Review—The “Real-Time” Revolution for In situ Soil Nutrient Sensing

Globally, farmers are seeking advanced precision technology to help transform their practices into a more sustainable and productive agri-tech process. Accurate and real-time soil data has become one of the most valuable resources among farmers. Real-time soil sensor data can be exploited in manners that increase farm production and profit, maintain and increase product quality, promote food security, and ensure environmental protection. Researchers have already attempted to develop real-time in situ soil nutrient sensors based on optical and electrochemical techniques. Of these sensor systems, only a few of them are commercially available for monitoring. In this review, we present both available sensors and sensors under research in agriculture. Then briefly discuss both advantages and challenges to overcome in order to produce systems that deliver real-time quality soil information. Optical and electrochemical sensors are becoming less expensive to manufacture and can provide results that are comparable to laboratory soil analysis. Based on the literature presented here, there still exists a need to understand the effects of soil heterogeneity on the analytical performance of both electrochemical and optical systems when used in situ. By doing so, these sensors can be fully adopted as suitable commercial platforms. Overall, these sensors harness the potential to revolutionize decision management systems in agriculture as internet of things (IoT) soil nutrient sensors.