Location: Soil and Water Management Research2011 Annual Report
1a. Objectives (from AD-416)
1. Integrate knowledge of retention, transformation, and transport of agrochemicals, including newer pesticides and veterinary pharmaceuticals, in soil and water, to facilitate selection and validation of management practices at the field to landscape scale that minimize potential offsite transport to surface and ground waters. 2. Identify practices that protect water quality and conserve soil resources in emerging farming systems of the North Central U.S. 3. Quantify the impact of agricultural drainage management systems on net greenhouse gas emissions and pesticide leaching losses. 4. Quantify the environmental impact of Best Management Practices on water quality in turf systems.
1b. Approach (from AD-416)
Results from research on factors affecting possible offsite transport of agrochemicals (nutrients, pesticides, and veterinary chemicals) to surface and ground waters, conducted on multiple scales (laboratory, field plots, and mini-watersheds) in an interdisciplinary manner, will be used to develop management practices that are relevant to protecting surface and ground waters in the North Central United States. Research will be conducted in interconnected experiments on basic processes affecting agrochemicals, spatial and temporal variation of processes, and impacts of management practices on environmental fate of agrochemicals. For instance, basic research on fate of pesticides and veterinary pharmaceuticals will be conducted in the laboratory on soils from selected field plots and watersheds to obtain basic information on processes. This information will be used in turn to help explain results of management practice effects on fate of agrochemical in fields and small watersheds. Management practices to be studied include: new cropping systems associated with large dairy operations; farming systems providing carbon sources for ethanol production; agricultural drainage management systems; and turf management systems. We will obtain information on the spatial and temporal variability of the processes and an assessment of the impact of altering the agronomic management practices on off-site transport of pesticides and fertilizers from non-agricultural, i.e. turf, and agricultural systems. Information obtained will include: an assessment of the predictive ability of transport models to simulate runoff and estimate chemical loading to surface and ground waters; identification of management practices that protect water quality and conserve soil resources in emerging farming systems in North Central U.S; and redefined agricultural systems models that can predict the impact of management of agricultural drainage systems on net greenhouse gas emissions in tile drained fields under the different climate and soil conditions of the Midwest corn belt.
3. Progress Report
Obj.1 Progress: To determine potential for offsite transport, sorption of the new herbicides aminocyclorpyrachlor and indaziflam has been characterized on a variety of glacial and tropical soils. Effects of soil amendments such as biochar and organoclays on sorption have also been determined. Sorption of three indaziflam metabolites has also been characterized for the soils. Extraction/ analysis methodology for veterinary pharmaceuticals and pesticides in surface waters were developed. Collection and extraction of river water samples has been initiated. Obj. 2 Progress: Center pivot irrigation application of dairy slurry to silage corn fields during the growing system offers the potential to reduce nitrate-N loads through subsurface tile drainage compared to injecting the slurry into the soil in the fall. We measured drainage N loads for a second spring snow melt season and are in the midst of the second crop year of monitoring this comparison at a large-field scale (65 ha). We also began intensive sampling of drainage effluent during rainfall-related events, which provides the opportunity to do a paired t-test comparison between the two field treatments. A new field site was established for research on companion cropping and its potential impact on water quality in irrigated corn systems. A center pivot irrigator was installed, and kura clover was vegetatively propagated into a 40 acre field. Soil samples were taken to determine initial conditions, and the field was managed to control weeds and develop a healthy clover crop prior to initiation of the field experiment. Obj. 3 Progress: We observed differences in the decomposition rate and resulting N2O production from soybean residues as a function of strobilurin fungicide application. Results to date suggest secondary effects on residue decomposition products and rates resulting from fungicide applications. Tile drain water was collected from corn plots managed with conventional or controlled drainage. Soil cores collected during the second field season were removed from frozen storage and cut at multiple soil depths in preparation for extraction. Obj. 4. Methodology for extraction/analysis of three fall fungicides and a fungicide metabolite from snow melt runoff were developed. Approximately 300 snow melt runoff samples were analyzed. Experiments were completed that evaluate the effectiveness of various cultivation practices to mitigate the off-site transport of dicamba, MCPP, and 2,4-D herbicides in runoff from turf managed as a golf course fairway. Experiments were completed that quantified phosphorus and nitrogen transport with runoff from turf plots maintained as a golf course fairway to identify which cultural practice, solid tine or hollow tine core cultivation, maximized phosphorus and nitrogen retention at the site of fertilizer application. Experiments were also completed that qualified pesticides transported with runoff from agricultural plots representing fresh market tomato production and turf plots maintained as a golf course fairway to evaluate the efficacy of management practices to mitigate chemical off-site transport from these systems.
1. Potential mobility of the new herbicide aminocyclopyrachlor. Aminocyclopyrachlor (trade name Imprelis) is a new herbicide from a new class of chemistry known as pyrimidine carboxylic acids. Although aminocyclopyrachlor has exhibited a number of positive stewardship attributes with very low impact to mammals and the environment, not much is known about its fate in soil. ARS researchers at St. Paul, MN, characterized the binding of aminocyclopyrachlor to soil for 14 soils from the United States and Brazil, presenting a range of pH, and organic carbon and clay contents. Data obtained suggest that although aminocyclopyrachlor would be very mobile based on its binding (sorption) coefficients, its potential for offsite transport may be overestimated. Due to its desorption characteristics, its potential mobility may be reduced; it does not readily desorb from soil. These data are the first published on aminocyclopyrachlor sorption-desorption in soil. Now scientists can better evaluate potential mobility, information that is needed for aminocyclopyrachlor, particularly in light of the reported possible damage to evergreen trees when it was applied to adjacent turf areas.
2. Soil temperature regulates nutrient loss from applied manure nitrogen. Land application of animal manures is challenging in northern latitudes because cool, wet spring time conditions typically prohibit manure spreading prior to planting. Thus, producers often spread manure during the period starting just after fall harvest and at times continuing throughout the winter. ARS researchers at St. Paul, MN, compared the amount of nitrogen lost through runoff and leaching when dairy manure is applied at soil temperatures characteristic of early fall (60 degF), late fall (40 degF), and winter (30 degF). Manure was applied to soil cores at three different times from October through December (2009) and the cores were subjected to rainfall simulations (November – December, 2009) and natural precipitation events (January – March, 2010). The results showed that the total overall winter losses of inorganic N (ammonium-N + nitrate-N) and total-N did not vary among application dates. However, there were differences in the timing and the pathway (runoff vs. leaching) of the losses. The amount of nitrate-N remaining in the soil at the conclusion of the test was greatest for the winter application treatment. Farmers now have needed information for manure management. For instance, based on the study findings, manure should be applied in late fall when the soil temperature is less than 40 degF and yet unfrozen. At these temperatures, volatilization losses are low, mineralization rates are also lower so there is less risk of NO3 leaching, and the soil is not frozen, thus reducing the risk of high runoff losses.
3. Selected biochars can reduce offsite transport of herbicides. Offsite transport of herbicides is a potential environmental problem. ARS scientists at St. Paul, MN, examined the impacts of six different biochars, activated charcoal, organoclay, and a biomass waste stream (olive mill waste) on the sorption and leaching of two herbicides [fluometuron and 2-methyl-4-chlorophenoxyacetic acid (MCPA)]. These amendments were added at 2% by weight to soil. Biochars are assumed to increase binding (sorption) of herbicides. However, in this study a biochar created by fast combustion (pyrolysis) of macadamia shells actually decreased observed sorption of the two herbicides in biochar amended soil. Activated carbon resulted in complete sorption and no detectable leaching of the herbicides. Two of the biochars (a fast pyrolsyis hardwood biochar and a slow pyrolysis hardwood biochar) increased observed sorption, but in the column study these two biochars resulted in increased leaching of the two herbicides. The organoclays also increased sorption and decreased leaching. These results indicate that the impact of biochar on herbicide transport is biochar specific and no general biochar behavior should be assumed. This finding could provide additional insight and direction in the focus of the benefits of biochar additions on improving water quality by sorbing agrochemicals. These results are significant to farmers and policy makers and will assist scientists and engineers in developing improved mechanisms of biochar additions for herbicide sorption to decrease agrochemical transport to groundwater.
4. Turf management practices can reduce offsite transport of herbicides. Herbicides associated with the turfgrass industry have been detected in stormwater runoff and surface waters of urban watersheds. ARS reseachers at St. Paul, MN, conducted experiments to evaluate the effectiveness of management practices to mitigate the off-site transport of pesticides in runoff from turf managed as a golf course fairway. Overall cultivation using hollow tine cores showed a reduction in the percentage of precipitation resulting as runoff relative to other commonly used cultivation methods. Likewise, the percentage of applied herbicides dicamba, MCPP, and 2,4-D measured in the runoff were less from turf managed with HTCC. Results of this research provide quantitative information that will allow for informed decisions on management practices for turf cultivation that can maximize pesticide retention at the site of application; improving pest control while minimizing environmental contamination and adverse effects associated with the off-site transport of herbicides to surface waters.
5. Field calibration of water vapor analyzers. Accurate measurements of evapotranspiration (ET) (water use) are critical for determining impacts of global climate change. Currently, ET measurement accuracy is limited by the lack of field-portable sources of precision water vapor standards. Field calibration of water vapor analyzers has always been a challenging problem for those making long-term flux measurements at remote sites. Automated sampling of standard gases, the method of choice for carbon dioxide calibration, cannot be used for water. Calibrations are typically done manually, and as a consequence are done less frequently, degrading the accuracy and utility of water flux data. To remedy this, ARS researchers at St. Paul, MN, have designed, built and tested a field-portable mixing ratio generator, also including features that facilitate its use in water vapor isotope research. The temperature of water in the cell is monitored with a thermocouple and a pressure transducer is used to measure the cell pressure. A data logger uses this information to compute the mixing ratio in the cell and control the polarity and duty cycle of the power input to the Peltier block in order to drive the system toward the desired mixing ratio and to maintain it. Testing has shown that the unit is accurate over a broad range of mixing ratios, able to compensate for changes in ambient pressure, and stable for long periods of time. This information is useful to scientists for calibrating both conventional gas analyzers and water vapor isotope lasers for their research so that accurate measurements of evapotranspiration (water use), which are critical for determining impacts of global climate change, can be made.
6. Polymer-coated urea fertilizers may increase post-season N losses. Potato is a nitrogen (N)-intensive crop with high potential for off-site N losses in the form of nitrate (NO3-) leaching, which can contribute to both water contamination and indirect nitrous oxide (N2O) emissions. ARS researchers at St. Paul, MN, compared NO3- leaching in an irrigated potato system using conventional applications of soluble N fertilizers and applications of two polymer-coated urea products, and used the measured NO3- leaching rates to estimate total N2O emissions. Averaged over three consecutive years (2007-2009), NO3- leaching rates measured during the growing season and into the fall of each year were not significantly different among the three fertilized treatments, but each were greater than an unfertilized control. Total N2O emissions from the polymer-coated urea applications were 30 to 40% less than the conventional N application, polymer-coated urea applications resulted in greater residual soil N after harvest in the fall and greater soil-water NO3- during the following. These data suggest that delayed N release may have increased the potential for post-season N losses, therefore farmers need to be concerned about polymer formulations N losses to groundwater in the following spring-thaw period.
Griffis, T.J., Sargent, S.S., Lee, X., Baker, J.M., Greene, J., Erickson, M., Zhang, X., Billmark, K., Schultz, N., Xiao, W., Hu, N. 2010. Determining the oxygen isotope composition of evapotranspiration with eddy covariance. Boundary Layer Meteorology. 137(2):307-326.