Soil macrofauna as indicators of soil quality and land use impacts in smallholder agroecosystems of western Nicaragua

The tropical dry forest region along the western slope of Central America represents a biodiverse and fragile area that is under increasing pressure from agricultural production, thus threatening the provision of ecosystem services, the integrity of these landscapes, and the rural communities who depend on them. To address this issue, we evaluated the influence of common agricultural management practices (cropping and livestock systems) vs. the Quesungual slash-and-mulch agroforestry system (QSMAS) on diverse parameters of soil quality and function. We then used this information to identify soil invertebrate bioindicators that represent key aspects of soil quality (chemical fertility, physical properties, aggregate morphology, and biological functioning). In February of 2011 soil sampling was conducted on six hillside farms near the town of Somotillo in western Nicaragua to assess soil properties and the abundance and diversity of soil macrofauna within four management systems: (1) QSMAS, based on maize production, (2) traditional maize cropping system with few trees (TC), (3) silvopastoral system with low tree density (SP), and (4) secondary forest (SF), used as a reference. The conversion of forest to agriculture demonstrated the greatest impact of management in this study. For example, SF presented significantly higher diversity of soil invertebrate taxonomic groups than either TC or SP (P<0.03), and demonstrated the lowest level of soil compaction, significantly less than SP (P<0.05). Additionally, SF demonstrated the highest value of soil quality according to a synthetic indicator that integrates chemical, physical and biological aspects of soil quality. Although overall soil quality under QSMAS was lower than SF, this system demonstrated the highest abundance (number of individuals) of soil macrofauna, and appeared to at least partially mitigate the negative consequences of forest conversion on soil functioning. Using the Indicator Value Index, which ranks species according to their specificity and fidelity across sites, along with farmer consultation we found seven indicator taxa of soil quality that could greatly facilitate future evaluation of land management impacts by farmers and technicians in the region. We suggest that the methodology applied is robust and adaptable to diverse agroecological contexts and would allow for more rapid responses to evolving land use issues as they arise.