Visual evaluation of soil structure in organic smallholder farms in the eastern Amazon: a useful tool to assess soil quality

摘要

ABSTRACT Different soil management strategies may either promote or degrade soil structure. This study aimed to test the Visual Evaluation of Soil Structure (VESS) method in a smallholder agroforestry system in the eastern Amazon. Three plots (P1, papaya field; P2, banana intercropped with cassava; P3, banana, cassava, and açaí), as well as an adjoining area under native vegetation (NV), were evaluated using VESS. Quantitative assessments of soil physical quality were also performed, including soil water retention curve (SWRC), bulk density (Bd), particle density (Pd), microporosity (Mi), macroporosity (Ma), total porosity (Tp), available water capacity (AWC), field capacity (FC), and permanent wilting point (PWP). The VESS scores in P2 (2.6) and P3 (1.8) were similar to NV (1.4), while P1 (2.8) had a poorer structure. P1 differed from the other plots, with lower Ma (0.05 m3 m−3) and Tp (0.39 m3 m−3), and higher Bd (1.57 Mg m−3), AWC (0.32 m3 m−3), and water retention at FC (θFC: 0.33 m3 m−3). VESS scores were significantly correlated with most quantitative measurements. These results indicate that VESS is effective to assess soil structure, providing a convenient strategy for soil structural quality assessment in smallholders from Amazon.