Observations have been made which suggest that clover is more effective than ryegrass in developingrapid improvements in soit structure. To test this hypothesis, grass, grass/clover and clover swards were grown in undisturbed field cores. Significant differences in drainage rates and plant biomass production, and visible changes in soil structure, all supported the hypothesis that clover improves structure rapidly, but there were no significant differences in bulk density, porosity or aggregate stability between the treatments. Soil moisture characteristic curves of soil/peat/grit compost planted with grass, grass/clover or clover and grown for two years indicate that a more free-draining structure develops under clover than under grass due to a higher ratio of macro-to micropores.

High concentrations of lead, copper, zinc and cadmium, are reported in agricultural soils of the southern Peak District in association with mining and smelting sites. A reliable background range of lead concentrations in non-contaminated soil was established and the relative topsoil enhancement (RTE) ratio was found to be a useful index of pollution. A wide range of amounts of lead was extracted from soils by dilute nitric acid; the higher end of the range m a y result from free lead oxides being present in some polluted soils. The amount of lead extracted also depended on the composition of the soil, a soil containing vermiculitic clay minerals maintained a very low lead wncentration in solution. The effects of site history, weathering and redistributive processes are discussed.

No abstract

No abstract

Acetylene blockage was evaluated as a method for measuring losses of N 2 0 + N, from two Denchworth series clay soils. The denitrification potential in anaerobic, dark incubations at 20°C with nitrate (equivalent to 100 kg N ha-' 0-20 cm depth), maximum water holding capacity, and acetylene ( IYo), was equivalent to 32 _+ 1 1 and 39 k 6 kg N ha-' per day for the two 0-20 cm soils and was positively correlated with carbon content (r=0.98). After 4 days N20 was reduced to Nz in the presence of C2H,.In April 1980 following irrigation (24 mm) and applications ofammonium nitrate (70 kg N ha-') and acetylene, the mean nitrous oxide flux from soil under permanent grass was 0.05f0.01 kg N2O-N ha-' per day for 8 days.In June 1980, the losses of nitrogen from cultivated soils under winter wheat after irrigation (36 mm) and acetylene treatment were 0.006 f0.002 and 0.04-0.07+0.0I kg N ha-' per day respectively before and after fertilizer application (70 kg N ha-'). The nitrous oxide flux in the presence ofacetylene decreased briefly, indicating that nitrification was rate determining in drying soil.