Location: Soil and Water Management Research2017 Annual Report
1. Develop irrigation and drainage strategies for emerging cropping systems in the North Central United States to protect water and soil resources. a. Develop methods to facilitate the success of living mulch systems through the use of supplemental irrigation, and evaluate their environmental impact. b. Develop N management strategies for large dairy operations to reduce nutrient losses through artificial subsurface drainage. 2. Reduce the potential adverse impacts of agronomic and horticultural practices on water quality: a) Identify and test innovative management practices; b) Determine factors that control the fate and transport of agrochemicals and contaminants of emerging concern. a. Identify and differentiate contaminants in surface water systems associated with the agriculture-urban interface in order to delineate contaminant sources and develop mitigation strategies. b. Compare water use requirements and characterize persistence, transport and loss pathways of contaminants with runoff from traditional and low-input turf managed with conventional or innovative practices. c. Develop management strategies to reduce nitrate-N leaching losses using fall-applied anhydrous ammonia. d. Determine factors controlling the fate and transport of agrochemicals and contaminants of emerging concern.
Development of agricultural management strategies and basic research on fate and behavior of agrochemicals are integral parts of both objectives. Research will be designed to maximize the information that can be used to attain multiple objectives. For instance, the research in Objective 1a and 1b will include development of irrigation and drainage strategies for emerging cropping systems that will require less N and reduce losses of nitrate-N to water bodies from agrochemicals, while Objective 2a will identify production management systems that minimize offsite transport of agrochemicals to surface water. Objective 2b will determine factors that control the fate and transport of agrochemicals and contaminants of emerging concern in the cropping systems with the irrigation and drainage strategies identified in Objective 1a and 1b, and in the production management systems identified in Objective 2a. The complementarity in fundamental processes studied, sample and data collection methods, and analytical methods across objectives will facilitate integration of results and provide important operational efficiencies. A cohesive, multidisciplinary team is needed to accomplish the presented range of research objectives.
1a: A two-factor, two-level field experiment was conducted to determine the impact of irrigation on the success of living mulch systems. All plots were in a corn-soybean rotation; half were in a kura clover living mulch & half were conventionally farmed with fall tillage. Of these, half were irrigated & half were rainfed. In the first two years, irrigation had a significant positive effect on yield for both conventional & living mulch systems, and the living mulch had a significant negative effect on yield of both irrigated & rainfed systems. In the second two years, there were no significant differences in yield. 1b:A major success of this project was the cooperation & trust built with the producer managing the fields in which the research was conducted. The end result was a downward trend in subsurface drainage nitrate-N concentrations since the beginning of the project (2007), thus meeting the project objective to reduce nutrient losses through artificial subsurface drainage for large dairy operations. The lesser concentrations were a result of lower manure application rates by standard fall application method & by additional lowering of rates enabled by in-season fertigation. Each winter, the previous year’s yield & environmental results were shared with the producer-cooperator, who saw that yield was not being sacrificed & noticed the benefits of management actions. In turn, the producer established custom manure application rates below the state-mandated maximum to 70+ neighboring customers, thus expanding the impact of our research involvement. Data collection was ended in the fourth year of the project due to change in support & program direction during the coming five-year cycle, & a one-year-earlier-than-planned conversion in one field from alfalfa to silage corn due to winter kill. Over the course of the project, two peer-reviewed journal articles were published on the environmental impacts of the manured corn silage cropping system and the benefit (reduced sediment and dissolved phosphorus losses) of a closed fine-gravel surface inlet design. A rich nine-year data set was built that is the source of one paper in review (long-term soil carbon stock changes) & several others in preparation. In summary, in spite of the lower nitrate-N concentrations, a manured silage corn production system loses more N than inorganically fertilized corn systems, although alfalfa-year N losses are minimal. On-farm research requires flexibility and is best supplemented with plot and/or modeling research to extend and maximize the substantial resource investment required. 2a: Water, sediment & passive samplers were collected from sub-watershed sites to evaluate the occurrence of contaminants of emerging concern in surface waters as associated with surrounding land uses. Samples were extracted by solid phase or accelerated solvent extraction & levels of contaminants (e.g. veterinary pharmaceuticals, hormones, & pesticides) were measured by liquid chromatography tandem-mass spectrometry. Principal components analysis was used to identify sources of emerging organic contaminants in the Zumbro River watershed in southeastern Minnesota. Two main principal components(PC) were identified. Principal component 1(PC1) was attributed to non-agricultural land use, including the effects from municipal wastewater & urban/residential land uses, while PC2 was attributed to agricultural land use. Based on these results, PCA can be used to broadly categorize sources of new & previously uncharacterized emerging contaminants. In addition, assessment of hydrographs & chemographs facilitated elucidation of transport pathways. A greater understanding of contaminant sources & transport pathways will assist focused efforts & resources on strategies to reduce contaminants & sources of contaminants with the greatest risk, improving water quality. 2b:Research was completed on the impact of various turf management, soil tillage, & soil biochar amendments on overall pesticide fate & transport properties. For the turf research, several multi-year studies were conducted comparing the off-site transport of pesticides & nutrients with runoff from traditional creeping bentgrass turf managed with different cultivation practices and low-input fine fescue turf, each maintained as a golf course fairway. Runoff flow rate & subsamples were collected, processed, and analyzed for pesticide and nutrient concentrations. Quantities of chemicals transported off-site with the runoff were compared in side-by-side studies to determine which management practices were most efficient at reducing the environmental impact of managed turfgrass. Additional studies were also performed to evaluate the efficacy of Creeping Bentgrass turf buffers to mitigate the off-site transport of pesticides with runoff. Buffers with different flow lengths were evaluated. In summary, we documented that management practices can reduce off-site chemical transport with runoff and improve the sustainability and environmental stewardship of these highly managed biological systems. For the three row-crop field sites, which were imposed as conventional (moldboard plow) versus ridge tillage, there was no significant difference observed in the sorption of pesticides as a function of the tillage style or row positioning (crop row or aisle) after 4 years of tillage treatments. The addition of raw organic material also did not result in a statistical difference in soils where there was organic matter already present in the soil system. However, biomass additions did increase pesticide sorption in low organic matter soils. On the other hand, the addition of biochar did phenomenally increase pesticide sorption (4X to 33X higher), but also significantly reduced their microbial mineralization (˜50%). There was also a decrease in efficacy of the pesticide with biochar application. These findings are important as it highlights the tremendous opportunity that exists for modifying pesticide transport with biochar additions. However, further research is needed to fully optimize these observations. 2c: This objective was initially designed to be addressed in a field experiment. However, we encountered several obstacles over the course of the project including high spatial variability in field soil properties which resulted in highly varying grain yields, delays in obtaining needed materials, and safety concerns associated with using anhydrous ammonia. Thus, in lieu of field experiments, we initiated a series of laboratory experiments evaluating the effects of nitrification inhibitor products and biochar amendment on nitrate production in several different Minnesota agricultural soils amended with nitrogen fertilizer. Laboratory experiments under more controlled conditions than possible in the field allowed for closer examination of the underlying chemical and microbial controls over the nitrification process. These experiments demonstrated significant differences by soil type in the effects of biochar and in the effectiveness of the nitrification inhibitor dicyandiamide on the production of nitrate and nitrous oxide. The results revealed the importance of pH, free ammonia and ammonium sorption capacity in regulating both steps of nitrification which was documented in two publications. It was also found that the addition of biochar significantly reduced nitrous oxide production. Although the exact mechanism of the suppression of nitrous oxide production by biochar is still unknown, a new hypothesis was proposed as the result of this research. Biochar readily absorbs water vapor, and thereby reduces the quantity of water vapor in the gas phase. This sorption is highly exothermic and lowers the relative humidity to <90% (which is lower than the corresponding equilibrium humidity at the wilting point). This observation opens the door for a new potential for controlling microbial activity (e.g. denitrification) in soil. This concept is identical to the manner in which food is preserved by limiting conditions for microbial spoilage (humidity & temperature). This same notion might be applicable for soil microbial communities, since no amendment to date has specifically targeted water vapor to reduce denitrification rates. These findings have led to additional ideas for laboratory experiments which have continued under our NP 212 plan. 2d: Recently, biochar has been proposed as a soil amendment that could increase sorption & decrease total chemical transport through the soil system. Typically, the environmental risk of soil applied agrochemicals is through laboratory batch sorption experiments to provide guidance to field management decisions. We evaluated a series of different hardwood tree biochars created at a range of temperatures (350-900 C) to investigate the mechanisms responsible for the observed sorption relationships with glyphosate. The size of the pores in the biochar appeared to influence total sorption capacity. Biochar with higher total amounts of macro-porosity (> 50 microns) possessed the higher glyphosate sorption capacities. Furthermore, it was observe the sorption of glyphosate was strong relative to water as a desorption solution. On the other hand, when the glyphosate sorbed biochar contacted phosphorus solutions, the glyphosate was readily released to the solution (>85%). Therefore, the net sorption capacity would be low in soils with high phosphate availability. Furthermore, very little attention has been focused on the different timings possible for herbicide (pre or post-emergence) & the impact of biochar on these different modes of action. Our research demonstrated soil amendments (biochar or biomass) impact the length of time the chemicals stay active in the protection against weeds. The data suggests that biochar additions reduce the time window the herbicide is effective, which is particularly important for pre-emergence applications of herbicides or chemicals with residual action in the soil.
1. Corn and soybean production with living mulch. ARS scientist at St. Paul, Minnesota showed that it is possible to attain yields of both corn and soybeans in living mulch systems that were equivalent to conventional yields by using rotary zone tillage to establish rows. This form of tillage creates a broader clean zone for newly planted corn and soybeans than the standard strip tillage that we had previously used. As a result, early season emergence and growth is not delayed.
2. Biochar weathering. Biochar has been proposed as a positive amendment for agriculture systems. ARS researchers at Saint Paul, Minnesota evaluated the impact of field exposure and small scale alterations in the biochar that occur due to its exposure in soil. Pre-treated biochar (through composting) was tested with a range of analytical techniques to investigate the mechanisms of nutrient retention in biochar. The un-treated biochar competes with plants and soil microbes for nutrients, since fresh biochar attracts nutrients and dissolved species creating a nutrient-rich “coating” on the biochar. Without pre-treating biochar, it could compete with plant roots and soil microbes for these nutrients. Additional information and guidance is needed before applying biochar to soils, since sorption behavior to pesticides also change as a result of this coating. These results are significant to farmers and policy makers and is critical for improving the use of biochar as a water remediation tool.
3. Comparing off-site transport of fertilizer with runoff from conventional and low-input turfgrass. Maintaining quality golf course turf often requires irrigation and application of fertilizer. The transport of excess nutrients with runoff water from highly managed biological systems to surrounding surface waters has been shown to result in enhanced algal blooms and promotion of eutrophication. Replacing traditional creeping bentgrass turf with grass species that require less irrigation and chemical inputs is one strategy to improve the sustainability of managed turfgrass systems. Side-by-side studies comparing runoff from plots planted in traditional creeping bentgrass or a fine fescue mixture, similarly managed as a golf course fairway, were conducted to measure runoff volumes and the amount of nitrate nitrogen (NO3-N) and ammonium nitrogen (NH4-N) transported off-site with runoff. Greater runoff volumes and overall quantity of applied nutrients were measured in the runoff from the fine fescue plots, representing a 48% and 53% average increase in the off-site transport of NO3-N and NH4-N with surface flow. Results of this research will be useful to grounds superintendents and researchers for selecting and developing management strategies to improve environmental stewardship of managed turf while providing desired turf quality.
4. Identifying management practices that reduce pesticide transport with runoff from golf course turf. Stormwater runoff from managed biological systems can transport pesticides to surrounding surface waters. The detection of pesticides in areas where they have not been applied and their potential to result in adverse effects to non-target organisms at environmentally relevant levels has raised public concern and a need to provide methodologies to control their off-site transport. Experiments were designed to evaluate the effectiveness of individual and combined cultivation practices to reduce runoff volumes and the off-site transport of pesticides with runoff from turfgrass managed as a golf course fairway. Overall, the pesticide chemographs followed trends in agreement with mobility classifications associated with their soil organic carbon partition coefficient and the individual cultivation practices performed as well or better than the combined cultivation practices. Data from the present study contribute to the understanding of pesticide transport with runoff from managed turf and equip golf course managers with information when selecting management practices.
5. Influence of biochar particle size and shape on soil hydraulic properties.Different physical and chemical properties of biochar, which is made out of a variety of biomass materials, have assumed to impact water transport through biochar-amended soil. Plastic beads of different size and morphology were compared to biochar particles to develop a decision support tool that could predict water transport through biochar-amended soils. ARS researchers at Saint Paul, Minnesota demonstrated that the intra-particle porosity of biochar made no significant contribution to the hydraulic conductivity, but the overall particle size and shape were the controlling factors. This data will improve our knowledge to ensure proper selection of biochar type to target specific soil hydraulic problems.
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