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Vadose Zone Journal Abstract - Original Research

Estimating Nitrate Leaching to Groundwater from Orchards: Comparing Crop Nitrogen Excess, Deep Vadose Zone Data-Driven Estimates, and HYDRUS Modeling

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This article in VZJ

  1. Vol. 15 No. 11
    unlockOPEN ACCESS
    Received: July 18, 2016
    Accepted: Sept 07, 2016
    Published: February 23, 2017

    * Corresponding author(s): sbaram@ucdavis.edu
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  1. S. Baram a,
  2. V. Couvreurd,
  3. T. Hartera,
  4. M. Readb,
  5. P.H. Brownc,
  6. M. Kandelousc,
  7. D.R. Smartb and
  8. J.W. Hopmansa
  1. a Dep. of Land, Air & Water Resources, Univ. of California Davis, One Shields Avenue, Davis, CA 95616
    d Earth and Life Institute, Agronomy, Université Catholique de Louvain, 1348 Louvain-la-Neuve, Belgium
    b Dep. of Viticulture and Enology, Univ. of California Davis, One Shields Avenue, Davis, CA 95616
    c Dep. of Plant Sciences, Univ. of California Davis, One Shields Avenue, Davis, CA 95616
Core Ideas:
  • Leaching below the root zone is estimated based on eight sites of intensive vadose zone monitoring.
  • Across methods N losses estimated at the annual orchard scale were in the same order of magnitude.
  • Simple N mass balance provided a good proxy of the orchard scale annual N accumulation in the soil
  • Under current BMP N load to groundwater is likely in the range of 60 to 100 kg N ha–1.


Large spatial and temporal variability in water flow and N transport dynamics poses significant challenges to accurately estimating N losses form orchards. A 2-yr study was conducted to explore nitrate (NO3) leaching below the root zone of an almond [Prunus dulcis (Mill.) D. A. Webb] orchard. Temporal changes in water content, pore water NO3 concentrations and soil water potential were monitored within and below the root zone to a soil depth of 3 m at eight sites, which represented spatial variations in soil profiles within an almond orchard in California. Orchard monthly average NO3 concentrations below the root zone ranged from 225 to 710 mg L−1 with mean annual concentration of 468 and 333 mg L−1 for the 2014 and 2015 growing seasons, respectively. Despite the huge variability in pore water NO3 concentration between sites, the larger spatiotemporal scale N losses estimated at the annual orchard scale from surface N mass balance, vadose zone based water and N mass balance, flow calculations, and HYDRUS modeling were all on the same order of magnitude (80–240 kg N ha−1 yr−1). All methods indicated that most of the N losses occur early in the growing season (February–May) when fertilizer is applied to wet soil profiles. Simple mass balance (i.e., N load applied minus N load removed) provided a good proxy of the annual N accumulation in the soil profile at the orchard scale. Reduction of N losses at the orchard scale would require alternative fertigation and irrigation practices to decrease the difference between the N load removed and the N load applied to orchards.

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