Soil quality evaluation under agro-silvo-pastoral Mediterranean management systems

According to Franzluebber (2002) the degree of stratification of soil organic C and N, as well as other parameters, with soil depth, expressed as a ratio, can indicate soil quality or soil ecosystem functioning and sustainability under different agricultural management. Stratification ratios > 2 indicate a higher soil quality and contribution to agriculture sustainability. A case study from northeastern Sardinia (Italy) is presented

Physical characteristics of soil under different cropping and natural system on the plain of jars, Xieng Khouang province, Laos

Conservation agriculture and direct seeding mulch-based cropping (DMC) systems greatly modify plant and soil interaction. Plants commonly provide energy that fuels biological processes and either directly or indirectly creates structure within soils. Under DMC systems 7 large biomass is produced both above and below ground, thereby influencing soil parameters. Different methods can be used to measure soil characteristics, but simple and cheap tools for on-site recording are not common. This study attempts to analyse the physical soil parameters (water-stable aggregate, bulk density and soil permeability) of various ecosystems: savannah grassland, pine forest, ploughed upland rice fields, and improved Brachiaria ruziziensis and Stylosanthes guianensis pasture lands. The results show that these forage species have a clear effect on soil structure: medium soil particles (<0.250mm) are fixed into water-stable aggregates, bulk density decreases, and as a result soil permeability is modified. The continued recording of such data over time will enable evaluation of the iterative and cumulative biological effects (organic content, root density, particle arrangement) of fodder species and cropping systems on soil characteristics. (Résumé d'auteur

Uncertainty in the determination of soil hydraulic parameters and its influence on the performance of two hydrological models of different complexity

Data of soil hydraulic properties forms often a limiting factor in unsaturated zone modelling, especially at the larger scales. Investigations for the hydraulic characterization of soils are time-consuming and costly, and the accuracy of the results obtained by the different methodologies is still debated. However, we may wonder how the uncertainty in soil hydraulic parameters relates to the uncertainty of the selected modelling approach. We performed an intensive monitoring study during the cropping season of a 10 ha maize field in Northern Italy. The data were used to: i) compare different methods for determining soil hydraulic parameters and ii) evaluate the effect of the uncertainty in these parameters on different variables (i.e. evapotranspiration, average water content in the root zone, flux at the bottom boundary of the root zone) simulated by two hydrological models of different complexity: SWAP, a widely used model of soil moisture dynamics in unsaturated soils based on Richards equation, and ALHyMUS, a conceptual model of the same dynamics based on a reservoir cascade scheme. We employed five direct and indirect methods to determine soil hydraulic parameters for each horizon of the experimental profile. Two methods were based on a parameter optimization of: a) laboratory measured retention and hydraulic conductivity data and b) field measured retention and hydraulic conductivity data. The remaining three methods were based on the application of widely used Pedo-Transfer Functions: c) Rawls and Brakensiek, d) HYPRES, and e) ROSETTA. Simulations were performed using meteorological, irrigation and crop data measured at the experimental site during the period June – October 2006. Results showed a wide range of soil hydraulic parameter values generated with the different methods, especially for the saturated hydraulic conductivity Ksat and the shape parameter a of the van Genuchten curve. This is reflected in a variability of the modeling results which is, as expected, different for each model and each variable analysed. The variability of the simulated water content in the root zone and of the bottom flux for different soil hydraulic parameter sets is found to be often larger than the difference between modeling results of the two models using the same soil hydraulic parameter set. Also we found that a good agreement in simulated soil moisture patterns may occur even if evapotranspiration and percolation fluxes are significantly different. Therefore multiple output variables should be considered to test the performances of methods and model

The effect of organic management on soil quality indicators

This report was presented at the UK Organic Research 2002 Conference. A range of physical, biological and chemical parameters were measured in organic soil that had been managed in different ways and in a conventional control. Factors were identified that could be used to construct an index of soil quality

Reduced tillage, but not organic matter input, increased nematode diversity and food web stability in European long‐term field experiments

Soil nematode communities and food web indices can inform about the complexity, nutrient flows and decomposition pathways of soil food webs, reflecting soil quality. Relative abundance of nematode feeding and life‐history groups are used for calculating food web indices, i.e., maturity index (MI), enrichment index (EI), structure index (SI) and channel index (CI). Molecular methods to study nematode communities potentially offer advantages compared to traditional methods in terms of resolution, throughput, cost and time. In spite of such advantages, molecular data have not often been adopted so far to assess the effects of soil management on nematode communities and to calculate these food web indices. Here, we used high‐throughput amplicon sequencing to investigate the effects of tillage (conventional vs. reduced) and organic matter addition (low vs. high) on nematode communities and food web indices in 10 European long‐term field experiments and we assessed the relationship between nematode communities and soil parameters. We found that nematode communities were more strongly affected by tillage than by organic matter addition. Compared to conventional tillage, reduced tillage increased nematode diversity (23% higher Shannon diversity index), nematode community stability (12% higher MI), structure (24% higher SI), and the fungal decomposition channel (59% higher CI), and also the number of herbivorous nematodes (70% higher). Total and labile organic carbon, available K and microbial parameters explained nematode community structure. Our findings show that nematode communities are sensitive indicators of soil quality and that molecular profiling of nematode communities has the potential to reveal the effects of soil management on soil quality

Atlas of soil reflectance properties

A compendium of soil spectral reflectance curves together with soil test results and site information is presented in an abbreviated manner listing those soil properties most important in influencing soil reflectance. Results are presented for 251 soils from 39 states and Brazil. A narrative key describes relationships between soil parameters and reflectance curves. All soils are classified according to the U.S. soil taxonomy and soil series name for ease of identification

Geosynthetic-encased stone columns: analytical calculation model

This paper presents a newly developed design method for non-encased and encased stone columns. The developed analytical closed-form solution is based on previous solutions, initially developed for non-encased columns and for non-dilating rigid-plastic column material. In the present method, the initial stresses in the soil/column are taken into account, with the column considered as an elasto-plastic material with constant dilatancy, the soil as an elastic material and the geosynthetic encasement as a linear-elastic material. To check the validity of the assumptions and the ability of the method to give reasonable predictions of settlements, stresses and encasement forces, comparative elasto-plastic finite element analyses have been performed. The agreement between the two methods is very good, which was the reason that the new method was used to generate a parametric study in order to investigate various parameters, such as soil/column parameters, replacement ratio, load level and geosynthetic encasement stiffness on the behaviour of the improved ground. The results of this study show the influence of key parameters and provide a basis for the rational predictions of settlement response for various encasement stiffnesses, column arrangements and load levels. The practical use of the method is illustrated through the design chart, which enables preliminary selection of column spacing and encasement stiffness to achieve the desired settlement reduction for the selected set of the soil/column parameters. (C) 2010 Elsevier Ltd. All rights reserved

Long-term fate of sewage-sludge derived cadmium in arable soils

The focus of this work was to improve knowledge of the long-term fate of cadmium supplied to arable soils by sewage sludge. Emphasis was placed on measured and modelled changes in the solubility and mobility of cadmium, resulting from long-term turnover of both sludge-derived and inherent organic matter of the soil. Measurements were conducted in a long-term sludge supplied field experiment, situated at Ultuna (60°N, 17°E), started in 1956. Furthermore, batch studies on soil samples and modelling exercises in WHAM were performed in order to study the speciation of cadmium in the soil-solution system. A comprehensive model -the SLAM model- was developed to increase the understanding of the influence of soil and sludge adsorption characteristics on cadmium solubility and bioavailability, and the migration rate of cadmium in soil profiles. The long-term sludge supplies had increased the solubility of cadmium, measured in crop cadmium concentration, as an effect of enhanced acidification and increased Cd concentration in the soil. A low Cd migration was measured, attributed to non-equilibrium Cd concentration in percolating water, a high cadmium sorption capacity in the subsoil and root driven Cd circulation in the soil profile. No increased Cd sorption capacity was measured in the sludge supplied soil, despite the almost doubled soil organic matter content. This might be partly attributed to the higher iron oxide and hydroxide concentration measured in the sludge, forming more stable complexes with soil humic compounds compared to cadmium complexes with soil humic compounds. A Monte-Carlo analysis of the SLAM model suggested that the major parameters affecting leaching and crop uptake of cadmium were the cadmium loading and the partitioning coefficient for sludge-derived inorganic material and parameters controlling the effect of pH on sorption. Long-term scenario simulations in SLAM identified critical factors influencing plant cadmium uptake: the cadmium concentration in the sludge, the adsorption capacity of the sludge in relation to the adsorption capacity of native soil and the proportion of the sludge adsorption capacity contributed by the inorganic fraction