Studies on the Basaltic Soils of Northern Ireland

Abstract

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-

STUDIES ON THE BASALTIC SOILS OF NORTHERN IRELAND v. CATION‐EXCHANGE CAPACITIES AND MINERALOGY OF THE SILT SEPARATES (2–20μ)

“…of the silts increase down the profile, the contribution by this separate to the C.E.C. of the soils will be considerable, especially in the lower horizons (McAleese and McConaghy, 1957). Whilst feldspars (which are considered to have negligible C. E.C.…”

“…Silt separates as isolated by the ordinary International Method of mechanical analysis are shown to contribute considerably to the total C.E.C. of the soils (McAleese and McConaghy, 1957), and in some cases these contributions are greater than those for the corresponding clay se arates. which is regarded as t K e seat of the physico-chemical activity, e.g.…”

“…Recent investigations (McConaghy and McAleese, 1957 ; McAleese and McConaghy, 19 7,1958) show the need to focus attention mining the potential fertility level of these soils. These studies have shown that it is not possible to account for the high total cation-exchange capacities (C.E.C.)…”

Studies on the Basaltic Soils of Northern Ireland

“…per cent.-i.e. as high as or higher than those for corresponding clay separates (McAleese and McConaghy, 1957). Sand fractions were also found to have appreciable exchange capacities.…”

An evaluation of the Olsen test as a measure of plant-available phosphorus in grassland soils derived from basalt parent material

“…Studies in the 1950s and 1960s indicated that the P fertility status of these soils could be difficult to determine. Some basaltic soils with very low extractable phoshorus (P) values were found to give good crop yields without P additions, whereas others did not (McConaghy 1955;McConaghy & Stewart 1963). Bailey et al (2000) noted that P recommendations (MAFF 1994) for basaltic soils, based on Olsen-P measurements, were completely unrelated to herbage P status, implying that the Olsen test had erroneously assessed the plant-available P contents.…”