Fire is one of the most prevalent disturbances in the Earth system, and its past characteristics can be reconstructed using charcoal particles preserved in depositional environments. Although researchers know that fires produce charcoal particles, interpretation of the quantity or composition of charcoal particles in terms of fire source remains poorly understood. In this study, we used a unique four-year dataset of charcoal deposited in traps from a native tallgrass prairie in mid-North America to test which environmental factors were linked to charcoal measurements on three spatial scales. We investigated small and large charcoal particles commonly used as a proxy of fire activity at different spatial scales, and charcoal morphotypes representing different types of fuel. We found that small (125-250 μm) and large (250 μm-1 mm) particles of charcoal are well-correlated (Spearman correlation=0.88) and likely reflect the same spatial scale of fire activity in a system with both herbaceous and woody fuels. There was no significant relationship between charcoal pieces and fire parameters <500 m from the traps. Moreover, local area burned (<5 km distance radius from traps) explained the total charcoal amount, and regional burning (200 km radius distance from traps) explained the ratio of non arboreal to total charcoal (NA/T ratio). Charcoal variables, including total charcoal count and NA/T ratio, did not correlate with other fire parameters, vegetation cover, landscape, or climate variables. Thus, in long-term studies that involve fire history reconstructions, total charcoal particles, even of a small size (125-250 μm), could be an indicator of local area burned. Further studies may determine relationships among amount of charcoal recorded, fire intensity, vegetation cover, and climatic parameters.

Descriptions and analytical data are given relating to nine basaltic profiles representing soils which have been used in detailed studies on cation-exchange properties and mineralogical constitution of basaltic soils in Northern Ireland.Three main groups of soils are considered : those with impeded or poor drainage, those with free drainage, and those which have good drainage in the agricultural sense but which show slight signs of mottling in lower horizons. In all three groups of basaltic soils the clay contents and the organic-carbon contents fall appreciably with depth, but the cation-exchange-capacity values do not follow the changes in clay and organic-matter contents. The total cation-exchange capacity in the C or G8-8 horizon may be as high as or higher than in the surface horizon. In freely drained profiles the cation-exchange capacity is generally lower in the B horizon than in the A(S) or in the C horizon, and usually in poorly drained profiles the cation-exchange-capacity value is also lowest in the B, G,, or the A,-G horizon (due mainly to the fall in organic matter). Exchangeable magnesium forms a considerable percentage (up to about 40 per cent.) of the total cations in the C (or the G,) horizons of basaltic soils, and values of the order of 20 m.e. exchangeable magnesium per IOO g. soil are recorded for some such horizons where drainage is impeded.IN discussing some of the characteristics of the soils of Northern Ireland, McConaghy (1948) showed that the cation-exchange capacities of the basaltic soils are much higher than the cation-exchange capacities of similarly textured soils derived from other parent materials in the region. The actual values for basaltic soils (35-55 m.e. per cent.) obtained in this work were in general agreement with those obtained in investigations on basaltic soils during 1946-7 by Brown (1951, 195 ). he studied there was an appreciable fall with depth in the clay contents without a corresponding fall in the cation-exchange ca acity. Brown drew attention to the high cation-exchange values t rou hout the of these soils and he compared his results with some quoted by Mitchell and Muir (1937), Glentworth (1944)' and Hallsworth et al. ( I 52). representative of the soils used in further recent studies on the physical chemical and mineralogical properties of basaltic soils and separates. versity of Belfast.An examination of Brown's data shows that in most o 9 the profiles profile and to the high exchangeable-magnesium values foun [ % for some In the present paper data are presented relating to nine soi P profiles I Formerly of the Ministry of Agriculture, Northern Ireland, and the Queen's Uni-

1. An experiment, lasting 3 years, was carried out to investigate the control of hypomagnesaemia on a medium-heavy loam soil in Northern Ireland, using as criteria herbage analysis and analysis of blood sera of grazing dairy cows.2. Applications of calcined magnesite and magnesian limestone as soil treatments raised the magnesium contents of herbage slightly but not to levels judged to be safe. Low blood sorum magnesium levels were recorded for cows grazing this herbage although no cases of tetany occurred.3. Magnesium sulphate, appliedas a spray, temporarily raised the ‘apparent’ magnesium content of the herbage but was easily washed off by rain.4. Finely powdered calcined magnesite applied as a dust to the herbage immediately before grazing appeared to be a promising method of control under Northern Ireland conditions.

Results are presented of analysis of radish, oats, barley, beet, swedes and ryegrass grown on a basaltic soil adjusted to a range of pH values. When the pH of the soil was as low as 4.5, little growth was obtained even with acid‐tolerant crops other than radish and, although the application of phosphate resulted in some increase in growth under these conditions, the main factor limiting growth was the so‐called ‘acidity complex’. There was an appreciable increase in manganese, magnesium and iron content with increasing acidity and, as expected, the calcium content of dry matter decreases with increasing degree of soil acidity. The calcium content of the dry matter was decreased by increasing phosphate application to a greater extent than by increasing acidity. Swedes, beet and radish growing on the heavily limed soil plots showed definite symptoms of boron deficiency which also apparently reduced the calcium uptake of beet. Zinc and copper contents were apparently not affected by treatment. The range for zinc was 20–63 p.p.m. and the range for copper 2–10 p.p.m. Aluminium content in plant dry matter showed a slight increase with increasing acidity in radish and swedes but showed no change with beet, oats, barley and ryegrass. Most of the latter crops failed to grow under conditions where the ‘active’ aluminium in the soil was high.

Results are presented of two groups of experiments involving radish and ryegrass crops in different soil types in the greenhouse. Several extractants were used to assess the ‘plant available’ phosphate contents of soils. Results by the Olsen bicarbonate and Egnér type extractants correlated well with phosphate uptake by the crops, although Egnér values had previously been found not to correlate well with yields of dry matter when results for basaltic soils were included. Phosphate contents of water extracts classified the soils in much the same order as Olsen soil‐P values. Total phosphate uptake was highly correlated with the percentage phosphate saturation of the soils. Phosphate uptake was also highly correlated with the ‘isotopic dilution factor’. The effect of fertiliser phosphate on the uptake of fertiliser P at two levels was studied in three soils using 32P also at two levels. Radioactive phosphate had no effect on total phosphate content of ryegrass but at the highest level (100μC of 32P/pot) it significantly reduced the uptake of fertiliser phosphate. The L value of the soils was increased significantly both by increasing phosphate fertiliser and by increasing the level of 32P incorporated in the fertiliser, although the utilisation of soil phosphate was increased in only one soil—the basalt soil—by the application of phosphate fertiliser. L values of the same order were obtained for two soils which differed noticeably in their capacity to supply phosphate for ryegrass growth.