The effect of soil pH on rates of ammonification and nitrification was studied. Soil samples which ranged in pH from 4.7 to 6.6 from an established lime and N fertility experiment were used. Soil pH values in the lime plots have been relatively constant for several years. Soil pH did not affect rates of ammonification appreciably; however it had a significant effect on nitrification rates. Length of the delay period (t′) was increased and rate of NO3‐ accumulation (Km) decreased with a decrease in soil pH. Previous field N treatments increased the length of t′ at low pH and decreased t′ and Km at high pH. Nitrification rates and production of NO3‐ were similar for soil pH values of 5.3, 6.0, 6.3, and 6.6 with a different pattern at pH 4.7.

Plant succession was investigated on sand waste heaps produced by kaolin mining in central Cornwall. It was found that relatively even aged, monospecific stands of vegetation were frequently present. The principal colonists were woody leguminous plants which, in some situations, were superceded by a massive growth of rhododendrons (Rhododendron ponticum) or native woodland species. Where legumes were absent, the waste was slowly colonised by Calluna vulgaris and other heathland species.The age structure of the vegetation was negatively and significantly correlated (r ~ --0.71) with the moisture deficit (evapotranspiration minus rainfall) during the spring and early summer. Drought, limited seed availability, and low nitrogen levels in the waste material are factors which contribute to the development of monospecific, even-aged legume communities of Ulex europaeus, Sarothamnus scoparius and Lupinus arboreus.Measurements were made of biomass and litter in five plant communities and nitrogen levels were determined in the soil/plant system within these communities and also in the soil of a woodland which had developed on sand waste. The low productivity and low rate of nitrogen accumulation in a stand of Calluna vulgaris contrasted with stands of the three woody legumes. Gorse (Ulex europaeus) accumulated nitrogen most rapidly and appeared to have preceded invasion by Rhododendron ponticum and transition to native woodland. Within the woodland and rhododendron thicket the soil nitrogen levels approached those characteristic of temperate climax woodland.The data indicate that the course of plant succession and the rate of soil development are strongly influenced by the biological properties of the colonising species. These processes are accelerated considerably following the invasion of woody legumes.Present addresses: -

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