Some aspects of the chemistry and mineralogy of soil magnesium in relation to Camellia growth on Sri Lankan acid tea soils
Preliminary effects of application of dolomitic limestone on growth and nutrient status of two different Camellia sinensis L. (tea) species, and on soil status in two Sri Lankan acid soils were investigated. The concentration of Mg in the leaves of TRI 206 species, grown under low-country climatic conditions, increased but Mg concentration was unaffected in CY9 species, grown under up-country climatic conditions. Dolomitic limestone had no effect on the yield of bud, and first and second leaves which are harvested for the production of made-tea. Ten representative profiles of Sri Lankan acid tea soils overlying dolomitic mineral belts and six profiles from different climatic regions were subjected to a detailed mineralogical investigation. No Mg bearing minerals were found to a depth of 75 cm, even at dolomitic sites. The release of Mg from six Sri Lankan acid tea soils was measured by intensive cropping with ryegrass. A minimum one fifth of total Mg uptake was obtained from non-exchangeable Mg forms in the soil, except St. Coombs top soil. Soils that contained less than 9 mg Mg kg-1 initial extractable Mg released 2.0 to 13.2 mg non-exchangeable Mg kg-1 of soil. The effect of Mg and Ca addition supplied in liming and non-liming materials on the growth of Camellia japonica in an acid soil was studied. Magnesium was taken up by Camellia japonica plants in preference to Ca when Mg and Ca were added. The amounts of soil nutrients extracted with mixed resin and ammonium acetate solution were compared with their uptake by Camellia japonica plants. Both methods extracted similar amounts of Mg and Ca but in limed soil the amount of Al taken up by plants was more closely related to ion-exchange resin Al values than ammonium acetate solution adjusted to the pH of the soils.