Piero Perucci

An improved method to evaluate the o-diphenol oxidase activity of soil

Phenolic compounds are intermediary transformation products of many naturally occurring substances and synthetic chemicals, including crop residues, organic wastes, pesticides and industrial products. They are suitable substrates for the phenolases and peroxidases produced by the soil microflora. Although measurement of the enzymatic oxidation of phenolic compounds is an important measure of the soil microfloras capacity to degrade potentially recalcitrant organics, the proposed methods to perform this measurement are few and questionable. In this paper a new, reliable and simple method to measure the o-diphenol oxidase activity in whole soil sample is proposed. The method is based on a spectrophotometric determination of a red compound (4-(N-proline)-o-benzoquinone) developed from enzymatic oxidation of catechol in the presence of proline.

The effect of initial concentration, co-application and repeated applications on pesticide degradation in a biobed mixture

A 180 d laboratory experiment was conducted to investigate the degradation rates of chlorpyrifos (10 and 50 mg kg(-1)) and metalaxyl (100 mg kg(-1)) separately and co-applied in a biomix constituted by topsoil, vine-branches and urban-waste-garden compost. The effect of repeated application of metalaxyl was also investigated. Microbial biomass-C (MBC) content and metabolic quotient (qCO(2)) were measured to evaluate changes in microbial biomass size and activity induced by the presence of the two pesticides. Degradation rate decreased with increasing concentration of chlorpyrifos in all treatments. Metalaxyl half-life was significantly reduced in co-application with chlorpyrifos indicating a synergic interaction between the two pesticides in favour of enhanced degradation rate for metalaxyl but not for chlorpyrifos. Furthermore, repeated application resulted in a sharp reduction of metalaxyl half-life from 37 d after first application to 4 d after third application. MBC content was negatively influenced by the addition of pesticides but it started to recover immediately, in both separate and co-applied treatments, reaching the control value when pesticide residues were about 50% of the initial concentration. The qCO(2) reached a steady-state after about 20 d in separately applied and 40 d in co-applied treatments, indicating a tendency to arrive at a new metabolic equilibrium. In conclusion, the biomix tested has been shown to degrade pesticides relatively fast and to have a microbial community that is varied enough to allow selection of those microorganisms able to degrade metalaxyl and chlorpyrifos.

Effectiveness of microbial indexes in discriminating interactive effects of tillage and crop rotations in a Vertic ustorthens

Abstract. Conservation tillage is a soil management practice able to reduce erosion, increase organic matter content and improve physical, chemical and biological soil properties. Conservation tillage reduces the incorporation of crop residues into the soil profile and minimises the exposure of humified organic matter to biotic and abiotic degradative processes. In this article the effect of conventional (ploughing at 40-cm depth coupled with harrowing at 20-cm depth) and reduced tillage (harrowing at 20-cm depth) and two rotations (vetch-oat/wheat and fallow/wheat) on biochemical and microbial properties of a Vertic Ustorthens, located in a semi-arid region of southern Italy, has been investigated. Tillage had a more pronounced effect on soil properties studied here than did rotations. By comparison to conventional tillage (CT), the reduced tillage (RT) resulted in improved soil C and microbial biomass content. Even though some of the selected enzymes showed seasonal variability and, when averaged across the sampling period, were not always able to discriminate among treatments, their sum showed a strong correlation with soil organic C and soil microbial biomass C (MBC), for all these parameters increased in RT plots.

Relationship between rimsulfuron degradation and microbial biomass content in a clay loam soil

Abstract The present research was conducted to determine the relationship between the degradation of rimsulfuron and soil microbial biomass C in a laboratory-incubated clay loam soil (pH=8.1; organic matter=2.1%) under different conditions and at different initial dosages (field rate, 10 and 100 times the field rate). The half-life values varied between 0.4 and 103.4 days depending on temperature, soil moisture and initial dose. Evidence suggested that rimsulfuron could pose environmental risks in cold and dry climatic conditions. Significant decreases in microbial biomass C content in rimsulfuron-treated soil, compared to untreated soil, were observed initially, especially at higher temperatures and low moisture levels, but never exceeded 20.3% of that in control soil. The microbial biomass C content then returned to initial values at varying times depending on incubation conditions. The relationship between herbicide degradation and microbial biomass C content gave parabolic curves (P<0.005 in all cases) under all conditions tested. Generally, maximum biomass C decrease coincided with the decrease in the concentration of rimsulfuron to about 50% of the initial dose, except at 10  °C and 100×, when biomass began to recover as early as 65–70% of the initial dose. The final equations could be useful to deduce the decrease of soil microbial biomass in relation to herbicide concentration. From the degradation kinetics of the herbicide, the time required to reach this decrease can also be calculated.

Retention capacity of an organic bio-mixture against different mixtures of fungicides used in vineyards.

A laboratory experiment was carried out to test the efficiency of a bio-mixture made up of pruning residues at two (PR2) and five (PR5) years of composting and wheat straw (STW) in the biological cleaning of water contaminated by different mixtures of fungicides usually employed in vineyards. The experiment was conducted and reproduced at a scale of 1:100 of operating field conditions. Commercial formulates of penconazole (PC), (RS)-1-[2-(2,4-dichlorophenyl)pentyl]-1H-1,2,4-triazole), dimetomorph (DM), (EZ)-4-[3-(4-chlorophenyl)-3-(3,4-dimethoxyphenyl)acryloyl]morpholine), azoxystrobin (AZ), (methyl (E)-2-{2-[6-(2-cyanophenoxy)pyrimidin-4-yloxy]phenyl}-3-methoxyacrylate), iprovalicarb (IP), (isopropyl 2-methyl-1-[(RS)-1-p-tolylethyl]carbamoyl-(S)-propylcarbamate), metalaxyl (MX), (methyl N-(methoxyacetyl)-N-(2,6-xylyl)-DL-alaninate), fludioxonil (FL), (4-(2,2-difluoro-1,3-benzodioxol-4-yl)-1H-pyrrole-3-carbonitrile) and cyprodinil (CY), (4-cyclopropyl-6-methyl-N-phenylpyrimidin-2-amine) were mixed in water and discharged into the bio-mixture following the time schedule of the treatments carried out in the grapevine in real field conditions. At each treatment, contaminated water with fungicides was circulated repeatedly through the bio-mixture to enhance the sorption of fungicides. In fact, it retained them between 98–100% with the exception of MX of which it was able to retain only 90.5%. The adsorption/desorption experiment showed that repeated circulation of water, instead of enhancing MX retention, can easily remove about 30% of MX already adsorbed by the bio-mixture. This finding suggests that water contaminated by very mobile pesticides should be discharged at the end of field treatments without re-circulating the water in order to avoid the release of pesticides weakly adsorbed on the bio-mixture.

Rimsulfuron in soil: Effect of persistence on growth and activity of microbial biomass at varying environmental conditions

The research was carried out toascertain the effect of rimsulfuron, a solfonylureaherbicide, on soil microbial biomass growth andactivity. Laboratory experiments were performed in asilty clay loam soil to relate changes of soilmicrobial biomass-C content and global hydrolyticactivity to the rimsulfuron persistence underdifferent conditions of temperature and soil humidity.The results showed that rimsulfuron persistencedepended significantly on temperature, while itremained almost unchanged by humidity changes. A rangeof half-life values from 3.5 to 14.8 days was found ina temperature range from 10 °C to 25 °C,with lower half-lives at higher temperature.Persistence data were processed with the VARLEACHmodel, in order to predict rimsulfuron persistenceunder different environmental conditions. On comparingtreated soils with untreated soil samples, decreasesin the microbial biomass-C content and increases inthe global hydrolytic activity were found to beconnected with rimsulfuron persistence at the variousexperimental conditions. These effects persisted fora short time and, they were evident earlier at highertemperature and more persistent at lower humidity.This behaviour is discussed in terms of rimsulfurontoxicity, with the consequent release of endocellularhydrolytic enzymes from the dead microorganisms. Anequation was derived to calculate the microbialbiomass-C content in response to the variation ofrimsulfuron persistence.

Biochemical parameter changes in urban-waste compost used as biofilter for pesticide decontamination

Urban-waste compost (UWC) can be used as a biofilter filling to reduce the effects of pesticide spills. Here, water that was contaminated by three different pesticides, the insecticide chlorpyrifos (Chl), the fungicide metalaxyl (Meta) and the herbicide glyphosate (Gly), was percolated through 2 kg of UWC material. The pesticide residues in the leached water and the modifications induced in some of the UWC biochemical and microbiological parameters (including microbial biomass carbon (MBC) and nitrogen (MBN), and fluorescein diacetate (FDA) hydrolysis, alkaline monophosphatase (AMP) and dehydrogenase (DH) activities) were investigated over 2 months of incubation at 20°C. The UWC showed a good retention capacity towards the three pesticides tested, with the highest efficiency for Gly. Chl caused an initial detrimental effect on the MBC content and a decrease in the FDA hydrolysis capacity, while Meta and Gly increased the MBC content throughout the incubation. The results demonstrate that UWC can be successfully used as a biofilter to reduce pesticide spills and to clean up water contaminated with pesticides. The evaluation of the modifications induced on the UWC MBC and MBN, and FDA hydrolysis, AMP and DH activities suggest different biodegradation potentials of the UWC micro-organisms vs. the three pesticides studied.

Moist olive husks addition to a silty clay soil: influence on microbial and biochemical parameters.

To investigate the effects of moist olive husks (MOH-residues) on soil respiration, microbial biomass, and enzymatic (o-diphenoloxidase, β-glucosidase, dehydrogenase and alkaline phosphatase) activities, a silty clay soil was incubated with 0 (control), 8 × 103 (D), 16 × 103 (2D) and 80 × 103 (10D) kg ha−1 of MOH-residues on a dry weight basis. Soil respiration and microbial biomass data indicated that the addition of MOH-residues strongly increased microbial activity proportionally to the amounts added. Data of qCO2 suggested that the respiration to biomass ratio of the microbial population was strongly modified by MOH-residues additions during the first 90 days of incubation. The qCO2 data suggested a low efficiency in energy yields from C oxidation during the first 2 months of soil incubation. qFDA seemed to be relatively unaffected for treatments D and 2D as compared to the control, but was significantly lowered by the application of 10D, showing the lowest hydrolytic activity of microbial biomass in this treatment up to 360 days of incubation. o-Diphenoloxidase activity was delayed, and this delay was extended with the addition of larger quantities of MOH-residues. Alkaline phosphatase, β-glucosidase and dehydrogenase activities were in line with the findings on microbial biomass changes and activities. The biological and biochemical data suggest that the addition of a large quantity of MOH-residues (80 × 103 kg ha−1) strongly modifies the soil characteristics affecting the r- and K-strategist populations, and that these changes last for at least the 360 days of incubation. The data also suggest that application rates exceeding 16 × 103 kg ha−1 are not recommended until the agro-chemical and -physical functions of the soil are further studied.