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This article in SSSAJ

  1. Vol. 51 No. 2, p. 271-276
     
    Received: Dec 23, 1985
    Published: Mar, 1987


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doi:10.2136/sssaj1987.03615995005100020001x

Vacuum Trough Extractors for Measuring Drainage and Nitrate Flux Through Sandy Soils1

  1. B. R. Montgomery,
  2. Lyle Prunty and
  3. J. W. Bauder2

Abstract

Abstract

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.

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