Modelling soil nitrogen mineralisation in semi-mature pine stands of South Africa to identify nutritional limitations and to predict potential responses to fertilisation

Table 4 Measured total \( {NH}_4^{+} \) and \( {NO}_3^{-} \)concentrations before and after 28 days of incubation with net N mineralisation and gross N availability estimates calculated

Site	Soil depth	\( {NH}_4^{+} \)+\( {NO}_3^{-} \) (before incubation)	\( {NH}_4^{+} \)+\( {NO}_3^{-} \) (after incubation)	Net N mineralisation	Gross N availability estimate
Site	cm	mg (kg topsoil)⁻¹	mg (kg topsoil)⁻¹	mg N (kg of topsoil)⁻¹ day⁻¹	mg N (kg of topsoil)⁻¹ day⁻¹
A	0–15	26.0	55.0	1.04	1.96
B	0–15	38.0	45.0	0.25	1.61
C	0–15	24.8	36.4	0.41	1.30
D	0–15	31.6	42.2	0.38	1.51
E	0–15	23.6	39.0	0.55	1.39
F	0–15	23.6	34.2	0.38	1.22
G	0–15	25.2	63.8	1.38	2.28
H	0–15	25.4	36.4	0.39	1.30
S1	0–15	3.17	6.53	0.12	0.23
S2	0–15	24.3	31.4	0.25	1.12
S3	0–15	5.60	12.6	0.25	0.45
S4	0–15	3.55	13.3	0.35	0.47
L2	0–15	3.92	8.40	0.16	0.30
L4	0–15	15.1	19.8	0.17	0.71

ISSN: 1297-966X