Fertilizer recommendations (FR) to improve yields and increase profitability are based on relationships between crop yields and soil nutrient levels measured via soil extraction methods. Within these FR, critical soil nutrient (CSN) levels are used to distinguish nutrient deficient from non-deficient soils. The variation in CSN levels is large, implying a risk of over- or under-fertilization. Here, we review and assess the factors influencing the derivation of CSN levels in order to increase both their reliability and applicability within FR systems. The evaluated factors included site conditions, i.e., crop type and location as a surrogate for climate and soil properties, and methodological factors, i.e., the experimental approach (field or pot experiments), and statistical methods and cut-off point. Results showed that the range of values used to define the medium soil fertility classes coincided with the range of CSN levels derived from experimental data. We show that harmonizing methodological aspects can substantially reduce the uncertainty in the CSN levels (> 50%), implying a substantial enhancement of the reliability of FR systems. Inclusion of site conditions might further improve the reliability. To enable reduction in CSN levels requires well-documented field experiments and standardization of data collection and analysis. We foresee the potential for generic FR systems that make use of reliable data, more process-based interpretation of nutrient pools and accounting for the interactions among nutrients.

提高产量和增加盈利能力的肥料建议 (FR) 基于作物产量和通过土壤提取方法测量的土壤养分水平之间的关系。在这些 FR 中，临界土壤养分 (CSN) 水平用于区分养分缺乏和非缺乏的土壤。 CSN 水平的变化很大，意味着存在施肥过度或不足的风险。在这里，我们回顾和评估影响 CSN 水平推导的因素，以提高其在 FR 系统中的可靠性和适用性。评估的因素包括场地条件，即作为气候和土壤特性替代的作物类型和位置，以及方法因素，即实验方法（田间或盆栽实验）以及统计方法和截止点。结果表明，用于定义中等土壤肥力等级的数值范围与实验数据得出的 CSN 水平范围一致。我们表明，协调方法方面可以显着降低 CSN 水平的不确定性（> 50%），这意味着 FR 系统的可靠性显着增强。纳入现场条件可能会进一步提高可靠性。为了降低 CSN 水平，需要有详细记录的现场实验以及数据收集和分析的标准化。我们预见通用 FR 系统的潜力，该系统利用可靠的数据、更多基于过程的营养池解释并解释营养物质之间的相互作用。