Humus quantity and quality of an entic Haplustoll under different soil‐crop management systems

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Abstract
The effects of different management systems on the level and composition of humified organic matter in an entic Haplustoll from the semiarid Pampean region were studied. The systems were: TPc, wheat-mixed pasture; TV, wheat (Triticum aestivum), oat (Avena sativa), corn (Zea mays) and triticale grasses; TP, wheat-cattle grazing; and V, virgin, non cultivated. Humic acids were extracted, fractionated, and analyzed for their organic carbon (OC) content, elemental composition, and E4:E6 spectral ratios. The infrared (IR), electron spin resonance (ESR). and C-13-NMR spectra were registered on these humic acids. The TP rotation showed the lowest humic acid-carbon to fulvic acid-carbon (HA-C:FA-C) ratio. The lower O:C ratio of humic acids from the cropped soils indicates a higher level of oxidation than that of the virgin one. The comparison of the different methodologies allowed us to conclude that crop rotations and conservation tillage were adequate to mantain the level and composition of the soil organic matter and humus which affected the soil fertility and level of productivity.