Table 1.

Summary of compartments and treatments. n/a = this compartment was not used for this particular treatment. DDW = double distilled water; FWt = fresh weight; L_abC = labelling compartment, T_raC = transfer compartment, R_ecC = receiving compartment

Treatment	LabC	TraC	Description of treatment
(i) Controls
No 15N addition	DDW + Sand	Soil	1 ml of DDW
Sterile	15N-Urea + Sand	Soil	Autoclaved soil used in TraC
(ii) Land management / N type
15N-urea only	15N-Urea + Sand	Soil	15N-urea only (1 ml 30 mM 98 atom% 15N)
Decomposition	n/a	15N-labelled clover incorporated in soil	15N-labelled clover shoots (2.1 ± 0.3 atom% 15N) produced via labelling with 15N urea (1 ml 30 mM 98 atom% 15N) Finely chopped clover shoot (0.7 g FWt) incorporated into TraC
Exudation	n/a	Soil watered with 15N-labelled root exudates	TraC watered with leachate containing 15N-labelled clover root exudates produced following clover labelling with 15N-urea(1 ml 30 mM 98 atom% 15N)
Defoliation	15N-Urea + Sand	Soil	Clover shoots removed at 100 h
(iii) Presence of organisms
Fungi	15N-Urea + Sand	Soil	15N-urea (1 ml 30 mM 98 atom% 15N) in LabC Fungi (Rhizophagus irregularis) on a growth medium (1.5 g) was mixed into the TraC
Weevil	15N-Urea + Sand	Soil	15N-urea (1 ml 30 mM 98 atom% 15N) in LabC 20 Weevil eggs (Sitona spp.) were injected into the soil TraC
(iv) Bidirectional N transfer
Clover to ryegrass	15N-Urea + Sand	Soil	15N-urea (1 ml 30 mM 98 atom% 15N) in LabC Receiver (ryegrass) split across TraC and RecC. RecC contained soil
Ryegrass to clover	15N-Urea + Sand	Soil	15N-urea (1 ml 30 mM 98 atom% 15N) in LabC Receiver (clover) split across TraC and RecC. RecC contained soil