Effects of low sub‐sterilising doses of gamma radiation on carbon, nitrogen and phosphorus in fresh soils

Changes in ammonium‐ and nitrate‐nitrogen have been shown to be a sensitive indication of response of soils to gamma radiation, even to doses as low as 1.5 kilorads, and are superior to measurements of carbon, phosphorus or respiration. The immediate increase in carbon in the soil solution after irradiation was significantly correlated with both subsequent nitrogen mineralisation and soil respiration, and a highly nitrogenous fraction of the soil organic matter was being decomposed. Nitrification proceeded at a fast rate in all soils after the highest dose of 200 kilorads, probably owing to the absence of effects on the oxidation process in non‐proliferating cells of the nitrifying bacteria rather than to increased proliferation of survivors.