Abstract
Soil arthropods comprise a substantial portion of soil biodiversity and regulate processes in the soil ecosystem. Despite this, cropping system diversification designed to improve soil health for agriculture is rarely evaluated for its effects on soil arthropod biodiversity and community structure. As a result, soil arthropods are not usually considered in management decisions.To address this gap, we evaluated the effects of agricultural diversification through rotation on soil arthropods and soil properties using replicated large-plot field studies representing two climatically distinct agroecological classes (AECs) in the dryland cereal-growing region of the inland Pacific Northwest, USA. We investigated how different 3-year annual crop rotations affected soil arthropod biodiversity and community structure. Treatments reflected 'business-as-usual' rotations in dryland systems and diversified rotations achieved by incorporating novel winter pea (WP) or forage crops (FORs). We also assessed relationships between the Soil Biological Quality index (QBS-ar), which uses soil arthropods as bioindicators of soil health, and other biological and physiochemical soil health indicators.We collected 710 community samples with 82,509 arthropod specimens across 66 taxa. Novel crops in diversified rotations promoted soil arthropod abundance and biodiversity relative to crops they could replace in rotation. Crop type determined community composition. Most taxa driving differences in community structure were predators and detritivores associated with WP and FORs. In addition to effects on soil arthropods associated with specific crops, effects were also detected across rotations. Incorporating WP into rotations improved QBS-ar across entire rotations, not just in the WP phases, in both AECs. Links between QBS-ar and other soil health indicators were complex and varied by AEC.Synthesis and applications: Soil arthropods respond to agricultural diversification and can be used as bioindicators to assess the effects of diversification on soil health. Below-ground arthropod communities are structured by crop type, suggesting that planting specific crops may promote soil arthropods and their services. We showed that incorporating winter pea and forage crops into dryland cereal rotations supported soil arthropod biodiversity and soil health. Results indicate that soil arthropod assessments can be included in the soil health framework to guide agricultural management decisions.