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The role of nitrogen (N) in limiting herbage production was assessed in an altitudinal sequence of Agrostis-Festuca grasslands in the Moor House National Nature Reserve. For most of the growing season the concentration of ammonium-N found in the soils at the times of sampling greatly exceeded that of nitrate-N. Laboratory determinations of soil N mineralization rates at field growing season temperatures showed that mineral N accumulated almost entirely as nitrate in samples from lower altitudes and as ammonium in soil samples taken at the highest altitude. A linear relationship between the mean annual concentration of N in the herbage and primary production in the four grassland sites suggests that soil N supply was a limiting factor (...)

(1) The precision of estimates of soil bulk density from organic matter content, expressed as % loss-on-ignition of dry weight, was examined for eight groups of data collected from surface and sub-surface soils on various sites by different workers. (2) The regression derived by pooling all data for surface soils differed significantly in elevation from its counterpart for sub-surface soils. (3) Regressions for individual groups of data for both surface and sub-surface soils, differed in slope and elevation from their respective overall equations and from each other. (4) For greatest precision in estimating soil bulk-densities, the authors recommend research workers to derive equations for their own research sites rather than to rely on general equations.