Location: Soil and Water Management Research2018 Annual Report
1a. Objectives (from AD-416):
1. Develop irrigation and drainage strategies in the North Central United States to protect water and soil resources a. Determine the potential of amendments to mitigate leaching and contamination of groundwater from agricultural operations. b. Identify materials and designs that will maximize contaminant removal from subsurface drainage water. 2. Identify and test innovative management practices to reduce potential adverse impacts on water quality or conserve water resources. a. Evaluate the effectiveness of low-input turf and management practices to reduce contaminant transport with runoff. b. Identify and test management practices to reduce reactive nitrogen leakage from dairy farming systems. c. Determine the impact of perenniallizing practices on the nutrient and water balances of corn/soybean systems. d. Determine the influence of management practices and water conservation strategies on water use and the occurrence and fate of contaminants in urban agriculture.
1b. Approach (from AD-416):
Protecting the integrity and supply of our water resources is one of the most important issues we will face this century and therefore the foundation of our project’s objectives (objectives 1 and 2). Our research approach requires laboratory to field scale investigations focusing on two strategies, prevention and mitigation. With the prevention strategy we will identify and understand the fate of potential water contaminants (e.g. agrochemicals: fertilizer, pesticides; anthropogenic compounds) and develop practices to prevent or minimize the off-site transport of contaminants from their site of application or point of origin. For instance, we will evaluate the fate of biochar and its efficacy as a soil amendment to reduce the leaching of agrochemicals (subobjective 1a), management practices to minimize agrochemical transport with storm runoff from low-input turf (subobjective 2a.1), and the occurrence of contaminants in urban agricultural systems and the influence of water conservation and management practices on contaminant availability (subobjective 2d). In addition, we will determine the influence of perennial cover crops and the use of different irrigation and nitrogen rates to reduce transport of nutrients with runoff and drainage from row crops (subobjective 2c). Model simulations will also be used to predict nitrate loads in tile drainage from a concentrated animal feeding operations (CAFO) dairy and simulate the efficacy of alternative practices to reduce loads (subobjective 2b). In circumstances where contaminants are transported off-site with overland flow or leaching, mitigation strategies will be taken to remove contaminants from runoff and tile drainage before they reach surface waters or groundwater. Mitigation approaches include plot-scale studies to identify optimal buffer size and management of low-input turf for the removal of contaminants transported with runoff (subobjective 2a.2), while field and modeling experiments will identify the most effective bioreactor design and materials for removing nutrients from subsurface drainage water (subobjective 1b). Our multidisciplinary team and the interrelationship of our project subobjectives within and across these strategies will make progress towards the national goal for improved water resource security.
3. Progress Report:
Objective 1a. Website at SciStarter (https://scistarter.com/project/20309-Biochar-Soil-Aging) has been established to solicit volunteers for the citizen science aging project. Experiments have been initiated for the colloidal transport of sorbed contaminants to assess net impacts on soil transport. Experiments into the interaction of water and CO2 with biochar have been initiated and the first series of biochars have been evaluated. Objective 1b. The test apparatus for the bioreactor laboratory experiment was designed and built. An experiment testing the addition of a readily available C source (acetate) to denitrifying bioreactor columns was conducted. Treatments included flow direction (up vs. down) and location of C source addition (inlet vs. midport). Water analyses were completed. The experimental data need to be analyzed. Installation of sensors and related equipment were completed at the field woodchip bioreactor site. Drainage flow to the system stopped from the end of July 2017 until snow melt runoff in March 2018. Since flow was re-established in the spring of 2018, flow through the bioreactor system has been impeded by sediment loads that occur after large precipitation events and subsequent high flows. ARS scientists in St. Paul, Minnesota are working with cooperators – Soil Water Conservation District, Minnesota Department of Agriculture, and engineering firm personnel – on solutions to the sediment issues, which have negatively impacted the capacity of the bioreactor cells to remove nitrate-N from subsurface drainage water. Objective 2a. Field plots were reconstructed and planted with low-input turfgrass, a fine fescue mixture. The rainfall simulator was modified and uniformity tests were completed. Runoff collection gutters were repositioned and tested. Instrumentation for runoff collection was repaired and installed in the plots. Manifold systems designed to deliver runon for the filter strip experiments were enlarged to accommodate a new experimental design. Methodology for the extraction and analysis of the compounds of interest were investigated and procedural modifications and validations were initiated. Rainfall simulation and runon/runoff experiments are underway. Objective 2b. Subsurface drainage flow, nitrate concentration, and nitrate load data were vetted and analyzed for a rich, nine-year hydrologic dataset from an on-farm collaboration. Six years of the data were used to investigate the potential to reduce nitrate-N subsurface drainage losses by shifting the timing and delivery of dairy manure to silage corn crops. Subsurface drainage losses were reduced by applying a lesser rate of manure during the growing season when crop uptake was high. The lower application rate and nitrate-N losses were associated with a reduction in soil nitrate concentration. Manurial N-use efficiency was also improved. Additional investigations of soil and water impacts of nutrient management in dairy systems are ongoing, including simulation modeling and influences of cold season processes on water quality. Objective 2c. Established new fields for our LTAR project, one which will be our “business as usual” treatment of conventional corn/soy rotation, and the other will be our “aspirational” treatment. Installed eddy covariance towers in each field, buried sample lines to convey gas back to a trailer where they feed a nitrous oxide analyzer, and installed soil moisture sensors and temperature sensors. Soil samples were also taken and analyzed to provide baseline soil carbon data. Objective 2d. A literature search and investigation of recorded historical land use is underway to determine potential contaminants of concern for urban agriculture. Established community gardens have been visited for observation of currently utilized management practices and identification of urban agricultural inputs. Collection of soil samples has been initiated from vacant lots and locations throughout the metropolitan area where urban food production is in progress or anticipated. A location for scientifically controlled replicated plots has been identified. Investigation and testing of extraction and analysis methodologies has been initiated and is ongoing.
1. Dairy manure management practices reduce tile drainage nitrate-nitrogen losses. The U.S. dairy industry is dramatically consolidating animals onto fewer, larger farms, increasing concern for negative soil, water quality, and atmospheric impacts. ARS researchers at Saint Paul, Minnesota, investigated environmental impacts of a manured silage corn-alfalfa cropping system on tile-drained fields on a large confinement dairy, amassing an extensive nine-year dataset of soil, water, and atmospheric measurements. By reducing manure application rates and applying manure via center pivot irrigation during the growing season, tile drainage nitrate-nitrogen losses were reduced without affecting silage corn yields. This work demonstrated that manure rate reductions and growing season application can be successful; however, additional research on these data is revealing that there may be negative consequences to carbon balance in the soils over the long term. Thus, the comprehensive approach to all relevant environmental balances is necessary to inform any system or management changes. The practice of applying manure through center pivot irrigation has not been widely adopted, primarily because of additional mechanical complexities compared to standard practice of injecting manure in the fall.
2. Chemical application setbacks safeguard water quality. Management of turfgrass on golf courses and athletic fields often involves application of plant protection products to maintain turfgrass health and performance. However, the carrying of fertilizer and pesticides with rainfall runoff from the area they were applied to neighboring surface waters can enhance algal blooms, promote eutrophication and may be harmful to sensitive aquatic organisms and ecosystems. ARS researchers at Saint Paul, Minnesota, evaluated the effectiveness of chemical application setbacks to reduce the off-site movement of chemicals with storm runoff. Experiments with water soluble tracer compounds confirmed that an increase in application setback distance by 6m resulted in a 43% reduction in the total percentage of applied chemical transported with the storm runoff to neighboring areas. Application setbacks offer turfgrass managers a mitigation approach that requires no additional resources or time inputs and may serve as an alternative practice when buffers are less appropriate for land management objectives or site conditions. This information is useful to grounds superintendents for designing chemical application strategies to maximize environmental stewardship, and to scientists and regulators working with chemical transport and risk models.
3. Biochar aging changes pesticide sorption influencing pest control and environmental fate. Impairment of water resources from applied agrochemicals typically involves transport through the soil system where colloidal particles may play an important role. Biochar, a carbon-rich soil amendment, can change with environmental aging (freeze-thaw and wet-dry cycles), which may alter its carbon sequestration potential and have water quality and ecosystem impacts. ARS researchers at Saint Paul, Minnesota, examined the impact of soil aging of an oak hardwood biochar that was buried in a silt loam soil for 6 months in the Upper Midwest (Wisconsin). There was a significant difference observed in the amount of pesticide sorption as a function of aging, with the soil aged biochar sample sorbing higher amounts (>85%) of all pesticides in the laboratory experiments compared to the fresh biochar samples which sorbed less than 15%. Both biochar samples had similar chemistries with no oxidation or chemical alterations observed after 6-months. These results are significant to farmers and policy makers and will assist scientists and engineers in understanding the potential alteration in the sorption potential for biochar once it is applied to soils. These results show the variability of biochar sorption capacities and changes with time after its addition to soil, which will affect the long-term control of pests and environmental fate of applied pesticides.
4. Nitrate recycling. Nitrate contamination of surface and ground waters is a serious problem in many agricultural regions. It is a human health risk, and also contributes to eutrophication of fresh water and the Gulf of Mexico. Most mitigation efforts focus on denitrification – encouraging microbes to convert nitrate to nitrogen gas. This is inherently wasteful, since much energy is required to initially manufacture nitrogen fertilizer, so it is desirable to develop methods to recycle nitrate. ARS scientists in St. Paul, Minnesota developed a system that can separate nitrate from contaminated water and concentrate it for re-use as fertilizer. It is DC powered and runs on solar panels, so it is suitable for remote locations. A feasibility test was successfully conducted on a contaminated trout stream that has a nitrate concentration in excess of 20 ppm. The system was able to remove an average of 42% of the nitrate from water passing through it, concentrating it in a tank that ultimately reached a concentration exceeding 500 ppm, which was subsequently used elsewhere as fertilizer. This approach could be used to recover nitrate not only from streams, but also from contaminated wells, ponds, and lakes.
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