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The performance and biomass yield of the perennial energy plant Sida hermaphrodita (hereafter referred to as Sida) as a feedstock for biogas and solid fuel was evaluated throughout one entire growing period at agricultural field conditions. A Sida plant development code was established to allow comparison of the plant growth stages and biomass composition. Four scenarios were evaluated to determine the use of Sida biomass with regard to plant development and harvest time: (i) one harvest for solid fuel only; (ii) one harvest for biogas production only; (iii) one harvest for biogas production, followed by a harvest of the regrown biomass for solid fuel; and (iv) two consecutive harvests for biogas production. To determine Sida's value as a feedstock for combustion, we assessed the caloric value, the ash quality, and melting point with regard to DIN EN ISO norms. The results showed highest total dry biomass yields of max. 25 t ha À1, whereas the highest dry matter of 70% to 80% was obtained at the end of the growing period. Scenario (i) clearly indicated the highest energy recovery, accounting for 439 288 MJ ha À1 ; the energy recovery of the four scenarios from highest to lowest followed this order: (i) ≫ (iii) ≫ (iv) > (ii). Analysis of the Sida ashes showed a high melting point of >1500°C, associated with a net calorific value of 16.5-17.2 MJ kg À1 . All prerequisites for DIN EN ISO norms were achieved, indicating Sida's advantage as a solid energy carrier without any post-treatment after harvesting. Cell wall analysis of the stems showed a constant lignin content after sampling week 16 (July), whereas cellulose had already reached a plateau in sampling week 4 (April). The results highlight Sida as a promising woody, perennial plant, providing biomass for flexible and multipurpose energy applications.

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A sustainable management of the residues from biogas plants has to be considered due its potential use as plant fertilizer and soil conditioner. Our objective was to evaluate the biogas-digestate as a nutrient source for biomass production of three different plants: sida (Sida hermaphrodita -Malvaceae), maize (Zea mays L. -Poaceae) and alfalfa (Medicago sativa L. -Fabaceae). The used biogas-digestate was obtained after the anaerobic digestion of maize silage, as the major feedstock, and minor amounts of chicken manure. The treatments were established in five replicates including biogas-digestate, NPK fertilizer and a control. Pots were filled with the fertilized soils (biogas-digestate and NPK treatments) and control soil, and seedlings were transplanted and grown for 30 days under greenhouse conditions. Analysis of the shoot and root dry mass and nutrients content (C, N and P) of Sida hermaphrodita, Zea mays L. and Medicago sativa L. revealed similar values for both biogas-digestate and the NPK fertilizer applications, which were greater than the control, showing a positive fertilizing effect of the biogas-digestate for biomass production of the respective plants.

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