Effects of biochar, N-enriched biochar and urea on tomato seed germination, vegetative growth, and fruit traits

Agronomic uses of biochar have been intensely explored in the last 15 years. Recently, a new generation of biochar-based fertilizers has been developed. Raw biochar (BCH), nitrogen-enriched biochar (N + BCH) or urea were added to a coir fiber-based substrate for tomato cultivation, to assess seed germination, growth and fruiting of two cultivars (Cuarenteno and Moneymaker).

BCH stimulated seed germination and early radicle growth, possibly because of the presence of karrikins detected in both BCH and N-BCH (0.039 and 0.044 mg kg^-1, respectively). However, BCH reduced growth in adult plants in both cultivars, probably because of ammonium retention, causing low-N-stress-related symptoms such as accumulation of flavonoids in the leaf. Urea was toxic for seed germination because of the fast release of ammonium, but caused a positive effect on adult plant growth and yield, increasing chlorophyll in both cultivars, quantum yield and ascorbic acid in cv. Cuarenteno, and decreasing flavonoids and peroxide in leaves of both cultivars. Unlike urea, N + BCH showed a positive impact on plant growth and yield, but without releasing high amounts of ammonium or negatively affecting seed germination. Nitrogen-rich amendments reduced phosphorus and increased iron leaf content in both cultivars.

BCH can be effectively used as a growth medium constituent in nurseries for seedling production, whereas N + BCH offers a promising alternative to urea or other nitrogen mineral fertilizers for crop cultivation. © 2024 The Author(s). Journal of the Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.