Differences between natural populations of Trifolium repens L. in response to mineral nutrients. 2. Calcium, magnesium and potassium.
Natural populations of Trifolium repens collected from contrasting soil types differed in response to Ca, Mg and K when grown in sand culture. Populations from acid soils low in Ca were less responsive to Ca but more responsive to Mg than were populations from calcareous soils. Calcareous populations showed yield depression at high K levels. Response to Ca was correlated (r = 0.76) with extractable Ca in the native soils. Response to Mg and K was apparently related to cationic ratios in the native soil. Shoot concentrations of Ca were higher in populations from acid soils than in populations from calcareous soils. The uptake of Ca into the shoots per unit weight of root (uptake efficiency) was also higher. Populations from calcareous soils had higher shoot concentrations and uptake efficiencies of Na. There was no overall difference between population types in concentration and uptake efficiency of Mg or K. Populations from acid soils had higher √ Ca + Mg/K + Na and K/Na ratios in the shoot material, but lower Mg/Ca and K/Ca ratios, than did calcareous populations. It was concluded that differences between populations in response to Ca were largely due to differences in selective uptake of Ca, but that differences in response to Mg and K were probably due to differences in efficiency of internal utilization of those cations. The root cation exchange capacities of populations from acid soils were significantly higher than those from calcareous soils in T. repens but not in Festuca ovina or Anthoxanthum odoratum. It was concluded that the observed differences in response to Ca, Mg and K in Trifolium repens were not the result of differences in root cation exchange capacity.-R.B.