The authors acknowledge financial support from NOAA-NIDIS, the National Coordinated Soil Moisture Monitoring Network (NCSMMN), and the USGS Next Generation Water Observing Systems (NGWOS) program. We thank members of the NCSMMN Executive Committee, including B. Baker, J. Bolten, S. Connelly, P. Goble, T. Ochsner, S. Quiring, M. Svoboda, and M. Woloszyn for input on this protocol. We thank M. Weaver (USGS) for their initial review of the draft protocol.

Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. This article is a U.S. Government work and is in the public domain in the USA. USDA is an equal opportunity employer and provider.

Soil moisture state is a result of many different environmental factors, including precipitation, vegetation, solar irradiance, and relative humidity, along with soil hydraulic and physical properties. These interact over space and time at differing spatial and temporal scales. To model and forecast the water, energy, and carbon cycles, it is necessary to understand the SWC state. One of the most common types of automated measurement technologies is an electromagnetic SWC sensor with tines meant to be inserted in situ into undisturbed soil. This protocol is designed to provide guidance for the process of installing these common types of buriable sensors. Accuracy, performance, and cost are typically proportional to the operating frequency of the sensors; lower-frequency sensors cost less but are more confounded by soil and environmental factors45. Soil- or site-specific calibration can improve the accuracy of lower-frequency sensors. The measurement method also affects sensor performance due to the underlying physics of the electromagnetic field (EMF).
Two major electromagnetic physical laws govern electromagnetic sensing. One is Gauss&#39; law, which describes how the sensor&#39;s propagated EMF is dependent on both the &#949; and BEC of the medium. Permittivity increases with SWC, however, so too does the BEC. Therefore, sensors dependent on Gauss&#39; law are affected by SWC, BEC, and the temperature effect on BEC, as well as any interference from salinity. Capacitance sensing methods obey Gauss&#39; law and thus are more prone to these effects46. Additionally, Gauss&#39; law describes the dependence of the capacitance on a geometric factor, which changes with the shape of the EMF in the soil. Research has demonstrated that the EMF shape changes with soil structure and the small-scale spatial variability of water content around the sensor tines. Small-scale spatial variability of water content and soil structure is large in most soils, resulting in geometric factor changes and consequent capacitance changes that have little to do with bulk mean soil water content changes. These factors decrease capacitance sensor accuracy and increase data variability46,47,48. The impedance and transmission line oscillation methods also depend on Gauss&#39; law, while time domain reflectometry and time domain transmissometry methods depend on Maxwell&#39;s equations, which do not include a geometric factor and are not dependent on BEC. While no sensor is problem-free, the time domain methods tend to be appreciably more accurate and less biased than either capacitance- or impedance-based methods.
There are several critical steps in the procedure. For a sparse network, proper site selection and sensor location are needed to have the most appropriate spatial representation of SWC. Site selection may be more influenced by external factors, such as land access, or other atmospheric monitoring requirements where soil moisture is the ancillary measurement. Meso-scale meteorological sites are located on broad and open, well-manicured grassy surfaces to minimize any microscale influences. Such locations may be less ideal for SWC monitoring. If applicable, wireless sensor technologies should be considered49,50,51,52,53 to allow SWC monitoring to occur away from the existing environmental monitoring station and in representative soil. Working around active farm operations and irrigation equipment is challenging. Most networks (e.g., SCAN and USDA-ARS) stay on the fringes of fields to avoid tillage activities such as plows or harvesters that can cut the cables and unearth sensors. Any in situ sensor and cable needs to be sufficiently buried and have a low-enough surface profile to avoid inferring with on-farm operations. Wireless systems53 and removable borehole sensors47 may be more appropriate. Groundwater conservation using large-scale, soil moisture-based irrigation54 is a growing field for SWC sensors; this protocol pertains to spatially representative long-term SWC data in undisturbed soils.
Some soils are more difficult to measure than others. In rocky, gravelly, or very dry soils, it may be impossible to insert the tines without any damage. One option is to excavate the soil pit and lay the sensors in place while backfilling, trying to compact to the original BD. Rocky soils tend to have little structure, which will likely heal after several wetting and drying cycles; however, such disturbance may never be truly representative of the soil hydrology of the site. Alternatively, if sensors are installed in the bottom of auger holes, the soil removed can be sieved to remove stones and repacked in the hole just deeply enough to accommodate the sensor tines. The sensor can then be installed vertically, and the auger hole refilled with the remaining non-sieved soil, with frequent compaction as soil is added.
Roots in forest soil pose similar challenges to probe insertion, however roots can be cut in some situations. Forest soils often have organic (O) horizons on top of the mineral soil, which can have very low BD and high specific surface area, with large amounts of bound water resulting in very nonlinear sensor responses at higher SWCs55. Furthermore, the practitioner sets the zero-datum as either the top of the O-horizon or the mineral soil-noting which in the metadata. Clay-rich soils and expansive clays with high shrink/swell potential can be extremely conductive to electromagnetic signals when wet and may crack when dry. Such soils may need additional corrections to get reasonable SWC from the raw measurements56,57. In shallow soils, bedrock or a restrictive soil horizon (e.g., caliche or hardpan) may be encountered before reaching the ideal maximum depth. It may be necessary to change location or simply not install the deeper sensor(s). Excessively dry or wet soils can be challenging, and it is also preferable to choose installation dates outside of seasonal extremes. Dry soil can be very strong, and it may prove impossible to insert a sensor without damage. If necessary, preaugered holes can be filled with water to soften the pit face, although it may take some time before the soils return to a natural state. Wet soils can be too weak to support pit faces or the trench can fill with water. It is also easier to over-compact a wet soil.
The sensor output should include permittivity, not just SWC, so that corrections or soil-specific calibrations can be made later. Higher-frequency sensors are more appropriate in high BEC soils, while shorter tines may be easier to install in more compact soils. Perhaps the most critical step, however, is soil contact; poor contact degrades the signal from any electromagnetic sensor. Finally, backfilling the excavation sounds trivial, but it is key to minimizing preferential flow into the area of the sensors, keeping cables protected, and discouraging animals from disturbing the area. A soil- or site-specific calibration can improve sensor accuracy but requires more detail than is possible in this protocol. Field soils adjusted or repacked to varying SWC levels are ideal to check the linearity of response and can serve as a site-specific calibration for some sensor types21. Dielectric liquids can also be effective media to check sensor response58. Temperature-controlled water baths can be used to improve soil temperature calibrations59. This protocol is the first step toward the establishment of a standard operating procedure for in situ SWC sensor installation, as there is no existing method, nor any accepted method of calibration for SWC sensors60,61.
While SWC monitoring has been the focus of this protocol, the method has limitations, and SWC alone cannot give a complete picture of soil water status. Many ecosystem processes are also regulated by soil water potential, which is less commonly measured in situ62. Soil water potential, recently reviewed by S. Luo, N. Lu, C. Zhang, and W. Likos 63, is the energy state of water; such sensors may be less affected by soil properties and provide quality control for SWC sensors64. Furthermore, the bulk field SWC includes gravels, rocks, roots, and void space (e.g., preferential flow paths). In situ SWC sensors are generally repositioned around rocks and roots, and the limited measurement volume, concentrated around the tines, may miss discrete yet important aspects of the bulk field SWC.
This protocol will hopefully lead to a more harmonized and uniform SWC data for a wide range of applications, including drought monitoring, water supply forecasting, watershed management, agricultural management, and crop planning. The advent of remote sensing platforms4 has greatly enhanced the ability to estimate SWC globally, but these products need ground validation, which is still only reasonably collected by in situ networks65. Computer advancements have allowed hyper-resolution SWC modeling66 to be developed, producing high-resolution and sub-daily SWC status, but these products also need&#160;in situ estimates of SWC to provide some basis for calculating uncertainty. Often, the first question asked when a new product is introduced is &#34;what is the uncertainty?&#34; For SWC products, the primary comparison for validation is in situ network data67.
There have been recent network expansions associated with the National Coordinated Soil Moisture Monitoring Network (NCSMMN), including the U.S. Army Corps of Engineers Upper Missouri River Basin soil moisture project and the NOAA-supported Southeast U.S. network buildup, all designed to improve water hazard prediction, monitoring, and provide resource management decision support. Certainty and accuracy of SWC estimates for such applications can only be accomplished with thorough protocols and procedures to provide confidence in data integrity. The NCSMMN is a federally led, multi-institution effort that aims to provide assistance, guidance, and support by building a community of practice around soil moisture measurement, interpretation, and application-a &#34;network of people&#34; that links data providers, researchers, and the public68. This protocol is a product of NCSMMN efforts. A data quality control workflow is forthcoming.

Soil moisture was recently recognized as an Essential Climate Variable in the Global Observing Climate System1. Soil moisture, or quantitatively volumetric soil water content (SWC), plays a major role in partitioning the flux of incoming radiation into latent and sensible heat between the earth&#39;s surface and the atmosphere, and partitioning precipitation between runoff and infiltration2. However, the spatiotemporal variability of soil moisture at the point, field, and watershed scales complicates our ability to measure SWC at the appropriate scale needed to meet research or management goals3. New methods to quantify SWC, including ground-based networks of in situ sensors, proximal detectors, and remote sensing, provide unique opportunities to map the variation of SWC at an unprecedented resolution4. In situ SWC sensors provide the most temporally continuous and depth-specific data records, but are also subject to small sensing volumes and local-scale variability inherent in soil properties, topography, and vegetation cover5.
Furthermore, there is a lack of standards or widely accepted methods for the installation, calibration, validation, maintenance, and quality control of in situ SWC sensors. Soil moisture is inherently a challenging parameter to measure and may be the most difficult variable to quality-assure6. While general protocols for SWC data collection have been produced by the International Atomic Energy Agency7, the Committee on Earth Observation Satellites8, federal agency reports9, and the American Association of State Climatologists10, there is limited specific guidance on the installation, maintenance, quality control, and verification of SWC data from buried in situ probes. This has made the adoption of such technologies challenging for operational monitoring networks, such as state Mesonets, to add SWC measurements. Similarly, it is also challenging for operational hydrologists, for example, at river forecast centers, to incorporate these data into their workflow. The objective of this videography and accompanying paper is to provide such guidance and document a cohesive installation protocol for buried in situ SWC probes.
Selecting a location for in situ soil moisture monitoring 
The soils within any area of interest (AOI) form through a unique and coupled feedback over time between the topography, ecology, geology, and climate11,12. The variability of SWC across landscapes makes site selection a critical aspect to any soil moisture study. For some research goals, a site may be chosen to represent a particular feature or microsite on the landscape or ecosystem. For the purposes of monitoring networks, the site should be spatially representative of a larger landscape component. The goal is to find a location that provides the best spatial representation of the AOI. In the field, more pragmatic considerations must be reached, such as the requirements of other meteorological instrumentation, accessibility, or permittance. However, the dominant soil map unit within the AOI is usually a good spatial representation of the environmental conditions of a larger area13. The dominant soil map unit can be determined using the Web Soil Survey (https://websoilsurvey.sc.egov.usda.gov/); this soil map unit should also be verified with a shallow pit or test hole.
A typical monitoring station can occupy 5-50 m2, depending on the sensor needs and number of ancillary measurements. Figure 1 depicts a typical monitoring station with a 3 m tower that holds an anemometer for wind speed and direction, an air temperature and relative humidity sensor, a pyranometer for solar radiation, and a National Electrical Manufacturers Association (NEMA) weather-resistant and watertight enclosure (NEMA rating 4). The NEMA enclosure houses the data control platform (DCP), cellular modem, solar panel charge regulator, battery, and other related hardware (see Table of Materials; System components). The tower also provides a platform for the communication antenna, solar panel, and lightning rod. A liquid precipitation (PPT) gage is also typically included, which should be placed away from the tower and at the lowest elevation possible to reduce wind effects on PPT capture. The SWC sensors should be installed a sufficient distance away (3-4 m) and upslope so that there is no potential interference from the tower on either rainfall or overland flow. Any related cables should be buried in conduit at least 5 cm below the surface.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/64498/64498fig01.jpg" /> 
Figure 1: A typical monitoring station. The USDA SCAN collects hourly information on soil water content and temperature at standard depths (5, 10, 20, 50, and 100 cm), air temperature, relative humidity, solar radiation, wind speed and direction, precipitation, and barometric pressure. There are over 200 SCAN sites across the USA. Abbreviations: SCAN = Soil Climate Analysis Network; NEMA = National Electrical Manufacturers&#39; Association. <a href="https://www.jove.com/files/ftp_upload/64498/64498fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Measurement depth, orientation, and number of sensors 
In situ SWC sensors are typically installed horizontally to represent specific depths in the soil (Figure 2). Federally funded, national networks such as the Soil Climate Network (SCAN)14, Snow Telemetry Network (SNOTEL)15, and U.S. Climate Reference Network (USCRN)16 measure SWC at 5, 10, 20, 50, and 100 cm. These depths were reached by consensus during SCAN development for a variety of reasons. The 5 cm depth corresponds to remote sensing capabilities17; 10 and 20 cm depths are historical measurements for soil temperature18; 50 and 100 cm depths complete root zone soil water storage.
Probes can be oriented vertically, horizontally, or inclined/angled (Figure 3). Horizontal installation is most common to achieve a uniform soil temperature measurement at a discrete depth. While the sensor may be centered at a discrete depth, SWC measurement is a volume around the tines (i.e., electrodes), which can vary with moisture levels, measurement frequency, and the geometry of the installation (horizontal, vertical, or angled). For horizontal installation, the sensing volume integrates moisture above and below the depth, and 95% of the sensing volume is typically within 3 cm of the tines19. Vertical or angled installations integrate SWC along the tines, so vertical installation can represent the storage along the entire length of the sensor depths20. Some sensors do not evenly measure along their tines. For example, transmission line oscillators are more sensitive to moisture near the probe head where the electromagnetic pulses are generated21. Vertical installations are more suitable for deeper probes where temperature and moisture gradients tend to be reduced.
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/64498/64498fig02.jpg" /> 
Figure 2: Installation of in situ SWC sensors. Horizontal sensor placement at chosen depths using (A,B) a zero-depth reference jig and (C) a zero-depth board or (D) a zero-depth shovel handle for reference. <a href="https://www.jove.com/files/ftp_upload/64498/64498fig02large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/64498/64498fig03.jpg" /> 
Figure 3: Orientation of probes vertically, horizontally, or at an inclination. (A) Slanted and vertical insertion and (B) horizontal-vertical insertion and horizontal-horizontal insertion center depth of a three-tined SWC sensor. Abbreviation: SWC = soil water content. <a href="https://www.jove.com/files/ftp_upload/64498/64498fig03large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Installation to depths less than 50 cm is relatively intuitive, while deeper sensors take slightly more effort. Root zone SWC or profile soil water storage typically requires measurements to 1 or 2 m. As illustrated in this protocol, 0-50 cm installations are completed in an excavated pit or auger-hole with probes installed horizontally into the undisturbed soil, minimizing the surface disturbance. For deeper sensors (e.g., 100 cm), both SCAN and USCRN install the sensor vertically in separate, hand-augered holes using an extension pole (Figure 4).
Given the heterogeneity of SWC, particularly near the surface, and the small measurement volumes of sensors, triplicate measurements allow for a better statistical representation of SWC. However, one profile of in situ sensors is typical for most networks (e.g., SCAN and SNOTEL). The USCRN uses three profiles spaced 3-4 m apart to make triplicate measurements at each depth16. Furthermore, redundancy in measurement adds resiliency and continuity to the station record if financial resources are available.
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/64498/64498fig04.jpg" /> 
Figure 4: Installation of sensors. (A) Shallow sensors are typically installed horizontally into the side wall of an excavated soil pit. For deeper sensors, (B) a hand auger is used to dig a hole to depth using a zero-depth reference (e.g., wood spanning the trench) and the sensors are pushed vertically into the bottom of holes using (C) a section of PVC pipe modified to secure the sensor and cable during installation or (D) an installation tool. Soil layers are noted as topsoil (A horizon) and subsoil horizons with translocated clays (Bt) and carbonate accumulation (Bk). <a href="https://www.jove.com/files/ftp_upload/64498/64498fig04large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
In situ SWC sensor type 
Commercially available sensors infer SWC from the measured response to an electromagnetic signal propagated along tines&#160;in direct contact with the soil22. Buried sensors fall into five classes depending on the type of electromagnetic signal propagated and the method of measuring the response: capacitance, impedance, time-domain reflectometry, time-domain transmissometry, and transmission line oscillation (Supplemental&#160;Table S1, with links to each manufacturer&#39;s information). These technologies tend to group by operating frequency and manufacturer. Longer tines integrate a larger volume of soil; however, they can be more difficult to insert and are more subject to signal loss in soils with clay and higher bulk electrical conductivity (BEC). Manufacturers report SWC measurement errors of 0.02-0.03 m3m&#8722;3, while users typically find these to be significantly larger23. Proper calibration and standardization of electromagnetic sensors improves performance22; however, these soil-specific calibrations are beyond the scope of this protocol, which focuses on installation.
Sensor selection should consider the desired output, measurement method, operating frequency, and compatibility with other measurements. Prior to 2010, most SWC sensors were analog and&#160; required the DCP to make measurements of differential voltages, resistances or pulse counts, which required more expensive components and individual channels (or multiplexers) for each sensor. Now, serial data interface at 1,200 baud (SDI-12) communication protocols (http://www.sdi-12.org/) allow smart sensors to implement internal measurement algorithms and then transmit digital data along a single communication cable. Each sensor can be wired together in sequence (i.e., a daisy chain) using a common wire connected by lever nut or terminal block connectors (Figure 5) with each sensor having a unique SDI-12 address (0-9, a-z, and A-Z).&#160;The common communication wire of SDI-12 sensors forms a single circuit along with a power and ground wire. Multiplexers or any measurements at the DCP are not required; instead, the DCP simply sends and receives digital commands and lines of text. Many SDI-12 SWC sensors also include soil temperature, relative permittivity (&#949;), and BEC measurements. Such measurements are useful for sensor diagnostics and soil-specific calibration. At this point, the user has selected a site, determined the sensor type, number, and depths, and obtained all the necessary hardware and field tools (Table of Materials). Thus, they can proceed to the installation protocol.
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/64498/64498fig05.jpg" /> 
Figure 5: Wire splice connectors and terminal blocks used to join common power, ground, and communication wires to a single input on the data collection platform. <a href="https://www.jove.com/files/ftp_upload/64498/64498fig05large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>System components, essential</td>
			<td></td>
			<td></td>
			<td>This system is the typcial micro-station used in the TxSON soil moisture network. The TxSON meteorlogical station is listed under optional components. https://acsess.onlinelibrary.wiley.com/doi/full/10.2136/vzj2019.04.0034&#160;</td>
		</tr>
		<tr>
			<td>Battery, sealed rechargable 12 V 12 AH&#160;</td>
			<td>Campbell Scientific&#160;</td>
			<td>BP12</td>
			<td>7 amp-hour (AH) minimum</td>
		</tr>
		<tr>
			<td>Charging regulator</td>
			<td>Campbell Scientific&#160;</td>
			<td>CH200</td>
			<td>Charge regulator, needed for any unregulated solar panel</td>
		</tr>
		<tr>
			<td>Conduit, schedule 40 PVC, 1 to 2&#34; diameter&#160;&#160;</td>
			<td>Any home supply store</td>
			<td></td>
			<td>Diameter sized appropriate to number of sensors and cable thickness. Length dependent on height of enclosure</td>
		</tr>
		<tr>
			<td>Data aquistion software</td>
			<td>Campbell Scientific&#160;</td>
			<td>PC400</td>
			<td>Free versions with limited programability, for more basic applications, manual downloads and simple sensor configurations</td>
		</tr>
		<tr>
			<td>Data control platform</td>
			<td>Campbell Scientific&#160;</td>
			<td>CR300</td>
			<td>Any SDI-12 compatible DCP is sufficint. Many also have integrated cellular modems available&#160;</td>
		</tr>
		<tr>
			<td>Enclosure (NEMA), 10 x 12 inch, -DC 2 conduits for cables, -MM tripod mast mount</td>
			<td>Campbell Scientific&#160;</td>
			<td>ENC10/12-DC-MM</td>
			<td>Two bottom conduits are required for above and below ground instruments</td>
		</tr>
		<tr>
			<td>Mounting pole (47 inch) with pedestal legs</td>
			<td>Campbell Scientific&#160;</td>
			<td>CM305-PL</td>
			<td>Smaller footprint, not tall enough for weather sensors</td>
		</tr>
		<tr>
			<td>Rain Gage with 8 in. Orifice, 20 ft of cable</td>
			<td>Campbell Scientific&#160;</td>
			<td>TE525WS-L20-PT</td>
			<td>Recommend installing rain gage on a separate vertical pole some distance from the instrument stand</td>
		</tr>
		<tr>
			<td>Sensors, 12 cm water content reflectometer, 17ft cable, -VS SDI-12 address varies</td>
			<td>Campbell Scientific&#160;</td>
			<td>CS655-17-PT-VS</td>
			<td>See Supplement Table 1 for more options&#160;</td>
		</tr>
		<tr>
			<td>Solar panel, 20 W</td>
			<td>Campbell Scientific&#160;</td>
			<td>SP20</td>
			<td>Use higher wattage panels for northern sites and lower for southern sites with higher exposre</td>
		</tr>
		<tr>
			<td>System components, optional</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Cellular Antenna, 2 dB multiband omnidirectional&#160;</td>
			<td>Campbell Scientific&#160;</td>
			<td>32262</td>
			<td>Directional antennas can improve signal, if the tower location is known.&#160;</td>
		</tr>
		<tr>
			<td>Cellular modem for Verizon/ATT</td>
			<td>Campbell Scientific&#160;</td>
			<td>CELL210/205</td>
			<td>Provider is site-dependent</td>
		</tr>
		<tr>
			<td>Crossarm mount, 4 feet</td>
			<td>Campbell Scientific&#160;</td>
			<td>CM204</td>
			<td>Ideal for mounting 2 m sensors&#160;</td>
		</tr>
		<tr>
			<td>Data aquistion software, advanced</td>
			<td>Campbell Scientific&#160;</td>
			<td>Loggernet</td>
			<td>More advanced commercial sofware that includes remote communications options and advanced programming</td>
		</tr>
		<tr>
			<td>DIN Rail Perforated Steel</td>
			<td>Phoenix Contact</td>
			<td>1207639</td>
			<td>Used to mount terminal blocks inside enclosure</td>
		</tr>
		<tr>
			<td>Galvanized steel water pipe, 1.5 or 2 inch diameter, 10 ft in length</td>
			<td>Any home supply store</td>
			<td></td>
			<td>The most economical option for an instrument mast. Can be cut to length. Replaces the 47 inch mounting pole with legs</td>
		</tr>
		<tr>
			<td>Instrument tripod, 10 foot stainless-Steel with grounding kit</td>
			<td>Campbell Scientific&#160;</td>
			<td>CM110</td>
			<td>Taller instrument stand for 2 m meteorologic sensors</td>
		</tr>
		<tr>
			<td>Lever nut connectors, five ports (Figure 5)</td>
			<td>Digi-Key</td>
			<td>222-415/VE00/1000</td>
			<td>Connect one SDI-12 wire to 4 sensor wires. Alternative to DIN rail.</td>
		</tr>
		<tr>
			<td>Null modem cable&#160;</td>
			<td>Campbell Scientific&#160;</td>
			<td>18663</td>
			<td>Inteface cable between DCP with modem. Not required for integrated cellular modems</td>
		</tr>
		<tr>
			<td>Plug-in bridge - FBS 3-5</td>
			<td>Phoenix Contact</td>
			<td>3030174</td>
			<td>Used to connect the curcuit of multiple terminal blocks. Available at mouser.com</td>
		</tr>
		<tr>
			<td>Secure Set Foam, 10 Post Kit (2 gallon)</td>
			<td>Any home supply store</td>
			<td></td>
			<td>Altnerative to concrete when using a steel pipe mast or for precipation gage pole. Two part foam mixture</td>
		</tr>
		<tr>
			<td>Sensor, air temperature and relative humidity, 10 ft cable&#160;</td>
			<td>Campbell Scientific&#160;</td>
			<td>HygroVUE10-10-PT</td>
			<td>Lower accuracy and pression option. Replacable chips are the fastest means to meet annual calibration cycles.&#160;</td>
		</tr>
		<tr>
			<td>Sensor, solar radiation pyranometer, digital thermopile&#160;</td>
			<td>Campbell Scientific&#160;</td>
			<td>CS320</td>
			<td>Most inexpensive, ISO class C (second class). Better options are available but much more expensive</td>
		</tr>
		<tr>
			<td>Sensor, wind speed anemometer, 10 ft cable</td>
			<td>Met One</td>
			<td>014A-10</td>
			<td>More expensive options include wind direction, or sonic sensors with no moving parts</td>
		</tr>
		<tr>
			<td>Solar shield for air temperature and relative humidity sensor</td>
			<td>Campbell Scientific&#160;</td>
			<td>RAD10E</td>
			<td>All air temperature sensors require sheilded from the sun</td>
		</tr>
		<tr>
			<td>Terminal blocks (Figure 5), feed-through&#160;</td>
			<td>Phoenix Contact</td>
			<td>3064085</td>
			<td>The most secure method to connect multiple SDI-12 sensor wires. Available at mouser.com</td>
		</tr>
		<tr>
			<td>Field tools, essential</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Freezer bags: quart and gallon sized</td>
			<td>Any grocery store</td>
			<td></td>
			<td>Storage for soil samples collected for characterization</td>
		</tr>
		<tr>
			<td>Miscellaneous digging tools including hand trowl, flat spade, and pointed spade</td>
			<td>Any home supply store</td>
			<td></td>
			<td>Backup tools to aid excavation&#39;</td>
		</tr>
		<tr>
			<td>Shovel (Sharpshooter) 16 in. D-handle drain spade</td>
			<td>Razorback</td>
			<td></td>
			<td>Manual tool for excavating soil pit. Any narrow pointed spade will work.&#160;</td>
		</tr>
		<tr>
			<td>Shovel, trenching, 4 in wide steel blade&#160;</td>
			<td>Any home supply store</td>
			<td></td>
			<td>Ideal trenching tool for burying cable or conduit</td>
		</tr>
		<tr>
			<td>Soil auger (&#60;4 in diameter) with T-handle or and extension bar as needed for r test holes</td>
			<td>AMS Samplers</td>
			<td>400.06</td>
			<td>Recommended for test holes. The auger type should match soil, but &#39;regular&#39; performs well in most soils</td>
		</tr>
		<tr>
			<td>Tarp (plastic) or plywood sheet</td>
			<td>Any home supply store</td>
			<td></td>
			<td>Soil management during excavation and trenching</td>
		</tr>
		<tr>
			<td>Field tools, optional</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>2,000 lb Mini Excavator</td>
			<td>Sunbelt Rentals</td>
			<td>350110</td>
			<td>Rental equipment for mechanical excavation</td>
		</tr>
		<tr>
			<td>Breaker or digging bar</td>
			<td>Any home supply store</td>
			<td></td>
			<td>Useful to break rocks and cut roots during excavation</td>
		</tr>
		<tr>
			<td>Galvanized Cattle Fence Panel, 16 ft x 50 in</td>
			<td>Tractor Supply Co.&#160;</td>
			<td>350207799</td>
			<td>Recommend cutting fencing panels into 8&#39; sections</td>
		</tr>
		<tr>
			<td>Pick mattock or pulaski&#160;</td>
			<td>Any home supply store</td>
			<td></td>
			<td>Great for loosening in hard or rocky soils&#160;</td>
		</tr>
		<tr>
			<td>Post Hole Auger Hydraulic Tow Behind with 18&#34; diameter auger</td>
			<td>Sunbelt Rentals</td>
			<td>700033</td>
			<td>Rental equipment for mechanical excavation</td>
		</tr>
		<tr>
			<td>Post hole digger, 48 in handle</td>
			<td>Any home supply store</td>
			<td></td>
			<td>Useful to clear soil in bottom of pit, or for test holes</td>
		</tr>
		<tr>
			<td>Steel fence T-posts, 6 feet tall and fence post driver, ~14 lb.</td>
			<td>Any home supply store</td>
			<td></td>
			<td>Fencing support and installation</td>
		</tr>
		<tr>
			<td>Steel rake</td>
			<td>Any home supply store</td>
			<td></td>
			<td>Ideal for smoothing disturbed soil at field area</td>
		</tr>
		<tr>
			<td>Every Day Carry (EDC), recommendations for any field technician&#39;s toolbag</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Adjustable wrench with insulated handle&#160;</td>
			<td>Any home supply store</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Assorted UV-resistant zip ties</td>
			<td>Any home supply store</td>
			<td></td>
			<td>Critical for neat wiring&#160;</td>
		</tr>
		<tr>
			<td>Diagonal cutting pliers</td>
			<td>Any home supply store</td>
			<td></td>
			<td>Efficient way to cut light and heavy wires and snip zip ties</td>
		</tr>
		<tr>
			<td>Digital camera, GPS, and compass</td>
			<td>Misc.&#160;</td>
			<td></td>
			<td>Ideally, these are all on your smartphone</td>
		</tr>
		<tr>
			<td>Digital multimeter</td>
			<td>Any home supply store</td>
			<td></td>
			<td>Key tool for troubleshooting power and connectivity issues in electrical systems</td>
		</tr>
		<tr>
			<td>Electrical tape&#160;</td>
			<td>Any home supply store</td>
			<td></td>
			<td>Non-black tape can be used for labeling&#160;</td>
		</tr>
		<tr>
			<td>Electrician&#39;s Puddy for filling entrance holes of enclosures</td>
			<td>Any home supply store</td>
			<td></td>
			<td>Needed to close and seal all conduit ports in the enclosure</td>
		</tr>
		<tr>
			<td>Hex key sets in both standard and metric sizes</td>
			<td>Any home supply store</td>
			<td></td>
			<td>Required for many sensor mounts</td>
		</tr>
		<tr>
			<td>Magnetic torpedo level (8 to 12&#34;)</td>
			<td>Any home supply store</td>
			<td></td>
			<td>Needed to get instrument stand vertical and leveling any meteorlogical sensors</td>
		</tr>
		<tr>
			<td>Metric tape measure&#160;</td>
			<td>Any home supply store</td>
			<td></td>
			<td>Critical for inserting probes and sampling soils - both use metric depths.&#160;</td>
		</tr>
		<tr>
			<td>Pliers: needle nose, lineman&#39;s, and channel-lock</td>
			<td>Any home supply store</td>
			<td></td>
			<td>Lineman&#39;s pliers are essential for bailing wire fences.&#160;</td>
		</tr>
		<tr>
			<td>Portable drill, bits, nut drivers</td>
			<td>Any home supply store</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Ratchet wrench and appropriate socket sizes&#160;</td>
			<td>Any home supply store</td>
			<td></td>
			<td>Ratch wrenches can get into tight spaces around sensor mounts where standard box wrenches do not work</td>
		</tr>
		<tr>
			<td>Safety: first aid kit, water (5 gallons),&#160; trash bags, gloves, sunscreen, insect repellent</td>
			<td>Any home supply store</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Screw drivers: small and large size with insulated handles&#160;</td>
			<td>Any home supply store</td>
			<td></td>
			<td>Screws on DCP and terminal blocks are very small. Small flat and phillips heads are required. Larger tools will also come in handy</td>
		</tr>
		<tr>
			<td>Sharpies, pencils, and notebook</td>
			<td>Forestry Supplier</td>
			<td></td>
			<td>Basic record keeping is essential for metadata</td>
		</tr>
		<tr>
			<td>Step ladder, 6 ft</td>
			<td>Any home supply store</td>
			<td></td>
			<td>Hard to install 2m sensors without a ladder</td>
		</tr>
		<tr>
			<td>Utility knife and box cutter</td>
			<td>Any home supply store</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Vegetation control: hand loppers, weed whacker, saw</td>
			<td>Any home supply store</td>
			<td></td>
			<td>Depending on the environment, vegetation can quickly overwhelm a fenced off areas.</td>
		</tr>
		<tr>
			<td>Wire strippers (8-20 gage)</td>
			<td>Any home supply store</td>
			<td></td>
			<td>Essential tool for preparing wires for insertion into DCP or terminal blocks. Self-adjusting strippers are the latest rage</td>
		</tr>
		<tr>
			<td>Annual Maintenance Supplies</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Battery cleaner (baking soda) and brush</td>
			<td>Any grocery store</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Cleaning:compressed air, isopropyl alcohol, tooth brush, pipe cleaners, paper towels&#160;</td>
			<td>Any grocery store</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Desiccant, silica gel bags</td>
			<td>Clariant</td>
			<td>Desi Pak</td>
			<td>Reusable after oven drying at 105 &#176;C for over 24 h. Swap out annually.&#160;</td>
		</tr>
		<tr>
			<td>Field calibration device for rain gage</td>
			<td>R.M. Young</td>
			<td>52260</td>
			<td>Device that drips water into a rain gage at varying intensity&#160;</td>
		</tr>
		<tr>
			<td>Handheld Weather Meter</td>
			<td>Kestrel Instruments</td>
			<td>0830</td>
			<td>Direct measurement of air temperature, relative humidity, and wind speed for field verification</td>
		</tr>
		<tr>
			<td>One quart and one gallon freezer bags</td>
			<td>Any grocery store</td>
			<td></td>
			<td>Storage for any gravimetric soil samples</td>
		</tr>
		<tr>
			<td>Portable soil moisture sensor&#160;</td>
			<td>Delta-T Devics</td>
			<td>SM150T</td>
			<td>A variety of sensors exist. See evaluation at https://acsess.onlinelibrary.wiley.com/doi/pdf/10.1002/vzj2.20033</td>
		</tr>
		<tr>
			<td>Soil core sampler, 2-1/4 in. Diameter</td>
			<td>Soilmoisture Equipment Corp.</td>
			<td>0200</td>
			<td>Gravimetric soil moisture and bulk density sampler&#160;</td>
		</tr>
	</tbody>
</table>

in situ soil moisture sensors in undisturbed soils

Soil moisture directly affects operational hydrology, food security, ecosystem services, and the climate system. However, the adoption of soil moisture data has been slow due to inconsistent data collection, poor standardization, and typically short record duration. Soil moisture, or quantitatively volumetric soil water content (SWC), is measured using buried, in situ sensors that infer SWC from an electromagnetic response. This signal can vary considerably with local site conditions such as clay content and mineralogy, soil salinity or bulk electrical conductivity, and soil temperature; each of these can have varying impacts depending on the sensor technology.
Furthermore, poor soil contact and sensor degradation can affect the quality of these readings over time. Unlike more traditional environmental sensors, there are no accepted standards, maintenance practices, or quality controls for SWC data. As such, SWC is a challenging measurement for many environmental monitoring networks to implement. Here, we attempt to establish a community-based standard of practice for in situ SWC sensors so that future research and applications have consistent guidance on site selection, sensor installation, data interpretation, and long-term maintenance of monitoring stations.
The videography focuses on a multi-agency consensus of best-practices and recommendations for the installation of in situ SWC sensors. This paper presents an overview of this protocol along with the various steps essential for high-quality and long-term SWC data collection. This protocol will be of use to scientists and engineers hoping to deploy a single station or an entire network.

Watch this Scientific Journal Video about In Situ Soil Moisture Sensors in Undisturbed Soils at JoVE.com

In Situ Soil Moisture Sensors in Undisturbed Soils

The determination of soil water content is a critical mission requirement for many state and federal agencies. This protocol synthesizes multi-agency efforts to measure soil water content using buried in situ sensors.

In Situ Soil Moisture Sensors in Undisturbed Soils

Soil moisture directly affects operational hydrology, food security, ecosystem services, and the climate system. However, the adoption of soil moisture ...

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5.8K Views.  U.S. Geological Survey. The determination of soil water content is a critical mission requirement for many state and federal agencies. This protocol synthesizes multi-agency efforts to measure soil water content using buried in situ sensors.

Video: In Situ Soil Moisture Sensors in Undisturbed Soils

Integrated Field Lysimetry and Porewater Sampling for Evaluation of Chemical Mobility in Soils and Established Vegetation

Potentially toxic chemicals are routinely applied to land to meet growing demands on waste management and food production, but the fate of these chemicals is often not well understood. Here we demonstrate an integrated field lysimetry and porewater sampling method for evaluating the mobility of chemicals applied to soils and established vegetation. Lysimeters, open columns made of metal or plastic, are driven into bareground or vegetated soils. Porewater samplers, which are commercially available and use vacuum to collect percolating soil water, are installed at predetermined depths within the lysimeters. At prearranged times following chemical application to experimental plots, porewater is collected, and lysimeters, containing soil and vegetation, are exhumed. By analyzing chemical concentrations in the lysimeter soil, vegetation, and porewater, downward leaching rates, soil retention capacities, and plant uptake for the chemical of interest may be quantified. Because field lysimetry and porewater sampling are conducted under natural environmental conditions and with minimal soil disturbance, derived results project real-case scenarios and provide valuable information for chemical management. As chemicals are increasingly applied to land worldwide, the described techniques may be utilized to determine whether applied chemicals pose adverse effects to human health or the environment.

Field lysimetry and porewater sampling allow researchers to evaluate the fate of chemicals applied to soils and established vegetation. The goal of this protocol is to demonstrate how to install required instrumentation and collect samples for chemical analysis during integrated field lysimetry and porewater sampling experiments.

Potentially toxic chemicals are routinely applied to land to meet growing demands on waste management and food production, but the fate of these chemicals ...

Measurement of Greenhouse Gas Flux from Agricultural Soils Using Static Chambers

Measurement of greenhouse gas (GHG) fluxes between the soil and the atmosphere, in both managed and unmanaged ecosystems, is critical to understanding the biogeochemical drivers of climate change and to the development and evaluation of GHG mitigation strategies based on modulation of landscape management practices. The static chamber-based method described here is based on trapping gases emitted from the soil surface within a chamber and collecting samples from the chamber headspace at regular intervals for analysis by gas chromatography. Change in gas concentration over time is used to calculate flux. This method can be utilized to measure landscape-based flux of carbon dioxide, nitrous oxide, and methane, and to estimate differences between treatments or explore system dynamics over seasons or years. Infrastructure requirements are modest, but a comprehensive experimental design is essential. This method is easily deployed in the field, conforms to established guidelines, and produces data suitable to large-scale GHG emissions studies.

This article showcases the static chamber-based method for measurement of greenhouse gas flux from soil systems. With relatively modest infrastructure investments, measurements may be obtained from multiple treatments/locations and over timeframes ranging from hours to years.

Measurement of greenhouse gas (GHG) fluxes between the soil and the atmosphere, in both managed and unmanaged ecosystems, is critical to understanding the ...

A Bending Test for Determining the Atterberg Plastic Limit in Soils

The thread rolling test is the most commonly used method to determine the plastic limit (PL) in soils. It has been widely criticized, because a considerable subjective judgment from the operator that carries out the test is involved during its performance, which may affect the final result significantly. Different alternative methods have been put forward, but they cannot compete with the standard rolling test in speed, simplicity and cost.
In an earlier study by the authors, a simple method with a simple device to determine the PL was presented (the &#34;thread bending test&#34; or simply &#34;bending test&#34;); this method allowed the PL to be obtained with minimal operator interference. In the present paper a version of the original bending test is shown. The experimental basis is the same as the original bending test: soil threads which are 3 mm in diameter and 52 mm long are bent until they start to crack, so that both the bending produced and its related moisture content are determined. However, this new version enables the calculation of PL from an equation, so it is not necessary to plot any curve or straight line to obtain this parameter and, in fact, the PL can be achieved with only one experimental point (but two experimental points are recommended).
The PL results obtained with this new version are very similar to those obtained through the original bending test and the standard rolling test by a highly experienced operator. Only in particular cases of high plasticity cohesive soils, there is a greater difference in the result. Despite this, the bending test works very well for all types of soil, both cohesive and very low plasticity soils, where the latter are the most difficult to test via the standard thread rolling method.

The traditional standardized test for determining the plastic limit in soils is performed by hand, and the result varies depending on the operator. An alternative method based on bending measurements is presented in this study. This allows the plastic limit to be obtained with a clear and objective criterion.

The thread rolling test is the most commonly used method to determine the plastic limit (PL) in soils. It has been widely criticized, because a ...

Extraction and Analysis of Microbial Phospholipid Fatty Acids in Soils

Phospholipid fatty acids (PLFAs) are key components of microbial cell membranes. The analysis of PLFAs extracted from soils can provide information about the overall structure of terrestrial microbial communities. PLFA profiling has been extensively used in a range of ecosystems as a biological index of overall soil quality, and as a quantitative indicator of soil response to land management and other environmental stressors.
The standard method presented here outlines four key steps: 1. lipid extraction from soil samples with a single-phase chloroform mixture, 2. fractionation using solid phase extraction columns to isolate phospholipids from other extracted lipids, 3. methanolysis of phospholipids to produce fatty acid methyl esters (FAMEs), and 4. FAME analysis by capillary gas chromatography using a flame ionization detector (GC-FID). Two standards are used, including 1,2-dinonadecanoyl-sn-glycero-3-phosphocholine (PC(19:0/19:0)) to assess the overall recovery of the extraction method, and methyl decanoate (MeC10:0) as an internal standard (ISTD) for the GC analysis.

Phospholipid fatty acids provide information about the structure of soil microbial communities. We present methods for extraction from soil samples with a single-phase chloroform mixture, fractionation of extracted lipids using solid phase extraction columns, and methanolysis to produce fatty acid methyl esters, which are analyzed by capillary gas chromatography.

Phospholipid fatty acids (PLFAs) are key components of microbial cell membranes. The analysis of PLFAs extracted from soils can provide information about ...

Assessment of Labile Organic Carbon in Soil Using Sequential Fumigation Incubation Procedures

Management practices and environmental changes can alter soil nutrient and carbon cycling. Soil labile organic carbon, a readily decomposable C pool, is highly sensitive to disturbance. It is also the primary substrate for soil microorganisms, which is fundamental to nutrient cycling. Due to these attributes, labile organic carbon (LOC) has been identified as an indicator parameter for soil health. Quantifying the turnover rate of LOC also aids in understanding changes in soil nutrient cycling processes. A sequential fumigation incubation method has been developed to estimate soil LOC and potential C turnover rate. The method requires fumigating soil samples and quantifying CO2-C respired during a 10 day incubation period over a series of fumigation-incubation cycles. Labile organic C and potential C turnover rate are then extrapolated from accumulated CO2 with a negative exponential model. Procedures for conducting this method are described.

Labile organic carbon (LOC) and the potential carbon turnover rate are sensitive indicators of changes in soil nutrient cycling processes. Details are provided for a method based on fumigating and incubating soil in a series of cycles and using the CO2 accumulated during the incubation periods to estimate these parameters.

Management practices and environmental changes can alter soil nutrient and carbon cycling. Soil labile organic carbon, a readily decomposable C pool, is ...

Methods of Soil Resampling to Monitor Changes in the Chemical Concentrations of Forest Soils

Recent soils research has shown that important chemical soil characteristics can change in less than a decade, often the result of broad environmental changes. Repeated sampling to monitor these changes in forest soils is a relatively new practice that is not well documented in the literature and has only recently been broadly embraced by the scientific community. The objective of this protocol is therefore to synthesize the latest information on methods of soil resampling in a format that can be used to design and implement a soil monitoring program. Successful monitoring of forest soils requires that a study unit be defined within an area of forested land that can be characterized with replicate sampling locations. A resampling interval of 5 years is recommended, but if monitoring is done to evaluate a specific environmental driver, the rate of change expected in that driver should be taken into consideration. Here, we show that the sampling of the profile can be done by horizon where boundaries can be clearly identified and horizons are sufficiently thick to remove soil without contamination from horizons above or below. Otherwise, sampling can be done by depth interval. Archiving of sample for future reanalysis is a key step in avoiding analytical bias and providing the opportunity for additional analyses as new questions arise.

Repeated soil sampling has recently been shown to be an effective way to monitor forest soil change over years and decades. To support its use, a protocol is presented that synthesizes the latest information on soil resampling methods to aid in the design and implementation of successful soil monitoring programs.

Recent soils research has shown that important chemical soil characteristics can change in less than a decade, often the result of broad environmental ...

Protocols for Quantifying Transferable Pesticide Residues in Turfgrass Systems

Plant canopies in established turfgrass systems can intercept an appreciable amount of sprayed pesticides, which can be transferred through various routes onto humans. For this reason, transferable pesticide residue experiments are required for registration and re-registration by the United States Environmental Protection Agency (USEPA). Although such experiments are required, limited specificity is required pertaining to experimental approach. Experimental approaches used to assess pesticide transfer to humans including hand wiping with cotton gloves, modified California roller (moving a roller of known mass over cotton cloth) and soccer ball roll (ball wrapped with sorbent strip) over three treated turfgrass species (creeping bentgrass, hybrid bermudagrass and tall fescue maintained at 0.4, 5 and 9 cm, respectively) are presented. The modified California roller is the most extensively utilized approach to date, and is best suited for use at low mowing heights due to its reproducibility and large sampling area. The soccer ball roll is a less aggressive transfer approach; however, it mimics a very common occurrence in the most popular international sport, and has many implications for nondietary pesticide exposure from hand-to-mouth contact. Additionally, this approach may be adjusted for other athletic activities with limited modification. Hand wiping is the best approach to transfer pesticides at higher mowing heights, as roller-based approaches can lay blades over; however, it is more subjective due to more variable sampling pressure. Utility of these methods across turfgrass species is presented, and additional considerations to conduct transferable pesticide residue research in turfgrass systems are discussed.

Transferable pesticide residue experiments in turfgrass systems are integral components of human risk exposure assessments. Experimental approaches to measure transferable residues should be adjusted to the human interaction of interest and turfgrass system dynamics. Three transferable pesticide residue protocols are presented and the suitability across three turfgrass systems is discussed.

Plant canopies in established turfgrass systems can intercept an appreciable amount of sprayed pesticides, which can be transferred through various routes ...

The Calibration and Use of Capacitance Sensors to Monitor Stem Water Content in Trees

Water transport and storage through the soil-plant-atmosphere continuum is critical to the terrestrial water cycle, and has become a major research focus area. Biomass capacitance plays an integral role in the avoidance of hydraulic impairment to transpiration. However, high temporal resolution measurements of dynamic changes in the hydraulic capacitance of large trees are rare. Here, we present procedures for the calibration and use of capacitance sensors, typically used to monitor soil water content, to measure the volumetric water content in trees in the field. Frequency domain reflectometry-style observations are sensitive to the density of the media being studied. Therefore, it is necessary to perform species-specific calibrations to convert from the sensor-reported values of dielectric permittivity to volumetric water content. Calibration is performed on a harvested branch or stem cut into segments that are dried or re-hydrated to produce a full range of water contents used to generate a best-fit regression with sensor observations. Sensors are inserted into calibration segments or installed in trees after pre-drilling holes to a tolerance fit using a fabricated template to ensure proper drill alignment. Special care is taken to ensure that sensor tines make good contact with the surrounding media, while allowing them to be inserted without excessive force. Volumetric water content dynamics observed via the presented methodology align with sap flow measurements recorded using thermal dissipation techniques and environmental forcing data. Biomass water content data can be used to observe the onset of water stress, drought response and recovery, and has the potential to be applied to the calibration and evaluation of new plant-level hydrodynamics models, as well as to the partitioning of remotely sensed moisture products into above- and belowground components.

The hydraulic capacitance of biomass is a key component of the vegetation water budget, which serves as a buffer against short and long-term drought stresses. Here, we present a protocol for the calibration and use of soil moisture capacitance sensors to monitor water content in the stems of large trees.

Water transport and storage through the soil-plant-atmosphere continuum is critical to the terrestrial water cycle, and has become a major research focus ...

Sampling Soils in a Heterogeneous Research Plot

Soils are highly heterogeneous. In general, the number of soil samples required for soil research has always been determined arbitrarily and the associated accuracy is unknown. Here, we present a detailed protocol for efficient and clustered soil sampling in a research plot and, relying on a pilot sampling using this design, for demonstrating soil spatial heterogeneity and informing reasonable sample sizes and associated accuracy for future study. The protocol mainly comprises four steps: sampling design, field collection, soil analysis, and geostatistical analysis. The step-by-step procedure is modified according to former publications. Two examples will be presented to demonstrate contrasting spatial distributions of soil organic carbon (SOC) and soil microbial biomass carbon (MBC) under different management practices. In addition, we present a strategy to determine the sample size requirement (SSR) given a certain level of accuracy based on the plot-level coefficient of variation (CV). The field sampling protocol and the quantitative determination of the sample size will assist researchers in seeking feasible sampling strategies to meet research needs and resources' availability.

The traditional soil-sampling procedure determines the number of soil samples arbitrarily. Here, we provide a simple yet efficient clustered soil-sampling design to demonstrate soil spatial heterogeneity and quantitatively determine the number of soil samples required and the associated sampling accuracy.

Soils are highly heterogeneous. In general, the number of soil samples required for soil research has always been determined arbitrarily and the ...

High-throughput Siderophore Screening from Environmental Samples: Plant Tissues, Bulk Soils, and Rhizosphere Soils

Siderophores (low-molecular weight metal chelating compounds) are important in various ecological phenomenon ranging from iron (Fe) biogeochemical cycling in soils, to pathogen competition, plant growth promotion, and cross-kingdom signaling. Furthermore, siderophores are also of commercial interest in bioleaching and bioweathering of metal-bearing minerals and ores. A rapid, cost effective, and robust means of quantitatively assessing siderophore production in complex samples is key to identifying important aspects of the ecological ramifications of siderophore activity, including, novel siderophore producing microbes. The method presented here was developed to assess siderophore activity of in-tact microbiome communities, in environmental samples, such as soil or plant tissues. The samples were homogenized and diluted in a modified M9 medium (without Fe), and enrichment cultures were incubated for 3 days. Siderophore production was assessed in samples at 24, 48, and 72 hours (h) using a novel 96-well microplate CAS (Chrome azurol sulphonate)-Fe agar assay, an adaptation of the traditionally tedious and time-consuming colorimetric method of assessing siderophore activity, performed on individual cultivated microbial isolates. We applied our method to 4 different genotypes/Lines of wheat (Triticum aestivum L.), including Lewjain, Madsen, and PI561725, and PI561727 commonly grown in the inland Pacific Northwest. Siderophore production was clearly impacted by the genotype of wheat, and in the specific types of plant tissues observed. We successfully used our method to rapidly screen for the influence of plant genotype on siderophore production, a key function in terrestrial and aquatic ecosystems. We produced many technical replicates, yielding very reliable statistical differences in soils and within plant tissues. Importantly, the results show the proposed method can be used to rapidly examine siderophore production in complex samples with a high degree of reliability, in a manner that allows communities to be preserved for later work to identify taxa and functional genes.

We present a protocol for rapid screening of environmental samples for siderophore potential contributing to micronutrient bioavailability and turnover in terrestrial systems.

Siderophores (low-molecular weight metal chelating compounds) are important in various ecological phenomenon ranging from iron (Fe) biogeochemical cycling ...