Biologia 64/3: 550—554, 2009 Section Botany DOI: 10.2478/s11756-009-0095-6 Comparison of aggregate stability within six soil profiles under conventional tillage using various laboratory tests Radka Kodešová1, Marcela Rohošková1& Anna Žigová2 1Department of Soil Science and Soil Protection, Czech University of Life Science, Prague, Kamýcká 129,CZ-16521 Prague, Czech Republic; e-mail: [email protected] 2Institute of Geology, Academy of Sciences of the Czech Republic, v.v.i., Rozvojová 269,CZ-16500 Prague, Czech Republic Abstract: Soil structure stability was studied in every diagnostic horizons of six soil types (Haplic Chernozem, Greyic Phaeozem, two Haplic Luvisols, Haplic Cambisol, Dystric Cambisol) using different techniques investigating various de- struction mechanisms of soil aggregates. Soil aggregate stability, assessed by the index of water stable aggregates (WSA), varied depending on the organic matter content, clay content and pHKCl . The presence of clay and organic matter coatings and fillings, and presence of iron oxides in some soils increased stability of soil aggregates. On the other hand periodical tillage apparently decreased aggregate stability in the Ap horizons. Coefficients of aggregate vulnerability resulting from fast wetting (KV1) and slow wetting (KV2) tests showed similar trends of the soil aggregate stability as the WSA index, when studied for soils developed on the similar parent material. There was found close correlation between the WSA index and the KV1 value, which depended also on the organic matter content, clay content and pHKCl . Less significant correlation was obtained between the WSA index and the KV2 value, which depended on the organic matter content and clay content. Coefficients of vulnerability resulting from the shaking after pre-wetting test (KV3) showed considerably different trends in comparison to the other tests due to the different factors affecting aggregate stability against the mechanical destruction. The KV3 value depended mostly on cation exchange capacity, pHKCl and organic matter content. Key words: fast wetting test; slow wetting test; shaking after pre-wetting test; wet sieving Introduction rigation, and use of fertilizers can also lead to soil struc- ture degradation (Pagliai et al. 2003, 2004; Servadio et Soil water regime is highly affected by soil structure al. 2005). On the other hand, the soil aggregate stability and its stability. Various soil structure types may cause may be improved by adding compost (Valla et al. 2000; preferential flow or water immobilization. Soil struc- Fernandez et al. 2007; Tejada & Gonzales 2008). The ture breakdown may initiate a soil particle migration, soil particle arrangement into the structure elements formation of less permeable or even impermeable lay- (aggregates) has a significant impact on the soil pore ers and consequently decreased water fluxes within the system and consequently on the soil hydraulic proper- soil profile. Soil aggregation is under control of different ties (Kodešová et al. 2006, 2007, 2008). The degree of mechanisms in different soil types. Flocculated clay par- the soil aggregate stability (aggregate breakdown and ticles, or their complexes with humus (organo-mineral consequently changes of soil porous system) influences complexes) and soil organic matter act as main cement- water flux and solute transport within the soil profile ing agents in soil aggregates development. The cement- (Kodešová et al. 2009). ing effect of free Fe and Al oxides is important in soils The study presented here was performed to assess with low organic matter content (Six et al. 2002). Gen- stability of the soil structure within the soil profiles. erally, level of aggregation and stability of aggregates The main goals of this study were: 1) Evaluation of increases with increasing organic matter content, sur- soil structure stability using different methods to study face area of clay minerals and cation exchange capacity various destruction mechanisms, and 2) Assessment of (Bronick & Lal 2005). The low soil pH may also in- soil composition impact on soil structure stability. crease the aggregate stability due to the behaviour of acidoids prevailing in soils, which peptize at abundance of OH− (Valla et al. 2000). Beside impact of soil com- Material and methods ponents, soil management has also very important in- Study was performed in six soil types (Table 1). A five year fluence on soil structure stability. By tillage, the topsoil rotation system with conventional tillage was used at all lo- is mixed and aggregates are exposed to different break- cations. Winter barley was planted at all areas when soil down mechanisms (Six et al. 1998). Soil processing at samples were taken from all horizons that were specified for improper soil moisture, crossing of heavy machinery, ir- each soil type. Particle size distribution, organic carbon con- c 2009 Institute of Botany, Slovak Academy of Sciences Comparison of aggregate stability using various laboratory tests 551 Table 1. Soil aggregate stability within the soil profiles expressed as the index of water stable aggregates (WSA), the coefficient of vulnerability (KV1) to aggregate slaking due to the compression of entrapped air (the fast wetting test), the coefficient of vulnerability (KV2) to aggregate disintegration caused by the micro cracking due to the different swelling, and physico-chemical dispersion due to the osmotic stress (the slow wetting test), the coefficient of vulnerability (KV3) to the mechanical aggregate breakdown (the shaking after pre-wetting tests), and soil properties affecting aggregate stability. Soil aggregate stability increases with the increasing WSA index and decreasing KV values. Organic Cation Carbon Clay Exchange Soil Type Horizon Depth Content Content pHKCl Capacity WSA Index KV1 KV2 KV3 [cm] [%] [%] [–] [mmol+ (100g)−1] [–] [–] [–] [–] Haplic Chernozem Ap1 0–20 1.91 25.3 6.28 24.5 0.46 11.15 5.68 2.72 on Loess Ap2 20–51 1.37 27.1 6.30 24.5 0.61 9.80 5.23 3.57 ACk 51–74 0.55 33.3 7.08 28.7 0.54 10.25 5.49 3.03 Ck 74–88 0.29 28.4 7.18 18.0 0.34 14.84 7.48 4.91 Greyic Phaeozem Ap 0–23 1.11 32.6 6.96 20.5 0.56 8.35 4.68 2.23 on Loess Bth 23–37 0.50 37.3 5.38 29.2 0.60 7.78 4.24 2.52 BCk 37–44 0.46 31.0 7.11 22.5 0.45 10.79 7.50 3.07 Ck 44–125 0.29 27.6 7.50 15.5 0.10 19.51 14.73 5.11 Haplic Luvisol 1 Ap1 0–29 1.11 24.4 4.52 14.0 0.48 11.58 6.76 2.93 on Loess Ap2 29–40 0.81 27.0 4.67 17.5 0.52 10.42 7.53 3.58 Bt1 40–75 0.49 34.6 4.58 21.3 0.61 10.06 5.40 2.96 Bt2 75–102 0.32 33.7 5.72 25.5 0.30 14.82 9.44 4.46 BC 102–120 0.31 28.9 6.80 19.0 0.34 17.25 11.42 5.56 Ck 120–145 0.16 24.0 7.04 16.5 0.05 20.40 15.64 7.86 Haplic Luvisol 2 Ap 0–29 1.49 18.7 4.84 12.7 0.65 6.63 4.68 2.64 on Loess Loam Bt1 29–51 0.38 27.1 4.30 12.0 0.46 12.72 12.44 5.52 Bt2 51–93 0.25 34.8 4.09 22.2 0.46 10.95 9.42 2.19 C 93–120 0.16 24.4 4.09 22.0 0.25 14.53 13.46 2.33 Haplic Cambisol Ap 0–29 1.77 15.0 4.09 14.2 0.75 3.80 2.94 1.94 on Paragneiss Bw 29–62 0.41 24.6 3.97 13.5 0.46 3.75 3.83 3.09 C 62–84 0.37 23.5 4.11 15.0 0.39 3.62 4.05 3.35 Dystric Cambisol Ap 0–20 2.08 18.1 4.49 19.0 0.64 2.99 2.57 1.35 on Orthogneiss Bw 20–43 0.46 19.7 4.12 10.7 0.28 3.24 2.77 1.77 tent, pHKCl and cation exchange capacity were measured wetting tests was utilized to study the mechanical aggregate using the standard laboratory techniques (Dane & Topp breakdown. Four grams of air dry soil aggregates of the size 2002; Sparks 1996) (Table 1). In addition micromorpho- of 2–5 mm were pretreated according to each test methodol- logical study on thin soil sections was performed to assess ogy: 1. fast wetted in 50 cm3 of distilled water (10 minutes), aggregate compositions. 2. slowly wetted on the saturation pan (up to aggregate sat- The aggregate stability was studied using two different uration), 3. wetted in 50 cm3 of ethanol (10 minutes), then approaches. The indexes of water stable aggregates were inserted into 50 cm3 of distilled weather and shaken (20 determined using the procedure presented by Nimmo & times). Then aggregates were removed from the liquids or Perkins (2002). Four grams of air-dry soil aggregates of the saturation pan and sieved for 6 minutes in ethanol (sieve size of 2–5 mm were sieved for 3 minutes in distilled water 0.25 mm). Finally, the distribution of particular aggregate (sieve 0.25 mm). Aggregates remaining on the sieve were size fractions (< 0.25, 0.25–0.5, 0.5–1.0, 1.0–2.0 and 2.0–5.0 next sieved in sodium hexametaphoshate until only sand mm) was measured. The coefficient of vulnerability, KV [–], particles remained on the sieve.