STRUCTURE AND PEDOFEATURES OF GUANAJUATO (MEXICO) VERTISOL UNDER DIFFERENT CROPPING SYSTEMS

Little is known about the crop influence and the long-term effects of tillage systems on physical and morphological properties of Vertisols in the high plateau of the intertropical zone of Mexico. The purpose o f the present study was to evaluate the impact of crop rotation on the development of structure and pedofeatures of Eutric Vertisols of Guan ajuato, Mexico. Disturbed and undisturbed samples from the top soil (0 -20 cm) of five agroecosystems differing in crop rotation (semipermane nt alfalfa, two cereal crops per year, one vegetable and one cereal cr op per year, three vegetable crops per year, and dryland maize) were c ollected. A second no-till soil sample was obtained from a nearby site under secondary vegetation and used as reference soil. Continuous and intensive cultivation lead to a significant reduction in Vertisol org anic matter and total nitrogen contents. Tillage and crop rotations af fected air-dried aggregate bulk densities, soil microstructure and dev elopment of pedofeatures. Calcite crystalline pedofeatures seemed to b e more directly affected by the management systems used. Nodules, the most common crystalline pedofeatures in top soil of all cultivated Ver tisols, were absent in no-till soils.