Sewage sludge amendment improved soil properties and sweet sorghum yield and quality in a newly reclaimed mudflat land.

Growing bioenergy crop on marginal lands has the potential to minimize land use conflicts and meet global energy demand. The newly reclaimed mudflats through sewage sludge amendment can be used as a potential marginal land for bioenergy production. This paper was one of first studies to investigate the persistent impact of sewage sludge application at the rates of 0, 25, 50, 125, and 250 t ha-1 on selected soil physicochemical properties, yields and quality of sweet sorghum (Sorghum bicolor L.) cultivated in newly reclaimed mudflat saline-alkaline soil. The results showed that sewage sludge amendment (SSA) improved physicochemical properties by decreasing bulk density, electric conductivity, pH, and increasing soil organic carbon, >0.25 mm water-stable aggregate fraction, cation exchange capacity, nitrogen, and phosphorus contents in mudflat soil. Consequently, the sweet sorghum biomass and gross energy content were significantly elevated by SSA. The sweet sorghum achieved the maximum biomasses of 4.73 and 6.62 t ha-1 at 250 t ha-1 SSA rate in 2016 and 2017, respectively. The gross energy content of sweet sorghum significantly increased with the SSA rates, although SSA slightly reduced the calorific values in stem and leaf of sweet sorghum. The maximum gross energy contents of sweet sorghum were 79.62 and 104.47 GJ ha-1 at SSA rate of 250 t ha-1 in 2016 and 2017, respectively. Although SSA led to accumulation of heavy metals in sweet sorghum, the growth of sorghum was not inhibited even at the highest SSA. In summary, cultivation of bioenergy crop in mudflat amended by sewage sludge is feasible and can be an innovative solution for mudflat reclamation, safe disposal of solid waste, resource reuse and recycle, and bioenergy production.