Spatial Variability and Transport of Nitrate in a Deep Alluvial Vadose Zone

We investigated NO3–N occurrence in a deep alluvial vadose zone and its relation to geologic site characteristics, hydraulic properties, and fertilizer application rates via an intensive three-dimensional core-sampling campaign beneath an irrigated orchard in semiarid Fresno County, California

Y. S. Onsoy

2009

Scholarcy highlights

  • Little empirical evidence exists about the spatial distribution of NO3–N in deep vadose zones and about the associated fate and transport of NO3–N between the root zone and the water table
  • The long-term potentially leachable N computed for the high subplot represents a potentially high risk for groundwater pollution
  • , the deep vadose zone storage can be computed by considering that all subplots were subject to the “control” leaching rate in 1995 and to the “standard” leaching rate in 1996
  • An intensive field sampling campaign resulted in a unique snapshot of the vadose zone NO3–N distribution throughout its 16-m depth under three different 12-yr fertilization trials
  • Our findings summarized below are relevant to heterogeneous, alluvial vadose zone sites below agricultural production areas in general
  • In the first year of the experiment, there were no significant differences in yield or average fruit weight among the subplots
  • The field data reveal significant variability in water content and in the NO3–N distribution throughout the deep vadose zone, with measured NO3 values varying by several orders of magnitude over relatively short distances
  • Almost one-third of the core samples had nondetectable levels of NO3–N

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