Real-time mapping of dissolved sulfur in soil with high spatial and temporal resolution

Sulfur-limitation impacting crop quality and yield is an increasingly common phenomenon as atmospheric deposition from sulfur dioxide (SO2) release has declined. As a result, the practice of adding sulfur fertilizer has dramatically increased in recent years. Like nitrogen and phosphorus, aligning the amount of applied sulfur fertilizer to crop demand is difficult; however, comprehensive monitoring of sulfur dynamics, especially in situ and over time, remains a technical challenge. Traditional laboratory-based methods for measuring sulfur content in soil involve time-consuming and labor-intensive sampling, transport, and analysis processes. In contrast, we propose real-time, in situ measurements allowing for immediate detection of changes in sulfur levels. This capability is especially important in agriculture, where rapid response to sulfur deficiency can prevent crop yield losses and optimize fertilizer usage.The measurement system proposed here will leverage recent advances in multiplexed soil solute extraction combined with a well-established method to convert total sulfur to SO2 and sensitive infrared detection of SO2 to map total dissolved sulfur in real-time with high spatial and temporal resolution. Microliter volumes of soil water collected with mm-scale spatial resolution will be sent to a reactor oven where the sample will be immediately vaporized and all soluble sulfur will be converted to SO2. The gas sample will then be injected into an infrared spectrometer which quantifies the SO2 concentration, thus providing information about the total sulfur concentration in the soil water sample.The ability to monitor total dissolved soil sulfur in real-time will be a major new tool for researchers studying plant nutrient needs, microbial processes involved in nutrient cycling,and the conditions driving these processes.This real-time tool to track nutrient dynamics in and out of the root zone can guide fertilization strategies by aligning nutrient applications with crop demands, thus enhancing productivity.