Abstract 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, P < 0.001) described the relationship between sap [NO 3 −–N] and NNI for both indeterminate and processing tomato, each grown under very different conditions. A single sap [NO 3 −–N] sufficiency value of 1050 mg N L−1 was subsequently derived for optimal crop N nutrition (at NNI = 1) of tomato grown under different conditions. In muskmelon, petiole sap [NO 3 −–N] was strongly linearly related to NNI (R2 = 0.75 – 0.88, P < 0.001) with very similar slope and intercept values for much of the crop (44–72 DAT, days after transplanting). A single linear relationship between sap [NO 3 −–N] and NNI (R2 = 0.77, P < 0.001) was derived for this period, but sap sufficiency values could not be derived for muskmelon as NNI values were >1. Relationships between petiole sap [NO 3 −–N] with crop N content, and leaf N content with both NNI and crop N content had variable slopes and intercept values during the indeterminate tomato and the muskmelon crops. Soil solution [NO 3 −] 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 [NO 3 −–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.

中文翻译：

---

使用植物和土壤监测技术评估灌溉施肥蔬菜作物的氮状况

摘要 作物氮状况评估将有助于集约化蔬菜生产的最佳氮管理。监测作物氮状态的简单程序，如叶柄汁液 [NO 3 -–N]、叶氮含量和土壤溶液 [NO 3 -] 用不确定的番茄和甜瓜进行评估。使用针对氮营养指数 (NNI) 和作物 N 含量的线性回归分析来评估它们对评估每种作物的作物 N 状况的敏感性。NNI 是作物实际氮含量与临界氮含量之间的比率（临界氮含量是实现最大生长所需的最小氮含量），是作物氮状况的既定指标。四种不同氮浓度的营养液（N1-N4 处理）应用于每一种作物。番茄中平均施氮浓度为 1、5、13 和 22 mmol L-1，而 2、7、甜瓜中的 13 和 21 mmol L-1。番茄中的 N 分别为 23、147、421 和 672 kg N ha-1，甜瓜中的 N 分别为 28、124、245 和 380 kg N ha-1。对于每种作物的每次施氮处理，叶柄汁液 [NO 3 -–N] 在整个作物中相对恒定。在这两种作物中，叶柄汁液 [NO 3 -–N] 和叶片 N 含量与 NNI 和作物 N 含量之间存在非常显着的（P < 0.001）线性关系。在不确定的番茄中，叶柄汁液 [NO 3 -–N] 与 NNI（R2 = 0.88–0.95，P < 0.001）呈非常强的线性相关，所有日期的斜率和截距值都非常相似。从已发表的加工番茄数据中获得了非常相似的关系。单一线性回归 (R2 = 0.77, P < 0.001) 描述了不确定和加工番茄的 sap [NO 3 −–N] 和 NNI 之间的关系，每个都在非常不同的条件下生长。随后推导出 1050 mg N L-1 的单一汁液 [NO 3 -–N] 充足值，用于在不同条件下生长的番茄的最佳作物 N 营养（NNI = 1）。在甜瓜中，叶柄汁液 [NO 3 −–N] 与 NNI 呈强烈线性相关（R2 = 0.75 – 0.88，P < 0.001），大部分作物（44–72 DAT，移栽后天数）具有非常相似的斜率和截距值）。在此期间，树液 [NO 3 -–N] 和 NNI 之间存在单一线性关系（R2 = 0.77，P < 0.001），但由于 NNI 值 >1，因此无法推导出甜瓜的树液充足率值。在不确定的番茄和甜瓜作物期间，叶柄汁液 [NO 3 -–N] 与作物 N 含量和叶片 N 含量与 NNI 和作物 N 含量之间的关系具有可变的斜率和截距值。根区的土壤溶液 [NO 3 -] 不是作物氮状况的敏感指标。在监测作物/土壤氮状况的三个系统中，叶柄汁液 [NO 3 −–N] 被认为是最有用的，因为它对作物氮状况很敏感，并且可以在农场快速分析。