Exploring the potential of ammoxidation of lignins to enhance amide-nitrogen for wood-based peat alternatives and its impact on plant development

Abstract This study explores the potential of nitrogen-enriched lignins produced via ammoxidation – a process combining oxidation and nitrogen incorporation with ammonia (NH 3 ) and oxygen (O 2 ) – to improve wood fibres as sustainable peat alternatives in horticultural substrates. Organocell lignin (OCL) and kraft lignin (KL) were assessed, focusing on the effect of ammoxidation conditions on total nitrogen and amide nitrogen incorporation using OCL as a reference. Total nitrogen content in nitrogen-enriched KL (NKL) reached 6.3 % under 60 bar oxygen pressure, but amide nitrogen remained low (0.64 %), indicating challenges in optimizing this nitrogen type. Attempts to selectively increase amide nitrogen through reaction adjustments proved unfeasible. First cultivation tests showed 2 % nitrogen-enriched OCL (NOCL) enhanced plant growth in substrates with 50 % and 100 % wood fibres compared to lignin-free controls. Adding 10 % NOCL improved growth in peat-free substrates, though less effectively than the 2 % concentration. Conversely, NKL had no notable effect in 50 % wood-fibre substrates and negatively affected 100 % wood-fibre substrates. The results underscore the importance of modifying lignin reactivity prior to ammoxidation to boost amide nitrogen incorporation, offering insights into the viability of wood fibres as peat substitutes in horticulture.