Twenty percent of 237 advisory soil samples were found sufficiently low in biological activity to restrict pyrophosphate hydrolysis. A field investigation, however, which measured initial ortho- and pyrophosphate uptake by barley, showed pyrophosphate hydrolysis to be restricted on 60% of the 98 sites. This more widespread restriction was due to low soil temperatures since uptake was related to temperature in the range 7 - 12[degree]C, and to biological activity in the range 12 -15[degree]C. The optimum temperature for hydrolysis was 30 - 35[degree]C. Differences in hydrolysis efficiency were found between soils and between temperatures in the same soil.