title: Proton binding by humic and fulvic acids from pig slurry and amended soils.
abstract: The knowledge of acid-base characteristics of humic acid (HA) and fulvic acid (FA) fractions of organic amendments and amended soils is of considerable importance for assessing their agronomic efficacy and environmental impact. In this work, the acid-base properties of HAs and FAs isolated from pig slurry, soils amended with either 90 or 150 m(3) ha(-1) yr(-1) of pig slurry for 3 yr, and the corresponding nonamended control soil were investigated by using a current potentiometric titration method. The nonideal competitive adsorption (NICA) model that describes proton binding by two classes of binding sites (carboxylic- and phenolic-type groups) was successfully fit to titration data. With respect to the control soil HA and FA, pig-slurry HA and FA were generally characterized by smaller carboxylic-type group contents, slightly smaller phenolic-type group contents, larger affinities for proton binding by the carboxylic-type groups, and much smaller, in the case of the HA fraction, or similar, in the case of the FA fraction, affinities for proton binding by the phenolic-type groups. Amendment with pig slurry determined a number of modifications in soil HAs and FAs, including decrease of acidic functional group contents, and slight increase of the proton affinity of the carboxylic-type groups. Further, a slight decrease of the affinities for proton binding by the phenolic-type groups of HAs was observed. These effects can have a large impact on the biological availability, mobilization, and transport of macro- and micronutrients, toxic metal ions, and xenobiotic organic cations in pig slurry-amended soils.
authors.affiliation: Centro de Ciencias Medioambientales, Consejo Superior de Investigaciones Científicas, Serrano 115 dpdo., 28006 Madrid, Spain. c.plaza@ccm.csic.es
authors.forename: César
authors.initials: C
authors.lastname: Plaza
authors.forename: Juan C
authors.initials: JC
authors.lastname: García-Gil
authors.forename: Alfredo
authors.initials: A
authors.lastname: Polo
authors.forename: Nicola
authors.initials: N
authors.lastname: Senesi
authors.forename: Gennaro
authors.initials: G
authors.lastname: Brunetti
mesh_terms: D000818:Animals; D001578:Benzopyrans / Q000737:chemistry*; D001682:Biological Availability; D006812:Humic Substances; D006863:Hydrogen-Ion Concentration; D008372:Manure; D019216:Metals, Heavy; D008962:Models, Theoretical; D011522:Protons; D013552:Swine; D015262:Xenobiotics
chemical_list: D001578:Benzopyrans; D006812:Humic Substances; D008372:Manure; D019216:Metals, Heavy; D011522:Protons; D015262:Xenobiotics; C005023:fulvic acid