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Phosphorus Movement through Subsoils to Tile Drains

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org

Citation:  Paper number  032317,  2003 ASAE Annual Meeting . (doi: 10.13031/2013.13831) @2003
Authors:   J.F. Lore, J.L. Baker, A.P. Mallarino, S.W. Melvin
Keywords:   nonpoint pollution, nutrients, leaching, adsorption

Results of some laboratory column and field studies indicate that soluble inorganic phosphorus (PO4-P) can move vertically through the root zone in a greater amount and shorter time than expected based on concentrations measured in tile drainage. One hypothesis to explain this is that once percolating water reaches the water table, the subsequent lateral movement of P-laden water through water saturated, low-P subsoils provides the time and opportunity for adsorption/precipitation to reduce P concentrations. In the study reported here, trenches dug parallel to and 3.0 m away from existing field tile drains were partially filled with a solution of PO4-P (9 mg/L) and the soluble, non-adsorbed bromide anion (Br; 100 mg/L). The level of ponding in the trenches was about 0.6 m below the ground surface about 0.5 m above the tile drains. The gradient drove some water and Br from the trenches to the tile drains in less than one day; and by the end of 18 days of ponding, Br concentrations were over 80 mg/L indicating that at least 80% of the tile flows were coming from water in the trenches. In one of two replications, PO4-P concentrations in tile flow did not increase above the background of 0.03 mg/L in 24 days of ponding of the P solution, or in the following 30 days of receding flow and flow from rainfall. In the second replication, the PO4-P concentration increased slowly up to 0.13 mg/L in 24 days, but then decreased back to background levels as the flow receded. These results indicate that the low-P sublsoils in this study area have considerable potential to retain P and reduce concentrations in water moving laterally through them.

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