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Sweet sorghum seems to be one of the most promising energy crops for a wide range of ecological conditions thanks to its high yield potential and drought tolerance. A two-year field trial was conducted in a semi-arid Mediterranean environment in Turkey to evaluate the interactive effects of different nitrogen fertilizer levels (100, 150, and 200 kg ha−1) and humic substances (0, 15, 30, and 45 L ha−1) applications on the biomass and bioethanol yields of sweet sorghum, and combustion characteristics of its bagasse. Sweet sorghum showed a positive response to increased nitrogen fertilizer and humic subtances application levels in terms of biomass and bioethanol production. Lignocellulosic and total bioethanol yields significantly increased up to 2910 and 3336.6 L ha−1 as a result of the combined application of the 200 kg ha−1 N and 15 L ha−1 humic subtances (HS), respectively. However, HS application had a detrimental effect on the bagasse combustion quality, because it caused a considerable increase in the mineral and ash concentrations. Briefly, combined application of 200 kg ha−1 N and 15 L ha−1 HS may be suggested to be applied for the sustainable bioethanol production from sweet sorghum, while the application of HS likely does not provide any economic and environmental benefit if bagasse would be used as solid biofuel feedstock.

The use of bio-stimulants (BSs) has become an important policy in managing many stressed crop plants through the regulation of the balance of phytohormones, osmo-protectors (OPs), antioxidant systems, and gene expression, all of which reflect plant growth and productivity. Garlic + onion extract (GOE) at a concentration of 2.0–3.0% and diluted bee honey solution (BHs) at a concentration of 1.0–1.5% were applied exogenously to squash (Cucurbita pepo) plants subjected to cadmium (Cd) + lead (Pb) stress (0.3 mM CdCl2 + 0.3 mM PbCl2). The objective was to determine the effects of these treatments on growth characteristics, organic metabolites/biomolecules, and mineral nutrients. Cd + Pb stress significantly increased electrolyte leakage (EL, 103%) and malondialdehyde (MDA, 90%) because of an increase in hydrogen peroxide (H2O2, 145%) and superoxide (O2•−, 152%) levels, and contents of abscisic acid (ABA, 164%), Cd (674–711%), and Pb (754–805%). Consequently, marked increases in the contents of OPs and non-enzymatic antioxidants (28–133%), activities of antioxidant enzymes (48–80%), and expressions of enzyme genes (60–84%) were observed. The administration of Cd + Pb treatment reduced plant growth and development parameters (25–59%), yield components (61–86%), photosynthetic components (27–67%), leaf proportional water content (26%), indole-3-acetic acid (IAA, 44%), gibberellic acid (GA3, 56%), and cyto-kinin (CKs, 49%) contents. Nonetheless, the administration of GOE, BHs, and GOE + BHs attenuated the adverse impacts of Cd + Pb stress. The best treatment was GOE + BHs which significantly decreased EL (52%) and MDA (49%) because of a reduction of O2•– (61%), H2O2 (60%), ABA (63%), Cd (89–91%), and Pb (89–91%) levels. This positive outcome was linked to an increase in the OPs’ (22–46%) and non-enzymatic antioxidant (27–46%) levels, activities of enzymes (26–44%), and enzyme gene expressions (35–40%), all of which contributed to the promoted relative water content (RWC, 37%), pigment contents (47–194%), hormonal levels (82–132%), growth traits (31–149%), yield components (154–626%), and fruit quality traits (31–92%). From these results, it can be concluded that treatment of GOE + BHs is recommended as a foliar application to reduce the adverse effects of Cd + Pb stress treatment in squash.