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This article in AJ

  1. Vol. 71 No. 4, p. 568-573
     
    Received: June 26, 1978
    Published: July, 1979


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doi:10.2134/agronj1979.00021962007100040012x

Soybean Leaf N as Influenced by Seedbed Preparation Methods and Stages of Growth1

  1. J. K. Young,
  2. F. D. Whisler and
  3. H. F. Hodges2

Abstract

Abstract

Recent interest and studies on nitrogen relationships in soybeans [Glycine max (L.) Merrill] have led to a better understanding of the processes regarding N accumulation during vegetative growth and remobilization during seed development. Most of the research work was performed with different N fertilizer treatments and isolines of nodulating and nonnodulating soybeans. Differences in cultural practices which modify the root environment and differences in soybean cultivar have not received much attention in N accumulation and remobilization studies. The objectives of this work are 1) To determine the effect of tillage treatments and cultivar on leaf N levels and 2) to develop a regression equation relating several plant and cultural variables to leaf N levels.

‘Forrest’ and ‘Tracy’ cultivars of soybeans were planted on Houston silty clay (very fine montmorillonitic, thermic family of Typic chromuderts) with seven different seedbed preparation methods and assayed for leaf N using the Kjeldhal method. Leaf N concentrations of the two cultivars showed similar patterns of change over the sampling period at each of three positions (top, middle, bottom) on the plant. Tracy had higher leaf N concentrations (5.3 to 3.2%) than Forrest (5.0 to 2.9%) throughout the growing season. Topleaf N remained fairly constant until late R2 maturity stage, after which it decreased rapidly. Middle-leaf N varied as a quadratic function of plant age. An inverse relationship between lower-leaf N and plant age was observed. For different cultivars, tillage affected leaf N within each leaf position in the early growing season. A regression model having factors of plant age, cultivar, leaf position and interactions of these factors predicted leaf N with a standard error of estimate of 0.33% and a coefficient of variation (R2) of 0.85.

 
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