosystem, in which the highest in-put of organic matter with a wider C:N ratio and hi-gher content of fulvic acids were. Therefore, in these conditions micro-aggregates of size from 0.01 to 0.05 mm will have the highest proportion.

Overall, in the case of micro-aggregates fulvic acids play important role. Negative correlation was recorded between the proportion of micro-aggrega-tes of size <0.001 mm and a content of free fulvic acids and bound with mobile R₂O₃ (r =- 0.594, P> 0.05) and positive correlation with a fraction of fu-lvic acids bound with divalent cations (r= 0.622, P>0.05). Rehák and Janský [2000] described the for-mation of smaller micro-aggregates (<0.01 mm) as a result of cohesion forces, which are the result of a large number of contact points and surfaces in

volu-TABLE 4. Average contents of micro-aggregates in soil types and ecosystems s r o t c a F 2–0.25 m m 0m.2m5–0.05 0m.0m5–0.01 m0.m01–0.001 <m0m.001 ] % [ s e p y t li o S C H F E 1260..4788 1261..3036 3550..4296 1173..5658 35..2152 m e ts y s o c E L A E F E M E U 2 4 . 7 1 6 7 . 6 1 7 7 . 3 1 8 5 . 6 2 6 0 . 2 2 2 9 . 0 2 1 7 . 4 2 0 1 . 7 4 0 . 8 3 1 2 . 7 4 4 9 . 3 4 2 3 . 2 4 3 1 . 8 1 5 8 . 1 1 4 9 . 3 1 8 9 . 8 1 7 3 . 4 8 2 . 3 6 0 . 4 4 0 . 5

Explanations: HC – Haplic Chernozems, EF – Eutric Fluvisols, FE – forest ecosystem, AL – agro-ecosystem, ME – meadow ecosystem, UE – urban ecosystem.

me unit, and sodium or electrolytes contribute to in-creasing of cohesion. Through this mechanism just a fraction of free fulvic acids bound with mobile R₂O₃ could participate in the formation of smaller micro-aggregate factions.

CONCLUSIONS

1. Proportion of larger dry-sieved macro-aggregates (>3 mm) was in negative correlation with the sta-bility of organic substances and contrast, smaller macro-aggregates (<3 mm) in positive correlation. Quantity and quality of humic acids, in particular those, which are bound with divalent cations, was in positive correlation with the aggregates of size 0.5-3 mm.

2. Proportion of water-resistant aggregates of size fraction <2 mm was in positive correlation with the ratio of humic acids carbon to fulvic acids car-bon and in negative correlation with colour coeffi-cients. The higher the proportion of fulvic frac-tions of free and bound with R₂O₃ was the smaller water-resistant aggregates content of size fraction 0.25–0.5 mm was.

3. In case of micro-aggregates negative correlation between the proportion of size fraction <0.001 mm

TABLE 5. Correlations between soil organic mater parameters and micro-aggregates s e t a g e r g g a -o r ci M 5 2 . 0 -2 m m 0m.2m5-0.05 0m.0m5-0.01 001.0m1m-0.0- <m0m.001 C O T T N N : C 2 2 4 . 0 -6 4 2 . 0 -5 7 2 . 0 -9 7 1 . 0 -3 4 1 . 0 -2 2 1 . 0 -* * 4 4 7 . 0 + 6 0 4 . 0 + * 5 8 5 . 0 + 2 6 4 . 0 -7 3 2 . 0 -4 7 3 . 0 -3 2 2 . 0 -4 5 0 . 0 + 6 1 4 . 0 -C_HA:CFA QHS A H Q 2 6 0 . 0 + 2 5 2 . 0 + 6 1 2 . 0 + 4 9 2 . 0 + 2 7 2 . 0 -5 0 0 . 0 + 1 8 1 . 0 -3 2 1 . 0 -7 7 3 . 0 -1 4 1 . 0 -5 6 1 . 0 + 8 0 3 . 0 + 0 1 0 . 0 + 6 5 2 . 0 + 7 0 2 . 0 + 1 A H 2 A H 3 A H S AH 8 1 3 . 0 -0 3 0 . 0 + * 6 3 5 . 0 -1 1 5 . 0 -6 3 2 . 0 + 6 0 0 . 0 -1 2 0 . 0 + 9 1 1 . 0 + 6 3 3 . 0 + 5 1 1 . 0 + 9 4 2 . 0 + 8 6 4 . 0 + 3 6 3 . 0 -3 7 1 . 0 -9 4 2 . 0 + 3 7 1 . 0 -3 8 3 . 0 -7 5 1 . 0 -0 8 1 . 0 -7 8 4 . 0 -a 1 A F 1 A F 2 A F 3 A F S AF 5 0 2 . 0 + 0 4 4 . 0 -0 0 3 . 0 + 8 5 2 . 0 -4 1 2 . 0 + 9 3 1 . 0 + 5 3 4 . 0 + 4 5 1 . 0 + 1 2 0 . 0 + 7 2 4 . 0 + 3 0 2 . 0 -7 0 3 . 0 + * * 1 9 6 . 0 -5 0 5 . 0 + 3 0 3 . 0 -1 1 2 . 0 -8 4 3 . 0 -0 4 1 . 0 + 2 8 4 . 0 -4 6 3 . 0 -8 9 3 . 0 + * 4 9 5 . 0 -* 2 2 6 . 0 + 8 8 2 . 0 -7 4 2 . 0 +

Explanations: * P < 0.05, ** P< 0.01; TOC – total organic carbon, NT – total nitrogen, C:N – carbon and nitrogen ratio, CHA:CFA – humic acids

carbon and fulvic acids carbon ratio, Q_HS – colour coefficient of humus substances, QHA – colour coefficient of humic acids, HA 1 – fraction of

humic acids free and bound with mobile R₂O₃, HA 2 – fraction of humic acids bound with Ca2+_{, HA 3 – fraction of humic acids bound with}

mi-neral particles of soil and with stabile R₂O₃, SHA – sum of humic acids, FA 1a – free aggressive fulvic acids, FA 1 – fraction of fulvic acids free and bound with mobile R₂O₃, FA 2 – fraction of fulvic acids bounded with Ca2+_{, FA 3 – fraction of fulvic acids bound with mineral particles}

of soil and with stabile R₂O₃, SFA – sum of fulvic acids.

and a fulvic acids of free and bound with mobile R₂O₃ was recorded and positive correlation with fulvic acids bound with divalent cations.

4. In the forest ecosystem micro-aggregate fraction of size from 0.01 to 0.05 mm was dominated and also the content of smaller dry-sieved macro-ag-gregates fractions (0.25–3 mm) was the highest, and on the other hand larger fractions (3-20 mm) had the highest proportion in the urban ecosystem. In Haplic Chernozems a higher proportion of smal-ler dry-sieved macro-aggregates (0.25–5 mm) were, while in Eutric Fluvisols larger macro-ag-gregates (5–20 mm) were dominated.

Acknowledgements

The work was financially supported by project VEGA 1/0300/11 and VEGA 1/0237/11.

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Erika Tobiašová

Tr. A. Hlinku 2, 949 01 Nitra, Slovak Republic