Abstract The intensive use of mineral fertilizers increases production costs and environmental impacts, highlighting the need for more sustainable nutrient management strategies. This study evaluated whether hydrochar and biochar, both produced from cashew bagasse, could partially replace mineral fertilizers in degraded soil, using maize as the test crop. A greenhouse experiment was conducted with five fertilization treatments: non-fertilized control (CT), mineral fertilization (MF), hydrochar (HC), biochar (BC), and the co-application of 50% hydrochar or biochar with 50% mineral fertilizer (HC + MF and BC + MF). Plant physiological parameters, biomass production, nutrient accumulation, soil chemical attributes, and fertilizer cost reduction were evaluated. The co-application of BC + MF promoted plant responses comparable to those obtained with MF. Compared with CT, these treatments increased photosystem II efficiency (ΦPSII) and electron transport rate (ETR) by approximately 49%, while shoot biomass and leaf area increased by 200% and 146%, respectively. Nutrient accumulation in leaves also increased, particularly for N and K, with average increases of 111% and 150%, respectively, compared with CT. Although HC and BC applied alone did not consistently promote plant growth, their co-application with MF reduced fertilizer costs by more than 50% while maintaining improvements in plant physiological responses and soil chemical attributes, including increased soil pH. BC + MF was more effective than HC + MF in improving plant performance. These results indicate that biochar derived from cashew bagasse can partially replace mineral fertilizers in maize cultivation in degraded soils, contributing to cost reduction, waste valorization, and more sustainable nutrient management strategies. Graphical Abstract
Gonçalves et al. (Thu,) studied this question.