Precision Agriculture in silvopastoral systems: A case study from the Montado (part I – Cone penetrometer applications).

Abstract

The Montado is a distinctive silvopastoral system of the Southern Iberian Peninsula, integrating pastures, trees (typically cork oak, Quercus suber, and/or holm oak, Quercus rotundifolia), and domestic livestock (ruminants or swine). Precision Agriculture (PA), predominantly explored in purely agricultural systems, offers substantial potential to optimize Montado management, thereby enhancing its economic, environmental, social, and cultural sustainability. Given the inherent high spatial heterogeneity within Montado plots, the deployment of PA technologies capable of detecting such variability is crucial for informed, site-specific management. Among these technologies are soil compaction sensors, notably the electronic cone penetrometer, which provides the Cone Index (CI) – a key metric for soil physical quality. During the 2021/2022 agricultural year, a holm oak Montado plot (area = 20 ha; location: Mitra/University of Évora), grazed by cattle under a rotational system (0,6 Normal Head/ha), was monitored at 24 distinct points (12 under tree canopy influence and 12 in open pasture, outside canopy influence). Significant correlations were established between CI and soil moisture content. Regarding the effect of animal trampling on soil compaction, this was found to be significant outside the tree canopy at all assessed depths (0-0.10m; 0.10-0.20m; 0.20-0.30m). Conversely, under the tree canopy, significant effects of trampling were confined to the uppermost 0-0.1m soil layer. Significant differences in CI were also observed according to sampling date, whereas overall plot-level effects (beyond the specific tree canopy vs. open area comparison) were not significant. Unsurprisingly, locations with higher animal congregation, indicative of preferential resting or transit areas, exhibited greater CI values. Instances where CI exceeded 2500 kPa – a widely recognized threshold indicative of mechanical impedance restricting root growth for many agricultural crops – were infrequent. The prevailing precipitation during the study year, which amounted to approximately two-thirds of the long-term average (mean 1994-2024 = 600 mm), likely attenuated the adverse impact of animal-induced soil compaction on the productivity of these rainfed pastures. The principal findings underscore that soil compaction in these silvopastoral systems is a dynamic and complex process, influenced by an interplay of factors including tree presence, animal behaviour, and temporal soil moisture variations. This complexity warrants the extension of such detailed investigations to other soil types and Montado configurations. Furthermore, there is a clear justification for conducting similar trials over longer evaluation cycles. Such longitudinal studies are essential for the robust calibration and validation of these PA technological tools, ultimately empowering farm managers with more precise data for enhanced decision-making and sustainable land stewardship.