Suitability of the Plant Root Simulator Probe for Use in the Mojave Desert

IEMs are left in contact with the soil has been addressed by many due to the differences found with ion adsorpTo find a quick, relatively inexpensive measure for soil chemistry tion over time (Sibbesen, 1977; Tabatabai, 1982; van Raij in the Mojave Desert (MD), we evaluated the use of the ion-exchange resin membrane (IEM) plant root simulator (PRS) probe. Tests were et al., 1986; Saggar et al., 1990; Schoenau and Huang, conducted along a floodplain of the Virgin River in Nevada. Probes 1991; Greer and Schoenau, 1996). Ion-exchange memwere buried at 15 and 40 cm. Probes were left in place for three time brane soil contact time recommendations range from intervals (30, 60, and 90 d) in two seasonal periods (wetter [WP] and 15 min to 2 wk; extraction time depends on one’s goals drier [DP], 2004), which were delineated according to the amount of when using IEMs. Compounding potential problems precipitation and soil temperature and moisture. The sampling design with extraction times in a soil media is the number of was replicated in three pits during the WP and DP. Soil moisture and times an IEM can be reused. For several styles of probes, soil temperature were monitored at 25, 50, 75, and 100 cm. The probes a counter-ion (usually H! and OH") on the probe is were able to detect differences in ion sorption between the two burial exchanged with the soil ions. After the soil ions are depths, although differences were not always statistically significant. eluted in the laboratory, the IEM undergoes a rejuvenaIon sorption onto the probes generally increased from Month 1 to 3, but the result was not linear. The sorption of some ions fluctuated tion process in which the counter-ions are added back during the three-month period, with ions desorbing and readsorbing onto the IEM surface. The probes used in this experior ion chemistry decreasing over the course of the study. Soil moisture ment underwent this process at Western Ag Innovations and temperature did not appear to affect the probe’s ability to detect (WAI) before implantation in the MD, however, Na! differences across depths or season. Based on results from this experiand HCO3 " were used as counter-ions (WAI, Saskatoon, ment, we conclude that the burial time required for assessing relative SK, Canada; http://www.westernag.ca/innov/main.html; differences in ion chemistries at our sites is one month or less and verified 15 Apr. 2005). Sherrod et al. (2003) concluded that the PRS probe may be useful for detecting relative differences that only a single use is appropriate for IEMs in calcarein ion chemistries among other soils in the MD. ous soils (similar to this study’s site) due to a lack of desorption of soil ions from the membrane after membranes are eluted. Other authors have found IEM reuse I resins have been used for the determito not be a problem (Saggar et al., 1990; Schoenau and nation of plant-available nutrients since approximately Huang, 1991; Cooperband et al., 1999). 1951 (Pratt, 1951) and IEMs since approximately 1964 Our study evaluates the use of the WAI probe in the (Saunders, 1964). Part of the reason for their popularity MD. Western Ag Innovations of Saskatchewan, Canada, stems from their ease of use, their reported ability to promarkets this type of IEM (an IEM embedded in a plasvide a reliable measure of nutrient availability over a tic frame), which has been used by several researchers range of soils and to extract a diverse suite of elements (Huang and Schoenau, 1996; Beckie et al., 1997; Huang from the soil at once, and their affordability and speed and Schoenau, 1997; Johnson et al., 2001; Koehn et al., of analysis (Saggar et al., 1990; Qian et al., 1992; Qian 2002; Hangs et al., 2004), mainly in agricultural soils in and Schoenau, 2002a). Compared with chemical-based Canada or in forested soils in Florida, USA. All IEMs extractions, ions measured with resins are thought to be in this study have undergone the rejuvenation process an index of relative plant nutrient availability (Qian and are in essence reused. This is the first study of its et al., 1992). Although the measure of relative nutrients kind to evaluate the use of this probe, or any IEM from with IEMs is not directly comparable with traditional our literature review, in such an arid climate. We hysoil testing methodologies, IEM values have been found pothesized that ion adsorption on the probe membrane to correlate well with these methods (Indiati and Neri, would be significantly affected by soil moisture and tem2004), and IEMs have been found to accurately preperature in the MD, resulting in an inability to use the dict plant uptake well (Schoenau and Huang, 1991; Qian probe to assess relative differences in soil chemistry in et al., 1992). the region. The use of IEMs has also presented some problems relating to the time the membrane is in contact with the MATERIALS AND METHODS soil and the reuse of membranes. The period of time that The study site is located on a floodplain along the Virgin River in Clark County, Nevada (Fig. 1). The soils formed in very P. Drohan and B.J. Buck, University of Nevada, Las Vegas, Dep. of Geoscience, 4505 Maryland Parkway, Las Vegas, NV 89154-4010; D.J. deep sandy alluvium derived primarily from unconsolidated, Merkler, NRCS, Resource Soil Scientist, 5820 South Pecos Rd., Bldg. calcareous and gypsic Tertiary basin fill material (Muddy Creek A, Suite 400, Las Vegas, Nevada 89120. Received 3 Dec. 2004. *CorreFormation) or weakly consolidated sandstone of older geosponding author ([email protected]). Abbreviations: CEC, cation exchange capacity; DP, dry period; EC, Published in Soil Sci. Soc. Am. J. 69:1482–1491 (2005). Forest, Range & Wildland Soils electrical conductivity; EDS, energy dispersive spectroscopy; IEM, ion-exchange membrane; MD, Mojave Desert; PRS, plant root simuladoi:10.2136/sssaj2004.0377  Soil Science Society of America tor; SAR, sodium adsorption ratio; SEM, scanning electron microscopy; WAI, Western Ag Innovations; WP, wet period. 677 S. Segoe Rd., Madison, WI 53711 USA 1482 Published online August 4, 2005