Summary
Dry aggregates of two virgin clay soils and their cultivated counterparts were sieved into size fractions ranging from >5 mm to <0.1 mm in diameter. Total nitrogen, organic carbon, particle size distribution, and waterlogged nitrogen mineralization measurements were made on the different fractions.
The cultivated soils were homogeneous with respect to the organic matter content of different aggregates, while the virgin soils were relatively heterogeneous. This result can be explained assuming a dynamic state of aggregation in cultivated soils and a relatively stable state in virgin soils.
In all soils, waterlogged nitrogen mineralization, expressed as a percentage of total nitrogen, increased with decreasing aggregate diameter. Previous workers, finding a similar trend in aerobic nitrogen mineralization, attributed such trends to differential aeration effects in aggregates of varying size. The results of this study suggest that small aggregates contain a larger proportion of readily mineralizable organic nitrogen than large aggregates.
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Craswell, E.T., Saffigna, P.G. & Waring, S.A. The mineralization of organic nitrogen in dry soil aggregates of different sizes. Plant Soil 33, 383–392 (1970). https://doi.org/10.1007/BF01378229
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DOI: https://doi.org/10.1007/BF01378229