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This article in AJ

  1. Vol. 71 No. 2, p. 309-314
     
    Received: Nov 11, 1977
    Published: Mar, 1979


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doi:10.2134/agronj1979.00021962007100020022x

Nitrogen Balance in Urine-affected Areas of a New Zealand Pasture1

  1. Roger Ball,
  2. D. R. Keeney,
  3. P. W. Thoebald and
  4. P. Nes2

Abstract

Abstract

The high rates of urine-N deposited during grazing offers the potential for considerable N loss through volatilization, leaching, and denitrification. A field experiment was conducted to evaluate the magnitude and pathways of N transformations and losses under warm, moist conditions. Urine was applied to 3-m2 plots in a ryegrass (Lolium perenne L.)-white clover (Trifolium repens L.) pasture at 300 or 600 kg N/ha. These rates simulate the urine affected area of sheep and cattle, respectively. Ammonia volatilization, inorganic N in the soil profile, symbiotic nitrogen fixation (by acetylene reduction assay), and herbage N yields were measured over 53 days. Four days after a plication from 30 to 35% of the added N could not & accounted for as either soil mineral N or volatilized NH3-N. Ammonia-N evolution was rapid only for the first 2 days, and I5 to 18% of the N was volatilized as NH3. Profile NH4-N was completely nitrified by 21 days. Considerable amounts of the applied N was lost from the 0 to 45 cm profile by 53 days. Since rainfall and irrigation exceeded estimated evapotranspiration, leaching of NO3-N is the probable loss mechanism. The apparent recovery of N in herbage was 37 and 22% of that added. Acetylene reduction was substantially less in the urine-treated swards. From 30 to 35% of the urine-N was not accounted for as inorganic N early in the experiment; immobilization and rapid leaching of urine below 45 cm are probable loss mechanisms. The experiment indicated that in a warm, moist environment, typical of late spring-early summer in New Zealand, more than half of the N in urine voided by sheep or cattle can be lost, and that an intensively grazed grass-legume system is far from a closed system, or cycle, with respect to N.

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