|Swan, J - IOWA STATE UNIVERSITY|
|Shen, F - IOWA STATE UNIVERSITY|
|Horton, R - IOWA STATE UNIVERSITY|
Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 15, 2000
Publication Date: N/A
Interpretive Summary: The movement of agrichemicals through field soils, where they are applied, to surface and ground water is of great concern for both environmental and public health. Measuring the time required for agrichemicals to move through the soil is difficult and often requires expensive and time consuming soil sampling methods. This research showed that a commonly available soil probe used to measure soil water content and soil electrical conductivity can be used to measure agrichemical movement through soil. The newly developed method uses a mass balance approach to accurately, quickly, and inexpensively measure chemical content in soil. This method represents a new way to accurately measure agrichemical movement through soil and will be of use to soil and environmental scientists, action agencies, and agrichemical manufacturers.
Technical Abstract: The solute mass balance of a soil volume is a valuable tool for assessing the effect of practices on solute leaching. Although the solute mass balance is a powerful research tool, it is seldom used with time domain reflectometry (TDR) measurements of volumetric water content (W) and bulk soil electrical conductivity (Sa) to estimate resident soil water solute concentration (Cr) break through curves (BTC). Our objective was to evaluate the use of TDR to determine the solute mass balance of a soil core under one-dimensional flow. Solute transport measurements were conducted on two 0.15-m diameter and 0.4-m long soil cores of undisturbed Monona silt loam (fine-silty, mixed superactive mesic, Typic Hapludoll) under steady state saturated and unsaturated flow and transient unsaturated flow. TDR and effluent mass balance measurements of total solute movement from the core agreed closely. Incremental TDR and input-effluent mass balances also oagreed closely (r**2>0.97) when water flux density(q)=0.2 cm/h, indicating that Cr was accurately estimated by TDR measured Sa and a Sa-W-Cr relationship developed on packed cores. At q>7.9 cm/h, the TDR mass balance method was poorly correlated (r**2=0.45 to 0.49) with the effluent BTC, apparently due to bypass flow. However, the effluent BTC was closely related (r**2=0.96) to the BTC estimated from solute input and change in TDR mass balance for the core at q=38 cm/h. The TDR based mass balance approach can provide a direct estimate of solute movement, estimate effluent BTC to determine transport parameters, and measure mobile soil water content.