Vacuum Trough Extractors for Measuring Drainage and Nitrate Flux Through Sandy Soils1
- B. R. Montgomery,
- Lyle Prunty and
- J. W. Bauder2
Vacuum trough extractors have been used in a number of studies for quantifying NO-3 leaching, despite limited data verifying their performance. In two studies, extractors were evaluated for measuring drainage, NO3-N concentrations, and NO3-N flux under irrigated corn (Zea mays L.). In the first, extractors were placed within four large (2.4 by 2.4 by 2.3 m deep) drainage lysimeters. Extractors were placed at either 1.4 or 1.8 m below the surface of a reconstructed Hecla loamy fine sand. Quality and quantity of monthly outflow from extractors and lysimeter tile drains were directly compared over a 5-yr period. Drainage and NO3-N flux from the extractors were significantly correlated to tile drain measurements during the entire study (r = 0.90*** and 0.69***, respectively). Overall, extractors underestimated drainage and NO3-N flux (6 and 13%, respectively). Excluding the first year's data, extractors underestimated tile drainage by 3% and NO3-N flux by 1%. Nitrate concentrations from tile drains appeared to lag 2 and 10 months behind the 1.8 and 1.4 m deep extractors, respectively. Nitrate-N concentrations (flow-weighted for duration of study) were 27 mg L−1 from tile drains and 25 mg L−1 from extractors. Vacuum levels at which the extractors were operated had very minor effects on quality and quantity of effluent collected. Extractors buried in narrow trenches 1.5 m below field plots were evaluated over a 5-yr period in the second study. These extractors were placed under a Maddock sandy loam receiving annual N rates of 0, 112, 224, and 224-split (3-way) kg ha−1. Drainage measured by these extractors was 70% less than predicted by a water balance, which used the Jensen-Haise equation to calculate evapotranspiration. Although the extractors were found incapable of supplying drainage flux, NO3-N concentrations were statistically the same as determined by nearby suction cups at the same depth.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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