= Bulk soil
<Bulk soil> is the surrounding or reference <soil> sampled separately from root-associated material in a specified experiment. Its meaning is operational: the sampling distance, <soil> layer and treatment history determine the comparison. A2012 <Arabidopsis thaliana> study used parallel pots without a <plant> as <bulk soil> controls when comparing root-associated bacterial communities.<Defining the core Arabidopsis thaliana root microbiome by Derek S. Lundberg and others>[Methods, General strategy; parallel unplanted-soil controls]{ref}
An invented example illustrates why the reference matters. Suppose an assay gives6 units in <bulk soil> A and10 units in its root-associated sample, but26 and30 units for the corresponding samples from <soil> B. Both within-soil differences are4 units. Comparing10 directly with30 would mix the difference in starting <soil> with the root-associated contrast. The example is a comparison of additive assay responses, not a claim about a measured bacterial population.
<Bulk soil> does not mean biologically empty <soil>, nor does it guarantee a history completely free of <root (botany)>[roots]. It names the reference selected for the stated question. For a useful comparison with the <rhizosphere>, report the sampling rule and measured quantity as well as the label.
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