Impact of conventional and no-tillage management on soil amino acids, stable and transient radicals and properties of humic and fulvic acids

While several studies have documented the effect of no-till (NT) and conventional-till (CT) practices on soil organic matter and nutrients, very limited information is available on the effect of tillage practices on amino acids in soil. This study was conducted to measure the concentrations of bound amino acids in humic (HA) and fulvic acids (FA) in samples collected from soils under NT and CT management. Samples were obtained from two long-term studies at the Horseshoe Bend Experimental Area and at the Bledsoe Research Farm in Georgia, USA. The total amount of bound amino acids in HA was higher in NT than in CT samples. In contrast, the concentration of bound amino acids in FA was higher in CT than in NT samples. Neutral amino acids dominated in all samples of HA and FA. Acidic amino acids had the lowest concentrations. In all samples of HA and FA, the dominant amino acids were: glutamic acid, alanine, glycine and valine. β-alanine and lysine concentrations in HA and FA were higher in NT than in CT, indicating a higher microbial biomass in NT soils. Proline concentrations in FA were higher in CT than in NT samples. Electron paramagnetic resonance (EPR) was applied to characterize HA and FA extracted from soils under NT and CT. The level of native radicals for each sample of HA and FA was estimated. Strong effects of gaseous ammonia on spin concentration enhancement and also higher values of g-value were found to be associated with the formed “transient” radicals. HA from NT management was characterized by higher molecular weight and a higher degree of condensation of aromatic constituents than HA from CT.