LAAS students present at UMN Earth & Environmental Sciences Student Research Symposium

Cold-Adapted Denitrifying Fungi for Nitrate Removal

Nour Aldossari, Brandy Toner, Satoshi Ishii

The agricultural watershed in the upper Midwest is one of the major causes of high nitrate (NO₃^-) concentration in the Mississippi River, leading eutrophication in the Gulf of Mexico. Denitrifying bacteria have been the main focus of study to remove nitrate in environments, including constructed wetlands and woodchip bioreactors. Some fungi can also perform denitrification; however, fungi have received less attention. Fungi
may play essential roles in NO₃^- removal, especially in woodchip bioreactors because fungi can efficiently degrade woodchips and use it as carbon and energy sources. Fungi can also grow well at relatively cold temperature conditions. Furthermore, fungal hyphae could also help them to stay in the reactors, in which bacteria may be washed out. In this study, we isolated denitrifying fungi and analyzed their ability to reduce NO₃^- for future nitrate bioremediation purposes. Fungal strains isolated from soil and woodchips were incubated at 5°C and 15°C in a liquid medium supplemented with ¹⁵N-labeled nitrate, and the productions of N₂O and N₂ gases were identified
using gas chromatography-mass spectrometry (GC-MS). A total of 165 denitrifying fungal strains were obtained in this study. Among those, 37
strains reduced NO₃^- to N₂O at 5°C, 121 strains reduced NO₃^- to N₂O at 15°C, and seven strains reduced NO₃^- to N₂ at 15°C. Based on the sequencing of the fungal internal transcribed spacer (ITS) regions, many of the denitrifying fungal strains belonged to Fusarium, Mortierella, and Cylindrocarpon genera. The nitrite reductase gene nirK was not detected in all strains by PCR, and denitrifying fungi may be useful for future nitrate
bioremediation. 

A New Approach to Indirect Quantification of Ammonia Acid Trap Capture Efficiency

Jonathan Alexander, Jared Spackman, Melissa Wilson, Rodney Venterea, Fabián Fernández

Volatile ammonia (NH₃) loss is an economically and environmentally significant loss pathway of fertilizer and organic N applied to agroecosystems. Accurate quantification of these losses can be accomplished with micrometeorological methods or indirectly with mass balance approaches or N-15 tracer analysis. These methods, while accurate, are expensive and may not fit within the confines of common experimental designs used in agricultural research. Ammonia acid traps are a low-cost option to quantify relative treatment differences in volatile ammonia flux, however, the accuracy of these methods is dependent on trap design and the external environment. We developed a simple and cost-effective method to quantify ammonia acid trap capture efficiency to determine the
effectiveness of four fundamentally different acid trap designs across variable wind environments. Our results help to inform design considerations for the utilization of ammonia acid traps in plot scale agricultural research.

Sewage Sludge Incinerator Ash as a Recycled Phosphorus Source

Persephone Ma and Carl Rosen

The Twin Cities incinerate sewage sludge to produce energy while reducing volume and organic contaminants. Research has shown that the remaining ash, which is usually landfilled, can be a viable phosphorus (P) source for crops. However, there are questions regarding the behavior of P release, the amount of plant available P compared to total P, and metals concentrations. To determine the viability of this ash as a P fertilizer, we conducted a 3-year corn and soybean field study on a Waukegen silt loam soil comparing this ash to other P sources including conventional P fertilizer (triple super phosphate), dried pelletized biosolids, and struvite. Each P source was applied in the spring at 20, 40, 60, and 80 kg P/ha, with a zero-P control included. Soil samples were taken before application, at midseason, and at the end of the season and were analyzed for available P and EPA 503 metals. In-situ (PRS) probes that act as a proxy for ions in soil water were also analyzed. Additionally, plant samples were taken at the end of the season and were analyzed for P and EPA 503 metals. Corn yields in 2017 and 2018 were high overall, though they were not significantly affected
by P source or rate. Data from the chemical analysis of 2017 and 2018 end-of-season soil in the top 15 cm showed a significant increase of Olsenand Bray-P with increasing application rates for all P sources. Additionally, DTPA-zinc and DTPAcopper increased significantly with increasing rates with biosolids and ash applications resulting in the highest concentrations. Overall, there were no detectable increases in any metals of concern including total Hg, Se, As, Cd, and Pb. Late season plant-available PRS-P increased with increasing P rate. Cumulative PRS-Cu and PRS-Zn were
highest in biosolids treatments in 2018. Available data from all three years (2017-2019) will be presented.

The Effect of Climate Change on Methylmercury in Boreal Peatlands

Caroline Pierce, Stephen D. Sebestyen, Randall K. Kolka, Natalie Griffiths, Edward A. Nater, Brandy M. Toner

Peatlands hold large quantities of atmospherically deposited Hg and can be
significant sources of methylmercury (MeHg). MeHg is a neurotoxin produced within peatlands and exported to aquatic systems where it bioaccumulates up the food chain resulting in human health effects. Because peatlands are saturated wetland systems they provide ideal conditions for methylation, so much so that the percentage of wetlands in a watershed is positively correlated with MeHg concentrations in fish. This study investigated how increased temperature may impact MeHg in peat porewaters and export to surface waters. Global models predict a 2–4.5°C increase in temperature with more drastic increases at higher latitudes, where most peatlands are located. Peatlands are expected to become drier due to reduced precipitation. The combination of these factors may turn peatlands from mercury sinks into sources. Samples were collected from 10 enclosures at the Spruce and Peatland Responses Under Changing
Environments (SPRUCE) site located in Minnesota. Each enclosure has above and belowground heating resulting in temperature treatments ranging from +0°C to +9°C relative to ambient. In porewaters, THg decreased with
increasing temperature and MeHg increased with temperature. In outflow, both THg and MeHg decreased with increasing temperature. Temperature and discharge volume are negatively correlated because as the temperature increases, the watertable drops. The trend in decreasing mercury flux with temperature can be attributed to the decrease in discharge volume. Our findings suggest that while temperature plays a role in the production of methylmercury within porewaters, the export of methylmercury is controlled by discharge volume. Temperature will produce more MeHg but rewetting events will be required to flush MeHg into streams/lakes where it will impact aquatic wildlife.

Identifying Phosphorus Hotspots in the Red River Valley of the North

Heidi R. Reitmeier and Lindsay A. Pease

This study explores a 40-year historical record of nutrient management data to identify how changing trends in cropping and fertilizer application has affected phosphorus loss risk in Northwest Minnesota. For this study, nutrient management records spanning from 1978 to 2018 were compiled across 1500 acres farmed by the University of Minnesota Northwest Research & Outreach Center (UMN NWROC). The UMN NWROC is located in the Red River Basin of the North—a critical watershed leading to Canada’s
Lake Winnipeg. Due to rising concerns about recurrent harmful algal blooms in Lake Winnipeg, there is a growing need to identify best management practices (BMPs) for phosphorus loss within the basin. This study combines long-term historical data with the Minnesota Phosphorus
Index to provide insight into the benefits and limitations of in-field phosphorus management (i.e., the 4 R's) as a BMP for water quality improvement in the Red River Basin of the North.

Integrating Cover Crops and Manure: Best Management Practices

Manuel J. Sabbagh and Melissa L. Wilson

Cover crop (CC) adoption rates are low, particularly in the upper Midwest such as in Minnesota. Producers are becoming more interested in integrating CC in their farm management systems, especially when manure is utilized as a nutrient source. We aim to develop and demonstrate the best management practices to integrate CC and manure in cold climates. This
three-year study began in spring 2019 and will be conducted at the University of Minnesota Research and Outreach Center in Waseca, MN. Various CC species and seeding methods were evaluated and liquid dairy and swine manure were injected through sweeps to minimize soil disturbance during early and late fall. We aim to determine the effects of the combination of CC and manure have on soil health, nutrient cycling, and agronomic responses in comparison to the two practices alone.

Irrigation management impacts on corn yield and nitrate leaching

Gurparteet Singh and Vasudha Sharma

Irrigated agriculture combined with fertilizer application, normally involves nutrient leaching. The environmental impacts of irrigated agriculture on ground and surface water resources are of major concern in Minnesota. Better irrigation scheduling has the potential in addressing these complex agricultural environmental challenges we face. Irrigation scheduling enables the irrigator to apply the right amount of water at the right time, which increases irrigation efficiency and reduces nitrate-N leaching. However, proper irrigation scheduling is a difficult task. Over-irrigation wastes water, causes nutrients to leach, contaminates ground water, increases energy and
labor costs, and reduces soil aeration. On the other hand, under irrigation creates plant water stress and reduces yield.

Four irrigation scheduling methods (1) infield soil moisture monitoring using soil moisture sensors, (2) Irrigation Management assistant tool (IMA), (3) the University of Minnesota checkbook method, and (4) crop growth model (EPIC) are evaluated and compared in terms of total volume of water used, nitrate leaching and corn yield for two corn growing seasons (2019-2020) at two different sites. The goal of this research is to identify and develop irrigation management strategies and techniques that will increase corn water use efficiency, while minimizing nitrate leaching and maximizing crop utilization of soil nitrogen without impacting the yield.