Claudio Colombo | Università del Molise (original) (raw)

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Papers by Claudio Colombo

Purpose The rationale of this paper is to review the state of the art regarding the biotic and ab... more Purpose The rationale of this paper is to review the state of
the art regarding the biotic and abiotic reactions that can
influence Fe availability in soils. In soil, the managementinduced
change from oxic to anoxic environment results in
temporal and spatial variations of redox reactions, which, in
turn, affect the Fe dynamics and Fe mineral constituents.
Measuring the Fe forms in organic complexes and the interaction
between bacteria and Fe is a major challenge in getting
a better quantitative understanding of the dynamics of Fe in
complex soil ecosystems.
Materials and methods We review the existing literature on
chemical and biochemical processes in soils related with the
availability of Fe that influences plant nutrition. We describe
Fe acquisition by plant and bacteria, and the different Fe–
organic complexes in order to understand their relationships
and the role of Fe in the soil carbon cycle.
Results and discussion Although total Fe is generally high in
soil, the magnitude of its available fraction is generally very
low and is governed by very low solubility of Fe oxides.
Plants and microorganisms can have different strategies in
order to improve Fe uptake including the release of organic
molecules and metabolites able to form complexes with FeIII.
Microorganisms appear to be highly competitive for Fe compared
with plant roots. Crystalline Fe and poorly crystalline
(hydro)oxides are also able to influence the carbon storage in
soil.
Conclusion The solubility of crystalline Fe minerals in soil is
usually very low; however, the interaction with plant, microbes,
and organic substance can improve the formation of
soluble FeIII complexes and increase the availability of Fe for
plant growth. Microbes release siderophores and plant exudates
(e.g., phytosiderophores, organic acids, and flavonoids),
which can bind and solubilize the Fe present in minerals. The
improved understanding of this topic can enable the identification
of effective solutions for remedying Fe deficiency or,
alternatively, restricting the onset of its symptoms and yield’s
limitations in crops. Therefore, development and testing of
new analytical techniques and an integrated approach between
soil biology and soil chemistry are important prerequisites.

Goethite and lepidocrocite are considered the stable species of Fe oxyhydroxides formed from Fe2+... more Goethite and lepidocrocite are considered the stable species of Fe oxyhydroxides formed from Fe2+ oxidation in
mildly acidic soil environments, while maghemite is formed in mildly alkaline conditions. Complexing ligands,
especially humic acid (HA), can change the pathway formation of these iron oxyhydroxides from Fe2+ oxidation.
This research aimed to assess the influence of HA on Fe2+ oxidation and its effect on crystalline Fe mineral products.
Ferrous iron was added to HA at increasing initial COOH/Fe(II) charge ratios (R) at pHs of 5.0 and 8.0 and
aged at 70 °C for 1 month and up to 8 years at room temperature. The precipitated products after aging were
analysed using XRD, FT-IR, TEM and AFM. The results indicate that oxidation of Fe2+ at pH 5.0, in the presence
of large amounts of HA (R = 0.1) promoted the formation of goethite together with ferrihydrite. Oxidation of
Fe2+ in slightly alkaline conditions (pH 8.0) yielded maghemite with small amounts of goethite. Further, longterm
aging of HA coprecipitated with Fe2+ perturbed the stacking of the Fe hydroxyl sheets at pH 5.0, favouring
the formation of ferrihydrite. At pH 8.0 the presence of humic acid does not influence the crystallinity of the precipitation
products and maghemite was still stable after 8 years of aging. This research confirms that the oxidation
of Fe2+ in soil and its subsequent hydrolysis is a very common process of Fe hydroxides/oxide formation in
acidic soil environments. The type of Fe oxide formed depends strictly on the pH and secondly on the rate of oxidation,
especially on the presence and amount of organic compounds that inhibit crystal growth. Humic acid are
the main organic molecules in soils, particularly in cool, humid weathering environments where they lead to a
decrease in crystalline perfection and promote the formation of ferrihydrite instead of goethite or lepidocrocite.
These results provide significant insights into the effect of the mobility of HA in association with Fe minerals.

The aimof this studywas to verify the significance of land use on nitrate availability (NO3–N) at... more The aimof this studywas to verify the significance of land use on nitrate availability (NO3–N) at landscape scale in
two different sites by using multivariate geostatistical methods. NO3–N and several other soil properties of Nitrate
Vulnerable Zone (NVZ) monitoring network of 71 and 63 top-soils, respectively were measured in Venafro
and Campomarino areas of Southern Italy (Molise region). Data analysis was performed firstly with classical descriptive
statistics assuming spatial independence of samples; secondly, geostatistical analysis was performed in
order to investigate spatial dependence and estimate map soil indices. The result of the distribution of NO3–N
contents indicates the existence of many hot spots (high kurtosis) with high NO3–N concentration in both the
study areas. Higher NO3–N levels in Venafro were distributed in the central zone that appeared to be correlated
with animal manure applied to the fields in the summer strongly associated to high values of soil organic matter
(SOM) and total nitrogen (Ntot). In Campomarino, the highest NO3–N concentrations occurred in random spots
that appeared lesser correlated with high SOMcontent and low C/N ratio. Factor co-kriging analysiswas applied
separately to the two data sets to synthesize the complex multivariate variation of the two areas in a restricted
number of zones so they could be ranked as at different risks of NO3–N leaching. The loading values of the factors
indicate that Venafro SOM and clay and, to a lesser extent, Ntot and C/N are the variables that mainly affect the
first factor at shorter range. On the other hand, cation exchangeable capacity (CEC) and, to a less extent, silt, SOM,
C/N and fine sand content weighed more, but negatively, on the first factor at longer range. For Campomarino,
clay content and available water capacity (AWC) and, to a lesser extent, NO3–N, weighed more and positively
on the first factor at shorter range. The first factor at longer range was quite exclusively dominated by elevation
and partially and negatively by pH and CaCO3. Soil factor map appears more variable in both the NVZ areas, characterized
by many spots indicative of intensive land use and management. The highest NO3–N levelswere found
in intensive land use and in dairy farming located for the most part in Venafro catchment. The maps of the two
factors at small scale for Campomarino appear to be quite erratic owing to the small size of the farmswith different
cropping systems differently managed. The results, of the present research, provide data useful to support
land use planning and soil management, to mitigate soil nitrate leaching. Reduction in soil NO3–N could be
achieved by enhancing useful recommendations in N fertilization and animal manure application to farmers.

Di r . Agricoltura Ambiente A lime nt i Univo degli Studi del Mo li se Via De Sanc tis 86 100 Cam... more Di r . Agricoltura Ambiente A lime nt i Univo degli Studi del Mo li se Via De Sanc tis 86 100 Campobasso Italv Roberto Como Ili Di p. di Scienze dell ' Ambi ente e del Terr ito rio e d i Scie nze de lla Te rra Univo degli Studi di Milano Bico cca P.zza de lla Scie nza 1 20126 M ilano lIaly Anna Maria 5tellacci Annamaria Castrignanò Consiglio per la ricerca e la sperimentaz io ne in agri co ltura Unità di ricerca per i sistem i co ltural i degli amb ient i caldo-aridi Via Ce lso Ulpi anl 5 70125 Bari ltaly