Resumen

HERNANDEZ-HERNANDEZ, Rosa Mary  y  LOPEZ-HERNANDEZ, Danilo. El tipo de labranza como agente modificador de la materia orgánica: Un modelo para suelos de sabana de los llanos centrales venezolanos. INCI [online]. 2002, vol.27, n.10, pp.529-536. ISSN 0378-1844.

A conceptual model of soil performance in the Venezuelan Central Plains is presented, based on the relations between soil structure and active and stabilized fractions of the organic matter. It shows how soil processes change with agronomic handling. Two contrasting types of farming are considered, direct sowing without tillage and with the presence of a vegetal cover, and conventional farming with strong mechanical procedures to break the soil and bury any kind of cover or residue. External variables (tillage and covers), state variables (organic matter fractions) and the processes involved are considered. Given the soil acidity, its low fertility with limitations for agricultural use and its ever increasing use for production of cereals, mostly maize, the changes in organic matter fractions due to tillage intensity and the location of vegetal residues are discussed. The latter aspects influence CO2 production, contributing to the greenhouse effect, and can also intensify erosion processes and nutrient losses, aggravating problems of fertility and soil degradation. The conventional farming process increases CO2 liberation and intensifies soil degradation, reducing organic matter. Alternatively, direct sowing is conservationist; it increases active and slow compartments which are potential sources of nutrients, improving fertility in the medium term, microbial decomposition processes are slower, and CO2 emissions are lower. The direct sowing model resembles the virgin savanna model, both in state variables related to conservation and in processes of loss and conservation, being an alternative that leads to a more sustained use of savanna soils.

Palabras clave : Labranza ; Llanos Centrales Venezolanos; Sabana ; Siembra Directa ; Suelo .