Globally, important nitrogen fertilizer decisions are often made at the early stages of plant development, when plants are not yet sufficiently indicative of their needs. Optimizing nitrogen fertilization of crops requires assessing the available soil mineral nitrogen content (N_min) at the beginning of the season and was assessed exemplarily for wheat and maize. Since 2020 a mandatory soil N_min analysis for each crop on a representative field is required in Germany in zones characterized by increased nitrate concentrations in the groundwater, encompassing approximately 28 % of the arable land. However, soil analysis is time-consuming, costly, and labor-intensive and requires further optimization beyond the current practice.

In this study, wheat fields in 2018 and 2019 and maize fields in 2018 were sampled in a grid pattern in spring, and the soil nitrate-N content was determined in 30 cm layers down to 60 cm soil depth in 11 fields and further down to 90 cm soil depth in two of the fields. For each single and the combined soil depths, all fields could be sampled with a deviation of less than 10 kg nitrate-N ha⁻¹ with only two soil samples. Overall, the reduced field-specific soil sampling strategy proved advantageous compared to crop-specific, regionally representative N_min values offered by the official advisory authorities based on multiple averaged field investigations with an increased sampling intensity of 16 samples per field. Further, the reduced field-specific soil sampling strategy delivered more precise N_min values by 11.2 kg nitrate-N ha⁻¹ for wheat fields and slightly less precise values by 4.8 kg nitrate-N ha⁻¹ for maize fields. The reduced field-specific soil sampling has great potential to reduce analysis and soil sampling costs. Nitrogen fertilization experiments supported the usefulness of the new simplified N_min strategy. Multispectral in-season satellite imagery from Sentinel-2 could not adequately capture the spatial nitrate-N level differences and confirms soil samplings needs early in the season.

Because most farmers base their fertilization strategy on regionally crop-specific aggregated N_min values delivered by the official advisory system, we consider a simplified strategy to be more indicative of the field-specific soil N_min status, which is eased by a markedly reduced sampling frequency and further simplifies the analysis by aggregating the separately analyzed soil depths to only one single depth. Further, currently available simplified on-farm analyses of the soil nitrate content allow for conducting more intensive field-specific soil N_min analysis, thus contributing to improved nitrogen demand management and decreasing adverse environmental effects.

在全球范围内，重要的氮肥决定通常是在植物发育的早期阶段做出的，此时植物尚未充分表明其需求。优化作物的氮肥施肥需要在季节开始时评估可用土壤矿质氮含量 (N _min )，并以小麦和玉米为例进行了评估。自 2020 年以来，德国要求在地下水中硝酸盐浓度增加的地区（约占耕地面积的 28%）对代表性田地的每种作物进行强制性土壤 N _min分析。然而，土壤分析耗时、成本高且劳动密集，需要在当前实践之外进一步优化。

在本研究中，2018 年和 2019 年的麦田和 2018 年的玉米田在春季以网格模式进行采样，并在 11 个田间测定了 30 cm 层至 60 cm 土深的土壤硝态氮含量。其中两个田地的土壤深度为 90 厘米。对于每个单一和组合土壤深度，所有田地都可以采样，偏差小于 10 kg 硝酸盐-N ha ^-1，只有两个土壤样品。总体而言，与特定作物、具有区域代表性的 N _min相比，减少的田间特定土壤采样策略被证明是有利的官方咨询机构根据多次平均实地调查提供的值，每个字段的抽样强度增加了 16 个样本。此外，减少的田间特定土壤采样策略提供了更精确的 N _min值，小麦田的 11.2 kg 硝酸盐-N ha ^-1和玉米田的4.8 kg 硝酸盐-N ha ^{-1 的}精确值略低。减少的田间特定土壤取样具有降低分析和土壤取样成本的巨大潜力。施氮实验支持了新的简化 N _min的有用性战略。来自 Sentinel-2 的多光谱季节性卫星图像无法充分捕捉空间硝酸盐 - N 水平差异，并确认需要在季节早期进行土壤采样。

由于大多数农民的施肥策略基于官方咨询系统提供的区域特定作物总 N _min值，我们认为简化的策略更能反映田间特定土壤 N _min状态，这通过显着减少的采样得到缓解频率并通过将单独分析的土壤深度聚合到一个单一深度来进一步简化分析。此外，目前可用的土壤硝酸盐含量的简化农场分析允许进行更密集的田间特定土壤 N _min分析，从而有助于改善氮需求管理并减少不利的环境影响。