Evaluation of the magnesium supplying powers of the Nigerian savannah soils

The cation exchange properties and microbial carbon, nitrogen and phosphorus in savanna Alfisol under continuous cultivation

“…The present data are below these critical ratios. In contrast, Lombin (1979) suggested that a Ca : Mg ratio of 3É2 might not lead to imbalances of Ca and Mg nutrition of crops, although this hypothesis was not rigorously tested in his study. It seems, from the perspective of cation exchange and prevention of nutritional imbalances involving basic cations, a rational fertilisation program for these soils is a combination of inorganic fertiliser with farmyard manure.…”

“…The results (Mg : K \ 2) would suggest widespread Mg deÐ-ciency after 45 years of continuous cultivation. The prospect of Mg deÐciency in the savanna was alluded to by Lombin (1979). He showed that Mg : K ratios of several savanna soils were already in a precarious balance.…”

“…This is particularly applicable to Mg availability, whose CEC saturation is not nearly as important as Mg : K ratio (McColluch et al 1957 ;Lombin 1979). The critical Mg : K ratio below which Mg deÐciency occurs is about 2 for several soils (McColluch et al 1957 ;Tinker and Smilde 1963).…”

Potassium–calcium and potassium–magnesium exchange equilibria in an acid savanna soil from northern Nigeria

“…Calcium and Mg 2+ are the dominant cations in the exchange complex of the soils, and there have been no reports of widespread deficiencies of Ca 2+ and Mg 2+ in the soils (Jones and Wild, 1975), except for two reports that alluded to the prospects of Mg 2+ deficiency for soils under continuous cultivation (Lombin and Fayemi, 1978;Lombin, 1979). Preferential retention of cations in soils is determined by a number of factors including valence, hydration size and/or the relative energies of hydration of various cations (Chung et al, 1994), and the clay mineralogy (Goulding and Talibudeen, 1980;Goulding, 1983).…”

“…Yet, there is little or no information on the K + exchange behaviour of these soils in relation to Ca 2+ and Mg 2+ ; information required for the efficient management of Ca 2+ , Mg 2+ and K + fertility without inducing deficiency of any of them through unfavourable cationic ratios (Lombin, 1979;Goladi and Agbenin, 1997). If selectivity or preferential retention of K + by these soils can be demonstrated, the implications for Ca 2+ and Mg 2+ nutrition of crops and leaching under continuous cultivation and K + fertilization would be serious.…”