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This article in AJ

  1. Vol. 74 No. 5, p. 820-823
    Received: Mar 23, 1981



Nitrogen Management for Irrigated Annual Ryegrass in Southwestern United States1

  1. C. F. Ehlig and
  2. R. W. Hagemann2



Annual ryegrass (Lolium multiflorum Lamb.) is becoming an important winter and spring pasture crop in the irrigated southwestern USA. A field study was conducted to determine the optimum N fertilization rates for producing maximum dry matter yields within tolerable NO3-N concentrations for livestock and to develop a diagnostic test using plant and/or soil NO3-N concentrations for recommending rates and frequency of N applications to ryegrass pastures. The cv. ‘Ucivex’ was seeded in an Imperial silty clay [fine, montmorillonitic (calcareous), hyperthermic Vertic Torrifluvents] in October, first harvested in December, and cut about monthly thereafter. In seven treatments, NH4NO3 was applied at seasonal rates of 0, 224, 448, 676, 896, and 1,120 kg N/ha, in five equal applications, or 90 kg N/ ha preplant plus 112 kg N/ha after each harvest.

Seasonal dry matter yield (Y) was related to N application rate (X) by the equation Y = 2.37 + 0.0272X + 0.0000118X2 (r = 0.999). Hay nitrate concentration increased with N application rate and was excessive, for animal tolerance, with single N applications above 112 kg/ha for the second test. Protein, ash, and fiber content of the hay increased, N-free extract and total digestible nutrients decreased, and fat was unaffected by increase in N application rate. Soil nitrate concentrations of 10 to 20 ppm in the upper 60 cm ensured near maximal yields at next cutting without excessive hay nitrate concentrations. A hay content of 2,000 to 3,000 ppm NO3-N was not adequate for satisfactory yield at the next cutting without additional N application. Multiple N applications at 112 kg/ha at about monthly intervals were recommended.

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