Fulvic acid carbon as a diagnostic feature for agricultural soil evaluation

The fulvic acid fraction is considered to be sensitive to agronomic and env ironmental factors. Therefore, the objectives of this study were to evaluat e total carbon (TC) and fulvic acid carbon (Fe) contents and to establish a possible relationship between the FC fraction and coarse organic matter in agricultural soils under different management practices: (i) conventional tilled soils (CVTs), (ii) conservation tilled soils (CSTs), and (iii) virgi n soils (VIRs) from a wide region in Argentina. The investigation included 114 surface samples of Hapludolls, Haplustolls, and Entisols ranging in tex ture from sand to silt loam. In 29 selected samples, two separate soil mine ral fractions were used (<0.05 mm and 0.1-2 mm) to determine FC and TC cont ents. No statistically significant differences were found in TC contents in the fine fraction <0.05 mm between VIRs, CSTs, and CVTs; however, FC conte nts were higher in VIRs than in CSTs and CVTs at the 0.05 probability level , In addition, statistically significant differences (P < 0.05) observed in FC contents among all three treatments in the coarse fraction 0.1-2 mm con firm that the FC fraction is more influenced by the farming-system than is TC, Moreover, FC/TC ratios tended to increase under agricultural land use ( CVTs > CSTs > VIRs), and this ratio also increased from finer textured soil s to coarser textured soils, Results from soil mineral fractions indicated that FC content was highly related to recently incorporated organic residue s.