Submitted to: Applied Engineering in Agriculture
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/25/2010
Publication Date: 6/16/2011
Citation: Palmer, R.E., Hill, R.L., Meisinger, J.J., Magette, W.L. 2011. Undisturbed soil columns for lysimetry II. Miscible displacement and field evaluation. Applied Engineering in Agriculture. 27(3):391-400. Interpretive Summary: The study of the movement of nutrients through soils is an important area of soil science, particularly when evaluating the water quality impacts of conservation tillage practices. Eight large undisturbed soil cores, each 18 inch diameter by 3 feet long, were converted into small lysimeters by installing seven suction devices. Four columns came from no-tillage plots and four from plow-tillage plots. Solute transport through each lysimeter was studied by saturating the columns with a mild salt solution, establishing steady-state infiltration, introducing a step input of a bromide tracer solution onto the soil surface, and sequential sampling the percolate for several days. The time-course of the appearance of the bromide tracer from each lysimeter was used to evaluate solute transport, with the data summarized with a mobile-immobile phase solute transport model. All soil columns showed preferential flow characteristics as shown by the rapid appearance of bromide in the percolate in less than one hour. Preferential flow is characterized by rapid flow of solute through the column that bypasses much of the soil matrix. The no-tillage lysimeters showed higher infiltration rates and greater hydraulic conductivities than moldboard plow lysimeters, which was attributed to more inter-connected large pores. It is concluded that the mini-lysimeters are reliable instruments for further investigations into nutrient leaching as affected by tillage practices.
Technical Abstract: Concerns about agriculture's effect on water quality and the expanding use of no-tillage, has produced a crucial need for in situ solute transport research of mobile nutrients as affected by tillage system. Eight undisturbed soil columns (41 cm diameter by 100 cm long) were sealed into PVC cylinders using bentonite-sand grouting instrumented with 7 high-flow porous ceramic candles, and converted to mini-lysimeters. Four columns were from long-term no-tillage (NT) plots and four from moldboard plow tillage (PT) plots. Each soil column was saturated with 0.005M CaSO4, steady-state flow conditions established using -15 to -25 kPa pressure in the suction candles, and a "step input" of 0.01M KBr was applied. Percolate was collected from each candle until 4-5 pore volumes had leached through each column. The percolates were analyzed for Br and the resulting breakthrough curves (BTC) were evaluated using a two-site/two-region non-equilibrium transport model. Preferential flow occurred in all soil columns as evidenced by rapid appearance of Br after less than 0.1 pore volume, skewed BTC's, and the slow approach of percolate Br concentrations to input Br concentrations. The Br breakthrough for suction candles directly under the soil column, compared to the outer-edge candles, confirmed the structural integrity of the bentonite-sand grouting. Statistical analysis of the miscible displacement parameters revealed significantly greater surface fluxes and Ksat's for the NT lysimeters compared to PT. The tillage effects occurred despite no significant difference in total porosity. The greater solute movement with NT is most likely due to more inter-connected large pores. It is concluded that the mini-lysimeters are reliable instruments for further investigations into nutrient leaching as affected by tillage practices.