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This article in AJ

  1. Vol. 75 No. 4, p. 672-676
    Received: Jan 14, 1982

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Nitrogen Use Efficiency of Trickle-irrigated Tomatoes Receiving Continuous Injection of N1

  1. J. C. Stark,
  2. W. M. Jarrell,
  3. J. Letey and
  4. N. Valoras2



The practice of applying N fertilizer through trickle irrigation systems is rapidly increasing in popularity. Fertilizer N requirements are usually divided into small increments and then applied at regular intervals during the season. This field study, conducted on an Arlington loam (coarseloamy, mixed, thermic Haplic Durixeralf), was designed to investigate the uptake and partitioning of N by trickle-irrigated tomatoes (Lycopersicum esculentum Mill.) and the potential for denitrification when N is continuously metered into the irrigation water. Solutions containing 1.8, 3.6, or 5.4 mol N m−3 were applied when the soil matric potential at the 25 cm depth reached either −10 or −30 kPa. The resulting N application totals ranged from 120 to 585 kg N ha−1. Early in the season, large differences in petiole NO3-N concentrations were observed which appeared to be directly related to the rate of N supply. However, these differences gradually decreased as the season progressed. Total N uptake, which was linearly related to N application, was less than the amount applied at N rates greater than 300 kg ha−1. As the N application rate increased, an increasingly greater proportion of total plant N was partitioned into the vines. Denitrification N losses, as indicated by direct field measurements of N flux during a 4-day period, were very small in the two lowest N treatments, ranging from 0.3 to 2.0 μg m−2 s−1. These low rates of denitrification were presumably due to competition between roots and denitrifiers. However, in the high N treatments, where N supply exceeded uptake, N fluxes ranged from 2.0 to 17.5 μg m−2 s−1. Aside from its influence on the rate of N supply, irrigation frequency had little effect on denitrification and N uptake. These results indicate that adequate N can be applied to tomatoes using high-frequency N fertilization without large denitrification N losses.

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