Novel bio-inorganic iron chelate from coffee by-products for agronomic purpose

Abstract The presence of polyphenols and melanoidins in spent coffee grounds (SCG) and SCG-hydrochars obtained through hydrothermal carbonization (HTC) has been previously linked to both phytotoxicity and the ability to mobilize nutrient elements. This study aimed to assess the potential of SCG and two SCG-hydrochars, functionalized with Fe salts (bio-chelates), to enhance the nutritional value of lettuce through in vitro biofortification. The study utilized two application methods: 1) A fixed Fe concentration of 10 mg kg-1 of soil and 2) A fixed dose of 0.5% bio-product. Control groups were also included, consisting of soil alone (control A) and commercial chelates (control B). The SCG and SCG-hydrochars were obtained at 160 and 200 °C, respectively. Hydrochars showed a severe decrease in chelating capacity regarding Fe (62.8%). The addition of SCG and hydrochars show the same inhibition effect. Fe showed a greater biofortification tendency with the addition of all bio-chelates. Utilizing SCG-hydrochars as micronutrient fertilizers has the potential to revolutionize the field, challenging the conventional practice of solely emphasizing organic carbon enhancement in soil. Nonetheless, further research is imperative to fully explore this promising avenue.