Properties of soil particle size separates after 40 years of continuous corn

Abstract

Changes in chemical and mineralogical characteristics associated with different particle size fractions in soil after 40 years of continuous production of corn by the conventional tillage method (CC) as compared with those of an adjacent native grassland site (NG) are investigated. Results indicate that corn cropping in a soil previously supporting native vegetation produces a decline in total and humified organic matter, phenolic compounds, enzymatic activities, cation exchange capacity (CEC), and hydrosoluble ions, both in the whole soil and in its particle‐size separates. The’ largest losses in organic carbon (C) and nitrogen (N) contents of the cultivated soil were observed in the sandy fractions, the lowest in the silt+clay separates. The humification index (HI) indicates a higher degree of humification of the organic matter in NG than in CC samples. For both NG and CC sites the finest fraction (silt+clay) resulted to be enriched in organic C, total N, humus, phenolic compounds, enzyme activity, CEC, and hydrosoluble ions with the only exception of mineral N forms and sulphates (SO₄). Slight differences were observed in the mineralogical composition of NG and CC soils. The sandy fractions of NG showed greater amounts of phyllosilicates while a lower content was found in the silt+clay fraction of CC as a consequence of a crumbling of parent rock into small pieces induced by repeated tillage practices.