Real-time detection and measurements of nitrogen, phosphorous & potassium from soil samples: a comprehensive review

Purpose

Soil nutrients such as Nitrogen (N), Phosphorus (P), and Potassium (K) play a vital role in plant growth. It is crucial to apply the right amount of nutrients based on crop needs and soil conditions. Excessive amounts of fertilizer (overfertilization) lead to environmental pollution, nutrients runoff, financial losses, and imbalances that may harm plants. On the other hand, under fertilization causes nutrient deficiencies in soil, limiting plant growth and reducing yields.

Material and methods

To measure NPK, three approaches are used: electrical conductivity testing, optical techniques, and electrochemical methods. These measurements are generally performed in a centralized laboratory. The onsite measurement of NPK levels can help farmers to apply variable-rate fertilizer and manage the resources in the most efficient and effective manner. This article enlists various electrical and optical methods for NPK measurements from soil samples. A comprehensive list of nutrient sensing techniques along with their advantages and limitations are also presented. A thorough literature search is conducted to examine various methods developed for NPK measurements. Each method is presented in detail and discussed the mechanisms for measuring NPK from soil.

Results and discussion

The article discusses syntheses, technical analyses, results, and conclusions of various technologies developed for the NPK measurements. There hasn't been much utilization of optical technology for on-site analyses of soil nutrients. Optical diffuse reflectance in the Ultra-Violet Visible and Near-Infrared wavelength ranges has been used as a non-destructive method for quickly determining soil properties for site-specific management. For real-time analysis, electrochemical sensing with ion-selective electrodes or field effect transistors is a promising technique. It offers direct analyte detection in a simple, rapid, and accurate manner. Laser Induced Graphene (LIG) and Ion Selective Material Electrodes (ISME) are more promising methods.

Conclusion

A practical and affordable three-in-one biosensor device for on-farm soil testing would be created in the future to help farmers. Farmers can measure real-time status of NPK from soil samples and apply the optimum amount of NPK fertilizer for getting significant financial benefits. The incorporation of real-time, cost-effective, portable, and easy-to-use sensors and devices can significantly help farmers in onsite NPK measurements. Nevertheless, this technique would require numerous field testing using different crops and soil types. To assist farmers in the future, a three-in-one biosensor device that is practical and economical for on-farm soil testing based on ion-selective material principle could be developed. This will allow farmers to have a handy tool to measure the NPK level of the soil separately. Real-time soil biosensors can be used to enable farmers for detection of NPK nutrient status of soil to choose the appropriate fertilizer application rate.