Cambios en el arreglo estructural y la mocroconstitucion de un vertisol (Typic Hapluderts)bajo tres sistemas de labranza Cambios en el arreglo estructural y la mocroconstitucion de un vertisol (Typic Hapluderts)bajo tres sistemas de labranza

Abstract

Disturbed and indisturbed Vertisol samples were collected from the top soil in the agricultural area in the San Andres Tuxtla, Ver. district Mexico, in fields with Vertisol tilled with minimum tillage (MT) and traditional tillage (TT), as in a field with the same soil without tillge (WT) covered with secondary vegetation. These samples were taken in transects along the length of the fields at 20 m intervals. The variations of the physical properties and the Vertisol microconstitution under the different tillage systems were compared, through analysis, as well as the relationship between the structural arrangement, the morphology of the porous space, the pedological features, and the level of tillage. The organic matter content in the Vertisol with TT (5%) was higher compared with levels fund in soil with MT and WT. The Vertisol showed a different structural arrangement with each of the different tillage system. In the MT system, there was a tendency toward soil compaction in the furrows between the beds.

The mean size of aggregates varied between 1.24 mm in WT and 1.56 in the furrows between the beds in MT, thus showing the soil compaction. The mean size of the pares varied between 0.23 and 0.13 mm in the same two systems. The lineal porosity dropped from 0.21 in WT to 0.13 in the MT furrows. Mean pare size was 20% greater in TT than in MT. Soil System structure entropy values reached a high of 0.66 in WT, dropped to 0.6] in the TT, and reached their lowest point of 0.50 in the furrows between the beds of MT, thus confirming their maximum compaction. These values are derived from site soil structure information and form the measure of the structure variability. The predominant pedological features in the Vertisol, under all three systems, were the amorphous and singular cryptocrystalline ferrogineous nodules with clear and regular limits. The yellow-orange nodules composed of Lepidocrocite 6 - FeO(OH)) were abundant in the MT soil. Red Hematite (X- Fe2 03) nodules were predominant ¡n Vertisol TT.

The abundance, size, and nature of the nodules indicated high immigratio and precipitation of iron solutions. These were highestin Vertisol TT. A The circular form of the nodules allows for the conclution that these are of biogenic nature ( bacterial activity ) and the larger size in the TT Vertisol indicates that the aerobiosis conditions were greater under this system. Smaller size and greater nodule hydration in MT soil confirms a greater anaerobiosis. These nodules indicate periodic surface hydromophism on the Vertisol in this study.