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The Effect of Shallow Subsurface Drains on Nitrate-N and Phosphorus Losses from Drained Agricultural Lands

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

Citation:  Paper number  052026,  2005 ASAE Annual Meeting . (doi: 10.13031/2013.18895) @2005
Authors:   C.A. Pool, R.W. Skaggs, G.M. Chescheir, J.W. Gilliam, M.R. Burchell II
Keywords:   Drainage, drain depth, nitrogen, nitrate, phosphorus, groundwater, wastewater, water quality

Nitrate and Phosphorus losses from agricultural and municipal land treatment sites are an important environmental concern. Data were collected from two drainage systems near Plymouth, NC to determine the effect of drain depth on losses of nitrate nitrogen (NO3 --N) and orthophosphate (OP). Drains in the deep system were 1.5 m deep and 25 m apart while drains in the shallow system were 0.75 m deep and 12.5 m apart. Both plots received swine wastewater applications during the study. Overall, the shallow drain system reduced outflows by 17.8% for the 3 year period. Lower NO3 --N concentrations were observed in the shallow groundwater beneath the shallow drain plot compared to the deep drain plot. In contrast, higher OP concentrations were observed in groundwater at the shallow drain plot. No significant differences were observed in the NO3 --N concentration of the drainage water between the plots. However, the OP concentration in the drainage water of the shallow plot was significantly higher. NO3 - -N export was reduced by 8.5% at the shallow drain plot during the course of the study. Average NO3 - -N export from the shallow drain plot was 49 kg/ha/yr while an average export of 54 kg/ha/yr was observed from the deep drain plot. OP export from the shallow drain plot was 1.89 kg/ha/yr, 95% increase over the OP export (0.97 kg/ha/yr) from the deep drain plot.

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