Monitoring nitrogen status of vegetable crops and soils for optimal nitrogen management

Optimal crop nitrogen (N) management is required to minimize N losses to the environment in vegetable crop production. There are several approaches based on soil and plant monitoring that can assist to improve N management. These include soil monitoring, destructive (tissue N analysis, petiole sap nitrate (NO3−) analysis) and non-destructive (optical sensors) crop-based methods, and portable rapid analysis systems. The most promising optical sensors for guiding N management in vegetable production, considering performance and practicality, are chlorophyll meters and canopy reflectance sensors. The crop-based methods are generally sensitive indicators of crop N status in a wide range of vegetable crops. However, they tend to have reduced sensitivity when N supply is excessive. A notable feature of soil monitoring methods (e.g. the Dutch 1:2 soil-water extract method, soil solution monitoring) is that they can detect excess N supply. The combination of crop and soil monitoring will provide vegetable growers with tools to detect crop N deficiency and excess N supply. The selection of the best monitoring approach for a given farm will depend on factors such as crop and farm characteristics, the farmer's technical level, technical support, and economic considerations. Soil and crop monitoring approaches could form part of improved management packages that include Decision Support Systems (DSS), to determine crop N and/or irrigation requirements, and monitoring of soil water status. The use of such packages, when combined with fertigation and drip irrigation, is key for very efficient N management of vegetable crops with reduced N loss to the environment.