For a long time, I have been arguing that we should focus on the micro-environment to understand where plants live, and where they will be going in a future with a changing climate. Studying the micro-environment experienced by plants however creates some interesting challenges. The more detail you want, and the closer you want to get to your study species, the more measurements you need to make. On a spatial scale, that is relatively easy to do: you can just put out a whole lot of sensors in the landscape.
Yet there is an often forgotten part to the microscale that is harder to measure: the temporal variation. You could measure the temperature on a thousand spots in the landscape, yet if you can only do this once (or even a few times), your data is virtually useless.
For temperatures, we have some pretty amazing tools to deal with both spatial and temporal microvariation. We have thermal cameras for the finest spatial resolution, and we can even use them to make stop motion movies to capture temporal variation. And we have (relatively) cheap temperature sensors (like the iButtons I wrote about earlier) that can be left outside for a whole year to satisfyingly cover the spatial scale.
For the measurement of soil moisture, the story is surprisingly entirely different. Detailed scanning, like we would do with a thermal camera, is currently hardly impossible for a reasonable price. Cheap sensors that trustworthy measure the soil moisture over time, without complicated wires and data logging issues, is also still lacking. One of the main issues is that the available water strongly depends on the soil type: water in clay is much harder to extract by a plant than water in a sandy soil, for example. It is thus still a search for solutions.
Yet these solutions are on the way, and scientists are showing their most creative side to tackle this issue: exotic sounding methods like using cosmic-ray neutrons, or through GPS-signals or even temperature measurements are rapidly gaining accuracy. Before I loose all my readers to these foreign words, I will just refer everybody on a search for good methods to this paper from Oschner et al. (2013).
Oschner et al. (2013). State of the Art in Large-Scale Soil Moisture Monitoring. Soil Sci. Soc. Am. J.