Texas Soil Research Articles

Validation of downscaled 1‐km SMOS and SMAP soil moisture data in 2010–2021

AbstractSoil moisture (SM) is an important component for many applications in agriculture, hydrology, meteorology, and ecology. In past decades, passive/active microwave sensors onboard Earth observation satellites are utilized to obtain SM estimates from radiometer or radar observations. In this study, the Soil Moisture and Ocean Salinity (SMOS) Level 3 daily SM retrievals at 25‐km spatial resolution between 2010 and 2021 were downscaled through an apparent thermal inertia principle‐based algorithm. The 1‐km downscaled SMOS SM retrievals were validated by in situ measurements from 635 sites of 19 SM networks in the world, which were acquired from the International Soil Moisture Network and Texas Soil Observation Network. Additionally, the validation results of the SMOS SM products were compared with those of the Soil Moisture Active Passive (SMAP) global Level 2 enhanced SM products at 1‐km downscaled and original 9‐km resolution in 2015–2021. It shows that the downscaled SMOS SM data have an overall improved accuracy and outperform the coarse‐resolution 25‐km data, with a lower unbiased Root Mean Squared Error of 0.114 m3/m3 on average.

Exploring the Spatial Autocorrelation in Soil Moisture Networks: Analysis of the Bias from Upscaling the Texas Soil Observation Network (TxSON)

Microwave remote sensing such as soil moisture active passive (SMAP) can provide soil moisture data for agricultural and hydrological studies. However, the scales between station-measured and satellite-measured products are quite different, as stations measure on a point scale while satellites have a much larger footprint (e.g., 9 km). Consequently, the validation for soil moisture products, especially inter-comparison between these two types of observations, is quite a challenge. Spatial autocorrelation among the stations could be a contribution of bias, which impacts the dense soil moisture networks when compared with satellite soil moisture products. To examine the effects of spatial autocorrelation to soil moisture upscaling models, this study proposes a spatial analysis approach for soil moisture ground observation upscaling and Thiessen polygon-based block kriging (TBP kriging) and compares the results with three other methods typically used in the current literature: arithmetic average, Thiessen polygon, and Gaussian-weighted average. Using the Texas Soil Observation Network (TxSON) as ground observation, this methodology detects spatial autocorrelation in the distribution of the stations that exist in dense soil moisture networks and improved the spatial modeling accuracy when carrying out upscaling tasks. The study concluded that through TBP kriging the minimum root-mean-square deviation (RMSD) is given where spatial autocorrelation takes place in the soil moisture stations. Through TBP kriging, the station-measured and satellite-measured soil moisture products are more comparable.

Field-scale soil moisture estimation using sentinel-1 GRD SAR data

Soil moisture is a critical land variable that controls the energy and mass balance in land–atmosphere interactions. Spaceborne Synthetic Aperture Radar (SAR) sensors offer an efficient way to map and monitor soil moisture because of their sensitivity towards the dielectric and geometric properties of the target. In addition, SAR acquisitions are weather-independent, providing a significant advantage over optical imaging during periods of cloud cover. However, vegetation cover makes these processes more complex and influences the interaction of SAR backscatter resulting from combined soil matrix and vegetation cover. Therefore, using SAR data, it is necessary to compensate for vegetation contribution in total backscatter while estimating soil moisture over the vegetated soil surface. This study presents a technique that utilizes a vegetation index derived from SAR data to generate high-resolution soil moisture maps. It is noteworthy that this proposed soil moisture retrieval method uses only the dual-polarimetric Ground Range Detected (GRD) SAR product, i.e., only backscatter intensities. Hence, the proposed method has a high potential for operational soil moisture monitoring globally. We validated over 34 soil moisture stations of the Texas Soil Observation Network (TxSON) using time-series Sentinel-1 SAR data. The Root Mean Square Error (RMSE) values for estimated volumetric soil moisture are within the range of 0.048 m3 m−3 to 0.055 m3 m−3 with the Pearson correlation coefficient r>0.79. The code to generate DpRVIc in Google Earth Engine is available at: https://github.com/Narayana-Rao/dual_pol_descriptors.

Exploring the Spatial Autocorrelation in Soil Moisture Networks: Analysis of the Bias from Upscaling the Texas Soil Observation Network (TxSON)

Exploring the Spatial Autocorrelation in Soil Moisture Networks: Analysis of the Bias from Upscaling the Texas Soil Observation Network (TxSON)

Computation Approach for Quantitative Dielectric Constant from Time Sequential Data Observed by CYGNSS Satellites

This paper describes a computation method for obtaining dielectric constant using Global Navigation Satellite System reflectometry (GNSS-R) products. Dielectric constant is a crucial component in the soil moisture retrieval process using reflected GNSS signals. The reflectivity for circular polarized signals is combined with the dielectric constant equation that is used for radiometer observations. Data from the Cyclone Global Navigation Satellite System (CYGNSS) mission, an eight-nanosatellite constellation for GNSS-R, are used for computing dielectric constant. Data from the Soil Moisture Active Passive (SMAP) mission are used to measure the soil moisture through its radiometer, and they are considered as a reference to confirm the accuracy of the new dielectric constant calculation method. The analyzed locations have been chosen that correspond to sites used for the calibration and validation of the SMAP soil moisture product using in-situ measurement data. The retrieved results, especially in the case of a specular point around Yanco, Australia, show that the estimated results track closely to the soil moisture results, and the Root Mean Square Error (RMSE) in the estimated dielectric constant is approximately 5.73. Similar results can be obtained when the specular point is located near the Texas Soil Moisture Network (TxSON), USA. These results indicate that the analysis procedure is well-defined, and it lays the foundation for obtaining quantitative soil moisture content using the GNSS reflectometry results. Future work will include applying the computation product to determine the characteristics that will allow for the separation of coherent and incoherent signals in delay Doppler maps, as well as to develop local soil moisture models.

Stabilization of expansive soils using ionic stabilizer

In many parts of the USA, expansive soils pose a significant hazard to infrastructures. These kinds of soils owe their characteristics to the presence of swelling clay minerals. As they get wet, they swell; conversely, as they dry, they shrink. Many stabilization methods have been developed to mitigate the adverse effects of expansive soil. One of them is the use of the ionic additive. In this research, a liquid ionic product is evaluated as a non-traditional stabilizer. Soil samples from a specific construction site in Texas and soil samples from Oklahoma were utilized. The evaluation tests involve the suction measurements, swelling, and plasticity index for treated and untreated soils. Cyclic swelling tests were also carried out on reconstituted specimens. From laboratory tests and analysis, it was found that this additive is effective in reducing swelling of both Texas and Oklahoma soils. It reduces swelling of Texas soils by 0.4–6% and Oklahoma soil by 2–7.4%. The results of swelling cycles reveal a permanent effect of this stabilizer on mitigating the swelling behavior. After the 3rd swelling cycle, the swelling for Oklahoma soils was 5.58% lower than the natural soil, and for Texas soils, it was reduced by 6.02–8.49% for different concentrations of the additive. However, no definitive trend was observed for reducing the shrinkage potential.

Enhancing landowner adoption of the Natural Resource Conservation Service’s recommended beef cattle grazing management practices

Water has a significant role in society, whether through human consumption or agricultural use. The Lavaca Watershed is an agricultural community affected by nonpoint source pollution, and water quality protection is of high concern. Beef cattle operations are linked to nonpoint source pollution which contaminates surrounding water sources. If proper grazing management practices are not used, wastes from the operation impair water quality in the area. Landowners should use proper stocking rates and implement best management practices to benefit land and water quality in addition to overall operation profit. Females reported a higher intention to adopt, indicating these respondents are more open to practice changes on their own operation. Results indicated a need for the Natural Resource Conservation Service (NRCS) and Texas Soil and Water Conservation Board to conduct further outreach to increase interaction with landowners. NRCS agencies could help increase the use of water conservation plans and inquiries by making this clear to current landowners participating in their program as well as potential clients by sending informational flyers or speaking at local organizational gatherings. The importance of adopting water management practices and barriers to adoption are ongoing global concerns.

92180 Prevalence of Clostridioides difficile strains found in Texas soil

ABSTRACT IMPACT: This work investigates C. difficile strains in soil as a potential exposure for gut colonization and community-acquired infection of C. difficile. OBJECTIVES/GOALS: Identifying environmental sources of C. difficile can inform how non-hospital reservoirs can potentially contribute to C. difficile exposure and subsequent gastrointestinal colonization. The objective of the study was to identify C. difficile and toxin genes across various soil sources. METHODS/STUDY POPULATION: This was a cross-sectional study utilizing soil samples obtained throughout Texas, USA. All samples were collected between August and November of 2019 and 2020. Samples were taken from human and animal high contact areas, such as recreational parks. Samples were stored at -80oC until processing. DNA extractions were performed using the DNeasy Powersoil Pro Kit (Qiagen) per manufacturer’s instructions. Real-time PCR was also performed on extracted DNA using the Microbial DNA qPCR Multi-Assay Kit for Clostridium difficile Pathogenicity (Qiagen) for the identification of C. difficile, toxin A (TcdA), and toxin B (TcdB) genes. RESULTS/ANTICIPATED RESULTS: A total of 137 soil samples including dry dirt, sand, and wet soil near water sources were collected and processed for the presence of C. difficile. These included samples from parks and trails (42.3%), water sources (36.5%), and other public spaces (21.2%). C. difficile was identified in 59 (43.1%) soil samples: 6 (4.4%) with Toxin A and 2 (1.5%) with toxin B production. C. difficile was most prevalent among samples taken from parks and trails (50.0%), followed by other public spaces (48.3%), and water sources (32.0%). The median (IQR) Cq value for the C. difficile gene was 39.24 (33.45-40.47) among samples that tested positive. DISCUSSION/SIGNIFICANCE OF FINDINGS: We identified a high prevalence of Clostridioides difficile in soil samples, though toxin gene detection prevalence was low. Future studies will analyze other sources, including water and varying surface samples to obtain a comprehensive view of C. difficile in the environment.

Soil Water Content and Soil Respiration Rates Are Reduced for Years Following Wildfire in a Hot and Dry Climate

AbstractIncreasing fire severity and frequency may stress ecosystems also impacted by climate change. We studied the physical limitations to regeneration after fire in an ecosystem that already experiences high summer temperatures and drought and is therefore a possible analog of the future. We compared soil respiration as an indicator of microbial activity in burned and unburned forest soils in central Texas, where two recent wildfires have occurred (2011 and 2015). We also measured soil temperature, water content, soil water δ18O and δD values, total C, N, pH, and δ13C values of total organic matter. Burned soils had lower total C and N than unburned soils; however, lab‐based respiration measurements, which controlled for temperature and water content, suggest that microbial activity in burned and unburned soils are similar. Conversely, field measurements show that during hot and dry months respiration rates in burned soils were much lower than they were in unburned soils due to differences in soil temperature and water content. Soil temperature at 5 cm reached 60°C in burned soils due to the removal of canopy cover, the removal of organic matter insulation, and the deposition of black ash on the soil surface. Higher temperatures increased evaporation as indicated by significantly lower deuterium excess of water in soils burned in 2015 than unburned soils. If the disturbance of vegetation by fire is substantial enough, the resulting perturbations to soils persist for years, most importantly increased heat absorption which results in lower water contents and ultimately reduced microbial activity.

Vertical mobility and cotton tolerance to trifludimoxazin, a new protoporphyrinogen oxidase-inhibiting herbicide, in three West Texas soils

AbstractTrifludimoxazin, a new protoporphyrinogen oxidase–inhibiting herbicide, is being evaluated for possible use as a soil-residual active herbicide treatment in cotton for control of small-seeded annual broadleaf weeds. Laboratory and greenhouse studies were conducted to compare vertical mobility and cotton tolerance of trifludimoxazin to flumioxazin and saflufenacil, which are two currently registered protoporphyrinogen oxidase–inhibiting herbicides for use in cotton, in three West Texas soils. Vertical soil mobility of trifludimoxazin was similar to flumioxazin in Acuff loam and Olton loam soils, but was more mobile than flumioxazin in the Amarillo loamy sand soil. The depth of trifludimoxazin movement after a 2.5-cm irrigation event ranged from 2.5 to 5.0 cm in all soils, which would not allow for crop selectivity based on herbicide placement, because ideal cotton seeding depth is from 0.6 to 2.54 cm deep. Greenhouse studies indicated that PRE treatments were more injurious than the 14 d preplant treatment when summarized across soils for the three herbicides (43% and 14% injury, respectively). No differences in visual cotton response or dry weight was observed after trifludimoxazin preplant as compared with the nontreated control within each of the three West Texas soils and was similar to the flumioxazin preplant across soils. On the basis of these results, a use pattern for trifludimoxazin in cotton may be established with the use of a more than 14-d preplant restriction before cotton planting.

Root morphological traits of winter wheat under contrasting environments

AbstractRoots strongly influence the growth and yield of field crops. We characterized root morphological traits of 10 winter wheat varieties in order to determine the extent they were influenced by the environments and impacted grain yield under two irrigation regimes at Bushland (a cooler, drier site with clay loam soil) and Uvalde (a warmer, wetter site with clay soil) in Texas, USA, from 2015 to 2017. Major root traits, including root diameter, specific root length (SRL), root surface area (SSA), tissue mass density (TMD), root length density (RLD), and root weight density, were measured and related to one another and to grain yield. RLD of wheat decreased but SRL and SSA increased with soil depth. Irrigation was second to environment in affecting root traits. Compared with Uvalde, the environment of Bushland promoted deeper root growth, higher TMD, but reduced SRL and SSA. Water deficit inhibited RLD and root: shoot ratio at Bushland, but moderately promoted them at Uvalde. Both SRL and RLD were positively associated with grain yield, with the former relation stronger under drought. The dichotomy of “conservative” versus “acquisitive” root strategy partially explained the variations of root traits of winter wheat in contrasting environments.

Simultaneous determination of β-glucosidase, β-glucosaminidase, acid phosphomonoesterase, and arylsulfatase activities in a soil sample for a biogeochemical cycling index

Four enzymes activities (EAs) have been targeted as soil health indicators for their important role in reactions releasing bioavailable nutrients within C (β-glucosidase), N and C (β-glucosaminidase), P (acid phosphomonoesterase) and S (arylsulfatase) cycling. Traditionally these EAs are assayed independently on air-dried soil by measuring the release of p-nitrophenol from a substrate analog. Previously, we suggested a novel approach to assess multiple EAs simultaneously in the same soil sample by adding two or three substrates to obtain a comparable index. Our current study provides a combined assay for simultaneous determination of these four EAs in the same soil sample. For the incubation step of our combined assay, we tested modified universal buffer (MUB) because it is used for assaying β-glucosidase and acid phosphomonoesterase activities and tested acetate buffer as it is used for assaying β-glucosaminidase and arylsulfatase activities. Using the acetate buffer (pH 5.8) for the combined assay showed the lowest percent of difference (average of −14%) compared with the sum of individual EAs, and showed positive significant correlations (p < 0.001) with the sum of the individual EAs (r = 0.97) and with soil organic C (r = 0.94) and total nitrogen (TN) (r = 0.93). This combined acetate buffer assay (“CNPS activity”) differentiated among agroecosystems similarly to the sum of the individual EAs in Texas soils (cotton < grass < Conservation Reserve Program) and both approaches showed a tendency for higher activities in a diversified rotation compared to corn-soybean and a grass system for Minnesota soils. Use of the novel CNPS activity will provide a uniform biogeochemical cycling index while reducing time and resources compared to assaying the EAs individually.

Registration of ‘CP 08‐1968’ Sugarcane

‘CP 08‐1968’ (Reg. No. CV‐185; PI 687332) sugarcane (a complex hybrid of Saccharum spp.) cultivar was developed through cooperative research conducted by the USDA‐ARS, the University of Florida, and the Florida Sugarcane League, Inc. At the 5 June 2017 Florida Sugarcane Variety Committee Meeting, CP 08‐1968 was released to growers for all soils in Texas; seedcane became available in September 2018. At the 30 Oct. 2017 Florida Sugarcane Variety Committee Meeting, CP 08‐1968 was approved as a co‐release to growers with sand soils in Florida and all soils in Texas. CP 08‐1968 was selected from a biparental cross of CP 01‐1178 × CP 00‐1301 made at Canal Point, FL, in November 2006. The female parent, CP 01‐1178, and the male parent, CP 00‐1301, are not commercial cultivars. Cane yield of CP 08‐1968 on sand soils in Florida, averaged across nine harvests through three crop cycles (plant‐cane, first‐ratoon, and second‐ratoon), was 15.0 and 10.1% higher (P &lt; 0.1) than that of CL 88‐4730, a commercial check for sand soils, and CP 89‐2143, a high commercial recoverable sucrose (CRS) commercial check for muck and sand soils. Although CP 08‐1968 had 2.8 and 6.0% lower CRS than CL 88‐4730 and CP 89‐2143, respectively (Glaz et al., 2000), high cane yield resulted in 11.3 and 2.1% higher (P &lt; 0.1) sucrose yield than CL 88‐4730 and CP 89‐2143, respectively. CP 08‐1968 was released because of its high cane and sucrose yields on sand soils, as well as its acceptable levels of resistance to brown rust, smut, Sugarcane mosaic virus strain E (mosaic), Sugarcane yellow leaf virus (Comstock et al., 1999), and ratoon stunt. CP 08‐1968 is susceptible to orange rust and has moderate to good freeze tolerance. CP 08‐1968 tested negative for the Bru1 quantitative trait locus, which is an indicator of brown rust resistance.

The Texas Soil Observation Network:A Comprehensive Soil Moisture Dataset for Remote Sensing and Land Surface Model Validation

Core Ideas TxSON is a Core Cal/Val Site for the NASA SMAP, SMOS, and Sentinel programs. TxSON consists of 40 in situ locations nested within a 36‐km EASE2 grid cell. Locations monitor soil moisture, temperature, and precipitation at 5, 10, 20, and 50 cm. Hourly, quality‐controlled data from 2015 to 2018 are available. The spatiotemporal variability of soil water content (SWC) at the remote sensing scale requires dense monitoring for calibration and validation. Here, we present an overview of the Texas Soil Observation Network (TxSON), an intensively monitored area in the semiarid rangelands of the central Texas Hill Country. TxSON is a dense network consisting of 40 in situ locations nested at 36, 9, and 3 km within the Equal‐Area Scalable Earth Grid and serves as a Core Calibration and Validation Site for NASA's Soil Moisture Active Passive mission. The 4‐yr dataset consists of hourly SWC measured at 5, 10, 20, and 50 cm. The SWC data are upscaled using arithmetic, Voronoi, and inverse distance weighting for 36‐, (2) 9‐, and (5) 3‐km grid cells. We present the site selection, environmental characteristics, network design, quality assurance (QA), upscaling algorithms, and data structure. Ancillary data include bulk density, particle size, and carbon content for each site and depth. We also provide automated QA for each location and scripts to use our binary flagging in upscaling methods. To summarize, the 36‐km grid cell has a mean bulk density of 1.34 ± 0.18 g cm−3 and a loam textural class. The in situ SWC has a root mean square error of 0.029 m3 m−3 against gravimetric data from 14 field campaigns. TxSON continues to add new locations with additional dense networks planned in other ecotones of the Edwards Plateau. The time series data along with scripts to import, plot, and upscaled SWC are available at https://doi.org/10.18738/T8/JJ16CF.

Root distribution patterns of reticulatus and inodorus melon (Cucumis melo L.) under subsurface deficit irrigation

Information on root growth patterns is crucial to understand cultivar adaptations to deficit irrigation, particularly for subsurface drip-irrigated crops, where root systems are more confined than furrow or sprinkler systems. A 2-year field experiment evaluated the effect of deficit irrigation (50% vs. 100% crop evapotranspiration, ETc) on root growth of melon (Cucumis melo L.) cultivars (Mission, Da Vinci, and Super Nectar) on a mollisol soil in southwestern Texas, USA. Root length intensity (La; mm cm−2), and root length density (RLD; cm cm−3) were measured at different growth stages using the minirhizotron and soil core methods, respectively. A higher La was recorded in 2012 than in 2011 (3.71 mm cm−2 vs. 0.50 mm cm−2), due to differences in temporal distribution of rainfall between years. Overall, deficit irrigation increased La as compared to 100% ETc, but significant effects occurred at depth (> 40 cm below the soil surface and > 25 cm below the subsurface drip tape). In 2012, moderate water deficit promoted deep root growth at the fruit setting stage but not in 2011, while root growth responses to cumulative deficit varied with cultivar. In 2012, deficit irrigation enhanced root growth in cv. Mission (cantaloupe; reticulatus) throughout the season, it was maintained in cv. Da Vinci (Tuscan; reticulatus), while it decreased in cv. Super Nectar (honeydew; inodorus) at the final harvest stage. Thus, the reticulatus melon cvs. Mission and Da Vinci can better adjust to moderate water-deficit conditions as compared to the inodorus melon cv. Super Nectar. Minirhizotron data provided useful information on root growth dynamics in deeper soil layers in a non-destructive way, which makes it a valuable tool in screening cultivars for water deficit adaptation.

Searching for the Immature Stages of Ixodes scapularis (Acari: Ixodidae) in Leaf Litter and Soil in Texas.

The standard tick collection methods of flagging and dragging are successful for collecting all stages of the blacklegged tick, Ixodes scapularis (Say) (Acari: Ixodidae), in the northern United States. However, for unknown reasons, these methods are unsuccessful for collecting the immature stages of I. scapularis in the southern United States. Thus, a different collection strategy was employed to search for the immature stages of I. scapularis in the southern state of Texas. Monthly sampling of three types of microhabitats potentially harboring ticks was conducted for 17 mo at the Big Thicket National Preserve. Samples of leaf litter, topsoil, and subsoil were placed within Berlese funnels to determine if the immature stages of I. scapularis are residing in these layers. No ticks were found in any of the 600 substrate samples examined. Along nearby trail edges in the same area, 656 adult I. scapularis (an average of 22.6 per 1,000 m2), as well as 268 immatures of other species (i.e., Amblyomma americanum (Linnaeaus) (Acari: Ixodidae) and Dermacentor variabilis (Say) (Acari: Ixodidae)) were collected using flagging and dragging. These results suggest that unlike speculations from previous studies in the southern United States, the immature stages of I. scapularis may not be residing in the leaf litter and soil layers in Texas. We hypothesize that they may be residing in their host's nests and burrows. Perhaps I. scapularis in the south is exhibiting a stage specific mixed host-seeking strategy by residing in nests and burrows as immatures, contributing to the geographical difference in Lyme disease prevalence between the northern and southern United States.

Soil organic carbon balance and nutrients (NPK) availability under treated wastewater irrigation for bioenergy sorghum production in an arid ecosystem

ABSTRACTThis column study evaluated the effects of irrigation with two water qualities (WW and FW) to produce bioenergy sorghum on SOC balance, nutrients availability and salt constituents in two soils (TX and NM) amended with gypsum & elemental sulfur (S) and un-amended. Study results indicated that SOC concentration was higher in freshwater irrigated columns (7.41 g kg−1) than wastewater irrigated soils (7.32 g kg−1) across growth year-soil type-amendments-depth. Soils amended with gypsum and sulfur registered significantly higher value of 7.52 and 7.41 g kg−1 compared to 7.30 and 7.23 g kg−1 in non-amended soils under fresh and wastewater irrigation, respectively. Lower SOC in WW irrigated columns could be due to the combined effects of increased salinity and priming effects. Although SOC content initially increased in gypsum and S amended soils to about 10g kg−1, at the end of the study SOC in all treatments decreased to levels significantly below the pre-study. WW irrigation added 2.00, 1.10 and 4.40 times the N, P and K added by fertilizers and was able to meet 65%, 87%, and 210% of bioenergy sorghum uptake of respective nutrients. Sulfates and chlorides of sodium and calcium were dominant salts, which significantly affected SOC and nutrients.Abbreviations: FW: freshwater; WW: treated wastewater; G + S: gypsum and elemental sulfur; NA: no amendment, TX: Texas soil and NM: New Mexico soil

Field and Laboratory Evaluation of the CS655 Soil Water Content Sensor

Core Ideas The CS655 measures two‐way travel time and attenuation of a low‐frequency EM pulse to derive Ka, EC, and SWC. Laboratory and field evaluations for five central Texas soils found the sensor robust but RMSE could be reduced by a soil‐ or site‐specific function. The factory calibration has a cross‐over point at Ka ∼15, with low bias below and high bias above. The TxSON network mean was unaffected by calibration but the variance was significantly reduced. Soil moisture sensors infer volumetric soil water content (SWC) from other properties of the bulk porous media. The CS655 water content reflectometer is a relatively new, low‐frequency electromagnetic sensor that determines relative permittivity (Ka) using the two‐way travel period and voltage attenuation of the applied signal along two 12‐cm rods. This measured attenuation is quadratically related to bulk electrical conductivity (EC). Along with an onboard thermistor, the CS655 allows a more robust correction of propagation time and Ka, which its predecessors, the CS615 and CS616, lacked. However, with new sensors it is necessary to quantify their practical accuracy in the field. Here, we present an overview of the CS655 sensor and an evaluation under both laboratory and field conditions, using five surface soils (0–10‐cm depth) in the laboratory and gravimetric samples collected in the field. Overall, a site‐specific calibration using a two‐term linearization of the SWC–Ka function reduced the root mean square error (RMSE) of the factory‐derived SWC of 0.073 and 0.043 m3 m−3 during batch and infiltration experiments, respectively, to 0.025 and 0.028 m3 m−3. Results further indicate that a soil‐specific calibration additionally reduced the RMSE to &lt;0.02 m3 m−3. Field evaluation across the Texas Soil Observation Network found that calibration reduced the variance across the network but did not affect the arithmetic mean or the RMSE against gravimetric sampling, which remained ∼0.05 m3 m−3 regardless of the SWC–Ka–EC function applied. At the regional scale, a global calibration is sufficient.

Screening Brassicaceous Plants as Biofumigants for Management of Rhizoctonia solani AG1-IA.

Brassicaceae plants rich in glucosinolates have been used as biofumigants for management of Rhizoctonia solani (teleomorph: Thanatephorus cucumeris) and other soilborne pathogens. Efficacy of brassica plant tissue has mainly been attributed to toxic isothiocyanates released upon hydrolysis of glucosinolates. Management of R. solani AG 1-IA, the causal agent of sheath blight in rice (Oryza sativa), using biofumigation, is promising but needs more validation. Biofumigation activity of nine Brassicaceae plants and two other related species were evaluated in vitro with soils from Texas, Arkansas, or Mississippi. All plants evaluated significantly suppressed the mycelium growth of R. solani AG 1-IA. Mustard (Brassica juncea) cultivars ('Brand 199', 'Ruby Streak', 'Florida Broadleaf', and 'Green Wave') consistently provided the greatest (>90%) mycelial inhibition, while sunn hemp (Crotalaria juncea) and Chinese cabbage (B. rapa) had the least suppressive effect. B. juncea 'Red Giant' and 'Sheali Hong', turnip (B. rapa), kale (B. oleracea), and arugula (Eruca sativa) showed intermediate efficacy or were inconsistent. Effects of soil pasteurization and plant tissue amendment rates were examined with B. juncea Brand 199 and Texas soil. Inhibition of mycelial growth became greater with increasing plant amendment rates up to 3.2% (wt/wt) in the soil. Soil pasteurization almost completely suppressed the release of allyl isothiocyanate (AITC). The nonpasteurized soil amended with 0.5% (wt/wt) of the plant material released 96% more AITC than the soil amended with 0.25% (wt/wt) of the plant material. The highest levels of AITC release were observed at 12 and 24 h after soil amendment, with 0.25 and 0.5% (wt/wt) of the plant material, respectively. Antifungal effects of B. juncea are attributed to dose-dependent production of volatile AITC and could be used for managing rice sheath blight caused by R. solani AG 1-IA.

Establishment of earthworms on reclaimed lignite mine soils in east Texas

Little is known about earthworm establishment after surface mining of lignite coal in continental climates such as the south central region of the United States. This study examined the abundance and species composition of earthworms in afforested lignite coal mine soils in east Texas. In a 3×3×2 factorial design, earthworms were sampled under two methods of land reclamation, haul-back (n=30) and mixed overburden (n=30). The study was conducted on a chronosequence of 2–28 years since afforestation under pine plantations and mixed pine and hardwood stands. The fieldwork was conducted from January 2012 through March 2014 using hand-sorting field methods. Forest cover type was significant at the mixed overburden sites (p=0.0128); mixed pine and hardwood forest soils (13.7±25.46ind.m−2) contained 43% more earthworms than pine plantation soils (7.6±17.06ind.m−2). The number of earthworm individuals was significantly lower in 2–8 year-old stands than in 12–18 and 22–28 year old stands (p<0.0001) at both haul-back and mixed overburden sites. Regression analysis found percentage of silt to positively influence earthworm abundance. Analysis of the species composition at both Beckville and Oak Hill mines revealed that 83% of earthworms were native earthworms species (from the genera Diplocardia and Bimastos) and 17% were exotic species (Aporrectodea trapezoides, Microscolex dubius, Lumbricus rubellus and Octolasion tytaeum).