Microbial extracellular polymeric substances (EPS) have been shown to alter soil moisture retention and to improve seedling survival and plant growth at the bulk scale. The mechanisms of EPS-mediated water retention include reversible swelling of the cross-linked polymer matrix and the promotion of an aggregated soil structure. However, the effects of EPS on water retention have never been directly observed at the pore scale. Here, emulated soil micromodels were developed to directly observe the effects of physical, chemical, and biological factors on pore-scale water retention. In this demonstration, a pseudo-2D pore structure was created to represent physical features of a fine sandy loam. Replicate micromodels were initially saturated with suspensions of different soil bacteria, and pore-scale air infiltration was directly imaged over time. External evaporativity was held constant through the use of a custom constant-humidity environmental chamber. Micromodels filled with suspensions of highly mucoid Sinorhizobium meliloti retained moisture about twice as long as physically identical micromodels filled with suspensions of non-mucoid S. meliloti. Relative drying rates in six replicate experiments ranged from 1.1 to 2.5 times slower for mucoid suspensions. Patterns of air infiltration were similar but not identical across replicates. The results suggest that pore fluid EPS and micromodel geometry act together to limit evaporation at pore throats. Advantages of the micromodel approach include direct observation of pore-scale dynamic process, and the ability to systematically replicate complex physical structures. These abilities will enable users to screen benefits from different structures and from microbial compositions, and build predictive understanding of the overall function of microbe-habitat systems.

Synergistic effects of soil microstructure and bacterial EPS on drying rate in emulated soil micromodels

Soil structure is an important physical property of soil and has a great impact on the environment and agriculture. Dry aggregate size distribution and related soil structure indices are essential parameters in understanding the structural state of the soil. This study was conducted to determine the effects of different soil types and land uses on structure parameters and to relate them to selected soil properties. The investigation was performed on five soil types (Arenosols, Fluvisols, Chernozems, Gleysols and Solonetz), each from three different locations and under three different land uses (cropland, meadow and forest), so that a total of 135 undisturbed soil samples were collected. Dry sieving analysis was performed to obtain eight aggregate size classes (ASCs) (>10, 10-5, 5-3, 3-2, 2-1, 1-0.5, 0.5-0.25 and 10, 5-3 and 3-2 mm ASCs. Chernozems and Gleysols have more favorable structure than Arenosols, Fluvisols and Solonetz. Long term cultivation leads to the deterioration of soil structure and the formation of clods. Forest soils have a significantly better structure than soils under meadows and croplands. The application of principal component analysis and regression models identifies water retention at -33 kPa, bulk density and pH value as for the most important factors in predicting dMWD and dGMD.

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Soil dry aggregate size distribution: effects of soil type and land use.

Bartlova J., Badalikova B., Pospisilova L., Pokorný E., Sarapatka B. (2015): Water stability of soil aggregates in different systems of tillage. Soil & Water Res., 10: 147–154. The influence of various agrotechnical measures on macrostructural changes in topsoil and subsoil was studied in the course of a four-year experiment. Macrostructure was evaluated according to the ability of soil aggregate to resist degradation. Three variants of soil tillage were established: ploughing to a depth of 0.22 m, reduced tillage (subsoiling to 0.35–0.40 m, and shallow disking of soil to a depth of 0.15 m). For observation, three locations were chosen in various production areas of the Czech Republic with differing soil and climatic conditions. In these locations crops were grown under the same crop rotation: rapeseed (Brassica napus L.), wheat (Triticum aestivum L.), maize (Zea mays ), wheat (Triticum aestivum L.), and barley (Hordeum vulgare ). After four years of different tillage, a change in the water stability of soil aggregates (WSA) was evident. It was found out that reduced tillage of soil positively influenced both the WSA and the yield of the crops grown. A relationship of positive dependence between WSA, the content of humus substances, and cation exchange capacity of soil was also found. According to the obtained results, for agricultural practice a classification scale of structural qual

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Water Stability of Soil Aggregates in Different Systems of Tillage

Soil aggregate structure and soil organic matter are closely interrelated and commonly considered as key indicators of soil quality. The aim of this study was to evaluate the effects of different fallow durations on indices of soil structure and humus status indicators. Studies were conducted on abandoned agricultural fields (15, 20 and, 35 years after abandonment). As a reference site, we used a cultivated field in the area. The experimental soil fields are classified as Gleyic Cambisols. Soil macroaggregates were separated with the sieve (dry sieve) to seven aggregate size fractions, i.e.> 10, 10–5, 5–2, 2–1, 1–0.5, 0.5–0.25 and < 0.25 mm. The humus status parameters of soils included the following indicators: soil organic carbon (Corg), humus reserves (QH), the degree of humification of organic matter (SOMdh), fractions of humic acids (HA) (free and bound with monovalent cations and Al2O3, Fe2O3, bound with Са2+ which forms humates, bound with clay minerals), fulvic acids (FA) (free aggressive) and ratio of HA to FA (CHA : CFA). After a fallow period of more than 20 years on the surface formation of a sod layer. A long-term fallow period had an impact on the mean weight diameter of the aggregates (MWD) and agronomically valuable aggregates (AVA). Fallow soils have a significantly better structure than soils under a cultivated field. Long-term cultivation leads to the deterioration of soil structure and the formation of large aggregates (>10 mm). The Corg content remains at the level of the background content when the soils are left fallow for less than 15 years and increases over time. The Corg in the upper 0–20 cm soil layer has been shown to increase from 3.55 to 8.74% on arable land that has been fallow for 35 years and has been largely associated with significant accumulation of organic matter within the plant root mass. Mature sites are characterized by an increase of fulvic acids in the humus composition in comparison with their arable analogues. The abandonment of soil agricultural use and the cessation of mechanical tillage results in the restoration of the natural structure of soils and the improvement of their agrophysical properties. Such studies have not been previously conducted in the Primorsky region of the Russian Far East.

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Impact of different fallow durations on soil aggregate structure and humus status parameters.

The aim of this study was to investigate the effects of land use changes on the aggregate size distribution, soil structural stability, and soil erodibility in Luvisols on Central Serbia's rainfed farms at a depth of 0.00-0.30 m. Six sites, selected for the study, contained adjacent land uses of natural grassland and arable land that have undergone conversion from grassland for more than 10 years. The inherent problems of Luvisols include weak structured surface horizons susceptible to structure deterioration, where tilled when wet or when heavy machinery is used. Aggregate size distribution and soil structural stability in the topsoil was tested by soil dry and wet sieving. Soil erodibility was assessed with the USLE-K factor. The natural grassland served as a control against which to assess changes in soil properties resulting from the removal of natural vegetation or cultivation of soil. The results showed that conversion of natural grassland to dry land farming led to a significant degradation of the soil structure. Aggregate separation by dry-sieving indicated that the natural grassland had significantly fewer unfavorable cloddy aggregates (>10 mm) and more agronomically most valuable aggregates (0.25-10 mm) than the arable soils. The mean weight diameter of dry aggregates (MWDdry) was greater in the grassland ( 7.0 mm) compared to the arable soils (9.7 mm). The arable soil had significantly lower (1.03) structure coefficient (Ks) than grassland soils (2.77). Higher percentages of water stable aggregates (WSA) >0.25 mm were found under natural grassland ( 50 %) than in arable fields ( 41 %). In addition, grassland soil had significantly higher mean weight diameter (0.92 mm) of wet stable aggregates (MWDwet) than arable soils (0.81 mm). Tillage of the unaltered grassland significantly increased the soil erodibility measured by the USLE-K factor. The USLE-K factor was approximately by 17% greater in the arable soil than in the grassland, indicating the vulnerability of the arable soil to water erosion. In summary, the results showed that the tillage of the grassland degraded the soil structure, leaving soils more susceptible to the erosion in the temperate climate zone. This suggests that land disturbances should be avoided in the grasslands in the study region of the Central Serbia.

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Land use effects on aggregation and erodibility of luvisols on undulating slopes

Conversion of meadow and forest ecosystems to agricultural land generally leads to changes in soil structure. This comparative study presents the composition and stability of structural aggregates in humus horizons (0-30 cm) of noncarbonate silty-clay Fluvisols in the Kolubara River Valley, W Serbia. Aggregates collected from under a native forest were compared to aggregates from meadows and arable fields which underwent crop rotation for > 100 y. The results show that size distribution and stability of structural aggregates in the humus horizons of arable soil are significantly impaired due to long-term anthropogenization. In the humus horizons, the content of the agronomically most valuable aggregates (0.25-10 mm) decreased by a factor of ≈ 2, from 68%-74% to 37%-39%, while the percentage of cloddy aggregates (>10 mm) increased by a factor of = 2, from 23%-31 % to 48%-62%, compared to forest aggregates. The long-term-arable soil had significantly (p 3 mm. Their content is = 2.5-3 times lower in arable soil (13%-16%) than in forest soil (32%-42%) at a depth of 0-20cm. The largest mean weight diameters of dry aggregates (dMWD) with a range between 12.6 and 14.7 mm were found in arable soil, vs. 9.5-9.9 mm in meadow and 6.5-8.3 mm in forest. The arable soil had significantly lower mean weight diameters of wet-stable aggregates (wMWD) and a lower structure coefficient (Ks) than forest and meadow soils. The dispersion ratio (DR) of arable soil was significantly higher than that of forest and meadow soils. Forest and meadow showed a significantly higher soil organic-matter content (SOM) by 74% and 39%, respectively, compared with arable soil, while meadow uses decreased the SOM content by 57% compared with forest at a depth of 0-10 cm. In conclusion, the results showed that long-term conventional tillage of soils from natural forest and meadow in the lowland ecosystems of W Serbia degraded soil aggregate-size distribution and stability and reduced SOM content, probably resulting in lower productivity and reduced crop yields.

Composition and stability of soil aggregates in Fluvisols under forest, meadows, and 100 years of conventional tillage.

Productive and non-productive use of water of common bean under full and deficit irrigation

The aim of this research was to figure out certain limitations of methods for drain spacing determination application in unsteady-state of flow rate to the drains in the eugley soil. The well-known Glover-Dumm method was taken in this analysis. The analysis was based on the results of drain discharge and water table depth measurements. Measurements were carried out on the experimental field. Three different drainage treatments were set up with three different drainage spacings such as 10 m, 20 m and 30 m. The results of analysis showed significant constraints of the method due to non-modeling dynamic of water flow to the drains. These effects are marked on the plot with the least drain spacing (10 m).

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Some constraints on the application of methods for drain spacing determination in unsteady-state of flow in eugley soil

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Application of two measures of adaptation to climate change for assessment on the yield of wheat, corn and sunflower by the aquacrop model

The aim of this work is to show out some properties of Guyon's method for drain spacing determination in unsteady state of flow. The analysis has been carried out in the marshy gley soil of the experimental field with drain spacing of 10 m, 20 m and 30 m. The method assumed modeled dynamics of water recharge, which hasn't been observed during the experimental trial. Therefore, its application is limited.

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Nevenka Đurović

Papers

Composition and stability of soil aggregates in Fluvisols under forest, meadows, and 100 years of conventional tillage.

Productive and non-productive use of water of common bean under full and deficit irrigation

Some constraints on the application of methods for drain spacing determination in unsteady-state of flow in eugley soil

Application of two measures of adaptation to climate change for assessment on the yield of wheat, corn and sunflower by the aquacrop model

Some properties of Guyon's method for drain spacing determination on the marshy gley soil