Effects of salt stress on biomass and ash composition of switchgrass (Panicum virgatum)

This study was to evaluate the effects of salt stress on the biomass production and fuel characteristics of energy crop switchgrass in Northern China. A greenhouse-pot experiment was conducted to investigate the salt tolerance of the Blackwell, Cave-in-rock and Sunburst cultivars, using the dominant native grass Leymus chinensis as a reference. All three switchgrasses yielded a greater aboveground biomass per plant than Leymus under low-salt conditions (<= 2 g NaCl kg(-1)). However, their biomass production declined significantly at higher salt concentrations. The most salt-tolerant cultivar with respect to biomass production was Cave-in-rock, followed by Blackwell and Sunburst. Among the biomass fuel characteristic studied, ash composition was more significantly affected by salt stress than calorific values. High salt concentrations in the soil increased the content of Ca, Cl and Na in the biomass ash but reduced that of K. The impact of salt stress on ash transformation during combustion was estimated by considering three molar ratios of mineral elements. Growth in high-salt soils reduced the slagging tendency of the fuel, as indicated by the K/(Ca + Mg) ratio. The added Na is unlikely to cause eutectic formation during switchgrass combustion because the Na/(K + Na) ratio was generally below 0.2. However, the addition of NaCl increased the risk of forming chlorine-rich deposits (probably from the fly ash), as indicated by the Cl/(K + Na) ratio.