Production of Sweet Sorghum Bio-Feedstock on Technosol Using Municipal Sewage Sludge Treated with Flocculant, in Ukraine

Abstract

This paper presents the influence of sewage sludge (SS) on the biometric parameters, absorption of mineral elements and thermal characteristics of sweet sorghum (Sorghum bicolor L.) grown on Technosol. Two types of sewage sludge were used: unmodified and modified with DAMET flocculant. Each type of sludge was applied in three doses (expressed as dry matter basis, DM): 20 t DM/ha, 40 t DM/ha and 60 t DM/ha, respectively. The yield of fresh biomass depended on the dose of sewage sludge: it increased by 14.5–41% and reached 104.6 t/ha after application of the sewage sludge with flocculant at a maximum rate of 60 t/ha. Sorghum biomass actively absorbs nutrients from the soil. Nitrogen was absorbed more actively; depending on the type and dose of sewage sludge application, its content in biomass increased from 12–40% (dose of 20 t/ha) to 80–112% (dose of 60 t/ha). By content in sorghum biomass, essential elements can be arranged in descending order as follows: Fe → Mn → Zn → Cu. Sorghum shows a low ability to accumulate some heavy metals in aboveground biomass. Despite the fact that large doses of sewage sludge contributed to an increase in the content of nickel, cadmium and lead in the substrate by 1.8–5.6 times, the ratio of the content of these elements in plants to the content in the substrate remained low. Sewage sludge affects the process of thermal degradation of sorghum biomass. The decomposition of the main components occurs at lower temperatures, and, as a rule, at higher rates. Sewage sludge (especially with flocculant) contributes to a more complete combustion of biomass. The results showed that sewage sludge with flocculant at a dose of 40 t/ha is the most optimal fertilizer option for growing sweet sorghum on such Technosols as loess-like loam.