This is a study of physiological changes associated with salt stress and the deleterious effects of salinity on cotton. I investigated how these effects may be minimized by the use of additional nutrients such as ammonium nitrate,
glycinebetaine and potassium chloride. Differences between ammonium and nitrate as nitrogen sources were also investigated. The effects of the method of NaCl and KCl application (foliar or root) on the morphology of cotton plant, ion
concentrations, and K⁺ uptake rate by roots have been examined.
Comparison between NH₄⁺ and N0₃^- nitrogen sources showed N0₃^- to be more beneficial than NH₄⁺. The low growth in a low N treatment, and the similar
reduction in relative growth (% of controls) by salinity at two N levels, indicated that N and salinity effects were independent. Increasing levels of salinity did not decrease nitrogen content in the leaves. Exogenous glycinebetaine did not influence the growth of the plant or the ion contents of its tissues.
The two methods of NaCl and KCl application produced distinct results. The leaves of cotton plants were capable of absorbing salt supplied in an aqueous
medium. This decreased leaf K⁺ concentrations and vegetative growth of cotton.
Soil-applied salinity resulted in a lower accumulation of Na⁺ in the leaves than
foliar-applied salinity and did not significantly alter leaf K⁺ concentrations.
Foliar application of KCl reduced the entry of Na⁺ into the leaves and substantially increased growth when the leaves were wetted with saline water. Foliar and root-applied salts inhibited K⁺ uptake by the roots and its translocation to the shoot in hydroponic culture. It is concluded that foliar application of KCl at 10 mol m^-3 is enough to reduce the passage of Na⁺ into the leaf cell and enhance plant growth under highly saline conditions.
The most important and interesting result was that K⁺ concentrations decreased in the leaves in response to salt application via foliage. It is postulated that this occurs as a result of some signal from shoot to root to slow down K⁺ uptake
which consequently decreased K⁺ concentrations in the leaves. A decrease in the rate of transpiration flow due to salinity could also reduce K⁺ uptake. In this study, however, the rate of transpiration was not decreased by foliar-applied salt.