Evaluation of crop N status will assist optimal N management of intensive vegetable production. Simple procedures for monitoring crop N status such as petiole sap [NO 3 −–N], leaf N content and soil solution [NO 3 −] were evaluated with indeterminate tomato and muskmelon. Their sensitivity to assess crop N status throughout each crop was evaluated using linear regression analysis against nitrogen nutrition index (NNI) and crop N content. NNI is the ratio between the actual and the critical crop N contents (critical N content is the minimum N content necessary to achieve maximum growth), and is an established indicator of crop N status. Nutrient solutions with four different N concentrations (treatments N1–N4) were applied throughout each crop. Average applied N concentrations were 1, 5, 13 and 22 mmol L−1 in tomato, and 2, 7, 13 and 21 mmol L−1 in muskmelon. Respective rates of N were 23, 147, 421 and 672 kg N ha−1 in tomato, and 28, 124, 245 and 380 kg N ha−1 in muskmelon. For each N treatment in each crop, petiole sap [NO 3 −–N] was relatively constant throughout the crop. During both crops, there were very significant (P < 0.001) linear relationships between both petiole sap [NO 3 −–N] and leaf N content with NNI and with crop N content. In indeterminate tomato, petiole sap [NO 3 −–N] was very strongly linearly related to NNI (R2 = 0.88–0.95, P < 0.001) with very similar slope and intercept values on all dates. Very similar relationships were obtained from published data of processing tomato. A single linear regression (R2 = 0.77, style="italic-in-any-context">P < 0.001) described the relationship between sap [ style="fixed-case">NO 3 −–N] and style="fixed-case">NNI for both indeterminate and processing tomato, each grown under very different conditions. A single sap [ style="fixed-case">NO 3 −–N] sufficiency value of 1050 mg N L−1 was subsequently derived for optimal crop N nutrition (at style="fixed-case">NNI = 1) of tomato grown under different conditions. In muskmelon, petiole sap [ style="fixed-case">NO 3 −–N] was strongly linearly related to style="fixed-case">NNI ( style="fixed-case"> style="italic-in-any-context">R2 = 0.75 – 0.88, style="italic-in-any-context">P < 0.001) with very similar slope and intercept values for much of the crop (44–72 style="fixed-case">DAT, days after transplanting). A single linear relationship between sap [ style="fixed-case">NO3−–N] and style="fixed-case">NNI ( style="fixed-case"> style="italic-in-any-context">R2 = 0.77, style="italic-in-any-context">P < 0.001) was derived for this period, but sap sufficiency values could not be derived for muskmelon as style="fixed-case">NNI values were >1. Relationships between petiole sap [ style="fixed-case">NO3−–N] with crop N content, and leaf N content with both style="fixed-case">NNI and crop N content had variable slopes and intercept values during the indeterminate tomato and the muskmelon crops. Soil solution [ style="fixed-case">NO3−] in the root zone was not a sensitive indicator of crop N status. Of the three systems examined for monitoring crop/soil N status, petiole sap [ style="fixed-case">NO3−–N] is suggested to be the most useful because of its sensitivity to crop N status and because it can be rapidly analysed on the farm.
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机译：评估作物氮素状况将有助于蔬菜精耕细作的最佳氮素管理。用不确定的番茄和番茄评估了监测作物氮状况的简单程序，例如叶柄汁液[NO 3 - –N]，叶氮含量和土壤溶液[NO 3 -]。甜瓜。使用针对氮营养指数（NNI）和作物N含量的线性回归分析，评估了他们评估每种作物N状况的敏感性。 NNI是作物实际N含量与临界N含量之比（临界N含量是实现最大生长所必需的最小N含量），是作物N状况的既定指标。在每种作物上都施用了四种不同氮浓度的营养液（处理N1-N4）。番茄平均施用的氮浓度为1、5、13和22 mmol L -1 ，甜瓜中施用的平均氮浓度为2、7、13和21 mmol L -1 。番茄中的N分别为23、147、421和672 kg N ha -1 ，甜瓜中分别为28、124、245和380 kg N ha -1 。对于每种作物的每种氮素处理，在整个作物中叶柄汁液[NO 3 - –N]相对恒定。在这两种作物中，叶柄汁液[NO 3 - -N]与叶氮含量（与NNI和作物氮含量）之间都存在非常显着的（P <0.001）线性关系。在不确定的番茄中，叶柄液[NO 3 - –N]与NNI呈极强的线性关系（R 2 = 0.88–0.95，P <0.001），斜率非常相似并在所有日期截取值。从加工番茄的公开数据中获得了非常相似的关系。单个线性回归（R 2 = 0.77， style =“ italic-in-any-context”> P <0.001）描述了树液[ style =“不确定和加工番茄的固定情况“>否 3 − –N]和 style =” fixed-case“> NNI 条件。随后得出一个单一的sap [ style =“ fixed-case”>否 3 - –N]充分值1050 mg N L -1 在不同条件下种植的番茄的最佳作物氮素营养（ style =“ fixed-case”> NNI = 1）。在甜瓜中，叶柄汁液[ style =“ fixed-case”> NO 3 - –N]与 style =“ fixed-case”> NNI < / span>（ style =“ fixed-case”> style =“ italic-in-any-context”> R 2 = 0.75 – 0.88， style =“ italic-in-any-context”> P <0.001），对于大部分农作物（44-72 style =“ fixed-case”> DAT < / span>，即移植后的几天）。汁液[ style =“ fixed-case”>否之间的单个线性关系3 − –N]和 style =“ fixed-case”> NNI （ style =“ fixed-case”> style =“斜体在任何上下文中“> R 2 = 0.77，在此期间得出了 style =” italic-in-any-context“> P <0.001），但由于 style =“ fixed-case”> NNI 值> 1，无法得出甜瓜的汁液充足值。叶柄液之间的关系[ style =“ fixed-case”>否3- –N]的作物N含量以及具有 style =“ fixed-case”> NNI 和作物N含量的叶片N含量在不确定期间具有可变的斜率和截距值番茄和甜瓜作物。土壤溶液[ style =“ fixed-case”>否3根区中的-]不是作物N状况的敏感指标。在三个用于监测作物/土壤氮素状况的系统中，叶柄汁液[ style =“ fixed-case”>否3建议使用- –N]，因为它对作物的氮素状况很敏感，并且可以在农场中快速分析。
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