Global tectonics and agriculture: A geochemical perspective

The global distribution of regions of sustained productive agriculture shows that an ample supply of fresh rock residues is vital to soil fertility. Once such rock debris is removed soil degradation will be evident in falling yields and trends within the clay fraction from chemically diverse smectite clays towards impoverished kaolinite-gibbsite soils. Increased erosion will follow the clay degradation. Reliance on N, P and K and organic residues alone will not be sufficient to counteract this trend unless Nature, through geological forces, or Man, through the application of appropriate rock dusts, intervenes to restore nutrient balance and a better clay spectrum. The geological evidence of natural weathering rates, and soil evidence of leaching rates, points to applications only of the order of 1 ton ha^?1 year^?1 being the amount of fresh rock replenishment required to hold the soil in balance for agriculture. Failure to achieve this makes way for a progressive trend towards soil degradation accelerating, as changes induced in the nature of the clay fraction enhance the leaching effect of the aerial environment.On a world scale these effects can best be seen by comparing the enhanced fertility of soils that have benefited from volcanic renewal near active plate boundaries or the fresh rock enrichment arising from the rock grinding involved in glaciation, with the almost ‘impossible’ soils typical of geologically quiescent areas, such as the Amazon and Congo basins where, merely to fertilise with N, P and K alone so impoverishes the soils of their critically limited supplies of other essential nutrients, that disaster is inevitable.     

Oxides of nitrogen in the greater Manchester conurbation,UK

Summary This paper reviews the emission sources of oxides of nitrogen and provides an estimate of the contribution from the Greater Manchester conurbation. The uncertainty attached to the estimate is large. Atmospheric and rainwater concentrations of oxides of nitrogen are reported from the Greater Manchester Acid Deposition Survey network. The health and ecological implications of these concentrations are commented upon and the measured values compared to a number of environmental guidelines, including recently formulated critical load and critical level estimates. Control technologies applicable to both mobile and large combustion sources are briefly reviewed.Dr James Longhurst is Director of the Acid Rain Information Centre which is based at Manchester Polytechnic.     

Harvesting and climate effects on organic matter characteristics in British Columbia coastal forests

As part of investigations into the effects of harvesting old-growth forest, we characterized carbon in five organic matter pools in eight forest chronosequences of coastal British Columbia. Each chronosequence comprised stands in four seral stages from regeneration (3-8 yr) to old-growth (>250 yr), with second-growth stands mostly of harvest origin. Stands were located in two biogeoclimatic subzones with contrasting climate (wetter, slightly cooler conditions on the west coast of Vancouver Island than on the east). Carbon concentrations in fine woody debris (FWD), forest floor (LFH), fine roots from LFH, and two water-floatable fractions from 10 to 30 cm mineral soil (MIN-ROOT, 2-8 mm and MIN-FLOAT, <2 mm) showed no significant effects due to climate, seral stage, or site. There were some significant differences in N concentrations, but none related to seral stage. Carbon-13 cross-polarization with magic-angle spinning (CPMAS) nuclear magnetic resonance (NMR) spectra with principal component analysis of relative areas also showed little harvesting effect, but greater variation related to input of coarse woody debris (CWD) vs. roots high in tannin. Overall, there tended to be more spectral features associated with wood and lignin in the west; whereas some MIN-ROOT samples from the drier east side had aromatic intensity attributed to charcoal. The minimal effects of one harvest on organic matter are most likely due to the large legacy effect; however, more intensive management will probably result in less CWD retention, less charcoal input, and less microsite variability in these pools of poorly decomposed organic matter.