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

Table 3 Indicators of N availability used to correlate with the relative yield response to applied N fertiliser (in the presence of P fertiliser)

#	Variable name	Description
1	Net N mineralisation	\( \Big({NH}_4^{+} \)+\( {NO}_3^{-} \) after incubation) minus \( \Big({NH}_4^{+} \)+\( {NO}_3^{-} \) before incubation) in sample
2	Basal N mineralisation (BNM)	Variable # 1, normalised to 40 °C and field water capacity (Paul et al. 2002)
3	Modelled N mineralisation (MNM)	Variable # 2, modelled over 1 year for ambient field conditions with SNAP
4	Gross N availability estimate (GNA)	\( \Big({NH}_4^{+} \)+\( {NO}_3^{-} \)) after incubation in soil sample without any subtraction
5	Normalised GNA	Variable # 4, normalised to 40 °C and field water capacity^a

^aNote that we only present GNA values normalised to optimum temperature and moisture for the purpose of finding the variable that best describes the relative yield response and that we do NOT present GNA values that had been further modelled by SNAP for field conditions because the gross N mineralisation estimates, when modelled and upscaled, may overestimate the actual available N in field

ISSN: 1297-966X