Suppression of decomposition of ¹⁴ C‐labelled plant roots in the presence of living roots of maize and perennial ryegrass

Summary The rates of decomposition of barley roots labelled with 14 C were investigated in soil planted with maize or perennial ryegrass and in fallow controls. Evolution of 14 CO 2 was significantly less from the planted soils than from fallow controls. Roots of maize and ryegrass appeared to compete substantially with soil microbes for 14 C‐labelled materials. Simple competitive effects were, however, insufficient to explain all of the observed effects of root growth on soil organic matter decomposition. There was no indication that the detrimental effects of maize roots on aggregate stability could be associated with increased degradation of native soil organic materials; the broader significance of the results is also discussed.