R. Riffaldi

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

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.

Evaluation of compost maturity by means of chemical and microbial analyses

Several chemical and microbiological parameters were tested during a 140 day period to characterize the stabilization process of a paper processing wastewater sludge composted with straw. The parameters indicate two months as a suitable period for the establishment of an equilibrium in the decay process, although some parameters show that compost reaches an acceptable level of stability in 30 days. Evaluation of stability in the end-product is difficult to define by only one parameter, whether it be chemical or biological.

Carbon mineralization kinetics as influenced by soil properties

In a short-term laboratory study C mineralization potentials were determined on soil samples obtained from some representative agricultural soils in Tuscany, Italy. All the kinetic models tested to describe the mineralization process provided a good fit to the experimental data. A modified first-order model best described C mineralization in the soil. Both potentially mineralizable C and the mineralization rate (k) varied considerably among soils, reflecting the differences in soil properties. Potentially mineralizable C was positively related to C evolved as CO2 and to the exchange capacity. Normalized values (potentially mineralizable C divided by organic C), representing on average about 2% of the total soil C, was positively correlated to soil pH and negatively to the soil C pool, the soil N pool, and total microbial activity. Values for k ranged between 0.050 and 0.104 day-1, being higher in fine-textured soils and in soils with a large free Fe content. A low C:N ratio was indicative of a high k value. Turnover times for mineralized C were relatively rapid, ranging from 10 to 20 days.

Carbon mineralization in soil amended with different organic materials

Abstract Laboratory incubation experiments were conducted (for 21 days) to determine the rate and extent of decomposition of 3 animal wastes (farmyard manure, pig slurry and poultry manure), 2 urban wastes (sewage sludge and municipal refuse compost) and one crop residue (rye straw) in a sandy loam soil. The extent of amendment decomposition was found to be a power function of time, related to the incubation temperature and chemical composition of the organic material. The different rates of application used, revealed the pronounced effect of straw on loss of native soil carbon. Farmyard manure and municipal refuse compost were found to be the materials most resistant to short-term decomposition.

Long-term effects of farmyard manure and sewage sludge on some soil biochemical characteristics

Abstract Changes in some soil biochemical properties were investigated following repeated applications of aerobically digested sewage sludge (SS) under field conditions over 12 years, and compared with those of an adjacent soil cultivated and amended with 5 t ha–1 year–1 (dry weight) farmyard manure (FYM) for at least 40 years, as well as with those of an adjacent uncultivated soil, in order to ascertain changes in soil quality. A short-term aerobic incubation was used to determine the potential of the samples to mineralize the organic C supplied. Results indicated that cultivation caused a reduction in total, humified and potentially mineralizable organic C, total N, light-fraction (LF) C, total and water-soluble carbohydrates, phenolic compounds, cation-exchange capacity (CEC), microbial biomass C, specific respiration, hydrolytic and urease activities, and an increase in the heavy metal content. Total and water-soluble carbohydrates and phenolic compounds expressed as a percentage of total organic C (TOC) were similar in the differently managed plots. Of the two amendments, FYM treatments showed higher amounts of TOC and N, LF-C, total and water-soluble carbohydrates, phenolic substances, CEC, specific respiration of biomass, hydrolytic and urease activities, similar amounts and characteristics of humified organic matter and lower concentrations of Cu, Zn and Cr. Both FYM and SS were inadequate treatments for the restoration of soil organic matter lost as a consequence of cultivation.

Biochemical activities in a degraded soil restored by two amendments: a laboratory study

Abstract. This study investigated the soil biochemical activity after different amounts of organic materials with varying degrees of stability [sewage sludge (SS), and farmyard manure (FYM)] were incorporated into a degraded Mediterranean soil. SS greatly enhanced the biomass C content and increased respiration. Soil treated with fresh material (SS) produced more CO2 than that treated with stabilized FYM, with higher values being obtained at the highest dose. FYM maintained high levels of dehydrogenase (DH-ase) activity, indicating a biochemical regeneration of the soil. C mineralization was less affected by FYM and SS than expected using an additive calculation, while additivity was observed for DH-ase activity only in SS-treated soil. Protease activity showed additivity in FYM-amended soil, while greater than additivity was found for the addition of SS.

Mineralization parameters from organic materials added to soil as a function of their chemical composition

Abstract Carbon mineralization of different organic materials added to soil was monitored over a short time in a laboratory incubation experiment. Several kinetic models were evaluated for their suitability in describing the decomposition processes. A modified first-order model best described carbon mineralization for each material. Parameters derived from such a model were tested as indexes for assessing the relationships between the decomposition in soil of the organic materials and their chemical compositions. The term ‘initial potential rate of C mineralization’, especially when normalized to total C added to soil, was found to be the most effective index for assessing the above-mentioned relationship.

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

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.

Humic fractions of organic wastes

Abstract The distribution and composition of humic and fulvic acids have been investigated in the following organic wastes: straw, farmyard manure, sewage sludge, poultry manure, municipal refuse compost and pig slurry. Of the total organic carbon, the proportion present as humic carbon varied from about 13% in the compost to 50% in the pig slurry; the humic compounds extracted are characterized by a variable chemical composition. As compared to the natural humic substances from soil organic matter, these compounds show a lower content of acidic functional groups, lower E4/E6 and C/H ratios and can be classified as young forms of humic substances.

Role of chemical constituents of wheat straw and pig slurry on their decomposition in soil

Abstract Carbon mineralization and microbial biomass content of wheat straw (WS), pig slurry (PS) and their mixture (WSPS), either intact or with extraction of soluble substances (–SS) or soluble substances plus hemicellulose (–SSH), added to soil, were monitored over 230 days in a laboratory incubation experiment. The WSPS showed a CO2 release of up to 23% above that predicted by summing the CO2 evolved from WS and PS. Of the several kinetic models tested to describe the mineralization process, a double exponential model best described the C mineralization of all the materials, both intact and with extractions. The extraction of the labile substances from WS, PS and WSPS lowered the values of the rapidly mineralizable C and of the amount of microbial biomass. The organic fraction of WS was found to be almost completely represented by mineralizable carbon, while PS and WSPS showed only 62% of mineralizable carbon. In spite of this, after 8 months, about half of the initial amount of the organic C in the intact residues still remained unmineralized.