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THE EFFECT OF PROLONGED CROPPING ON THE EXCHANGE SURFACES OF THE CLAYS OF BROADBALK FIELD
Author(s) -
BECKETT P. H. T.,
NAFADY M. H. M.
Publication year - 1969
Publication title -
journal of soil science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.244
H-Index - 111
eISSN - 1365-2389
pISSN - 0022-4588
DOI - 10.1111/j.1365-2389.1969.tb01549.x
Subject(s) - soil water , lamellar structure , chemistry , ion exchange , fertilizer , cation exchange capacity , mineralogy , materials science , geology , soil science , crystallography , organic chemistry , ion
Summary Earlier studies have shown that the K‐(Ca+Mg) exchange isotherms of field soils are not greatly changed by cropping, by additions of K‐fertilizer, nor by moderate release of K from fixed forms. The present work shows that very prolonged K‐enrichment or depletion in the Broadbalk trials has led to substantial differences between the exchange isotherms of soils from adjacent plots in proportion to the severity of their K‐depletion. It is suggested that the changes result from the removal of inter‐lamellar K and the consequent increases in the inter‐lamellar spacings of parts of the clay crystals, which have increased the extent of the surface areas accessible to K‐(Ca+Mg) exchange. It is possible that increases sufficient to cause substantial changes in the exchange isotherms may not be apparent in X‐ray diffraction diagrams. Treatment of the K‐depleted clays with m CaCl 2 appears to contract the newly expanded parts of the clay crystals, so that exchange on the occluded surfaces is once again too slow to be observed by the procedures used.