Hand-Held Optical Sensors for Optimizing Nitrogen Application and Improving Nutrient Use Efficiency

The traditional use of fertilizers as per the recommendations has some limitations as it does not consider the site-specific and timely application. In this practice, less emphasis was given to resource use efficiency which may leads to various problems related to non-judicious use of essential inputs and agricultural sustainability. In terms of fertilizer nitrogen application, there are various approaches available in resent day agriculture. Among them, site-specific nutrient management through variable rate application can be considered as an advanced method for optimization of nitrogen requirement in cereal crops. By using optical sensors like chlorophyll content meter and crop reflectance sensors, nitrogen can be optimized by application at right time in a right amount. These optical sensors work on the greenness of the leaf which is a directly related component of leaf nitrogen content. The threshold value given by these sensors called as chlorophyll Index value or Normalized Difference Vegetative Index (NDVI) can be considered to estimate the nitrogen deficiency or nitrogen sufficiency in plant tissue. The application of these sensors has a greater impact on resource conservation and precise application of nutrients. However, in developing countries like India, the economic viability and limitation of application of these sensors in small land holdings for fertilizer nitrogen management are still not adequately studied. The review article focuses on benefits of use of various hand-held optical sensors for optimizing N application and N use efficiency.