Soil fertility changes in the long-term experimental plots at Kybybolite, South Australia. III. Changes in cation exchange capacity and exchangeable cations

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Abstract
Changes in the cation exchange complex are one of the secondary effects arising out of the increasing organic matter content of soils, due to the influence of phosphorus fertilizers on leguminous pastures. Analysis of solonetzic soils from the long-term Kybybolite P plots indicates that there is a close relation between organic matter increase and increases in cation exchange capacity. For each increase of 0.1 % soil nitrogen, there has been a corresponding increase of 3.48 m-equiv.jl00 g in cation exchange capacity. Associated with these changes there have been increases in the level of exchangeable calcium and exchangeable hydrogen. Changes in exchangeable calcium appear related to the amount and form of fertilizer or amendment applied. Where little calcium has been added, the increase in cation exchange capacity has been satisfied almost entirely by hydrogen, and base saturation has decreased. There appears to have been little upward movement of metal cations from the lower horizons to the surface by plants, possibly owing to the species involved, or to the intractable nature of the B horizon. The possible effects of changes in the cation exchange complex on plant growth are discussed. Also, the possibility of maintaining base saturation on infertile soils where cation exchange capacity is being increased, is examined.