Effect of Long-Term Semiarid Pasture Management on Soil Hydraulic and Thermal Properties.

Semiarid pasture management strategies can affect soil hydraulic and thermal properties that determine water fluxes and storage, and heat flow in unsaturated soils. We evaluated long-term (>10 years) perennial and annual semiarid pasture system effects on saturated hydraulic conductivity (ks), soil water retention curves (SWRCs), soil water thresholds (i.e., volumetric water content (θv) at saturation, field capacity (FC), and permanent wilting point (PWP); plant available water (PAW)), thermal conductivity (λ), and diffusivity (Dt) within the 0-20 cm soil depth. Forage systems included: Old World bluestem (Bothriochloa bladhii) + legumes (predominantly alfalfa (Medicago sativa)) (OWB-legume), native grass-mix (native), alfalfa + tall wheatgrass (Thinopyrum ponticum) (alfalfa-TW), and annual grass-mix (annual) pastures on a clay loam soil; and native, teff (Eragrostis tef), OWB-grazed, and OWB-ungrazed pastures on a sandy clay loam soil. The perennial OWB-legume and native pastures had increased soil organic matter (SOM) and reduced bulk density (ρb), improving ks, soil water thresholds, λ, and Dt, compared to annual teff and alfalfa-TW (P < 0.05). Soil λ, but not Dt, increased with increasing θv. Grazed pastures decreased ks and water retention compared to other treatments (P < 0.05), yet did not affect λ and Dt (P > 0.05), likely due to higher ρb and contact between particles. Greater λ and Dt at saturation and PWP in perennial versus annual pastures may be attributed to differing SOM and ρb, and some a priori differences in soil texture. Overall, our results suggest that perennial pasture systems are more beneficial than annual systems for soil water storage and heat movement in semiarid regions.

Biochar Implications Under Limited Irrigation for Sweet Corn Production in a Semi-Arid Environment.

The integration of biochar and deficit irrigation is increasingly being evaluated as a water-saving strategy to minimize crop yield losses under reduced irrigation in arid and semi-arid regions such as West Texas. A 2-year (2019 and 2020) open-field study evaluated the effect of two types of biochar amendments (hardwood and softwood) and three irrigation rates [100, 70, and 40% crop evapotranspiration (ET c ) replacement] on the physiology, plant growth, and yield of sweet corn in semi-arid West Texas. All experimental units were replicated four times in a split-plot design. The chlorophyll content (Chl SPAD ) in 40% ET c dropped significantly compared to 100% ET c and 70% ET c during the reproductive phase. Although water stress under 40% ET c decreased photosynthesis (P n ) to limit transpiration (E) by stomatal closure, it improved intrinsic water use efficiency (iWUE). The above-mentioned gas exchange parameters were comparable between 100% ET c and 70% ET c . Both biochar treatments increased Chl SPAD content over non-amended plots, however, their effect on gas exchange parameters was non-significant. All growth and yield-related parameters were comparable between 100% ET c and 70% ET c , but significantly greater than 40% ET c , except water productivity (WP). Both deficit irrigation treatments improved WP over full irrigation in 2019, but in 2020, the WP gains were observed only under 70% ET c . Hardwood biochar decreased soil bulk density and increased soil porosity, but it had a marginal effect on the water retention characteristics. These results suggest that 70% ET c can be used as an alternative to full irrigation to save water with a minimal yield penalty for sweet corn production in the West Texas region. The hardwood biochar application improved the vegetative biomass significantly but yield marginally during the first 2 years of application. A long-term study is required to test the effect of biochar under deficit irrigation beyond 2 years.

The Effects of Soil Organic Carbon Content on Plant Uptake of Soil Perfluoro Alkyl Acids (PFAAs) and the Potential Regulatory Implications.

Perfluoro alkyl acids (PFAAs) are known to bioconcentrate in plants grown in contaminated soils; the potential risk from consuming these plants is currently less understood. We determined that the current daily reference doses (RfDs) of the US Environmental Protection Agency (USEPA) could be met by consuming a single radish grown in soils with a perfluorooctanoic acid (PFOA) concentration of 9.7 ng/g or a perfluorooctane sulfonate (PFOS) concentration of 90.5 ng/g. Using a combination of our own research and literature data on plant uptake of PFAAs from soil, we developed equations for predicting PFAA bioconcentration factors (BCFs) for plant shoot and root tissues grown in soils with a known percentage of organic carbon. This calculated BCF was then applied to 6 scenarios with measured soil PFAA concentrations to estimate PFAA concentrations in plants and potential exposure to humans and animals consuming harvested vegetation. Five of the 6 scenarios showed potential for surpassing USEPA PFAA RfDs at soil concentrations as low as 24 ng/g PFOA and 28 ng/g PFOS. Environ Toxicol Chem 2021;40:832-845. © 2020 SETAC.

Perfluoroalkylsulfonic and carboxylic acids in earthworms (Eisenia fetida): Accumulation and effects results from spiked soils at PFAS concentrations bracketing environmental relevance.

Effects of perfluorobutanesulfonic acid (PFBS), perfluorohexanesulfonic acid (PFHxS), perfluorononanoic acid (PFNA), and perfluoroheptanoic acid (PFHpA) on earthworms (Eisenia fetida) in soils contaminated with these compounds at 0.1, 1, 10, 1,000, and 100,000 µg kg-1 dry weight, covering concentration levels found in background, biosolid-amended, and facility-surrounding soils, were investigated. Earthworms were exposed to spiked soil for 21 days. Concentrations of these compounds in earthworms after 21-d exposure ranged from below detection to 127 mg kg-1 wet weight with the rank order of PFNA > PFHxS > PFHpA > PFBS; no mortality of earthworms was observed in all treatments including controls, except PFBS at 1,000 µg kg-1 and all PFASs at 100,000 µg kg-1. The highest weight loss (29%) was observed for earthworms exposed to PFNA at 100,000 µg kg-1, which was significantly different from all other treatments except PFHpA at 100,000 µg kg-1. These results are expected to fill some data gaps in toxicity of PFASs in terrestrial environments and provide helpful information on the potential for trophic transport of PFASs from soil to higher organisms.

Compost salinity assessment via portable X-ray fluorescence (PXRF) spectrometry.

Compost salinity is an ongoing concern for compost producers, especially with certain feedstocks and in arid or semiarid regions. Current testing protocols call for sampling and testing ex-situ via 1:5 (w/v) slurries via electrical conductance. For this research an alternate approach has been proposed, the use of portable X-ray fluorescence (PXRF) spectrometry. Adapting methods developed for soil and water salinity analysis via PXRF, elemental data was used as a proxy for the prediction of compost salinity. In total, 74 compost samples were scanned with PXRF followed by traditional laboratory analysis. Results indicated a strong correlation between the datasets (R2 0.80; RMSE 1.04 dS m-1), similar to findings for soil and water salinity. Furthermore, using the same elemental dataset, compost pH was reasonably predicted (R2 0.63; RMSE 0.35). PXRF has the benefit of being able to be conducted in-situ or in the laboratory. And, multiple chemical parameters of interest can potentially be predicted from the same dataset. In conclusion, PXRF shows promise for rapid, in-situ salinity determination of composted products.