The concept of the critical nitrogen (N_crit) dilution curve and the derived NNI is generally accepted and used for many crops to describe the crop N status during vegetative growth. Based on field trials with different N treatments carried out in northern Germany, we identified N_crit curves based on shoot DM, leaf DM and stem DM for winter wheat (2003/04 - 2007/08), winter oilseed rape (OSR, 2003/04 - 2005/06, 2012/13 - 2014/15), and maize (2007 + 2008), and related the derived organ-specific NNI (Nitrogen Nutrition Index) values. For each sampling date, N_crit values were estimated using 'Linear-Plateau' functions, in order to fit a broken function for the shoot and stem fraction consisting of a constant N concentration and a negative power function describing the decrease of the N concentration. For the leaf fractions of wheat and OSR, a linear regression gave the best fit, in maize a negative power function. The relationship between the organ-specific NNI was described by a broken function with two linear branches differing in their slope.

Shoot dry matter (DM) based N_crit curves were comparable to previously published dilution curves. Maize leaf N concentration was clearly lower than that of wheat and OSR. Leaf N_crit of wheat and OSR decreased only slightly during the growth period, but maize N_crit showed a more substantial decrease at low DM. Contrarily, all crops showed similar stem N_crit curves. Comparison of organ-specific N nutrition index (NNI) revealed that at lower NNI_shoot, the increase in NNI_leaf was initially higher, while NNI_stem exhibited a steeper increase at higher NNI_shoot. Our results suggest that plants use primarily the stem compared to the leaves as temporary N storage at high N availability; however, the effect in wheat was less pronounced leading to the question of the capacity of N translocation for an adequate grain protein concentration.

临界氮 (N _crit ) 稀释曲线的概念和导出的 NNI 被普遍接受并用于许多作物来描述营养生长期间作物的氮状态。根据在德国北部进行不同的氮处理的田间试验，我们发现ñ_暴击根据拍摄DM，DM叶和茎冬小麦DM（2003/04 - 2007/08）曲线，冬油菜（OSR，2003 / 04 - 2005/06、2012/13 - 2014/15) 和玉米 (2007 + 2008)，以及相关的衍生器官特异性 NNI（氮营养指数）值。对于每个采样日期，N _crit使用“线性平台”函数估计值，以便拟合由恒定 N 浓度和描述 N 浓度降低的负幂函数组成的枝条和茎部分的破碎函数。对于小麦和 OSR 的叶部分，线性回归给出了最佳拟合，在玉米中为负幂函数。器官特异性 NNI 之间的关系由具有两个斜率不同的线性分支的断函数描述。

基于芽干物质 (DM) 的 N_临界曲线与之前公布的稀释曲线相当。玉米叶片 N 浓度明显低于小麦和 OSR。小麦的叶片 N_临界值和 OSR 在生长期仅略有下降，但玉米 N_临界值在低干物质下下降更为显着。相反，所有作物都显示出相似的茎氮_临界曲线。器官特异性氮营养指数（NNI）的比较表明，在较低的 NNI_枝条处，NNI_叶的增加最初较高，而 NNI_茎在较高的 NNI_枝条处表现出更陡峭的增加. 我们的研究结果表明，与叶相比，植物主要使用茎作为高氮可用性的临时氮储存；然而，在小麦中的影响不那么明显，导致了氮转运能力的问题，以获得足够的谷物蛋白质浓度。