Key Message Estimates of available nitrogen (based on topsoil nitrogen mineralisation rates) in semi-mature stands of Pinus radiata (D Don.) as well as pure species and hybrids of Pinus elliottii (Engelm.) in South Africa display a strong, significant, negative relationship with growth response to applied fertilisers in field experiments. This inexpensive technique can be incorporated in a fertiliser decision support system to minimise wasteful fertiliser applications. Context South African mid-rotation pine stands respond with high variability to nitrogen fertiliser supplements in the presence of phosphorus. Aims We aimed to find a screening tool for stands that are responsive to fertilisation. Methods The volume growth response relative to control plots (3 years after fertilisation with 200 kg ha −1 N in the presence of 100 kg ha −1 P) was determined across 14 pine fertiliser experiments in South Africa. These values were correlated to soil and other properties for each site and also to estimates of N availability and N mineralisation rates using the Soil Nitrogen Availability Predictor (SNAP) model. Results The relative volume growth response to fertilisation ranged with a factor from 0.05 to 0.96. No single result from standard soil analyses showed a strong positive or negative correlation with this growth response. However, highly significant negative correlations were observed between an estimate of N availability based on topsoil aerobic nitrogen mineralisation rates and the relative volume growth responses to fertilisation. Conclusion The estimate of N availability derived from incubation studies may assist us to predict the magnitude of the response to N fertilisation (in the presence of P) with a fair degree of accuracy. The accuracy can be improved if the N availability estimate from aerobic incubation is used with other variables (pH and soil C content) in a multivariate regression to predict relative yield response to fertilisation.

中文翻译：

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模拟南非半成熟松林的土壤氮矿化，以确定营养限制并预测对施肥的潜在反应

关键信息 辐射松 (D Don.) 半成熟林分以及南非松 (Engelm.) 纯种和杂交种中可用氮的估计值（基于表土氮矿化率）显示出强烈的、显着的、在田间试验中与对施肥的生长反应呈负相关。这种廉价的技术可以纳入肥料决策支持系统，以最大限度地减少浪费的肥料施用。背景 南非中轮松林在磷存在的情况下对氮肥补充剂的反应具有高度可变性。目标我们的目标是找到一种筛选工具，用于对施肥有反应的林分。方法 在南非的 14 次松肥试验中确定了相对于对照地块（在 100 kg ha -1 P 存在下施肥 200 kg ha -1 N 后 3 年）的体积生长响应。这些值与每个地点的土壤和其他特性相关，也与使用土壤氮可用性预测器 (SNAP) 模型对 N 可用性和 N 矿化率的估计相关联。结果 对施肥的相对体积增长响应范围为 0.05 至 0.96。标准土壤分析的单一结果没有显示与这种生长反应有很强的正相关或负相关。然而，在基于表土有氧氮矿化率的氮可用性估计值与施肥的相对体积增长响应之间观察到非常显着的负相关。结论 孵化研究得出的氮可用性估计可以帮助我们以相当准确的程度预测对施氮（存在磷）的反应程度。如果在多变量回归中将有氧孵化的 N 可用性估计值与其他变量（pH 值和土壤碳含量）结合使用，以预测对施肥的相对产量响应，则可以提高准确性。