Table 1. Carbon and nitrogen content of three humic substances (% of dry weight).

Humic substance	C(% of dw)	N(% of dw)	C:N
Humic acid (Fluka) (HF)	47.6	0.8	60∶1
Humic acid (Aldrich) (HA)	39.2	0.5	72∶1
Fulvic acid (Öre river) (FO)	48.1	0.8	61∶1

Standard deviation of the replicates varied between 1 and 10%.