Characterization of Humic Fractions in Leachates from Soil Under Organic and Conventional Management and Their Interactions with the Root Zone

Humic fractions were shown to be closely involved in gene expression and promotion of different PM H+-ATPase isoforms, as well as in lateral root development, indicating an enhanced nutrient absorption capacity of the plant root system. HPLC-SEC confirmed that water-soluble humic substances (WSHS) correspond to a subfraction of the fulvic fraction of humic substances. This was supported by E 465/E 665 ratios higher than 8.5. These ratios generally increased over the growing season in cultivated soils but showed significant differences between conventionally and organically managed bare soils. FTIR data and the analytical quantification of carboxyls confirmed relevant structural changes in bare soil under both organic and conventional farming management. Absorption intensities ratios at 1,590–1,570 cm−1 and 1,440–1,380 cm−1 showed the predominant aliphatic character of these molecules.