Table 4.

Exudation of organic acid anions by roots of white lupin, faba bean and maize grown for 12 days with low (LP) and high P supply (HP) under two N forms [ca(NO₃)₂ and NH₄NO₃].

Crops	Organic acids	Root exudation (µmol g−1 dry root h−1)
		Ca(NO3)2-N		NH4NO3-N		LSD	P level	N form	P × N
		LP	HP	LP	HP
White lupin	Tartaric	0.96	0.54	0.49	0.50	0.04	***	***	***
	Malic	1.67	0.92	1.66	1.24	0.27	**	n.s.	n.s.
	Citric	0.59	0.47	n.d.	n.d.	0.04	***	*	*
	Fumaric	0.02	0.03	n.d.	n.d.	0.00	n.s.	n.s.	n.s.
	T-aconitic	0.04	n.d.	n.d.	0.03	0.00	n.s.	n.s.	***
	Total organic acids	3.29	1.95	2.15	1.82	0.29	***	**	**
Faba bean	Tartaric	1.35	0.83	2.87	2.25	0.20	***	***	n.s.
	Malic	0.75	0.81	0.89	0.79	0.39	n.s.	n.s.	n.s.
	Citric	0.31	0.42	0.48	0.35	0.15	n.s.	n.s.	n.s.
	Fumaric	0.05	n.d.	n.d.	n.d.	0.02	**	**	**
	T-aconitic	n.d.	0.01	n.d.	0.02	0.00	***	**	**
	Total organic acids	2.47	2.08	4.24	3.81	0.35	**	***	n.s.
Maize	Tartaric	0.41	3.62	0.49	2.19	1.08	**	n.s.	n.s.
	Malic	n.d.	1.20	n.d.	0.91	0.27	***	n.s.	n.s.
	Citric	n.d.	n.d.	n.d.	n.d.	0.00	n.s.	n.s.	n.s.
	Fumaric	0.03	0.05	0.02	0.02	0.01	n.s.	*	n.s.
	T-aconitic	0.48	0.29	n.d.	n.d.	0.15	n.s.	***	n.s.
	Total organic acids	0.92	5.16	0.51	3.12	1.42	**	n.s.	n.s.

*P ≤0.05;

**P < 0.01;

***P < 0.001; n.s., not significant at P = 0.05. n.d., not detected.