Thomas F. Ducey

Soil Microbial Community Response to Corn Stover Harvesting Under Rain-Fed, No-Till Conditions at Multiple US Locations

Harvesting of corn stover (plant residues) for cellulosic ethanol production must be balanced with the requirement for returning plant residues to agricultural fields to maintain soil structure, fertility, crop protection, and other ecosystem services. High rates of corn stover removal can be associated with decreased soil organic matter (SOM) quantity and quality and increased highly erodible soil aggregate fractions. Limited data are available on the impact of stover harvesting on soil microbial communities which are critical because of their fundamental relationships with C and N cycles, soil fertility, crop protection, and stresses that might be imposed by climate change. Using fatty acid and DNA analyses, we evaluated relative changes in soil fungal and bacterial densities and fungal-to-bacterial (F:B) ratios in response to corn stover removal under no-till, rain-fed management. These studies were performed at four different US locations with contrasting soil-climatic conditions. At one location, residue removal significantly decreased F:B ratios. At this location, cover cropping significantly increased F:B ratios at the highest level of residue removal and thus may be an important practice to minimize changes in soil microbial communities where corn stover is harvested. We also found that in these no-till systems, the 0- to 5-cm depth interval is most likely to experience changes, and detectable effects of stover removal on soil microbial community structure will depend on the duration of stover removal, sampling time, soil type, and annual weather patterns. No-till practices may have limited the rate of change in soil properties associated with stover removal compared to more extensive changes reported at a limited number of tilled sites. Documenting changes in soil microbial communities with stover removal under differing soil-climatic and management conditions will guide threshold levels of stover removal and identify practices (e.g., no-till, cover cropping) that may mitigate undesirable changes in soil properties.

Soil biology for resilient, healthy soil

What is a resilient, healthy soil? A resilient soil is capable of recovering from or adapting to stress, and the health of the living/biological component of the soil is crucial for soil resiliency. Soil health is tightly coupled with the concept of soil quality (table 1), and the terms are frequently used interchangeably. The living component of soil or soil biota represents a small fraction (<0.05% dry weight), but it is essential to many soil functions and overall soil quality. Some of these key functions or services for production agriculture are (1) nutrient provision and cycling, (2) pest and pathogen protection, (3) production of growth factors, (4) water availability, and (5) formation of stable aggregates to reduce the risks of soil erosion and increase water infiltration (table 2). Soil resources and their inherent biological communities are the foundation for agricultural production systems that sustain the human population. The rapidly increasing human population is expanding the demand for food, fiber, feed, and fuel, which is stretching the capacity of the soil resource and contributing to soil degradation. Soil degradation decreases a soils production capacity to directly supply human demands and decreases a soils functional capacity to perform numerous critical services, which…

Designer, acidic biochar influences calcareous soil characteristics

In a proof-of-concept study, an acidic (pH 5.8) biochar was created using a low pyrolysis temperature (350 °C) and steam activation (800 °C) to potentially improve the soil physicochemical status of an eroded calcareous soil. Biochar was added at 0%, 1%, 2%, and 10% (by wt.) and soils were destructively sampled at 1, 2, 3, 4, 5, and 6 month intervals. Soil was analyzed for gravimetric water content, pH, NO3-N, plant-available Fe, Zn, Mn, Cu, and P, organic C, CO2 respiration, and microbial enumeration via extractable DNA and 16S rRNA gene copies. Gravimetric soil water content increased with biochar application regardless of rate, as compared to the control. Soil pH decreased between 0.2 and 0.4 units, while plant-available Zn, Mn, and P increased with increasing biochar application rate. Micronutrient availability decreased over time likely due to insoluble mineral species precipitation. Increasing biochar application raised the soil organic C content and remained elevated over time. Increasing biochar application rate also increased respired CO2, yet the CO2 released decreased over time. Soil NO3-N concentrations significantly decreased with increasing biochar application rate likely due to microbial immobilization or denitrification. Depending on application rate, biochar produced a 1.4 to 2.1-fold increase in soil DNA extracted and 1.4- to 2.4-fold increase in 16S rRNA gene abundance over control soils, suggesting microbial stimulation and a subsequent burst of activity upon biochar addition. Our results showed that there is promise in designing a biochar to improve the quality and water relations of eroded calcareous soils.

Soil physicochemical conditions, denitrification rates, and abundance in north Carolina coastal plain restored wetlands.

Over the last century, North Carolina has seen a severe reduction in the percentage of wetlands and a rise in negative environmental impacts related to this loss. To counter these effects, efforts have been enacted to mitigate wetland loss and create new wetland areas. The objective of this study was to assess the impact of hydrological restoration at several sites in the North Carolina coastal plain. Nine sites were selected for study. Hydrologically restored wetlands were compared with natural wetlands and prior converted (PC) croplands (i.e., historic wetlands under agricultural production). Each site was analyzed along a relative wetness gradient, and physicochemical properties, denitrification enzyme activity, and NO reductase gene () abundances using real-time PCR were measured. Physicochemically, restoration resulted in significantly increased levels of total C as compared with PC cropland sites. Restored wetland sites also saw pH, soil moisture, P, and NO+NO approximate levels similar to those of natural wetlands. Denitrification enzyme activity rates varied based on relative wetness within individual sites, generally increasing with increasing soil moisture. However, denitrification tended to be lower in restored wetland sites relative to natural wetlands. Gene abundances of saw statistically significant decreases in restored wetland soils. In conclusion, although analysis of restored wetlands reveals clear changes in several physicochemical characteristics and significant decreases in gene abundances, restoration efforts appear to have not significantly affected the denitrification component of the N cycle.

An analysis of the link between strokes and soils in the South Carolina coastal plains.

The Stroke Belt is a geographical region of the Southeastern United States where resident individuals suffer a disproportionately higher rate of strokes than the rest of the population. While the “buckle” of this Stroke Belt coincides with the Southeastern Coastal Plain region of North and South Carolina and Georgia, there is a paucity of information pinpointing specific causes for this phenomenon. A number of studies posit that an exposure event–potentially microbial in nature–early in life, could be a risk factor. The most likely vector for such an exposure event would be the soils of the Southeastern Coastal Plain region. These soils may have chemical and physical properties which are conducive to the growth and survival of microorganisms which may predispose individuals to stroke. To this aim, we correlated SC stroke mortality data to soil characteristics found in the NRCS SSURGO database. In statewide comparisons, depth to water table (50 to 100 cm, R = 0.62) and soil drainage class (poorly drained, R = 0.59; well drained, R = −0.54) both showed statistically significant relationships with stroke rate. In a 20 county comparison, depth to water table, drainage class, hydric rating (hydric soils, R = 0.56), and pH (very strongly acid, R = 0.66) all showed statistically significant relationships with stroke rate. These data should help direct future research and epidemiology efforts to pinpoint the exact exposure events which predispose individuals to an increased stroke rate.

Biofuel Production from Catalytic Thermochemical Conversion of Animal Manure and Biomass

The objective of the research is to identify suitable catalysts to convert animal manure-based and biomass-based synthesis gas (syngas) to liquid biofuels such as mixed alcohols and hydrocarbons. Two pathways of catalytically converting syngas are investigated: (1)a two-step process involving the intermediate methanol and (2) one-step direct conversion process. A mixed stream of calibrated gases resembling the product synthesis gas composition from gasifying animal wastes and/or biomass is used as simulated feed syngas. The temperature controlled batch system consists of a 300 mL high-pressure vessel that can maintain high pressure (2 – 15 MPa) and mild temperature (100 – 300 oC). A series of batch runs include varying catalyst size, reaction time, temperature and pressure. To date, we have evaluated the efficacy of the Ru and Rh catalysts in synthesizing dimethylether (DME). The results show that under the operating conditions of 150-200oC and 2 MPa, dimethyl ether (C-O-C bond formation) was the main product formed in preference to ethanol (C-C bond formation). The efficacy of synthesizing mixed alcohols from the simulated synthesis gases having the same composition is now underway. Furthermore,the effects of sulfur on the performance of sulfur resistant catalyst such as MoS2 will also be investigated.