Date of Award:


Document Type:


Degree Name:

Doctor of Philosophy (PhD)


Plants, Soils, and Climate


William F. Campbell


Extreme salinity is one of the most common environmental constraints with which legume/rhizobia symbionts must deal in arid and semi-arid regions of the world. In some areas, with good management, it has been economically possible to ameliorate the saline soil with calcium. The objective of this study, therefore, was to investigate calcium amelioration of salinity (sodicity) on nitrogen fixation, stomatal resistance, potassium/sodium ratio, and total nitrogen of Phaseolus vulgaris L. Seeds of snapbeans were grown in pots under green house conditions and were irrigated with NaCl concentrations of 0, 0.4, 0.8 or 1.2 S m-1 combined with CaS04 . 2H20 or CaCl2. 2H20 , each at concentrations of 0, 4, and 8 mM .

The results show that increasing NaCl concentration decreased leaf water potential, total leaf chlorophyll, shoot and root dry weight, and nitrogen fixation but increased stomatal diffusive resistance. At the highest level of NaCl, addition of CaS04to NaCl increased leaf water potential via increasing stomatal diffusive resistance. Such effects were not observed with the addition of CaCl2 to NaCl.

Addition of CaS04 to all levels of NaCl increased total leaf chlorophyll. The shoot and root dry weight and nitrogen fixation was also increased when CaS04 was added to 0.4 and 0.8 S m-1 NaCl. Again, such effects were not observed with the addition of CaCl2 to NaCl.

Furthermore, analysis of leaf mineral composition showed that leaf Ca2+ , Mg2+ and K+ were increased with each increase in NaCl concentration, whereas the K+/ Na+ ratio was decreased. Also, the total leaf nitrogen increased with 0.4 and 1.2 S m-1 NaCl as well as with all levels of CaS04.

Neither CaS04 nor CaCl2 had any significant effect on leaf K+, Na+, or Mg2+ of the plant when they were added to different levels of NaCl. However, leaf Ca2+ increased with an increase in concentration of CaS04 or CaCl2, but only CaS04 exhibited an interaction when combined with NaCl.

Speciation modeling showed that a considerable amount of S04 was complexed as the CaS04° and NaS04- species. In spite of this, CaS04 treatment had ameliorating effect on NaCl induced salinity symptoms in snapbeans.