G. Vanni

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.

Laboratory studies on the application of wheat straw and pig slurry to soil and the resulting environmental implications

Abstract In a laboratory experiment, wheat straw (WS), pig slurry (PS) and a mixture of the two materials (WSPS) were added to soil at the rate of 2% on a dry soil basis. Samples of the soil alone and with the amendments were collected at various intervals of time during a one year period and analysed for: pH, electrical conductivity (EC.), NO−3, HPO2−4, phenolic compounds and volatile acids. A germination index (G.I) using the Lepidium sativum test was carried out. The fractionation of the different forms of Cu and Zn was investigated. In comparison with the control, the WS-treated soil showed a constant diminution of NO−3, a slight lowering of pH and a net increase of EC. Sixty days after amendment, phenolic compound and volatile acid contents became equal to those of the control. The WS did not show any germination effect and did not significantly influence the content and distribution of soil Cu and Zn. The addition of PS to soil produced an increase of EC., NO−3 and HPO2−4, with a consequent lowering of the pH, a moderate effect on phenolic substances and volatile acids and a toxic effect on seed germination until the 7th day after the amendment. Total levels of Cu and Zn and their organic and inorganic bound fractions increased. The most consistent effect on soil properties from the WSPS mixture was for NO−3, which was released slowly but progressively. This mixture increased the germination index in comparison with PS added alone to the soil.

Effect of the disposal of sludge from olive processing on some soil characteristics : laboratory experiments

A laboratory experiment was performed during a 40-day incubation period in order to evaluate changes in organic and inorganic compounds of soil amended with two doses of sludge obtained from olive-oil processing waste waters.Differences between the amounts of organic components of the amended soil and those of the control, although related to doses and sampling time, disappeared at the end of the experimental period. On the contrary, the inorganic anion contents were still different for the various treatments, which suggest, especially for NO3− and SO42−, a transient inhibition in the soil-sludge system.A germination test, carried out on the soil amended with different doses of sludge, indicates that after about twenty days even the soil containing the highest dose of sludge did not show toxicity any longer.

Decomposition of vegetation water sludge in soil

Abstract A laboratory study was designed to provide data on the effects of application rates (0, 1, 2, 3, and 4% of soil), moisture content (50, 100, and 150% WHC), and incubation temperature (4, 17, and 29°C) on the extent and rate of decomposition in soil of sludge organic matter derived from dehydrated vegetation waters. Cumulative CO2C loss was described by the equation C = Ktm. At 3 and 4% loading rates, the CO2C evolution showed a short transitory inhibition, after which decomposition started. The CO2C evolved at 17°C was proportional to the amount of sludge added, and, after two months of incubation, the percentage of CO2C evolved was about 50% of the C applied. A log-log plot of the cumulative CO2C evolution against time showed two stages representing the decomposition of the active and less readily decomposable organic carbon, respectively. The moisture level at 100% WHC had a small positive effect on the degradation of the sludge, while at 150% EHC carbon loss was lower. The rising temperatures accelerated the rate of the decomposition with a Q10 factor ranging from 1·44 to 1·89.

Are the Physiological and Biochemical Characteristics in Dandelion Plants Growing in an Urban Area (Pisa, Italy) Indicative of Soil Pollution?

Physiological and biochemical characteristics were evaluated in dandelion plants (Taraxacum officinale) growing naturally in an urban environment. The study area was located in Pisa, Italy, and 27 sites in the municipality were chosen to assess the biochemical and physiological features of dandelion plants and the trace metal content in the urban soil. Concentrations of elements including, Cr, Cu, Mn and Zn were analysed in the soil together with dandelion shoot and root tissues collected from the various sites. Chlorophyll a fluorescence analysis, the pigment content, antioxidant power and phenol content were determined in dandelion. The results showed very limited soil pollution due to trace metals in the urban sites. However, dandelion showed Zn uptake and translocation although no damage was observed in the plants. Our results highlight that dandelion plants are able to survive in a constrained environment thanks to the high phenol content which is effective in combatting the oxidative stress induced by heavy metals.