Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 15, 2001
Publication Date: May 1, 2002
Citation: Logsdon, S.D., Keller, K.E., Moorman, T.B. 2002. Measured and predicted solute leaching from multiple undisturbed soil columns. Soil Science Society of America Journal. 66(3):686-695. Interpretive Summary: Groundwater can be contaminated when applied agrochemicals move rapidly through wormholes, cracks, and other large holes in the soil. Computer models potentially can be used to predict this rapid movement. We conducted this study to compare the measured with the predicted movement of chemicals through soil. A computer model was able to predict the initial rapid chemical movement through the soil; however, after longer times the model underpredicted the chemical movement. This information is vital to scientists who need to understand why chemical movement is sometimes faster than at other times. With this knowledge scientists can refine the models so they can better predict chemical movement through soil and the contamination of groundwater. The importance of this work for society is that the computer models can be used to help us predict when groundwater contamination may occur. Then we can modify our agricultural management practices to reduce contamination.
Technical Abstract: The preferential flow model MACRO can separately simulate reactive and nonreactive solutes and tritium, and can include anion exclusion and a variety of boundary conditions. The objective of this study was to compare measured and predicted bromide and tritium leaching for multiple soil columns. We collected 48 undisturbed columns (0.35 m long and 0.20 m in diameter), that represented three soils and two tillage treatments (no-till and chisel). We dripped bromide slowly unto the prewetted and drained columns. Two days later we applied 30-mm rain spiked with tritium, followed by 7 d of drainage. We applied three additional 30 mm rains with nontritiated water, each followed by 7 d of drainage. For half of the columns, the first rain was high intensity, and for the other half of the columns the last rain was high intensity. We determined bromide and tritium concentrations in the leachate. We used three extra columns for each soil and tillage combination to determine soil properties. We determined model input parameters from these measured values and from sensitivity analyses. For the first rain event, measured bromide loss was 175% larger than tritium loss, but predicted bromide leaching was 2% smaller than tritium loss. Tritium retention could have reduced tritium leaching. The root mean square error values (of differences between measured and predicted concentrations) were as much as four times the treatment mean for bromide, and up to eight times a treatment mean for tritium. Lack of agreement between measured and predicted bromide and tritium leaching may suggest further important mechanisms should be incorporated into MACRO.