A MICROPLATE METHOD FOR DETERMINATION OF UREA AND ITS USE IN STUDIES OF NITROGEN MINERALISATION IN GROWING MEDIA

Few studies have reported the fate of urea in growing media, although the mineralisation of urea in soil has been extensively investigated.
Urea concentrations were monitored in growing media using a microassay conducted in microtitre plates.
Colorimetric tests using such microplates are quick and enable the use of small amounts of reagents, reducing risks of contamination as well as disposal problems of excess reagents.

Concentrations of urea decreased markedly within a few days in a peat-based potting medium fertilized with a liquid urea-based feed.
The decrease was temperature related.
Studies with peat-free media containing wood (chipboard) waste showed a constant release of urea during storage.
The urea was probably released from ureaformaldehyde used as a bonding agent in the chipboard.
Mineralisation of the urea-nitrogen to ammoniacal and nitrate-nitrogen was evident in peat free media containing chipboard waste.
Such release and mineralisation may be beneficial to established plants raised in media containing chipboard waste, but may be detrimental to germination and seedling growth due to the high concentrations of ammoniacal and nitrate-nitrogen which may accumulate after the breakdown of urea.

International Symposium Growing Media and Plant Nutrition in Horticulture

W.R. Carlile, K. Dickinson

Growing media, urea, microplates

https://doi.org/10.17660/ActaHortic.1997.450.7