This study aimed to (a) analyze the influence of pyrolysis temperature on pistachio shell-based biochar (PSB) properties and (b) assess the PSB effect on green bell pepper (Capsicum annuum L.) growth. Pyrolysis experiments were conducted at different temperatures, determining 450 °C as optimal for soil amendment. The effect of PSB addition at different mass ratios was analyzed considering the physicochemical properties of the mixtures and the agronomic parameters of green bell pepper plants and fruits under greenhouse conditions. Results demonstrated enhancements in soil properties upon biochar incorporation, including a decrease in pH by 1%, a decrease in electrical conductivity (EC) by 4–14%, and increases in cation exchange capacity (CEC) by 4–8%, organic matter (OM) and organic carbon (OC) by 100–200%, and total nitrogen (TN) by 35%, relative to unamended soil. Agronomic variables revealed improvements, particularly during the reproductive and maturity stages, with plants treated with 1% biochar (SB1) exhibiting enhanced growth and chlorophyll content, alongside increased flower and fruit yields. Notably, the 2% biochar treatment (SB2) yielded superior fruit weight and length results, suggesting the potential for biochar to enhance both the quality and quantity of green bell pepper fruits, thereby contributing to sustainable agricultural practices.

This study investigated the phytotoxicity of agro-industrial wastes (almond, walnut, pistachio and peanut shells, asparagus spears, and brewer’s spent grain) and their biochar through germination bioassays in several horticultural species: green pea, lettuce, radish, and arugula. Biowaste was pyrolyzed under controlled conditions to produce biochar, and both biowaste and biochar were characterized. Germination bioassay was conducted using seeds exposed to different dilutions of aqueous extract of biowaste and their biochar (0, 50, and 100%). Germination percentage, seed vigor, germination index, and root and aerial lengths were evaluated. The results showed that the phytotoxicity of the biowaste was significantly different to that of its biochar. The biochar obtained demonstrated changing effects on germination and seedling growth. In particular, biochar extracts from spent brewers grains, walnut shells, and pistachio shells showed 5–14% increases in seed vigor and root and aerial length. Furthermore, the response of different species to both agro-industrial waste and biochar revealed species-specific sensitivity. Seeds of lettuce and arugula species were more sensitive to aqueous extracts than radish and green peas. This knowledge not only elucidates the behavior of agro-industrial waste-based biochar in the early stage of plant development but also provides valuable insights regarding phytotoxicity, seed sensitivity, and the variables involved in germination.

Water scarcity and soil fertility loss are major limitations for agricultural production. This study evaluated the effects of walnut shell biochar (WSB) and fertilizer on the growth of lettuce (Lactuca sativa L. “Gran rapid”) in hydroponic and conventional systems. WSB alone and WSB + fertilizer were applied at different mass ratios to soil (0, 5, 10, and 15%) in the conventional system and to the substrate (0, 10, and 20%) in the hydroponic system. Agronomic parameters such as fresh weight, dry weight, leaf area index, and the number of leaves were evaluated. The results showed that fertilizer addition improved growth in both systems. In hydroponics, the combination of WSB and fertilizer increased fresh weight by 45% and dry weight by 38% compared to the control without biochar or fertilizer. In the conventional system, WSB alone increased fresh weight by 30% and the number of leaves by 25%, without requiring additional fertilizer. Lettuce grown in conventional soil with 15% WSB and fertilizer achieved a 1.8 times higher leaf area index than the control without biochar. These findings suggest that WSB and fertilizer applications enhance lettuce crop yield, supporting the principles of circular economy and sustainable waste management in agriculture.

The growing demand for sustainable agriculture requires strategies that simultaneously recover soil quality, improve crop yield, and add value to food products. This study evaluates walnut shell biochar (450 °C) as a circular amendment applied at 0, 10, and 20 t ha⁻¹ to an arid soil cultivated with pea (Pisum sativum L. cv. Onward) in San Juan, Argentina. Biochar enhanced soil porosity, respiration, organic carbon, and cation exchange capacity, resulting in higher plant biomass and a 30.9% increase in pod yield for the 20 t ha⁻¹ treatment. Pea grains were dehydrated by far-infrared drying at 70 °C, producing flour with improved lipid content, water absorption, and swelling capacity, which increased from 0.21 to 0.26 mL g⁻¹ under the 20 t ha⁻¹ treatment. The combined use of biochar and controlled drying highlights a viable pathway to close the soil–plant–food loop through resource valorization. This work contributes practical evidence of biochar’s multifunctional role in sustainable agri-food systems, aligned with circular economy principles.

This study investigates the influence of pyrolysis temperature on the main properties of BSG (brewer's spent grain) biochar and evaluates its suitability as an energy vector and as a substrate component. Pyrolysis tests were carried out at 673, 773, and 873 K. Bioenergy indexes were calculated for BSG and its biochar, and germination tests were carried out to obtain lentil sprouts. The results showed that the BSG biochar obtained at the lowest temperature biochar presented the best performance for use as biofuel. Regarding the germination tests, the different biochars were applied at 4 doses, and the evaluated parameters such as germination percentage, germination rate, mean germination time, and seed vigor were strongly influenced by the biochar addition. The biochar at 773 K added at a dose of 5% doubled the values of mean germination time, seed vigor, and time for 50% of the seeds to emerge compared to the control, constituted only with distilled water. The sustainable BSG valorization through pyrolysis reduces waste and contributes to circular economy practices by transforming industrial by-products into valuable resources for energy and agriculture. This approach highlights the importance of sustainability in reducing the environmental impact of industrial waste and promoting renewable energy sources.