Resumen

TORRES, Duilio; FLORENTINO, Adriana  y  LOPEZ, Marisol. Soil quality indexes in an Ultisol submitted to different conservation practices in Guárico State, Venezuela. Bioagro [online]. 2006, vol.18, n.2, pp.83-91. ISSN 1316-3361.

Conservation practices were applied in a degraded soil (Ultisol) trying to improve soil quality. The practices consisted in the use of organic residues from graminea (RG) and leguminous (RL), and a treatment without organic residues (SR), combined with the inorganic fertilizers phosphoric rock from Riecito (RFR) and diammonium phosphate (FDA). The effect of those practices on different physical, chemical, and hydrologic properties was evaluated after four years. A multivariate analysis was performed for integrating these factors and to determinate which of them could explain changes in soil quality. Soil and nitrogen losses were measured on erosion plots, using simulated rainfall of 120 mm·h^-1 intensity. Nitrogen (NO₃ y NH₄) was measured by continuous flow colorimetric method. Results showed water runoff were lower in the treatments with organic residues (RG and RL) whereas they were higher in treatment without residues (SR). The same trend was found for soil losses, so they were higher in SR. These results could be ascribed to the protection effect of organic residues against water drop impact on the soil surface, thus improving the soil hydrological conditions, and promoting the increase of organic matter and calcium content. The hydrological factors and those associated to soil and nutritional losses were important to explain the changes. Thus, indicators and quality indexes were selected from hydrological and nutritional degradation to classify the soil according to the management practices applied.

Palabras clave : Soil quality; organic residues; runoff; multivariate analysis.