U.S. Mean Annual Precipitation
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We are asking participants to tell us about the methods they use at their research site(s). These data will be used to better understand the range of methods used across investigations, and will help to develop a set of standard methods for suggested use at all sites. This information will also help to perform meta-analyses of methods and results across projects. Please download the query form, complete it and send it to Michael Loik, University of California, Santa Cruz. We recognize that each research project has its own goals, and that not all of the questions asked will be relevant to all projects.

Many thanks for your participation!

I've measured lot's of water potentials and water contents over the years. Soil water potential is of course the best data point to have from a physiological point of view. However, psychrometer-type WP probes yield point measurements. I have seen way too many papers that have psycrometers at 10 cm or 30 cm or whatever, and report that as soil water potential. That data point may have absolutely no relevance to what the plant root system is "seeing". Because of that, I've switched to TDR and neutron probe based soil water content measurements, then try to do the soil work to convert soil theta to WP. That way you get integrated soil water content and WP over soil depth gradients.
    - Stan Smith

I refer to Table 3.1 on page 34 of Pearcy et al. (1989). Although it may be outdated, it is a good general comparison of the advantages and disadvantages of different sensor types. Some sensor types might be easier to log than others. Installation might be easier for some compared to others (e.g. seems most people put their TDR probes in horizontally to avoid thermal effects, which may require more disturbance per plot.) In my recent conversations with Austin McHugh at Campbell, it is apparent that a lot of things come up when starting to design a TDR system. For example, the wires for some of their sensors can only go 80 feet, then have to be multiplexed, requiring multiplexers every so many plots, depending on how far apart your plots are, etc.
   - Michael Loik

At one of our sites we're using an array of new soil matric sensors to get really accurate WP data around individual shrubs. It's expensive and simply cannot be duplicated across a site with lot's of factorial treatments (at least with a finite budget). However, it's the only way we can get biologically realistic soil WP data in heterogeneous soils with heterogeneous root systems. TDR and neutron probes are based soil water content measurements, they can be converted to soil theta to WP, using empirically determined moisture release curves. That way you get integrated soil water content and WP over soil depth gradients.
   - Stan Smith

There is a new type of sensor available now, called EnviroScan. It is produced by Sentek (Australia) and distributed in the USA through Campbell Scientific and Simplot Soilbuilders. The measurement principle is similar to TDR probes, in that it is based on water content effects on electrical capacitance, but they are in many ways simpler to install than TDR probes and may be, because of that, more precise. For one, they can be top-loaded into PVC pipes, and need not be horizontally inserted like TDR probes. They can remain in place for continuous monitoring, or can be moved around between PVC tubes for spot measurements
   - Susan Schwinning

We bought some ECH2O soil moisture sensors with data loggers for the Big Bend Field site. The ECHO probe measures the dielectric constant of the soil in order to determine volumetric water content. It does this by finding the rate of change of voltage applied to the sensor once it is buried in the soil. The probe has low sensitivity to saline and temperature effects in the soil, has low power requirements and high resolution. Up to 5 probes can be connected to the EM5 data logger that is designed for use with the ECHO probes. The probes are about $75 each and the data logger is about $400.
   - David Tissue