a compelling need to utilize advanced technologies in the agriculture sector to increase agricultural productivity and reduce food losses to guarantee food security. [2] In this regard, "smart agriculture" or "precision agriculture" has been attracting increasing attention due to its capability for using less to grow more compared to traditional agricultural practices. In addition, it improves the quality of the work environment and social aspects of farming, ranching, and other relevant professions. [4] Smart agriculture comprises a set of technologies that combines sensors, information systems, enhanced machinery, and informed management to optimize production by accounting for variabilities and uncertainties within sustainable agricultural systems. [3][4][5] Among the set of technologies, advanced sensing systems that monitor soil health and conditions and crop developments are of paramount importance because they collect and evaluate critical data for decision making and management, especially when crop growth conditions vary considerably over space and time. Spatial variation may result from soil properties, diseases, weeds, pests, and previous land management. In particular, some soil properties (e.g., moisture, pH, nutrients) and plant diseases may form long-term spatial patterns. Temporal variability arises from weather patterns and management practices. In summary, the soil properties relevant to crop growth include a range of soil conditions including soil gas, moisture, temperature, nutrients, pH, and pollutants in the soil (Figure 1). [6,7] Monitoring the soil conditions will provide key information not only to improve resource utilization to maximize farming outputs and minimize environmental side effects but also to build site-specific databases of relationships between soil conditions and plant growth for intelligent and sustainable agriculture systems. Traditionally, soil properties are measured by soil sampling and offsite laboratory analysis or by on-site measurement to provide an extensive knowledge of soil information. [8] Seasonally varying crop growth conditions, such as water stress, lack of nutrients, diseases, weeds, and insects, are evaluated by visual inspection and laboratory analysis of plant tissues. The relatively periodically coarse sampling/measurement rate of these conventional strategies may not be sufficient to reveal variation at the appropriate spatial and temporal resolution. Novel technologies for collecting soil information with sufficient spatiotemporal resolutions are in demand to build efficient smart or precision agriculture systems. With the Soil sensors and plant wearables play a critical role in smart and precision agriculture via monitoring real-time physical and chemical signals in the soil, such as temperature, moisture, pH, and pollutants and providing key information to optimize crop growth circumstances, fight against biotic and abiotic stresses, and enhance crop yields. Herein, the recent advances of the important soil sensors in agricultural applications, in...