Agronomic and taxonomic consequences of agricultural use of marginal soils in Argentina

Expansion of the agricultural frontier over marginal soils leaves a signifi cant environmental imprint on the southern semiarid region of the Argentina pampas. A chronosequence of anthropogenic soils in a cultivated area was investigated to determine the role of human actions on the development of a highly compacted horizon below the plow layer observed during a detailed soil survey in Villarino County. A model area of 300 ha (6 × 0.5 km) representative of the county soilscapes was used to (i) characterize the main physical, chemical, and morphological features of the soils in the chronosequence, and (ii) discuss taxonomical issues that can be improved on to facilitate information transfer. Based on our observations, we propose a new diagnostic feature to classify these soils according to USDA Soil Taxonomy guidelines placed at a taxonomical level above series. Our investigation confi rmed that soil morphology is modifi ed within 27 yr of cultivation. Tillage leads to the development of a noncemented plowpan immediately below the Ap, here called ACd, with distinctive morphological features. The ACd is compact and massive with extremely hard rupture resistance when dried. Cultivation-induced alterations were considered important enough to classify the soils into unique soil series. Given the widespread environmental and fi nancial costs and implications of soil compaction, and the genetic connotations of the plowpan, we propose the densipan as a diagnostic horizon and a new class densic to be use at the family level. Advantages of its use will lead to increased utility and precision in published soil maps and improved communication and understanding among stakeholders.