Soil Chemical Analysis

An increasing body of evidence suggests that microorganisms are far more sensitive to heavy metal stress than soil animals or plants growing on the same soils. Not surprisingly, most studies of heavy metal toxicity to soil microorganisms have concentrated on effects where loss of microbial function can be observed and yet such studies may mask underlying effects on biodiversity within microbial populations and communities. The types of evidence which are available for determining critical metal concentrations or loadings for microbial processes and populations in agricultural soil are assessed, particularly in relation to the agricultural use of sewage sludge. Much of the confusion in deriving critical toxic concentrations of heavy metals in soils arises from comparison of experimental results based on short-term laboratory ecotoxicological studies with results from monitoring of long-term exposures of microbial populations to heavy metals in field experiments. The laboratory studies in effect measure responses to immediate, acute toxicity (disturbance) whereas the monitoring of field experiments measures responses to long-term chronic toxicity (stress) which accumulates gradually. Laboratory ecotoxicological studies are the most easily conducted and by far the most numerous, but are difficult to extrapolate meaningfully to toxic effects likely to occur in the field. Using evidence primarily derived from long-term field experiments, a hypothesis is formulated to explain how microorganisms may become affected by gradually increasing soil metal concentrations and this is discussed in relation to defining “safe” or “critical” soil metal loadings for soil protection.

Toxicity of heavy metals to microorganisms and microbial processes in agricultural soils: a review.

B6nassy, C., 1955. R6marques sur deux Aphelinid6s: Aphelinus mytilaspidis Le Baron et Aphytis proclia Walker. Annls l~piphyt. 6: 11-17. Lord, F. T. & MacPhee, A. W., 1953. The influence of spray programs on the fauna of apple orchards in Nova Scotia II. Oyster shell scale. Can. Ent. 79: 196-209. Pickett, A. D., 1946. A progress report on long term spray programs. Rep. Nova Scotia Fruit Grow. Ass. 83 : 27-31. Pickett, A. D., 1967. The influence of spray programs on the fauna of apple orchards in Nova Scotia XIV. Can. Ent. 97: 816-821. Tothill, J. D., 1918. The predacious mite Hemisarcoptes malus Shimer and its relation to the natural control of the oyster shell scale Lepidosaphes ulmi L. Agric. Gaz. Can. 5 : 234-239.

http://link.springer.com/content/pdf/10.1007/BF01976688.pdf

Soil enzymes: Kuprevich, V. F. & Shcherbakova, T. A.: Translated from the Russian edition (1966), published by the Indian National Scientific Documentation Centre, New Delhi 1971. 392 pp., offset printing from type script, paper cover. Obtainable from U.S. Department of Commerce, National Technical Information Service, Springfield, Va. 22151

An overview on olive mill wastes and their valorisation methods.

Soil biochemical properties are indicators of soil quality, but there is still no consensus as to how they should be used. We review the trends in their use over the last decade. Generally, biochemical properties related to the biocycles of the elements (C, N, P and S) are used to diagnose soil quality. These properties include both general biochemical parameters (i.e. microbial biomass C, dehydrogenase activity and N mineralization potential) and specific biochemical parameters (i.e. the activity of hydrolytic enzymes, such as phosphatase, urease and β-glucosidase). Biochemical properties can be used both individually, as simple indices, or in combination using complex equations derived from mathematical combinations or the application of statistical programs. The results described in the literature for both are contradictory and question the validity of the use of biochemical properties as quality indicators. Complex expressions, in which different properties are combined, are thought to be highly suitable for estimating soil quality, although their use is limited to the area and situation in which they have been described. Generally, the greatest problems posed by the use of biochemical properties as soil quality indicators include the lack of reference values, the contradictory behaviour shown by these properties when a soil is degraded, and the regional variations in expression levels. Most of these problems are derived from the scarce information available on the biochemical properties of soil. For this reason, obtaining soil quality indicators of general use will require a coordinated effort from the international scientific community to standardise the analytical methods and to compile databases of biochemical properties from soils under diverse geographic conditions and with different uses and management.

Different approaches to evaluating soil quality using biochemical properties

Changes in soil quality after 45 years of continuous production of corn (Zea mays L) by the conventional tillage method (C) compared with adjacent poplar forest (F) and native grassland (G) sites were examined The investigated parameters were: total and humified organic C, total N, light fraction content and composition, water-soluble organic C (WSOC), water-soluble carbohydrates (WSC), phenolic substances, biomass C, cumulative CO2-C (soil respiration) (Cm), enzyme activities (alkaline phosphatase, protease, β-glucosidase, urease, catalase and dehydrogenase) Empirical indexes of soil quality were also calculated: biomass C/organic C, specific respiration of biomass C (qCO2), death rate quotient (qD), metabolic potential (MP), biological index of fertility (BIF), enzyme activity number (EAN) and hydrolysing coefficient (HC) Results indicate that long-term corn production at an intensive level caused a marked decline in all examined parameters Between the undisturbed systems, native grassland showed higher values of soil quality parameters than forest site The indexes most responsive to management practices that may provide indications of the effects of soil cultivation, as well as of the differently undisturbed ecosystems were: organic C, WSC, Cm, protease, β-glucosidase, urease and HC Soil enzyme activities were well related with, and not more sensitive than organic carbon

A comparison of soil quality in adjacent cultivated, forest and native grassland soils

The effects of two different biological treatments on hydrocarbon degradation and on soil biological activities were determined during a 100-d incubation period. An evaluation of soil biological activities as a monitoring instrument for the decontamination process of diesel-oil contaminated soil was made using measurements of organic carbon content, soil microbial respiration, soil ATP and dehydrogenase, β-glucosidase, lipase enzyme activities. Five samples were used: S (control, uncontaminated soil), CS (contaminated soil), SCS (sterilized contaminated soil), CFS (contaminated soil plus N and P), CCS (contaminated soil plus compost). The relationships between soil parameters and the levels of total petroleum hydrocarbons (TPH) residues were investigated. Results showed that inorganic nutrients NP and compost stimulated hydrocarbon biodegradation but not all biological activities to a significant extent. The residual hydrocarbon trend was positively related with that of the organic C content, microbial respiration and with β-glucosydase activity, while both soil lipase and dehydrogenase activities were negatively related with the hydrocarbon trend. Lipase activity was found to be the most useful parameter for testing hydrocarbon degradation in soil.

Soil Biological Activities in Monitoring the Bioremediation of Diesel Oil-Contaminated Soil

An experiment was performed to evaluate the possibility of cocomposting wet husk and wastewater, the two main olive oil mill by-products. The pH, E.C., total C and N, humic substances, phenolics, volatile acids, lipids, P and K plus yeast, fungi, heterotrophic-, cellulolytic- and nitrifying bacteria and phytotoxicological parameters were monitored during a 120-day stabilization process. Performances of the composting system adopted, together with physicochemical characteristics of starting material and final product, are reported. Composting was found to induce a high level of organic matter change, with decrease of organic carbon, total nitrogen and C/N ratio, as well as of the easily biodegradable lipids. Good metabolic activity of the microbiological population, with the exception of the nitrifying bacteria, and a complete detoxification of starting material were also observed. The results obtained suggested that composting might be an adequate low-cost strategy for the recycling of olive oil by-products.

Cocomposting of olive oil mill by-products: chemical and microbiological evaluations

Soil biochemical properties under long-term crop management systems may be useful indicators of soil quality. We measured seven enzyme activities and six calculated biological indices at four adjacent study sites on an andosol in a semiarid area of eastern Sicily. Soils were sampled under natural grassland (NG), orange-grove (OG), winter wheat (WW) and horticultural crop (HC) managed according to local agricultural usage. The enzymes investigated were dehydrogenase, catalase, protease, alkaline phosphatase, β-glucosidase and amylase. The calculated biological indices were hydrolyzing coefficient, enzyme activity number, biological index of fertility, metabolic potential, lability index and C management index. Tilled management systems (WW and HC) were lower in total organic C and N and in all the enzyme activities and biological indices than in untilled management systems (NG and OG). Catalase activity and hydrolyzing coefficient were the most suitable soil biochemical properties for differentiating between the effects of different crop management systems, because of their analytical simplicity and rapidity.

Biochemical properties of a Mediterranean soil as affected by long-term crop management systems

A laboratory experiment was performedto evaluate the suitability of moist olive pomace(MOP) as soil amendment. Moist olive pomace wasobtained from a new olive-oil industrial processcalled the `two-phases method'. Soil samples weremixed with MOP to approximate a field application of40 t ha-1 and incubated under aerobic conditionsat 20 °C and 60% of soil water holdingcapacity. To estimate the effect of different loadingrates and N supply on mineralization, 40, 80, 120 and160 t ha-1 of MOP and 200 ppm of N as(NH4)2SO4 were used. CumulativeCO2-C evolution, total microbial activity andbiomass-C were monitored during a 60-day period.Results indicate that the CO2-C evolution fromMOP depends on soil type and is temporarily inhibitedin acidic soils. Evolution of CO2-C increaseswith incremental addition of MOP, but the percentagesof the added C that were mineralized decreased withincreasing application rates. Mineral N supplementsresult in more efficiency of the mineralizationprocess. Among the kinetic models tested to describethe mineralization dynamics, a first-order exponentialmodel including a constant term provides the best fitto the experimental data. Both amount and activity ofsoil microbial biomass are enhanced by MOP added atthe 40 t ha-1 rate, at least in the first periodof incubation. At higher rates of MOP addition, aconstant increase of biomass C during incubation isobserved, while the biological activity decreases atthe end of incubation. Following application ofmineral N, both amount and activity of microbialbiomass is enhanced.

Roberto Cardelli

Papers

A comparison of soil quality in adjacent cultivated, forest and native grassland soils

Soil Biological Activities in Monitoring the Bioremediation of Diesel Oil-Contaminated Soil

Cocomposting of olive oil mill by-products: chemical and microbiological evaluations

Biochemical properties of a Mediterranean soil as affected by long-term crop management systems

Suitability of moist olive pomace as soil amendment