Development of a Critical Nitrogen Dilution Curve for Basil ( Ocimum basilicum L.) Under Greenhouse Conditions

Nitrogen (N) is the most limiting nutrient for crops growth and development. The optimal application of N significantly enhances crop metabolic process. On the other hand, overuse of nitrogenous fertilizer leads to excess N accumulation in crop tissues that increases the risk of health-related problems. Therefore, it is mandatory to develop a quantitative approach for monitoring the crop N status during growth period. The main objective of this study was to establish the critical nitrogen dilution curve as an effective method to diagnose nitrogen status of sweet basil ( Ocimum basilicum L.) grown under controlled greenhouse conditions. Two experiments were carried out with seven N application rates in the research greenhouse of University of Tehran, Iran. Values of crop shoot biomass (t ha −1 ) and N concentration (%) were measured in each sampling date to develop the critical nitrogen concentration (N c ) equation. The relationship between N c and shoot dry matter (DM) was described by a power function (N c = 4.80DM -0.38 , R 2 = 0.98). The validation results showed that the developed equation effectively distinguishes N-limiting from non-N-limiting treatments. The N nutrition index (NNI) ranged from 0.52 to 1.18 and 0.53 to 1.26 for the first and second experiment, respectively. It was concluded that the developed N dilution curve could provide useful insight into determination of basil N nutrition status and proper fertilizer management.