Recent work suggests that resource economic traits might help predict the strength and direction of plant-soil feedback interactions, both in natural systems and in agriculture. However, there are many competing hypotheses to explain the effects of plant resource economics on plant-soil feedbacks. Faster-growing plants may have positive fertilizing effects if their tissues are incorporated and mineralized by soil microbes, but may also have negative effects if pathogens build up, or if fungal

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... mbionts are lost through fertilization. Identifying the direction of effects may be confounded if nutrients are exported through herbivory, leaching, or crop harvesting. To determine causality in the effect of plant traits on plant-soil feedbacks it is essential for plant-soil feedback experiments to (1) quantify the mass of nutrients held in standing, or harvested plant biomass, and in losses to other sources in the field, and (2) undertake soil chemistry measurements (e.g. gross and net nitrogen mineralization) of nutrients limiting for plant growth throughout all phases of the feedback cycle. If rigorous nutrient budgeting in plant-soil feedback research is more widely practiced this will provide the data needed to synthesise results in comparable ways, and will enable mechanistic insights into the role of plant traits in mediating plant competition in both natural and applied settings.