Girisha K. Ganjegunte

Soil and Plant Responses from Land Application of Saline-Sodic Waters : Implications of Management

Land application of co-produced waters from coalbed natural gas (CBNG) wells is one management option used in the Powder River Basin (PRB) of Wyoming and Montana. Unfortunately, the co-produced CBNG waters may be saline and/or sodic. The objective of this study was to examine the effects of irrigation with CBNG waters on soils and plants in the PRB. Soil properties and vegetation responses resulting from 1 to 4 yr of saline-sodic water (electrical conductivity [EC], 1.6-4.8 dS m(-1); sodium adsorption ratio [SAR], 17-57 mmol(1/2) L(-1/2)) applications were studied during 2003 and 2004 field seasons on sites (Ustic Torriorthent, Haplocambid, Haplargid, and Paleargid) representing native range grasslands, seeded grass hayfields, and alfalfa hayfields. Parameters measured from each irrigated site were compared directly with representative non-irrigated sites. Soil chemical and physical parameters, including pH, EC, SAR, exchangeable sodium percent, texture, bulk density, infiltration, and Darcy flux rates, were measured at various depth intervals to 120 cm. Multiple-year applications of saline-sodic water produced consistent trends of increased soil EC and SAR values to depths of 30 cm, reduced surface infiltration rates, and lowered Darcy flux rates to 120 cm. Significant differences (p < or = 0.05) were determined between irrigated and non-irrigated areas for EC, SAR, infiltration rates, and Darcy flux (p < or = 0.10) at most sites. Saline-sodic CBNG water applications significantly increased native perennial grass biomass production and cover on irrigated as compared with non-irrigated sites; however, overall species evenness decreased. Biological effects were variable and complex, reflecting site-specific conditions and water and soil management strategies.

Cumulative soil chemistry changes from land application of saline-sodic waters.

Management of large volumes (60,000 ha-m) of co-production water associated with coal bed natural gas (CBNG) water extraction is a potential concern in the Powder River Basin (PRB) of Wyoming and Montana due to elevated water salinity and sodicity levels. Land application of saline-sodic CBNG water is a common water management method being practiced in the PRB, which can result in deterioration in soil quality. The objective of this study was to evaluate effects from 1 to 4 yr of land application with CBNG water on soil chemical properties at six study sites (fine to loamy, mixed to smectitic, mesic, Ustic Ardisols and Entisols) in the Wyoming PRB region. Changes in chemistry of soils collected from six depths irrigated with CBNG water were compared with representative nonirrigated soils. Applications of CBNG water significantly increased soil EC, SAR, and ESP values (up to 21, 74, and 24 times, respectively) compared with nonirrigated soils. Differences in soil chemical properties between an irrigated and nonirrigated coarse-textured soil were less than that of fine-textured soils, emphasizing texture as an important factor for salinity buildup. Pretreatment of CBNG water using a sulfur burner and application of gypsum and elemental S soil amendments reduced soil pH but did not prevent the build-up of salts and sodium. Study results suggest that current CBNG water management strategies are not as effective as projected. Additional research is needed to develop management strategies appropriate for mitigating adverse effects of CBNG water irrigation.

Effects of mixing radiata pine needles and understory litters on decomposition and nutrients release

A microcosm experiment was conducted to understand the impacts of mixing radiata pine (Pinus radiata D. Don) needle litter and understory (gorse—Ulex europaeus L., broom—Cytisus scoparius L., bracken—Pteridium aquilinum L., and lotus—Lotus pedunculatus L.) litter materials on decomposition and nutrient release dynamics. Mixing of pine needle litter with understory litter material had significant impacts on both the rate of decomposition and nutrient release patterns of pine litter as well as that of the understory species. Incubation in microcosms over 10 months resulted in significantly lower mass loss of radiata pine needle litter mixed with broom and lotus litters (35.8±8.4 and 41.3±0.8%, respectively) than pure pine needle litter (63.5±2.3%). Mixing with pine needle litter significantly increased the mass loss of broom (53.1±6.1%) compared to that of pure broom (30.2±1.0%). Significant transfers of nutrients, especially of magnesium and potassium, were observed in litter mixture treatments. Concentration of K in litter materials was found to be the most limiting factor for the decomposing microorganisms in the present study. The findings of this study suggest that management of understory litter composition via weed control could be used to manipulate carbon turnover and nutrient release in the forest floor. Also, initial selection of understory species will be important and could be managed.

Salinity management using an anionic polymer in a pecan field with calcareous-sodic soil.

Soil salinity and sodicity have long been recognized as the major concerns for irrigated agriculture in the Trans-Pecos Basin, where fields are being flood irrigated with Rio Grande River water that has elevated salinity. Reclamation of these salt-affected lands is difficult due to fine-texture, high shrink-swell soils with low permeability. Conventional practice of subsoiling to improve soil permeability is expensive and has had limited success on the irrigated soils that have appreciable amounts of readily weatherable Ca minerals. If these native Ca sources can be effectively used to counter sodicity, it can improve soil permeability and reduce amelioration costs. This study evaluated the effects of 3 yr of polyacrylamide (PAM) application at 10 mg L concentration during the first irrigation of the season to evaluate soil permeability, in situ Ca mineral dissolution, and leaching of salts from the effective root zone in a pecan field of El Paso County, TX. Results indicated that PAM application improved water movement throughout the effective root zone that resulted in Na leaching. Polymer application significantly decreased CaCO (estimated based on inorganic C analysis) concentrations in the top 45 cm compared with baseline levels, indicating solubilization and redistribution of calcite. The PAM application also reduced soil electrical conductivity (EC) in the top 60 cm (4.64-2.76 dS m) and sodium adsorption ratio (SAR) from 13.1 to 5.7 mmol L in the top 75-cm depths. As evidence of improved soil conditions, pecan nut yields increased by 34% in PAM-treated fields over the control. Results suggested that PAM application helped in effective use of native Ca sources present in soils of the study site and reduced Na by improving soil permeability.

Evaluating the accuracy of soil water sensors for irrigation scheduling to conserve freshwater

In the Trans-Pecos area, pecan [Carya illinoinensis (Wangenh) C. Koch] is a major irrigated cash crop. Pecan trees require large amounts of water for their growth and flood (border) irrigation is the most common method of irrigation. Pecan crop is often over irrigated using traditional method of irrigation scheduling by counting number of calendar days since the previous irrigation. Studies in other pecan growing areas have shown that the water use efficiency can be improved significantly and precious freshwater can be saved by scheduling irrigation based on soil moisture conditions. This study evaluated the accuracy of three recent low cost soil water sensors (ECH2O-5TE, Watermark 200SS and Tensiometer model R) to monitor volumetric soil water content (θv) to develop improved irrigation scheduling in a mature pecan orchard in El Paso, Texas. Results indicated that while all three sensors were successful in following the general trends of soil moisture conditions during the growing season, actual measurements differed significantly. Statistical analyses of results indicated that Tensiometer provided relatively accurate soil moisture data than ECH2O-5TE and Watermark without site-specific calibration. While ECH2O-5TE overestimated the soil water content, Watermark and Tensiometer underestimated. Results of this study suggested poor accuracy of all three sensors if factory calibration and reported soil water retention curve for study site soil texture were used. This indicated that sensors needed site-specific calibration to improve their accuracy in estimating soil water content data.

Delineating Salinity and Sodicity Distribution in Major Soil Map Units of El Paso, Texas, Using Electromagnetic Induction Technique

A majority of the irrigated area in the Trans-Pecos basin in the United States is affected by both salinity and sodicity that affect the long-term viability of irrigated agriculture in the region. Accurate information on spatial distribution of salinity and sodicity in the irrigated areas at a field scale is necessary for developing effective management practices. Currently, information on the amount and the distribution of salts within the irrigated areas of the Trans-Pecos basin is not available. Conventional method of soil salinity (saturated paste electrical conductivity) and sodicity (sodium adsorption ratio) assessment at a high spatial resolution is expensive, time consuming, and labor intensive. Electromagnetic induction technique can offer a low-cost, noninvasive, and rapid alternative for determining the spatial distribution of both salinity and sodicity. In this study, we evaluated the accuracy of EMI technique to delineate salt and sodicity distribution within a 12-ha study site that had all four dominant soil map units (Saneli-clayey over sandy or sandy-skeletal, montmorillonitic [calcareous], thermic Vertic Torrifluvents; Tigua-very fine, montmorillonitic (calcareous), thermic Vertic Torrifluvents; Harkey-coarse-silty, mixed [calcareous], thermic Typic Torrifluvents; Glendale-fine-silty, mixed [calcareous], thermic Typic Torrifluvents) of the Trans-Pecos basin. Salinity and sodicity values estimated by EMI technique ranged from 0.73 to 10.55 dS m−1 and sodium adsorption ratio ranged from 1.2 to 21.6 mmol1/2 L−1/2. Results of this project indicated that the EMI technique can produce accurate information on salinity distribution. Soil clay and moisture content at the time of the survey strongly influenced the accuracy of the EMI technique.

Application of electromagnetic induction technique for soil salinity and sodicity appraisal

Salinity is a major problem affecting the sustainability of agriculture and environment in the Rio Grande river basin in Texas, USA. An accurate data on the spatial distribution of salinity is necessary for developing effective salinity management practices. However, at present information is lacking on the amount and distribution of salts within the Rio Grande river basin. Manual methods of salinity assessment at high spatial resolution are labor intensive, time consuming and involve expensive laboratory analysis. Electromagnetic induction technique (EMI) can be a relatively low cost, non-invasive and rapid alternative for measuring and mapping soil salinity. This project evaluated utility, accuracy and factors affecting the accuracy of EMI technique to delineate salt affected areas within the Rio Grande river basin in the Far West Texas, USA. Results of this project indicated that the EMI technique provided accurate data on spatial distribution of salinity within a geographical location. Furthermore, accuracy of EMI data was influenced by factors such as amount of clay and soil moisture content at the time of EMI survey. Results also indicated that the EMI technique is rapid, cheaper, and provides accurate spatial data at a much higher resolution than the conventional manual method.

CHANGES IN SOIL PHYSICAL AND CHEMICAL PROPERTIES OF A CROPLAND IRRIGATED WITH CBNG CO-PRODUCED WATER 1

Significant quantities of water are being produced and discharged as a by-product of coalbed natural gas (CBNG) development in the Powder River Basin (PRB). Elevated salinity and sodicity in CBNG water has become a major concern, particularly with regard to its use or disposal. If land applied, elevated salinity and/or sodicity in CBNG water may adversely affect soil physical properties such as structure, infiltration, permeability, and aeration. Soil chemical properties impacted by CBNG water utilized for irrigation include changes in nutrient supply, modification of the soil exchange complex with dispersion, and pH effects. A sodic soil has been shown to maintain good soil structure if the salinity level is maintained above the threshold electrolyte concentration (TEC). In this study, cropland that was irrigated with Piney Creek (control) and CBNG waters were sampled two years after CBNG water irrigation and compared to baseline and post irrigation data to evaluate changes in soil physical and chemical properties. CBNG water was treated with gypsum (CaSO4●2H2O), sulfur (S) via a S burner, or both, and soils were amended with CaSO4●2H2O, elemental S, or both (GS). Changes in soil physical and chemical properties were monitored using a split plot experiment. Single ring infiltration experiments were conducted within each plot to determine if infiltration rates were affected by water type and/or water and soil treatments. A significant decrease in infiltration rate was observed for plots irrigated with CBNG water without soil amendments or water treatments. Soil samples were taken and analyzed for chemical parameters including pH, electrical conductivity (EC) and sodium adsorption ratio (SAR) before CBNG water application and two seasons following final CBNG water application. Decreases in EC and SAR were determined for most CBNG irrigated plots. Higher EC levels were detected in S and GS plots due to delayed microbial conversion of S. It appears Na + is moving through the soil profile with all soil amendment and water treatment combinations; however, CBNG-GSB+GS treatment results in the lowest SAR in the A and Bt1 horizons.

USE OF COAL BED NATURAL GAS (CBNG) WATERS: SOIL AND PLANT RESPONSES 1

With about 20,000 coal bed natural gas (CBNG) wells currently permitted or drilled in the Powder River Basin (PRB) of Montana and Wyoming and projections of more than 50,000 future wells, CBNG water production in the PRB over the next 15 years will exceed 366,000 ha-m. Therefore, proper CBNG product water utilization is warranted. Land application using conventional center-pivot and side-roll irrigation systems is a common strategy for managing saline-sodic waters derived from CBNG production within the PRB. Various soil and plant impacts resulting from 1 to 4 years of saline-sodic water (EC = 1.8 to 4.0 dS m -1 ; SAR =15 to 38) applications were examined during the 2003 and 2004 field seasons on 6 (2003) to 8 (2004) study sites representing native range grasslands, seeded grass hayfields and alfalfa hayfields. Because soil and plant types, water application rates and water and soil treatment strategies were variable across study sites, parameters measured from each treated (irrigated) site were compared directly to those from representative control (non-irrigated) sites. Soil chemical and physical parameters including pH, EC, SAR, texture, bulk density, surface infiltration rate and Darcy flux rates were measured at various depth intervals to 120 cm. Multiple year applications of saline-sodic water produced consistent trends of increased soil EC and SAR values at depths to 30 cm, reduced surface infiltration rates and reduced Darcy flux rates to 120 cm. Significant (P=0.05) differences in EC, SAR, infiltration rates and Darcy flux (P=0.10) were determined at most sites. Up to 4 years of saline-sodic water applications significantly (P=0.05) increased native perennial grass biomass production and cover on treated vs. control sites. However, overall species evenness was reduced. Biological effects were variable and complex, reflecting site specific conditions and management strategies.

IMPACTS OF LAND APPLICATION OF SALINE-SODIC COALBED METHANE WATER ON SOIL PHYSICAL AND CHEMICAL PROPERTIES IN WYOMING 1

Changes in soil physical and chemical properties due to land application of coalbed methane (CBM) waters were investigated in study sites located in northwest Powder River Basin (PRB) of Wyoming. Samples of CBM water used for land application and analyzed for pH, electrical conductivity (EC), and sodium adsorption ratio (SAR) values. Water quality data indicated that EC and SAR values of CBM water samples were greater than the recommended values for irrigation use (0.75 dS m -1 and <10 SAR). Impacts of these poor- quality CBM waters on soil physical and chemical properties were evaluated by collecting soil samples during the 2003 irrigation season from 6 depths (0-5, 5-15, 15-30, 30-60, 60-90 and 90-120 cm) from 6 sites that received CBM water applications for up to 3 years, which were compared to control sites. Changes in soil physical (e.g., infiltration rates, bulk density) and soil chemical (pH, EC, and SAR of saturation paste extracts) properties were determined. Our study indicates that the pH values are significantly (p = 0.05) greater in irrigated plots than control plots at depths of 0-5 and 30-60 cm in site 1 and 0-60 cm in site 4. The EC values were significantly greater in irrigated sites than control plots at 0-60 cm depth in sites 1, 4 and 6, 5-30 cm in site 3, and 0-15 cm in site 5. SAR values were significantly greater in irrigated sites than control plots in the upper 60 cm in sites 1 and 5, 0-5 cm site 4, and 5-30 cm in site 6. Irrigated sites 1, 3, and 4 had significantly lower %clay. Hydraulic conductivity in sites 1 and 5 were significantly lower than control plots. Thus, irrigation with poor-quality CBM water had significant impacts on soil chemical and physical properties. It has been estimated that over the next 15 years CBM water production in the PRB will exceed 366,000 ha-m. The results of this study will be useful to understand the potential changes in soil properties due to land application of CBM waters and to develop possible mitigating criteria for preserving impacted PRB ecosystems.