Background and aims The objective of this study is to understand how soil microorganisms interact with cover crop-derived allelochemicals to suppress weed germination and growth following cover crop residue incorporation. Methods We conducted a time series experiment crossing sterilized and non-sterilized soil with four different residue treatments. We measured weed seed germination rates, radicle elongation, and disease incidence in seed germination bioassays. We also monitored cover crop-derived, isoflavone allelochemicals in these bioassays. We partitioned the total weed suppression into three sources: microbe-only inhibition, residue-only inhibition, and the microbe-residue interaction. Results Microbial activity suppressed weed germination and growth for 30 days, while cover crop-derived allelochemicals provided suppression for a limited time. There was an antagonistic interaction between microbes and allelochemicals. This interaction was strongest for water-soluble allelochemicals, while residue fractions containing intact plant tissues retained greater suppressiveness even in the presence of a live microbial community. Conclusions Microbial activity can directly suppress weed germination and growth, but microorganisms also indirectly help weeds by degrading cover crop-derived allelochemicals. As a result of these interactions, cover crop-derived weed suppression in agricultural soils shifts from an early allelochemical-dominated phase to a later phase where microbial suppression is more important.

Increasingly, funding agencies are investing in integrated and transdisciplinary research to tackle “grand challenge” priority areas, critical for sustaining agriculture and protecting the environment. Coordinating multidisciplinary research teams capable of addressing these priority areas, however, presents its own unique set of challenges, ranging from bridging across multiple disciplinary perspectives to achieve common questions and methods to facilitating engagement in holistic and integrative thinking that promotes linkages from scholarship to societal needs. We propose that structural equation modeling (SEM) can provide a powerful framework for synergizing multidisciplinary research teams around grand challenge issues. Structural equation modeling can integrate both visual and statistical expression of complex hypotheses at all stages of the research process, from planning to analysis. Three elements of the SEM framework are particularly beneficial to multidisciplinary research teams; these include (i) a common graphical language that transcends disciplinary boundaries, (ii) iterative, critical evaluation of complex hypotheses involving manifest and latent variables and direct and indirect interactions, and (iii) enhanced opportunities to discover unanticipated interactions or causal pathways as empirical data are tested statistically against the model. Using our ongoing multidisciplinary, multisite field investigation of climate change adaptation and mitigation in annual row crop agroecosystems as a case study, we demonstrate the value of the SEM framework for project design, coordination, and implementation and provide recommendations for its broader application as a means to more effectively engage and address issues of critical societal concern.

There is increasing global demand for food, bioenergy feedstocks and a wide variety of bio-based products. In response, agriculture has advanced production, but is increasingly depleting soil regulating and supporting ecosystem services. New production systems have emerged, such as no-tillage, that can enhance soil services but may limit yields. Moving forward, agricultural systems must reduce trade-offs between production and soil services. Soil functional zone management (SFZM) is a novel strategy for developing sustainable production systems that attempts to integrate the benefits of conventional, intensive agriculture, and no-tillage. SFZM creates distinct functional zones within crop row and inter-row spaces. By incorporating decimeter-scale spatial and temporal heterogeneity, SFZM attempts to foster greater soil biodiversity and integrate complementary soil processes at the sub-field level. Such integration maximizes soil services by creating zones of ‘active turnover’, optimized for crop growth and yield (provisioning services); and adjacent zones of ‘soil building’, that promote soil structure development, carbon storage, and moisture regulation (regulating and supporting services). These zones allow SFZM to secure existing agricultural productivity while avoiding or minimizing trade-offs with soil ecosystem services. Moreover, the specific properties of SFZM may enable sustainable increases in provisioning services via temporal intensification (expanding the portion of the year during which harvestable crops are grown). We present a conceptual model of ‘virtuous cycles’, illustrating how increases in crop yields within SFZM systems could create self-reinforcing feedback processes with desirable effects, including mitigation of trade-offs between yield maximization and soil ecosystem services. Through the creation of functionally distinct but interacting zones, SFZM may provide a vehicle for optimizing the delivery of multiple goods and services in agricultural systems, allowing sustainable temporal intensification while protecting and enhancing soil functioning.