To evaluate the impact of management practices on the soil environment, it is necessary to quantify the modifications to the soil structure. Soil structure conditions were evaluated by characterizing porosity using a combination of mercury intrusion porosimetry, image analysis and micromorphological observations. Saturated hydraulic conductivity and aggregate stability were also analysed. In soils tilled by alternative tillage systems, like ripper subsoiling, the macroporosity was generally higher and homogeneously distributed through the profile while the conventional tillage systems, like the mouldboard ploughing, showed a significant reduction of porosity both in the surface layer (0–100 mm) and at the lower cultivation depth (400–500 mm). The higher macroporosity in soils under alternative tillage systems was due to a larger number of elongated transmission pores. Also, the microporosity within the aggregates, measured by mercury intrusion porosimetry, increased in the soil tilled by ripper subsoiling and disc harrow (minimum tillage). The resulting soil structure was more open and more homogeneous, thus allowing better water movement, as confirmed by the higher hydraulic conductivity in the soil tilled by ripper subsoiling. Aggregates were less stable in ploughed soils and this resulted in a more pronounced tendency to form surface crust compared with soils under minimum tillage and ripper subsoiling. The application of compost and manure improved the soil porosity and the soil aggregation. A better aggregation indicated that the addition of organic materials plays an important role in preventing soil crust formation. These results confirm that it is possible to adopt alternative tillage systems to prevent soil physical degradation and that the application of organic materials is essential to improve the soil structure quality.

/pdf/soil-structure-and-the-effect-of-management-practices-2dke791wz7.pdf

Soil structure and the effect of management practices

Soil quality indicators (SQIs) can be used to evaluate sustainability of land use and soil management practices in agroecosystems. The objective of this study was to identify appropriate SQI from factor analysis (FA) of five treatments: no-till corn (Zee mays) without manure (NT), no-till corn with manure (NTM), no-till corn‐soybean (Glycine max) rotation (NTR), conventional tillage corn (CT), and meadow (M) in Coshocton, Ohio. Soil properties were grouped into five factors (eigenvalues > 1) for the 0‐10 cm depth as: (Factor 1) water transmission, (Factor 2) soil aeration, (Factor 3) soil pore connection 1, (Factor 4) soil texture and (Factor 5) moisture status. Factor 2 was the most dominant, with soil organic carbon (SOC) the most dominant measured soil attribute contributing to this factor. For the 10‐20 cm depth, factors identified were: (Factor 6) soil aggregation, (Factor 7) soil pore connection 2, (Factor 8) soil macropore, and (Factor 9) plant production. At 10‐

Determining soil quality indicators by factor analysis

Effects of compost produced from town wastes and sewage sludge on the physical properties of a loamy and a clay soil

The biological clogging of natural porous media, often in conjunction with physical or chemical clogging, is encountered under a wide range of conditions. Wastewater disposal, artificial groundwater recharge, in situ bioremediation of contaminated aquifers, construction of water reservoirs, or secondary oil recovery are all affected by this process. The present review provides an overview of the techniques that are used to study clogging in the laboratory, or to monitor it in field applications. After a brief survey of the clogging patterns most commonly observed in practice, and of a number of physical and chemical causes of clogging, the various mechanisms by which microorganisms clog soils and other natural porous media are analyzed in detail. A critical assessment is also provided of the few mathematical models that have been developed in the last few years to describe the biological clogging process. The overall conclusion of the review is that although information is available on several aspects of the biological clogging of natural porous media, further research is required to predict its extent quantitatively in a given situation. This is particularly true in cases that involve complicating factors such as predation or competition among organisms.

Environmental impact and mechanisms of the biological clogging of saturated soils and aquifer materials

Highly weathered soils in humid Asia are characterized by low soil fertility and high soil erosion potential. This study evaluates the influences of biochar made from the waste wood of white lead trees ( Leucaena leucocephala (Lam.) de Wit) on the physicochemical and biological properties of long-term cultivated, acidic Ultisol. This study used three application rates (0%, 2.5%, and 5% (wt/wt)) of the biochar with an incubation time of 105 d for all cases. Soils were collected at 21 d, 42 d, 63 d, 84 d and 105 d during the incubation period to evaluate changes in soil properties over time. A simulated rainfall event (80 mm h − 1 ) was performed to estimate soil loss for all treatments at the end of the incubation time. Experimental results indicate that applying biochar improved the physicochemical and biological properties of the highly weathered soils, including significant increases in soil pH from 3.9 to 5.1, cation exchange capacity from 7.41 to 10.8 cmol (+) kg − 1 , base cation percentage from 6.40 to 26.0%, and microbial biomass carbon (MBC) from 835 to 1262 mg kg − 1 . Compared with the control (i.e., no biochar), biochar application decreased bulk density from 1.4 to 1.1 Mg m − 3 , increased K sat by 1.8 times and increased the mean weight diameter (MWD) of soil aggregates from 2.6 cm to 4.0 cm. Incorporating biochar into the soil significantly reduced soil loss by 50% and 64% at 2.5% and 5% application rates, respectively, compared with the control. The formation of macroaggregates in the biochar-amended soils is the critical factor to improve soil erosion potential. Based on these results, a 5% application rate of biochar is considered as suitable for highly weathered soil because this application rate efficiently improves soil physiochemical properties and reduces soil loss.

Effects of biochar on soil properties and erosion potential in a highly weathered soil

This chapter describes several laboratory methods of determining the hydraulic conductivity and hydraulic diffusivity. Water moves through soil in response to various forces acting upon it. The chemical species water may be transported due to bulk movement of the liquid phase or soil solution, or it may be transported by diffusion relative to the mean motion of the liquid phase. The chapter deals with bulk movement, under isothermal conditions, of the liquid phase in response to mechanical driving forces. However, the transport of water in the gas phase by vapor diffusion will be included in the measured hydraulic conductivity and diffusivity, especially at low water contents. The concept of parameter identification has been applied to the determination of the parameters in the hydraulic conductivity and water retention functions. The method involves the measurement of some aspect of the response of a soil water flow system to a set of applied boundary conditions.

C. Dirksen

Papers

Hydraulic Conductivity and Diffusivity: Laboratory Methods