Nodulation Response of Soybeans (Glycine max L. Merr.) to Application Rate and Placement of Combined Nitrogen1
- James E. Harper and
- Richard L. Cooper2
Uniform incorporation of ammonium nitrate (dispersed throughout a 30.5 cm soil column) impaired nodular development of soybeans (Glycine max L. Merr.) more than deep application (lower 10 cm of soil column) when ammonium nitrate was applied at a rate of 150 ppm N in growth chamber studies. Nodule fresh weight and haemoglobin content were decreased by nitrogen application, while nodule number was not as markedly affected, indicating an effect on nodule development rather than on root infection or nodule initiation. Greater nitrate content of roots and tops under dispersed nitrogen application, compared with deep application at the same rate, suggested that internal nitrate may be influencing nodulation. However, deep placement of 150 ppm combined nitrogen allowed greater root nitrate uptake than uniform incorporation of 50 ppm N, without concomitant inhibitory effects on nodulation. Nodulation response was not, therefore, strictly dependent upon internal nitrate content of the roots, indicating that application site may provide a means of partially alleviating the detrimental effect of combined nitrogen on nodulation.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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