Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 20, 2006
Publication Date: September 19, 2006
Citation: Lentz, R.D. 2006. Solute response to changing nutrient loads in soil and walled, ceramic-cup samplers under continuous extraction. Journal of Environmental Quality. 35:1863-1872. Interpretive Summary: A newly developed soil water percolation sampler accurately collects soil water draining through a cross-section of soil and measures the amount of water and chemicals that may potentially enter the groundwater. To correctly interpret field results obtained from the sampler, users need to understand how chemical concentrations in collected water respond to fluctuations in inflowing water chemistry, and how soil may influence this response. This laboratory study examined the effect of changing nutrient inputs on the rate of corresponding chemical changes in collected water, for sampler components, with and without soil. Results showed that the percolation sampler was fully responsive in 38 h; that sampler components had little impact on nutrient concentrations of collected water; and that changing input water nutrient concentrations can induce anomalously high phosphorus levels in drainage water from a thin soil layer. This information will further our understanding of nutrient leaching processes in irrigated soils and aid development of sustainable agricultural management practices.
Technical Abstract: To evaluate a newly designed vacuum-assisted percolation sampler and better understand the dynamic response of leachate solutes, we determined how changing inflow solute load influenced extracted leachate solute concentrations derived from sampler components and soil during continuous extraction. The 20-cm-walled percolation sampler extracted soil water under tension via a ceramic cup collector imbedded in a silica flour layer, whose upper surface interfaced with field soil. In the laboratory, alternating solutions with high- and low-load nitrate-N (232 or 3.6 mg/L), molybdate-reactive P, MRP (1.75 or 0.0 mg/L), K+ (568 or 3.6 mg/L), and Br- (9.6 or 0.0 mg/L) concentrations were delivered directly to the i) sampler ceramic cup; ii) silica flour bed surface, or iii) a 12-mm soil layer placed over the silica flour bed. For input solutions delivered to the silica-flour-bed surface, solute breakthrough (95% equivalency) occurred in 38 h, or 4 pore volumes and was the same for both the high-load and low-load input leg of the application. Under continuous extraction, adsorption/desorption phenomenon played a minor role in the transport of nitrate-N, Br-, and MRP through the silica flour bed and ceramic cup of the percolation sampler. Alternating inputs of high- and low-load nutrient waters to the calcareous soils caused a highly concentrated pulse of MRP-enriched water (1.6x the high-load MRP concentration) to leach from the soil. The dynamic character of phosphorus transport in fertilized soils deserves further study and may have important environmental implications.