Physicochemical Properties of Humus of a Semiarid Pampean Soil Under Two Crop Rotations

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Abstract
Prairie soils, mainly Mollisols, initially contain high levels of organic carbon (OC) that decrease with cultivation, thus impairing their biological, physical, and chemical properties. However, the effect of cultivation on the quality of humus is not clearly known. For this reason, it was necessary to study the effects of two crop production systems on the chemical and structural composition of the organic carbon of an entic Haplustoll (fine sandy loam, mixed, thermic). The two crop systems were continuous wheat (Triticum aestivumj and wheat and cattle grazing. Humus was extracted, fractionated, and analyzed for OC and lignin content, and structural C distribution. The evaluation, made using different methodologies, allowed us to conclude that cropped soils had a higher degree of humification than the uncultivated soils and that the annual incorporation of wheat straw resulted in a buildup of lignin‐type structures and carbohydrates in the continuous wheat treatment.