ASSOCIATION BETWEEN SOIL STRUCTURE STABILITY INDICATORS AND ORGANIC MATTER IN VENEZUELAN AGRICULTURAL SOILS

Abstract

Soil structure stability depends on several factors and its assessment is conducted using different methods and prediction indices. One of the indicators is soil organic matter (MOS) since it helps to keep mineral particles together against the destabilizing forces such as wetting and raindrop impact. However, the studies carried out have emphasized the relationship between aggregate stability and MOS content, without considering its type or quality. Therefore, the present study assessed the association between quality and MOS content and topsoil structure stability in five Venezuelan agricultural soils. With simple random sampling nine observation points were selected in each soil, where samples were taken in order to determine: stable aggregate size distribution, particle size distribution, content and fractionation of MOS, and prediction indices of surface sealing and crusting derived from these characteristics. In order to determine the runoff percentage, simulated rainfall was used under field conditions. The soils showed low structure stability (except for El Salao soil) validated by the percentage of surface runoff obtained under field conditions. There was high association between the sizes (between 4 and 2 mm and < 0.25 mm) of water-stable aggregates and the different MOS fractions; fulvic acids fraction (CAF) had a negative relationship with aggregates of smaller size (R=−0.84). Finally, from the structure stability prediction indices assessed, the level of soil structure stability could be established only with the FAO crusting index.