SOIL STRUCTURAL STABILITY INDEX IN INTEGRATED LIVESTOCK-FORESTRY SYSTEMS IN THE BRAZILIAN SUBTROPICS

Maintaining soil structural quality is essential for the sustainability of conservation agricultural systems. The objective of this study was to evaluate the Structural Stability Index (SI) across different agricultural production systems. The study was conducted at the Center for Technological Innovation in Agriculture (NITA/UFPR) in Pinhais, Brazil, on a clayey Ferralsol under a humid subtropical climate (Cfb). Two systems established in 2012 were evaluated in 2023 crop season: Livestock (L), consisting of Megathyrsus maximus cv. Aries (summer) and Avena strigosa (winter) under continuous grazing (mean height 24 cm); and Livestock-Forestry (LF), integrated with Eucalyptus benthamii rows (28 × 6 m). Undisturbed soil samples were collected using rings (6 cm height × 4 cm diameter) at 0-0.10 m depth. Particle size distribution and soil organic carbon (SOC) were analyzed to calculate the SI according to Reynolds et al. (2009). Data were subjected to ANOVA (p ≤ 0.05). No significant differences were observed between treatments. The Livestock and Livestock-Forestry systems showed mean SI values of 13.7 and 13.2, respectively. Considering the critical threshold of SI > 9% for "stable structure" soils, both systems exhibited high physical quality. It is concluded that long-term conservation management (10 years), with continuous biomass input and grazing control, promoted soil structural resilience.