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Sandy loam soil was amended with different concentrations of glucose and was incubated at different pO2 levels. Under many conditions of incubation time and treatment, N2 ase activity as determined by 1-h aerobic C2H2 reduction assay (flushed with Ar:O2, 4:1 before assay) was significantly less than that determined by means of ambient assay (carried out at the pO2 of incubation without flushing with Ar:O2, 4:1 before assay). The difference between the N2ase activity in aerobic assay and that in ambient assay increased with decreasing glucose and O2 concentrations imposed during incubation. The inhition in aerobic assays was analogous to O2-induced shut-off of N2ase and amounted to 75 per cent inhibition after incubation at 0.06 atm pO2 of samples amended with 0.75% glucose (w/w). Similar O2 inhibition was observed after amendment with mannitol and with lactate. Times of incubation were chosen such that development of anaerobic N2ase activity was either absent or too low to account for the observed effects of O2 during assay. It was shown that 0.05 atm pC2H2 was adequate for routine 1-h assays of the soil system employed. Individual soil samples could be subjected to repeated 1-h assays (with removal of C2H2 and C2H4 by evacuation after each assay) thus avoiding side-effects of long exposure to C2H2.  相似文献   
995.
Soil cores from under senesced legume swards were partitioned into (1) soils, (2) legume roots, (3) nodules and (4) debris. The viable population of Rhizobium trifolii under subterranean clover was found to be predominantly in the nodule fraction; but with R. lupini under Serradella the distribution was more even. In commercially sown stands the rhizobia often failed to migrate from the original sown rows into the soil between the rows. The relative importance of the various fractions as contributors to the “pool” of rhizobia available for nodulation of subsequent generations of host-plants is discussed.  相似文献   
996.
R.C. Mondal 《Geoderma》1973,9(1):35-41
Ground waters with electrical conductivity of 4.9–7.4 mmhos/cm, a pH of 7.7–8.8 and a Mg/Ca ratio of 0.8–41.5 were equilibrated with a Na-illite in the presence and absence of CaCO3. In the presence of CaCO3, exchangeable Ca, exchangeable Ca+Mg and the exchangeable Ca/Mg of the equilibrated clay increased but exchangeable Mg and Na decreased. The pH values of the ground waters were positively correlated with (1) exchangeable Ca, (2) exchangeable Ca+Mg, and (3) exchangeable Ca/Mg ratio, both in the presence and absence of CaCO3.  相似文献   
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