BIOLOGICAL ACTIVITY OF SUBTERRANEAN RESIDUES OF CYNODON DACTYLON L., SORGHUM HALEPENSE L. AND CYPERUS ROTUNDUS L.*

Summary. . Dried subterranean organs of Cynodon dactylon, Cyperus rotundus and Sorghum halepense were incubated in light and heavy soils for 1, 2 or 3 months. After removal of the decayed plant material, the residual bioactivity of the soil was assayed by barley sown directly into the soil and by a barley radicle‐length test on an ethanolic extract of the soil. The two assays gave similar results. In general, the inhibition of growth was proportional to the concentration of plant material in the soil, and was greater in light than in heavy soil. Greater inhibition was caused by C. rotundus and S. halepense than by C. dactylon. A few instances of growth stimulation were recorded.