SSSAJ Grow Your Career with SSSA
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

Published online 4 August 2005
Published in Soil Sci Soc Am J 69:1482-1491 (2005)
DOI: 10.2136/sssaj2004.0377
© 2005 Soil Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
This Article
Right arrow Abstract Freely available
Right arrow Figures Only
Right arrow Full Text (PDF) Free
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Drohan, P. J.
Right arrow Articles by Buck, B. J.
Right arrow Search for Related Content
PubMed
Right arrow Articles by Drohan, P. J.
Right arrow Articles by Buck, B. J.
Agricola
Right arrow Articles by Drohan, P. J.
Right arrow Articles by Buck, B. J.
Related Collections
Right arrow Dryland Soils
Right arrow Ecosystem Management
Right arrow Soil Chemistry

Forest, Range & Wildland Soils

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

P. J. Drohana,*, D. J. Merklerb and B. J. Bucka

a University of Nevada, Las Vegas, Dep. of Geoscience, 4505 Maryland Parkway, Las Vegas, NV 89154-4010
b NRCS, Resource Soil Scientist, 5820 South Pecos Rd., Bldg. A, Suite 400, Las Vegas, Nevada 89120

* Corresponding author (drohanp{at}unlv.nevada.edu)


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSIONS
 REFERENCES
 
To find a quick, relatively inexpensive measure for soil chemistry in the Mojave Desert (MD), we evaluated the use of the ion-exchange resin membrane (IEM) plant root simulator (PRS) probe. Tests were conducted along a floodplain of the Virgin River in Nevada. Probes were buried at 15 and 40 cm. Probes were left in place for three time intervals (30, 60, and 90 d) in two seasonal periods (wetter [WP] and drier [DP], 2004), which were delineated according to the amount of precipitation and soil temperature and moisture. The sampling design was replicated in three pits during the WP and DP. Soil moisture and soil temperature were monitored at 25, 50, 75, and 100 cm. The probes were able to detect differences in ion sorption between the two burial depths, although differences were not always statistically significant. Ion sorption onto the probes generally increased from Month 1 to 3, but the result was not linear. The sorption of some ions fluctuated during the three-month period, with ions desorbing and readsorbing or ion chemistry decreasing over the course of the study. Soil moisture and temperature did not appear to affect the probe's ability to detect differences across depths or season. Based on results from this experiment, we conclude that the burial time required for assessing relative differences in ion chemistries at our sites is one month or less and that the PRS probe may be useful for detecting relative differences in ion chemistries among other soils in the MD.

Abbreviations: CEC, cation exchange capacity • DP, dry period • EC, electrical conductivity • EDS, energy dispersive spectroscopy • IEM, ion-exchange membrane • MD, Mojave Desert • PRS, plant root simulator • SAR, sodium adsorption ratio • SEM, scanning electron microscopy • WAI, Western Ag Innovations • WP, wet period


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSIONS
 REFERENCES
 
ION-EXCHANGE RESINS have been used for the determination of plant-available nutrients since approximately 1951 (Pratt, 1951) and IEMs since approximately 1964 (Saunders, 1964). Part of the reason for their popularity stems from their ease of use, their reported ability to provide a reliable measure of nutrient availability over a range of soils and to extract a diverse suite of elements from the soil at once, and their affordability and speed of analysis (Saggar et al., 1990; Qian et al., 1992; Qian and Schoenau, 2002a). Compared with chemical-based extractions, ions measured with resins are thought to be an index of relative plant nutrient availability (Qian et al., 1992). Although the measure of relative nutrients with IEMs is not directly comparable with traditional soil testing methodologies, IEM values have been found to correlate well with these methods (Indiati and Neri, 2004), and IEMs have been found to accurately predict plant uptake well (Schoenau and Huang, 1991; Qian et al., 1992).

The use of IEMs has also presented some problems relating to the time the membrane is in contact with the soil and the reuse of membranes. The period of time that IEMs are left in contact with the soil has been addressed by many due to the differences found with ion adsorption over time (Sibbesen, 1977; Tabatabai, 1982; van Raij et al., 1986; Saggar et al., 1990; Schoenau and Huang, 1991; Greer and Schoenau, 1996). Ion-exchange membrane soil contact time recommendations range from 15 min to 2 wk; extraction time depends on one's goals when using IEMs. Compounding potential problems with extraction times in a soil media is the number of times an IEM can be reused. For several styles of probes, a counter-ion (usually H+ and OH–) on the probe is exchanged with the soil ions. After the soil ions are eluted in the laboratory, the IEM undergoes a rejuvenation process in which the counter-ions are added back onto the IEM surface. The probes used in this experiment underwent this process at Western Ag Innovations (WAI) before implantation in the MD, however, Na+ and HCO3– were used as counter-ions (WAI, Saskatoon, SK, Canada; http://www.westernag.ca/innov/main.html; verified 15 Apr. 2005). Sherrod et al. (2003) concluded that only a single use is appropriate for IEMs in calcareous 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 to not be a problem (Saggar et al., 1990; Schoenau and Huang, 1991; Cooperband et al., 1999).

Our study evaluates the use of the WAI probe in the MD. Western Ag Innovations of Saskatchewan, Canada, markets this type of IEM (an IEM embedded in a plastic frame), which has been used by several researchers (Huang and Schoenau, 1996; Beckie et al., 1997; Huang and Schoenau, 1997; Johnson et al., 2001; Koehn et al., 2002; Hangs et al., 2004), mainly in agricultural soils in Canada or in forested soils in Florida, USA. All IEMs in this study have undergone the rejuvenation process and are in essence reused. This is the first study of its kind to evaluate the use of this probe, or any IEM from our literature review, in such an arid climate. We hypothesized that ion adsorption on the probe membrane would be significantly affected by soil moisture and temperature in the MD, resulting in an inability to use the probe to assess relative differences in soil chemistry in the region.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 CONCLUSIONS
 REFERENCES
 
The study site is located on a floodplain along the Virgin River in Clark County, Nevada (Fig. 1). The soils formed in very deep sandy alluvium derived primarily from unconsolidated, calcareous and gypsic Tertiary basin fill material (Muddy Creek Formation) or weakly consolidated sandstone of older geologic age, with minor admixtures of limestone and gypsum (NRCS, 2004). The soils are mapped as the Virgin River soil series (clayey over loamy, smectitic over mixed, superactive, calcareous, thermic Aquic Torriorthents) (NRCS, 2004), but are an inclusion.



View larger version (120K):
[in this window]
[in a new window]
  		Fig. 1. Study area—Clark County, Nevada.

 
Soils on the site were characterized following the methods of Schoeneberger et al. (1998) (Tables 1 and 2). Soil chemical and physical analyses were completed at Utah State University's Analytical Laboratory and the University of Nevada Las Vegas (UNLV) Pedology Laboratory. Soil pH and electrical conductivity (EC) were calculated by saturated paste and glass electrode (USDA, 1954); the sodium adsorption ratio (SAR) was calculated following USDA (1954); cation exchange capacity (CEC) was determined by ammonium acetate at pH 7 (Black et al., 1965); water-soluble elements were determined by saturated paste (USDA, 1954); and saturation percentage was determined by saturated paste (Wilcox, 1951). Particle size was determined by the hydrometer method (Gee and Bauder, 1986). Salt mineralogy of surface salt crusts and subsurface Stage I pedogenic gypsum precipitates (snowballs) (Buck and Van Hoesen, 2002) were determined at UNLV Electron Microanalysis & Imaging Laboratory (EMIL) laboratory by scanning electron microscopy (SEM)/ energy dispersive spectroscopy (EDS) analyses using a JEOL 5600 scanning electron microscope and an Oxford ISIS energy dispersive x-ray system (JEOL, Peabody, MA). One hundred ten SEM images and 213 EDS analyses were used to determine the chemistry and mineralogy of the pedogenic salts.


View this table:
[in this window]
[in a new window]
  		Table 1. Pedon description for the study site. Field notes below table. Descriptive coding follows the U.S. National Soil Information System.

 

View this table:
[in this window]
[in a new window]
  		Table 2. Soil chemistry data for sampled horizons.{dagger}

 
The site vegetation consists dominantly of T. ramosissima, Atriplex lentiformis, Sporobolus airoides, and Pluchea sericea. The elevation of the site is 377 m. Precipitation data (Fig. 2) were collected from a NOAA weather station (id: 265846) on Mormon Mesa located approximately 28 km from the research site. The soil temperature regime is thermic and the soil moisture regime is aridic. The USDA-NRCS recorded volumetric soil water using Theta Probes (ML2x) (Fig. 3) and soil temperature using HOBO H8 Outdoor/Industrial 4-Channel External Loggers (Fig. 4) at 25, 50, 75, and 100 cm in a pit approximately 2 m from the buried probes. An error in a logger for the 75- and 100-cm volumetric soil water probes resulted in lost data for the period 8 Feb. to 3 May 2004 for this parameter.



View larger version (83K):
[in this window]
[in a new window]
  		Fig. 2. (A) Scanning electron microscopy (SEM) image of euhedral, skeletal (hollow) halite from 1 surface salt crust. (B) SEM image of euhedral, lenticular gypsum from Stage I snowball in 2By horizon (46–89 cm).

 


View larger version (14K):
[in this window]
[in a new window]
  		Fig. 3. Precipitation data for the study periods. Wet period (WP) and dry period (DP) refer to the two study periods.

 


View larger version (14K):
[in this window]
[in a new window]
  		Fig. 4. Volumetric soil water content (expressed as a percentage) for the four probe depths. Data before and beyond the study period are provided to show seasonal patterns. Legend symbols refer to the burial depth for the moisture probes.

 
We evaluated the WAI probes under the two different seasonal periods (WP: 1/23/04–4/23/04; DP: 5/4/04–8/1/04) based on known differences in precipitation and soil temperature during these two times of the year. In each period, the study design was the same. Three pairs of probes, each consisting of a cation and an anion probe, were buried at a depth of 15 cm and three pairs at 40 cm. Root exclusion collars were not used at either depth. Thus, there were six pairs of probes per hole, and 18 pairs all together. This setup was replicated in three different holes all within a meter of each other. Probes in Hole 1 were left buried for 30 d, in Hole 2 were left buried for 60 d, and in Hole 3 were left buried for 90 d.

The probe (15 cm by 3 cm by 0.5 cm) consists of a plastic housing with an IEM embedded in the housing (WAI). One PRS probe membrane adsorbs cations and another adsorbs anions; therefore, two probes are needed to measure anions and cations in one location. The housing holding the membrane is buried in the soil. The WAI probe uses Na+ and HCO3– as counter-ions on the cation- and anion-exchange membranes (WAI) instead of the traditional H+ and OH–.

Probes were removed from the pits after their respective time periods, and all soil was removed from the probe by brush and ion-free water. Probes removed before the end of the 90-d study were stored at 4°C as recommended by WAI. At the end of the study period, probes were shipped to WAI for processing and analysis. Probes were eluted with 0.5 M HCl and analyzed at WAI. Inorganic NO3––N and NH4+–N (summed for total N) were analyzed colorimetrically using an autoanalyzer (WAI). Phosphate content was measured colorimetrically (WAI). The remaining nutrient ion contents (Ca, Mg, K, Fe, Mn, Cu, Zn, B, S [sulfate], Pb, and Al) were measured using inductively coupled plasma spectrometry (WAI). Ion contents are reported as mg m–2 of membrane surface.

All data were screened for normality and homogeneity of variance, and data not meeting assumptions of normality underwent log–normal transformations (log10). Sorbed ion variables were used in analysis of variance (Tukey multiple comparisons) by burial period or with a univariate t test by depth class (15 or 40 cm) or burial season (WP or DP). An {alpha} of 0.05 was used to indicate significance. Results are presented using untransformed data.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Pedon descriptions are reported in Table 1 and soil profile chemistry data in Table 2. The pedon contains a thin (1–2 mm) surficial salt crust, and several Stage I gypsic horizons (Buck and Van Hoesen, 2002). The SEM analyses indicate that the surface salt crust primarily is composed of halite (NaCl) with minor amounts of gypsum, and rare thenardite (Na2SO4) (Fig. 2a). The Stage I snowballs in all of the subsurface horizons are composed of gypsum (Fig. 2b). Rare KCl and Mg-Ca-SO4 salts were also found in SEM/EDS analyses. Soil chemistry data indicated very high EC, Na, and Cl in the surface crust and A horizon (approximately three to nine times higher for Na and Cl than in the By horizon) (Table 2). A lithologic discontinuity was found at 46 cm. Clay lenses were found in the By horizon, as were Stage I gypsum snowballs (Buck and Van Hoesen, 2002) and clay coatings on sand grains. The 2By horizon contained Stage I gypsum snowballs and concentrations of salts around roots.

During the wet period (WP), 3.7 cm of precipitation fell; in the dry period (DP), 0.03 cm fell (Fig. 3). Volumetric soil water content and soil temperature data for the start and end dates for each period are presented in Table 3 and for the duration of the study in Fig. 4 and 5, respectively. Soil temperature was lowest at the start of the WP (9.7°C at 25 cm) and highest at the end of the DP (33.8°C at 25 cm) (Table 3). Soil moisture was lowest at the start of the WP (2.2% at 25 cm) and highest at the end of the DP (44.1% at 75 cm) (Table 3). Except for the 25-cm depth moisture sensor (which was still extremely dry), over the course of the study, there was little difference in moisture at each respective depth, regardless of period (DP or WP). The chemistry probes were buried at 15 and 40 cm, therefore, data most comparable with their depths are at the 25- and 50-cm depths. For the WP, soil temperature in the depth range of the probes was 9.7 to 21.1°C for the 15-cm probe and 11.0 to 19.8°C for the 40-cm probe. For the DP, soil temperature in the depth range of the probes was 24.7 to 33.8°C for the 15-cm probe and 22.1 to 31.7°C for the 40-cm probe. For the WP, soil moisture in the depth range of the probes was 2.2 to 5.3% for the 15-cm probe and 29.1 to 31.3% for the 40-cm probe. For the DP, soil moisture in the depth range of the probes was 4.8 to 5.9% for the 15-cm probe and 31.9 to 33.8 for the 40-cm probe.


View this table:
[in this window]
[in a new window]
  		Table 3. Soil moisture and temperature for the start and end date for each period by depth.

 


View larger version (15K):
[in this window]
[in a new window]
  		Fig. 5. Soil temperature for the four probe depths. Data before and beyond the study period are provided to show seasonal patterns. Legend symbols refer to the burial depth for the temperature probes.

 
Mean ion sorption values (mg m–2) as measured from the 18 pairs of probes for the two depths (15 and 40 cm) across the WP, DP, and for both seasons are presented in Table 4. Probes were able to detect significant differences between the two depths when both time periods were grouped together (Mg and K); in the WP (Ca, K, and B); and in the DP (Mg, K, P, Mn, and B).


View this table:
[in this window]
[in a new window]
  		Table 4. Mean ion sorption values (mg m–2) for the probes for the two depths (15 and 40 cm) across both seasons, wet period (WP) and dry period (DP). Total N (sum of inorganic NO3––N and NH4+–N).

 
Mean ion sorption values (mg m–2) for the three burial periods (1 mo, 2 mo, and 3 mo) during the WP, DP, and for both seasons are presented in Table 5. Probes were found to significantly accumulate different amounts of ions between the three burial periods. Significant differences in sorbed ions by burial periods were found for both seasons (total N, NO3––N, Mg, K, P, and Fe) (Table 5). In the WP, total N, NO3––N, Mg, K, and Zn had significant differences across burial periods; in the DP, significant differences across burial periods were found for total N, NO3––N, Ca, P, and Fe. While a trend often existed with increasing adsorption by the probe over time, some exceptions existed (Cu, Zn, B, and S in both seasons; Ca, Fe, Mn, Zn, B, and S in the WP; and Cu, B, and S in the DP).


View this table:
[in this window]
[in a new window]
  		Table 5. Mean ion sorption values (mg m–2) for the three burial periods (one month, two months, and three months) across both seasons, wet period (WP) and dry period (DP). Total N (sum of inorganic NO3––N and NH4+–N).

 
Mean ion sorption values (mg m–2) for the three burial periods across both seasons, and in either the top or bottom depth are presented in Table 6. Data were grouped together by period (WP and DP) for analysis (both seasons, Table 6). Significant differences were found within the top depth (15 cm) across the three burial periods for total N, NO3– N, Mg, K, and S and within the bottom depth (40 cm) across the three burial periods for total N, NO3– N, Mg, K, P, and Zn. The trend across the three burial periods generally showed an accumulation of ions on resin membranes, however, exceptions existed (top horizon-Cu, Zn, B, and S and bottom horizon-total N, NO3– N, Mn, Cu, Zn, B, and S).


View this table:
[in this window]
[in a new window]
  		Table 6. Mean ion sorption values (mg m–2) for the three burial periods (one month, two months, and three months) across both seasons, and in either the top or bottom depth. Total N (sum of inorganic NO3–N and NH4+–N).

 
Mean ion sorption values (mg m–2) for the three burial periods and within the top horizon depth or bottom horizon depth for each season are presented in Table 7. Sample sizes were low (n = 3) for each analysis, so results should be interpreted with caution. Significant differences were found across the three burial periods. In the DP, top horizon, Mg, Fe, and Zn were significantly different across the three periods; in the WP, top horizon, total N, NO3––N, Mg, K, and S were significantly different. In the DP, bottom horizon, total N, NO3––N, Mg, P, and S were significantly different; in the WP, bottom horizon, total N, NO3––N, Mg, K, B, and S were significantly different. In general, trends showed increasing adsorption across the three time periods regardless of season or depth; however, exceptions existed (DP, top horizon: Cu, Zn, B, S, and Al; WP, top horizon: Ca, Fe and S; DP, bottom horizon: total N, NO3––N, Fe, B, and S; and WP, bottom horizon: total N, NO3––N, Ca, P, Fe, Mn, Zn, B, and S).


View this table:
[in this window]
[in a new window]
  		Table 7. Mean ion sorption values (mg m–2) for the three burial periods (one month, two months, and three months) and within the top horizon depth or bottom horizon depth of the DP and WP. Total N (sum of inorganic NO3––N and NH4+N).

 
For mean ion sorption analysis (mg m–2) between the two burial seasons (WP or DP) by period, burial depth, and within burial depth only the few variables that were significantly different are presented (Table 8). Probes were able to detect some significant differences by season, burial period, and across both depths.


View this table:
[in this window]
[in a new window]
  		Table 8. Mean ion sorption values (mg m–2) between the two seasons (wet period [WP] and dry period [DP]), for each burial period across both depths, and within the top depth or bottom depth for each respective season. Total N (sum of inorganic NO3––N and NH4+–N). All data significant at {alpha} = 0.05.

 

   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
CONCLUSIONS
 REFERENCES
 
While not always statistically significant, the WAI probes were able to detect differences between the two burial depths in each seasonal period and across both (Table 4). The differences trend in the same direction as the pedon chemistry description (Table 2). Because the PRS probe was able to detect differences between depths, we believe that further research with the probe in the MD, and other desert regions, is warranted and that the probe might be useful in other areas of the region to examine chemical differences between soils. Since different depths in our soil had different soil physical and chemical properties that might be similar to patterns found in other soils, we believe that this suggests that the probe may be suitable in comparisons between soils. A question is how useful are relative differences? Results from Qian et al. (1992) showed a positive correlation between traditional soil testing chemistry results and IEM chemistry. However, since data are not directly comparable, differences between depths can be inferred only as relative differences. In our opinion, this seems to be a weakness in using the probes to assess soil chemistry; without other probe data with which to make comparisons, results are difficult to interpret. This may change over time as IEMs become more commonly used. One might likewise argue that various methods of traditional soil testing are not directly comparable with each other because of the differences in the pH at which extractions are done or the concentrations of the extractants used.

Probes accumulated ions over the course of the three-month study, and this adsorption trend generally occurred regardless of seasonal period or depth (Tables 5, 6, and 7). However, as seen in Table 5, some ions continuously adsorbed over the three months (Ca and Mg for instance) while others seemed to plateau and decrease over the course of the study (Cu, B, and S).

Although we expected to find more differences in ion values because of differences in precipitation and soil temperature (especially at the shallower depths) during the study, a lack of differences may have been due to the fairly uniform soil moisture across the two study periods (Table 3). Soil temperature varied more than soil moisture at the two depths of probe placement (Table 3), but there were no significant differences in probe chemistry between seasonal periods regardless of burial time and depth (Table 8). Therefore, our results suggest that neither soil moisture nor temperature influenced probe sorption.

Most surprising was the fact that the probes adsorbed at 15 cm, in such a low moisture, high temperature environment. Qian and Schoenau (2002a) stated that as the moisture content of the soil becomes lower, the diffusion path for adsorption becomes greater and more convoluted. This may result in adsorption differences on probes. Qian and Schoenau (1996) found that NO3––N, phosphate, K, and sulfate adsorption significantly decreased with decreasing moisture content in the soil. Results from Schaff and Skogley (1982) were similar to Qian and Schoenau (1996) for K, Ca, and Mg with resin beads. In a greenhouse/refrigerator experiment under controlled temperature conditions, membrane adsorption of reused probes was found to vary by temperature and soil type (Sherrod et al., 2003). Temperature was the climate variable that varied the most at the 15- and 40-cm depths in our study (Table 3), yet few significant differences were found between burial periods (WP and DP) at the 15-cm depth (Table 8), suggesting that the temperature may not have been interfering enough in adsorption kinetics to cause problems in data interpretation.

Significant differences between burial periods were found between Months 1 and 3 regardless of depth or season. While probes tended to accumulate ions from Month 1 to 3, in some instances the pattern of adsorption plateaued (e.g., Table 5 [both seasons]: K, P, Fe, Mn, and Cu), decreased over the 3-mo period (e.g., Zn in Table 5 [both seasons and WP]; Ca and Mn in Table 7 [WP, bottom horizon]), or decreased and then increased and vice versa (e.g., NO3–N in Table 6 [both seasons, bottom horizon]; NO3–N and Zn in Table 7 [WP, bottom horizon]). Because of this change in adsorption with time, the sorption after a three-month burial period was generally not three times the sorption after a one-month burial period. This has been found in a previous study with IEMs (Schoenau and Huang, 1991). Therefore, we conclude that burial periods longer than one month present difficulties in interpreting relative differences in ion sorption. Mn, Cu, B, S, and Zn adsorption were quite variable across the three-month study period regardless of depth or season. It is unknown why this occurred.

Ion interference and microbial effects may explain some of the anomalies in our results, such as found with Mn, Cu, B, and S (Table 5). Qian and Schoenau (2002a) reported that the physical and chemical properties of the resin and soil are important factors influencing adsorption of ions from the soil. Interference from other ions can lead to differences in adsorption. For example, Qian and Schoenau (2002a) reported that in soils in which more Ca is adsorbed by the membrane, there may be less adsorption of K and NH4+ (Qian and Schoenau, 2002a). Several ions in our pedon could be considered as potential interference ions because their sheer quantity could out-compete lesser ion quantities on the probe (Table 2: Ca, Mg, S, Na, and Cl). This may partly be influenced by the site plant community. T. ramosissima appears to be altering surface soils (crust and A horizon) by concentrating Na and Cl at the surface. T. ramosissima is known to move salts from the subsoil, translocate them through the plant, and excrete the salts through the leaves, which are then redeposited on the surface (Arndt et al., 2004). The resulting excess Na and Cl could cause adsorption–desorption kinetics that favor the adsorption of Na and Cl on the probes. High S, Ca, and Mg found in the B horizons could also be affecting soil chemistry by soil microbial interactions at the probe–soil interface. Microbes have been found to be active in calcite formations in desert climates (Monger et al., 1991) and are suspected of forming gypsum snowball morphology (Buck and Van Hoesen, 2002). The SEM analyses of the snowballs in this study did not find any evidence for microorganisms, in this case. Competition from microorganisms has also been documented with resins (Giblin et al., 1994) and IEMs (Subler et al., 1995). Nutrient release kinetics may also explain some of the adsorption or desorption differences from the soil and probe membrane in this study (Table 5 Cu, B, and S). Changes in the adsorption of ions over time have been found in P research because of the kinetics of nutrient release and transport (Curtin et al., 1987; Abrams and Jarrel, 1992). We hypothesize that this could result in the need for different periods of burial to assess different ion chemistries.

Increasing time generally led to increasing ion accumulation on the membrane. However, based on our results, one month (regardless of soil moisture content, temperature, or season) under similar soil moisture and temperature conditions as in this study, seems sufficient to detect relative differences. A 2-wk burial period should be evaluated. Traditionally, the extraction time (in our case, burial period) for IEMs in bench-top experiments has been 16 h or longer (Sibbesen, 1977; Tabatabai 1982; van Raij et al., 1986; Saggar et al., 1990), but the ideal duration is still in contention. Schoenau and Huang (1991) compared 1-, 6-, and 16-h periods and found increased ion accumulation over time using resin membranes in a growth chamber experiment. For a typical agricultural soil, WAI recommends a 2-wk burial period.

Several authors using the WAI probes have used this recommendation in a variety of ecosystems—Johnson et al. (2001) in a scrub-oak ecosystem in Florida, USA; Huang and Schoenau (1997) in a boreal ecosystem in Saskatchewan, Canada (for results from a 2-h burial period for the same location, see Huang and Schoenau [1996]); and Hammermeister et al. (2004) in a native prairie ecosystem in southeastern Alberta, Canada. Qian and Schoenau (2002a)( 2002b) stated that the time that resin materials should be kept in contact with the soil depends in part on the resin, its capacity to adsorb ions, the nutrient availability of the soil, the likelihood of chemical and biological conversion, and the temperature and moisture conditions of the media. Short burial periods, during which the IEM's capacity to adsorb ions is not exceeded, result in the IEM acting as a sink for adsorption, but long periods during which the IEM's capacity for adsorption is exceeded may result in the IEM becoming a source in equilibrium reactions with the soil (Qian and Schoenau, 2002a). These processes may have been at work in our study, where some ions plateaued after the 2-mo burial period or where ion chemistry fluctuated over the course of the study.


   CONCLUSIONS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSIONS
REFERENCES
 
Based on results from this experiment with the WAI PRS probe in the MD, we conclude that a one-month burial period is likely suitable for detecting relative differences in ion chemistry at similar sites to ours in the MD. The effect of soil moisture and temperature on the probe's effectiveness at adsorbing ions in the MD was not a dominant factor in interpreting relative differences by depth. In addition, because the probe was suitable for detecting relative differences between horizons (depths) that contain significantly different physical and chemical characteristics, we believe these probes will be useful in detecting differences among highly variable desert soils. Future research should examine the influence of soil microbial processes and ion adsorption/desorption processes beyond a burial period of one month in the MD. Research with the PRS probe in other soils in the MD, and other desert environments, would be beneficial.


   ACKNOWLEDGMENTS
 
The authors gratefully acknowledge the financial support of the University of Nevada, Las Vegas; Andre Hanson, Amy Brock, and Brien Park for assistance with field sampling; Evelyn Coleman for SEM analyses; Guy DeMayo and Randy Laczniak, USGS, Henderson, NV for allowing us to use the research site: Tim Rash, NPS, Lake Mead National Recreation area for site access maintenance; and Bob Boyd, BLM, Las Vegas, NV for permit assistance.

Received for publication December 3, 2004.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSIONS
 REFERENCES
 





This Article
Right arrow Abstract Freely available
Right arrow Figures Only
Right arrow Full Text (PDF) Free
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Drohan, P. J.
Right arrow Articles by Buck, B. J.
Right arrow Search for Related Content
PubMed
Right arrow Articles by Drohan, P. J.
Right arrow Articles by Buck, B. J.
Agricola
Right arrow Articles by Drohan, P. J.
Right arrow Articles by Buck, B. J.
Related Collections
Right arrow Dryland Soils
Right arrow Ecosystem Management
Right arrow Soil Chemistry

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
The SCI Journals Agronomy Journal Crop Science
Journal of Natural Resources
and Life Sciences Education		 Vadose Zone Journal
Journal of Plant Registrations Journal of
Environmental Quality		 The Plant Genome