Quantifying the Effect of Soil Salinity on the Physiology of Three South African Sugarcane Varieties

Salinity is of significant economic importance in the sugar industry because it affects the growth rate and sucrose yield of sugarcane. The aims of this study were to assess how various aspects of the physiology of sugarcane are affected by increasing levels of soil salinity during the growing season, and to determine whether or not there are differences in the physiological responses of different varieties to saline conditions. The trial focused solely on salinity, with the cations Ca and Mg (predominantly as chlorides) as the dominant salts, and excluded the effects of Na and sodicity as a variable, when assessing the effect of high electrical conductivity (EC) (ranging from about 100 to 800 mS/m) on the physiology and yield of varieties N17, N22 and NCo376. Investigations were carried out to assess leaf water potential, stomatal conductance and light-saturated rate of photosynthesis of these varieties under the experimental conditions provided. It was evident throughout the trial that high levels of salt adversely affected growth for all three varieties; total above-ground biomass decreased significantly with increasing salinity. Although sucrose yields (tons/ha) of all three varieties showed a trend of decline with increasing salinity, only NCo376 showed significant treatment effects. Leaf water potentials at both pre-dawn and midday were found to be lower as EC increased, implying a mild water stress. N17 and NCo376 showed moderate sensitivity to salt because their responses to salinity, although variable depending on the parameter being assessed, were never as severe as the response of N22, which displayed more pronounced reactions at higher levels of salinity.