Table 2.

Amounts of N coming from nitrate absorption (N absorbed) or atmospheric N fixation (N fixed) of white clover plants grown for 140 d at three sulphate concentrations in the nutrient solution, expressed per plant or per metre of roots

${\mathbf{S}\mathbf{O}}_4^{2-}$ (mM)	N absorbed		N fixed
	(g plant−1)	(g m−1 roots)	(g plant−1)	(g m−1 roots)
0	0.23 a	0.30 a	0.14 a	0.18 a
0.095	0.35 b	0.22 a	0.29 b	0.19 a
0.380	0.51 c	0.44 a	0.74 c	0.94 b
H	12.50	5.66	10.50	9.50
P	<0.01	ns	<0.01	<0.01

White clover plants were grown at three sulphate concentration of the nutrient solution (0, 0.095, and 0.380 mM) and 2 mM K¹⁵NO₃ (0.5 atom% excess) to measure N absorbed from the nutrient solution (N absorbed) and N derived from the atmosphere (N fixed). Values are presented as means (n=5). Different letters indicate significant differences between S treatments (P <0.01). H and P: Kruskall–Wallis statistics (ns: non significant).