Effects of Pig Slurry Application on Soils and Soil Humic Acids

Abstract

The effect of three annually consecutive additions of pig slurry at two rates (90 and 150 m3 x ha(-1) x year(-1) on soils and soil humic acids (HAs) was investigated in a field experiment under semiarid conditions. Soils and pig slurries were analyzed by standard methods. The HAs were isolated from soils and pig slurry by a conventional procedure based on alkaline extraction, acidic precipitation to pH 1, purification by repeated alkaline dissolutions and acidic precipitations, water washing, dialysis, and final freeze-drying. The HAs obtained were analyzed for elemental (C, H, N, S, and O) and acidic functional group (carboxylic and phenolic) composition, and by UV-vis, FT-IR, fluorescence, and ESR spectroscopies. With respect to the control soil, the pig slurry amended soils had greater pH and electrical conductivity, slightly larger total N content, and smaller values of C/N ratio. A decrease of total organic C was observed only in soils amended for 2 and 3 years at the higher slurry rate. With respect to control soil HA, pig slurry HA was characterized by larger contents of S- and N-containing groups, smaller acidic functional group and organic free radical contents, a prevalent aliphatic character, extended molecular heterogeneity, and smaller aromatic polycondensation and humification degrees. Amendment with pig slurry HA determines a number of modifications in soil HAs, including increase of C, S, and COOH contents, C/N ratios, and aliphaticity and decrease of extraction yields and N, O, phenolic OH, and organic free radical contents. These effects are generally more evident after the first year of slurry application and tend to disappear with increasing number of treatments. Most probably, over the years the slightly humified slurry HA is mineralized through extended microbial oxidation, whereas only the most recalcitrant components, such as S-containing, phenolic, and aliphatic structures, are partially accumulated by incorporation into soil HA.

Role of Humification Processes in Recycling Organic Wastes of Various Nature and Sources as Soil Amendments

“…As a whole, the results of elemental, functional, FT IR, fluorescence, ESR and NMR analyses described above together with additional evidence provided by other authors [29,40,[86][87][88][89] indicate that, with respect to soil HA and FA, HA-and FA-like fractions isolated from LSM and other animal manures are rich in incompletely humified materials characterized by a prevalent aliphatic character, small acidic oxygenated functional group content, small polycondensation and polymerization degree, and larger presence of polysaccharide and S-and N-containing groups, most probably proteinaceous materials. yr -1 of LSM over a seven-year period, were investigated by use of a current potentiometric titration method and fitting the NICADonnan model to titration data [90].…”

Little fertilizer response but high N loss risk of maize on a productive organic-sandy soil

“…It has also been suggested that adding slurry to the soil enhances mineralization as a priming effect and that this is larger in soils with higher C and N (Kuzyakov et al 2000;Plaza et al 2002). Application of pig slurry resulted in DM yields of silage maize that were almost similar to those receiving mineral N. This is astonishing as the NH 4 proportion in pig slurry was 75% of total N. The effect of cattle slurry was smaller but still stronger than expected (Sommer and Hutchings 2001).…”

The Effect of Organic Matter Amendment on Native Soil Humic Substances

“…With increasing amendment rate and number, free radical concentrations of amended soil HAs and FAs decrease with respect to those of the corresponding unamended soil HAs and FAs (Plaza et al, 2002(Plaza et al, , 2003Gonz á lez -P é rez et al, 2006 ). The concentration of organic free radicals in HS is generally related positively to the aromatic polycondensation, polymerization, and humifi cation degree and may infl uence (a) their reactivity with metal ions and organic chemicals and (b) their physiological activity (Steelink, 1987 ;Senesi and Steelink, 1989 ;Senesi, 1990aSenesi, ,b , 1996Cheshire and Senesi, 1998 ).…”

“…The free radical concentrations of HAs and FAs from organic amendments are generally much smaller than those of native soil HAs and FAs (Figure 4.10 ) (Hervas et al, 1989 ;Jerzykiewicz et al, 1999 ;Plaza et al, 2002Plaza et al, , 2003SolerRovira et al, 2002SolerRovira et al, , 2003Gonz á lez -P é rez et al, 2006 ). With increasing amendment rate and number, free radical concentrations of amended soil HAs and FAs decrease with respect to those of the corresponding unamended soil HAs and FAs (Plaza et al, 2002(Plaza et al, , 2003Gonz á lez -P é rez et al, 2006 ).…”

“…Generally, this resonance is accompanied by a number of other signals of various complexity and intensity possibly arising from paramagnetic metal ions present as organic complexes and/or mineral impurities (Figure 4.9 ) (Hervas et al, 1989 ;Jerzykiewicz et al, 1999 ;Plaza et al, 2002Plaza et al, , 2003Soler -Rovira et al, 2002, 2003Gonz á lez -P é rez et al, 2006 ). sludge ( b , c , and d , respectively).…”