Mineralisation, during incubation, of the organic nitrogen compounds in soils as related to soil pH

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Abstract
Mineral nitrogen accumulation (mineralised nitrogen) during incubation, with and without added chalk (calcium carbonate), of 25 cultivated soils of varying texture, pH and total nitrogen content was determined. There was little difference in nitrogen mineralised per unit of total soil nitrogen between soils having an original pH greater than about 6.5. As pH decreased below 6.5, nitrogen mineralisation per unit of total nitrogen increased. This increase was much greater where calcium carbonate had been added prior to incubation. When all soils were considered, there was a highly significant negative correlation between original soil pH and nitrogen mineralised per unit of total nitrogen present for both untreated and chalk‐treated soils. The results obtained indicate that acid soils tend to accumulate organic nitrogenous residues to a greater extent than do soils of high pH and that the nitrogen in such residues tends to mineralise readily if soil pH is increased.