Agricultural application of ammonium-enriched hydrochars: Cultivation practices to improve quality and yield of Matricaria recutita L.

The disposal of organic agricultural waste is a global issue that countries are addressing. Transforming this waste into hydrochar, which has notable advantages for soil improvement and pollutant removal, is drawing increasing interest. This study examined the impact of ammonium-enriched hydrochars on various agricultural properties of Matricaria recutita (medicinal chamomile), a widely used herbal tea plant. A hydrothermal process was employed to optimize the creation of ammonium-enriched hybrid hydrochar using two types of agricultural waste (olive pits and sunflower seed shells). To identify the optimal conditions for ammonium adsorption, four variables were assessed: pH, initial ammonium concentration, hydrochar concentration, and temperature. The ideal hydrochar production conditions from sunflower seed shells and olive pits were established as a 20/80 mixing ratio, 240 °C, and 160 minutes of processing time. The maximum ammonium adsorption to the hybrid hydrochar was 14.60 mg NH 4 + /g HC at pH 6.5, with an adsorbent concentration of 1.5 g/L, 35 °C, and an ammonium concentration of 40 mg/L. Different hydrochar doses (0.5 ton/da - T-1; 1 ton/da - T-2; 2 ton/da - T-3; raw hydrochar 0.4 ton/da - T-4; and a control with no hydrochar) were applied to luvisol-classified soil. Their effects on plant height, number of branches per plant, fresh/dry flower yield, and essential oil composition were evaluated. The hydrochar treatments influenced soil Ca, Mn, and Zn levels, as well as water saturation rates. T-4 increased plant height, while T-2 enhanced branch count and dry flower yield. Additionally, bisabolene oxide, bisabolol oxide A, and chamazulene were detected across all treatments in varying concentrations. • Ammonium-absorbed and raw hydrochar had different effects on plant growth and essential oils. • Ammonium-absorbed hydrochar positively impacted agronomic traits and essential oil content. • Adjusting hydrochar doses is crucial for optimizing plant growth and essential oil yield. • T1 and T2 treatments increased organic matter, branches, and flower yields. • The study highlights hydrochar's potential as an eco-friendly fertilizer for improving crop quality.