The location and distribution in soil of rhizobia under senesced annual legume pastures

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.     

Effects of substituted p-benzoquinones on urease activity in soils

The effectiveness of substituted p-benzoquinones as inhibitors of urease activity in soils depends largely upon their substituent groups. Methyl, chloro-, bromo- and fluoro-substituted p-benzoquinones have a marked inhibitory effect on soil urease activity, whereas phenyl-, r-butyl-and hydroxy-substituted p-benzoquinones have little, if any, effect. Methyl-substituted p-benzoquinones differ from other substituted p-benzoquinones in that their effects on soil urease activity usually increase markedly with increase in their time of contact with soil.A study of the effects of selected substituted p-benzoquinones on urea hydrolysis and volatilization of urea N as ammonia in a sandy soil treated with urea showed that methyl- and chloro-substituted p-benzoquinones had very marked effects, whereas hydroxy- and phenyl-substituted p-benzoquinones had little or no effect. Gaseous loss of urea N as ammonia when this soil was incubated at 20°C for 14 days was reduced from 62.8 to 0.1 per cent by addition of 2,3-dimethyl-, 2,5-dimethyl-, or 2,6-dimethyl-p-benzoquinone (2.3 parts/100 parts of urea).The work reported indicates that, of the 34 substituted p-benzoquinones studied, 2,3-dimethyl-, 2, 5-dimethyl- and 2,6-dimethyl-p-benzoquinone are likely to prove the most effective for retardation of urea decomposition in soils and reduction of the problems caused by the normally rapid hydrolysis of fertilizer urea by soil urease.     

Alpine disturbance studies: Olympic national park,USA

Measurements of downslope rock-creep, of the slow rate of plant establishment on alpine and subalpine road-cuts, and of the reduction in plant cover and plant production in two alpine plant communities, illustrate the degree of disturbance that can occur. The development of large trails or roads should not be permitted in areas of such active downslope rock movement, because of the natural rate of mass-wasting. If more people are to visit and enjoy the alpine communities, asphalt paths to confine their walking are desirable, for trampling experiments showed that plant cover and plant production were rapidly reduced in even one season of light use. Recovery during the following year was, however, quite rapid—especially in the snow-bank community. Different alpine and subalpine habitats have different sensitivities to disturbance, and any plans for increased human use must incorporate this kind of information.