The use of destructive and nondestructive techniques in concrete nitrogen assessment in plants

Nitrogen (N) is the key macronutrient for sustainable growth and higher productivity of crops. Optimized nitrogen-use-efficiency (NUE) enhances productivity and reduces the environmental impacts as well as input cost of production. NUE can be improved by the site-specific application of nitrogen fertilizer. Variable rate nitrogenous fertilizer can be applied after assessing the real-time status of the plant nitrogen. The assessment of the plant nitrogen can be obtained by various destructive and nondestructive techniques. This article aims to provide a thorough overview of the approaches available for determining plant N levels. The destructive techniques (Kjeldahl method and Dumas combustion) are tedious and time-consuming but more accurate. The most adopted nondestructive methods such as the use of Leaf Color Chart (LCC), digital sensors (SPAD meter, CCM-200, GreenSeeker, Crop Circle and Yara N-Sensor, OptRx® Crop Sensor, ISARIA, CropSpec, Multiplex®) and digital imaging-based techniques of plants are rapid in N level estimation. Nondestructive techniques utilize the optical property of leaves to assess the N level of plants. However, digital sensor-based estimation has certain limitations, including chlorophyll saturation, illumination effect, less accuracy and the high initial cost of instruments. Furthermore, more research should be carried out to overcome these limitations and improve their efficiency.