Pyroligneous acid (PA) is a reddish-brown liquid obtained through the condensation of smoke formed during biochar production. PA contains bioactive compounds that can be utilized in agriculture to improve plant productivity and quality of edible parts. In this study, we investigated the biostimulatory effect of varying concentrations of PA (i.e., 0%, 0.25%, 0.5%, 1%, and 2% PA/ddH₂O (v/v)) application on tomato (Solanum lycopersicum ‘Scotia’) plant growth and fruit quality under greenhouse conditions. Plants treated with 0.25% PA exhibited a significantly (p < 0.001) higher sub-stomatal CO₂ concentration and a comparable leaf transpiration rate and stomatal conductance. The total number of fruits was significantly (p < 0.005) increased by approximately 65.6% and 34.4% following the application of 0.5% and 0.25% PA, respectively, compared to the control. The 0.5% PA enhanced the total weight of fruits by approximately 25.5%, while the 0.25% PA increased the elemental composition of the fruits. However, the highest PA concentration of 2% significantly (p > 0.05) reduced plant growth and yield, but significantly (p < 0.001) enhanced tomato fruit juice Brix, electrical conductivity, total dissolved solids, and titratable acidity. Additionally, total phenolic and flavonoid contents were significantly (p < 0.001) increased by the 2% PA. However, the highest carotenoid content was obtained with the 0.5% and 1% PA treatments. Additionally, PA treatment of the tomato plants resulted in a significantly (p < 0.001) high total ascorbate content, but reduced fruit peroxidase activity compared to the control. These indicate that PA can potentially be used as a biostimulant for a higher yield and nutritional quality of tomato.

Microgreens are immature young plants grown for their health benefits. A study was performed to evaluate the different mixed growing media on growth, chemical composition, and antioxidant activities of four microgreen species: namely, kale (Brassica oleracea L. var. acephala), Swiss chard (Beta vulgaris var. cicla), arugula (Eruca vesicaria ssp. sativa), and pak choi (Brassica rapa var. chinensis). The growing media were T1.1 (30% vermicast + 30% sawdust + 10% perlite + 30% PittMoss (PM)); T2.1 (30% vermicast + 20% sawdust + 20% perlite + 30% PM); PM was replaced with mushroom compost in the respective media to form T1.2 and T2.2. Positive control (PC) was Pro-mix BX™ potting medium alone. Root length was the highest in T1.1 while the shoot length, root volume, and yield were highest in T2.2. Chlorophyll and carotenoid contents of Swiss chard grown in T1.1 was the highest, followed by T2.2 and T1.1. Pak choi and kale had the highest sugar and protein contents in T2.2, respectively. Consistently, total phenolics and flavonoids of the microgreens were increased by 1.5-fold in T1.1 and T2.2 compared to PC. Antioxidant enzyme activities were increased in all the four microgreens grown in T1.1 and T2.2. Overall, T2.2 was the most effective growing media to increase microgreens plant growth, yield, and biochemical composition.

The cost of producing organic crops is increasing. Agricultural wastes can be used as biostimulants to increase plant growth and productivity and reduce the dependence on chemical fertilizers. A pouch assay and a potted greenhouse experiment were conducted to investigate the effect of pyroligneous acid (PA) and sea lettuce (SL) on kale (Brassica oleracea subsp. acephala (DC.) Metzg) seed germination and growth. Although previous studies have demonstrated that these two biostimulants could promote plant germination and growth, there is little research to compare their effects on seed germination and plant growth. The pouch assay showed that PA liquid affected the seed germination rate under different concentrations; the seed germination rate decreased as the concentration of PA liquid increased. However, the effect of seed germination was less pronounced in SL liquids. Kale seeds treated with 0.01% PA showed the best elongation and seedling growth performance. Moreover, the greenhouse experiment indicates that SL liquids significantly (p < 0.05) affected kale growth production, while PA liquid had less difference on kale growth under various concentrations. The 0.25% PA and 1% SL increased the aboveground fresh weight by ca. 26% and 29%, respectively. Also, the phytochemical contents of kale leaves, including phenolics, flavonoids, ascorbate, and protein, were significantly increased with 0.25% PA and 1% SL application. These results suggest that low concentrations of PA are more suitable for seedling root growth in kale and 1% SL had the most significant growth-promoting effect on kale. Hydrothermal carbonization sea lettuce liquid can be used as a good biostimulant for agricultural production to improve kale germination and growth.