Temporal Variation of N Isotopic Composition of Decomposing Legume Roots and Its Implications to N Cycling Estimates in ^𝟏𝟓𝐍 Tracer Studies in Agroforestry Systems

Table 3

Simulation steps, optimal parameter values and performance of the residue decomposition model. Values indicated in bold were obtained through model optimisation; other values were fixed in the respective simulation steps. Residue parameter values are for labile fraction, except for the final simulation step for which values are given for both labile and stable fraction. For CV (RMSE), asterisk (*) indicates statistically significant fit between observed and simulated δ ¹⁵N values of the N recipient plant (<0.05).

Step	Fraction	Characteristics
		C : N	N (mg)	δ ^15N (‰)	N source factor (Sf)^a	CV (RMSE)
Residue application experiment (RA)
(i) Single residue fraction	labile	14.5	97	180	0.0	0.820
	labile	14.5	97	180	1.0	0.579
(ii) Two fractions with equal δ ^15N	labile	3.0	29	180	0.0	0.764
	labile	3.0	29	180	1.0	0.164
(iii) Two fractions with different δ ^15N	labile	3.0	29	600	0.0	0.630
	labile	3.3	29	273	0.50	0.029*
	stable	19.3	68	140
Full interaction experiment (FI)
(i) Single residue fraction	labile	30.2	1332	318	0.0	0.553
	labile	30.2	1332	318	1.0	0.454
(ii) Two fractions with equal δ ^15N	labile	3.0	400	318	0.0	0.538
	labile	3.4	41	318	0.38	0.093
(iii) Two fractions with different δ ^15N	labile	3.0	400	495	0.0	0.482
	labile	3.3	66	167	1.0	0.047*
	stable	31.6	1266	330

^a0 corresponds to proportionally equal uptake from the two soil inorganic N pools, and 1 to preferential uptake from N mineralised from residue over soil native N (1).