Short‐term releases of CO2 from newly mixed biochar and calcareous soil

The work aimed to quantify native organic C mobilized in one calcareous soil in the 21 days after addition of biochar at a range of large to very large applications. The experiment was carried out in unplanted microcosms, and CO₂ flux was used as a measure of net mineralization. A rapid methodological approach, which does not require ¹³C as a tracer, was used to assess any priming effects induced by the biochar. The amount of CO₂‐C mobilized was small relative to the amount of biochar C and proportional to the amount of the biochar added. The additional CO₂‐C was similar to the content of the water‐soluble organic carbon in the biochar added with each application. No interaction with native soil C, that is priming effect, was observed.     

Antioxidants, free radicals, storage proteins, puroindolines, and proteolytic activities in bread wheat (Triticum aestivum) seeds during accelerated aging

Seeds of bread wheat were incubated at 40 degrees C and 100% relative humidity for 0, 3, 4, 6, and 10 days. The effects of accelerated aging on seed germinability and some biochemical properties of flour (carotenoid, free radical, and protein contents and proteolytic activity) and gluten (free radical content and flexibility) were investigated. Seed germinability decreased during aging, resulting in seed death after 10 days. A progressive decrease of carotenoid content, in particular, lutein, was observed, prolonging the incubation, whereas the free radical content increased in both flour and gluten. A degradation of soluble and storage proteins was found, associated with a marked increase of proteolytic activity and a loss of viscoelastic properties of gluten. On the contrary, puroindolines were quite resistant to the treatment. The results are discussed in comparison with those previously obtained during accelerated aging of durum wheat seeds.     

Antioxidants,free radicals,storage proteins,and proteolytic activities in wheat (Triticum durum) seeds during accelerated aging

Accelerated aging was performed by incubation of wheat seeds at 40 degrees C and 100% relative humidity for 3, 4, 6, 10, and 14 days. The effects of the treatment on seed germinability and on several biochemical characteristics of flour (carotenoids, free radical and protein contents, and proteolytic activity) and gluten (free radical content and flexibility) were evaluated. A decrease of germinability was found during aging, the germination being completely inhibited after 14 days. The lutein content decreased gradually, without going to zero, while that of free radicals increased. A reduction of soluble proteins and a degradation of glutenins and gliadins were observed, associated with a substantial increase of protease activity and a decrease in gluten flexibility. The results were discussed in reference to those previously obtained by natural aging of wheat seeds of the same species and cultivar.     

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

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.     

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

 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. Received: 20 October 1998     

Relationships between biological and physico-chemical soil characteristics in a mediterranean agricultural area

Fourteen agricultural soils from various areas of Tuscany were characterized by a range of measurements indicative of soil biological activity. The objective of our research was to identify soil parameters suitable as indicators for evaluating their quality. In general, enzyme activities were found to vary widely, with the highest activity for each enzyme being distributed among only five of the 14 soils studied. The narrowest range (14-fold) in enzyme activities for the various soils was observed for catalase and the widest range (577-fold) for g -glucosidase. Biomass C and, among the measured enzyme activities, amylase, were well correlated with total organic carbon, total N, cation and anion exchange capacity. Positive correlations were found between the maximum water holding capacity and dehydrogenase, amylase, biomass C, FDA hydrolytic activity, the biological index of fertility and the enzyme activity number, so showing that soil moisture may play an important role in affecting soil biological characteristics. No significant correlations were observed among the soil enzymes themselves. The FDA hydrolytic activity appeared to be the index most related with the other biological characteristics tested in this study and, for this reason, can be considered the most effective index for putting in evidence relationships existing between the different biological characteristics in the soils investigated.     

Dimeric inhibitors of human salivary alpha-amylase from emmer (Triticum dicoccon Schrank) seeds

The proteins belonging to the cereal trypsin/alpha-amylase inhibitor family are abundant water/salt-soluble flour proteins active against alpha-amylases from several seed parasites and pests and inactive against endogenous alpha-amylases. Three alpha-amylase inhibitor families have been described in cereals that vary in size and are differently expressed among Triticeae seeds. The present work investigates the presence of human salivary alpha-amylase inhibitors in emmer (Triticum dicoccon Schrank) flour. The isolation was obtained by a series of chromatography steps, and the purification progress was monitored through the inhibition of human salivary alpha-amylase activity. The purified fraction was subjected to protein sequencing by tandem mass spectrometry (MSMS) of the tryptic digests obtained after the sample separation on 2-DE. MSMS data indicated that the emmer alpha-amylase inhibitory fraction was composed of two newly identified proteins [emmer dimeric inhibitor 1 (EDI-1) and emmer dimeric inhibitor 2 (EDI-2)] sharing very high identity levels with related proteins from Triticum aestivum.     

Biochar impact on the estimation of the colorimetric‐based enzymatic assays of soil

This study was carried out in order to assess the influence of biochar applications on the estimation of colorimetric‐based enzymatic assays and to verify the effectiveness of the most common methods. Since most methods used to determine enzymatic activities in the soil are based on colorimetry, biochar may absorb substrates and/or coloured products thereby distorting the analytical result. Biochar was added to two soils, with different textures and cation exchangeable capacities, at a rate of 2% (w/w), and seven enzyme activities were determined following standard methods. The biochar amendment lowered the spectrophotometer reading of the activity of FDAase and dehydrogenase in the sandy soil. In the three enzymatic activities based on p‐nitrophenol production (β‐glucosidase, phosphatase and arylsulphatase), the addition of biochar did not change the enzyme assays. The biochar led to an overestimation in terms of the protease and urease activities in the sandy soil. In the clay loamy soil, biochar did not change the response of any of the enzyme activities tested. A biochar dose of up to 2% only guarantees the effectiveness of the most common spectrophotometric methods for not excessively sandy soils.     

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.     

Suitability of Moist Olive Pomace as Soil Amendment

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.