Soybean Leaf N as Influenced by Seedbed Preparation Methods and Stages of Growth1
- J. K. Young,
- F. D. Whisler and
- H. F. Hodges2
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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