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This article in AJ

  1. Vol. 68 No. 4, p. 621-627
    Received: Nov 20, 1975

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Soil Nitrate Loss During Irrigation: Enhancement by Plant Roots1

  1. M. G. Volz,
  2. M. S. Ardakani,
  3. R. K. Schulz,
  4. L. H. Stolzy and
  5. A. D. McLaren2



Since roots can both absorb NO-3 and supply organic matter for NO-3 reduction by soil microbes, the influence of a root system on NO-3 N loss from soil solution during irrigation was studied. Two Hanford sandy loam plots (Typic Xerorthent), one fallow, and the other planted to CM-67 barley (Hordeum vulgare L.), were ponded for 44 hours with a solution containing 100 ppm N and 46 ppm CI- (tracer for NO-3) as KNO3 and CaCl2, respectively. Nitrate — N, NO-2-N, NH+4-N, and Cl- concentrations in soil solution were determined and related to N uptake by roots and microbial transformation of NO-3.

During irrigation, concentrations of NO-3-N were lower in most soil solution samples from O to 60 cm under barley than in those from the fallow plots. However, Cl- concentration profiles were identical in both plots to a depth of 45 cm. While nitrate uptake by barley in the top 15 cm led to some solution N loss, soil NO-2 and NO-2 reduction reactions are thought to have been responsible primarily, especially in deeper layers, after 26 hours. Data also indicate that, during irrigation, organic C is produced in the root zone of barley and that redox potentials in the planted plot decreased relative to those in the fallow plot. This organic C, percolating with NO-3 solution, is thought to have facilitated NO-3 loss both in, and below the root zone, by stimulating microbial activity and by decreasing redox potentials.

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