Agroforestry systems improve soil physical quality in northwestern Colombian Amazon

Land use change is a global threat to soil quality and related ecosystem services. In Colombian Amazon, forest-cleared lands are predominantly covered by low-input and degraded pastures; but gradually, agroforestry systems (AFS) have been introduced as a sustainable alternative for soil reclamation and increasing land productivity. Although soil physical quality changes can be monitored by multiple indicators, the Visual Evaluation of Soil Structure (VESS) method has emerged as a straightforward, reliable and low-cost tool for assessing and monitoring the impacts of land uses and management agricultural practices on soil quality in different parts of the world. However, the VESS has never been tested in AFS and in Colombian soils. Thus, we conducted a pioneering assessment of soil physical quality in six typical land uses (i.e., forest, pasture and four AFS) using the VESS method in northwestern Colombian Amazon. The VESS assessment takes account characteristics of soil aggregate and biological activity (roots and macrofauna) to assign scores ranging from Sq 1 (good) to Sq 5 (poor physical quality). Moreover, quantitative soil indicators (i.e., bulk density, soil resistance to penetration, soil moisture and soil organic C) were evaluated to correlate with VESS scores. Soil physical changes induced by land use change were efficiently detected by VESS scores. The VESS scores were significantly correlated with key indicators of soil quality. Conversion from Amazon forest to low-input pasture intensively degraded soil physical quality (overall Sq 1.3 vs Sq 4.0). Nevertheless, the adoption of AFS improves soil physical quality (overall Sq 3.2, 2.8, 2.4 and 2.2) in areas previously occupied with pasture, indicating greater potential of soil reclamation under more diversified systems. This study shows that adopting AFS can be a strategy for recovering soil quality and reincorporating degraded lands into productive and sustainable production systems in Amazon regions, and the VESS method can be an useful tool to monitoring soil physical changes in these areas.