ISSN 10642293, Eurasian Soil Science, 2015, Vol. 48, No. 7, pp. 754–758. © Pleiades Publishing, Ltd., 2015. Original Russian Text © Lucia Ko r enková, Peter Matúš, 2015, published in Pochvovedenie, 2015, No. 7, pp. 865–871. ˆ
SOIL PHYSICS
Role of Water Repellency in Aggregate Stability of Cultivated Soils under Simulated Raindrop Impact1 ˆ
Lucia Korenková and Peter Matúš Institute of Laboratory Research on Geomaterials, Faculty of Natural Sciences, Comenius University, Mlynská dolina G, 84215 Bratislava, Slovak Republic email:
[email protected] Abstract—Soil aggregate stability (AS) is an important indicator of soil physical quality. For the purpose of this research it was hypothesized that particular properties such as water repellency (WR) influence soil aggre gation and AS. Directly after sampling, WR was detected for three soils, after a week of airdrying two of these soils still showed some resistance to penetration by a water drop placed on the surface (WDPT test). The study examines AS of airdried texturally different aggregates of size 0.25–0.5 mm taken from surface layers (5– 15 cm depth) of six agriculturally used soils. The procedure involves exposure of soil aggregates to direct impact of water drops. Results showed that soil AS increases in order: cutanic Luvisol (siltic) < haplic Cher nozem < calcic mollic Fluvisol < mollic grumic Vertisol (pellic) < mollic Fluvisol (calcaric) < gleyic Fluvisol (eutric). Gradual increase in AS can be explained by the increase in soil organic matter content and its hydro phobic properties. Although WR has been most commonly observed in soils under forests and grass cover, the results confirmed that cultivated soils may also create waterstable aggregates, especially in the case when their organic matter induces WR under particular moisture conditions. Keywords: aggregate stability, agricultural soils, soil aggregates, water repellency DOI: 10.1134/S1064229315070054 1
INTRODUCTION Soil aggregation and its stability has attracted an interest of many researchers, e.g., in [1, 26, 27]. It is because aggregate stability (AS) influences several aspects of a soil’s physical behavior, in particular water infiltration and soil erosion [31]. According to The Office of Labor Surveyor, Cartography and Cadaster [44], in Slovak Republic, agricultural soils cover 2414291 ha, which accounts for nearly half of the total land area. In this country, the removal of soil by water is considered to be the most severe soil degradation process, 44% of soils suitable for agriculture are poten tially vulnerable to moderate—extreme water erosion [47]. The eroding process is the result of rain detach ing and transporting vulnerable soil, either directly by means of rainsplash or indirectly by rill and gully ero sion. If the rain falls with sufficient intensity, the rain drops hit the soil and their kinetic energy is able to detach and move soil particles along a slope. The main onsite impact is the reduction in soil quality which results from the loss of the nutrientrich upper layers of the soil, and the reduced waterholding capacity of many eroded soils. In addition, the soil that is detached by accelerated water or wind erosion may be transported at considerable distances. This gives rise to the offsite problems, such as siltingup of dams, dis ruption of the ecosystems of lakes, and contamination
1 The article is published in the original.
of drinking water resulting from the movement of sed iment and agricultural chemicals into watercourses. Also, the reduced capacity of eroded soil to absorb water may lead to increased downstream flooding [17]. The resistance of soil to detachment by raindrop impact depends upon its shear strength that comes from the cohesion between soil particles and internal friction. The soil is less prone to wash or blow away when it is wellstructured and high in content of water stable aggregates in the plow layer. In fact, the more organic matter and clay there are in a soil, the better its structure and the more stable its aggregates in with standing the destructive effects of raindrops [40]. The importance and overall role of soil organic matter (SOM) in the structural stability of aggregates was dis cussed by several authors [7, 9, 35]. Some authors focused specifically on the effect of humic substances on AS [8, 29, 36]. Chaney and Swift [7] used wet siev ing to measure the AS of 26 agricultural soils with dif fering properties, and they found a high positive corre lation between AS and SOM content, suggesting that SOM is an important controlling factor. Benito and DíazFierros [4] studied the effects of various crop ping systems on the structural stability of soils contain ing various organic matter contents. They found that a decrease of organic matter content in the soil led to a decrease in soil structure stability. Emerson [16] sug gested that SOM stabilizes the aggregates mainly by forming and strengthening bonds between the parti
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ROLE OF WATER REPELLENCY IN AGGREGATE STABILITY OF CULTIVATED SOILS
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Table 1. The soil classification and coordinates of the soil profiles Coordi gl FL eu gleyic cc mo FL calcic mo FL ca mollic nates Fluvisol, eutric mollic Fluvisol Fluvisol, calcaric N E
48°44′01.8″ 17°01′23.9″
47°54′23.3″ 17°35′26.1″
49°03′19.08″ 16°39′43.08″
ha CH haplic Chernozem
ct LV sl cutanic Luvisol, siltic
mo gm VR pe mollic grumic Vertisol, pellic
48°17′03.0″ 17°33′10.9″
48°35′57.3″ 17°41′07.4″
48°44′46.1″ 17°08′41.2″
The soils were classified according to WRB [52].
Table 2. Selected physical and chemical properties of the soils studied Property Sand, % Silt, % Clay, % Corg, % CaCO3 content, % pH KCl CaCO3, % Moisture, %* WDPT, c* MED, %*
eu gl FL
cc FL hu
ca FL hu
ha CH
LV sl ct
pe VR mo gm
9.1 39.1 51.8 2.0 6.7 5.1 0 4.1 37 6
4.4 54.6 41.0 2.3 6.0 7.4 23.5 2.4 0 0
25.4 49.4 25.2 1.0 6.9 7.5 6.9 2.3 0 0
4.6 63.4 32.0 1.2 4.6 6.5 0.3 3.6 0 0
2.0 65.3 32.7 0.8 3.6 7.2 0.6 2.4 0 0
3.7 30.3 66.0 1.2 7.7 4.5 0 7.4 67 8
SOC⎯soil organic carbon, SOM⎯soil organic matter, WDPT⎯water drop penetration time, MED⎯molarity of an ethanol droplet. *⎯measured on airdried samples.
cles within them. Cultivation alters structural stability of soil and reduces the amount of SOM [46] and thus reduces the proportion of micro and macroaggregates in cultivated soil [2, 45]. Elliott [14] reported that cul tivation results particularly in a loss of the labile organic matter which binds microaggregates into macroaggregates. Moreover, SOM is a prime substrate for microbial populations and selective microbial activity is essential in the development and appearance of water repellency (WR) [19, 20] that enhances AS against slaking and dispersion [53]. Some inorganic compounds such as carbonates, iron and mangan hydroxides and silicate gels that cement soil particles together may also contribute to resistance of soil to erosion [21]. The wet AS can be measured by several proce dures which share the common principle that unsta ble aggregates will break apart more easily than do stable ones when immerged into water. This study examines the stability of airdried aggregates of the 0.25–0.5 mm size fraction taken from texturally dif ferent soils. The method tests the soil’s physical qual ity with regard to its capacity to sustain its structure during most impactful conditions: a heavy rain storm after surface drying weather. OBJECTS AND METHODS Soil aggregates of six agricultural soils were taken from Ahorizons (5–15 cm) at different experimental sites in western Slovakia. The soil classification [52] EURASIAN SOIL SCIENCE
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and GPS coordinates of each sample point are given in Table 1. Airdried and sieved (85%) were recorded for mollic grumic Vertisol (pellic), mollic Fluvisol (calcaric) and gleyic Fluvisol (eutric). All of these soils were marked by slight to severe WR under particular moisture conditions. In these aggregates, particles were bound by some hydro phobic forces. Although the presence of calcium car bonate increases the AS, two of soils with a tendency to form the most waterstable aggregates had zero car bonate content in their surface horizons. The positive correlation of organic matter with AS was observed. In contrast to some previous studies, the relationship between AS and the content of clay was not found. ACKNOWLEDGEMENTS
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