Competition for Nitrogen‐15‐Depleted Ammonium Nitrate between Arrowleaf Clover and Annual Ryegrass Sown into Bermudagrass Sod1

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Abstract
Ability to compete for mineral N effects stand stability of arrowleaf clover (Trifolium vesiculosum Savi) and annual ryegrass (Lolium multiflorum Lam.). Two field experiments were conducted on a Darco soil (loamy, siliceous, thermic Grossarenic Paleudult) to investigate the competitive ability of ‘Yuchi’ arrowleaf clover and ‘Gulf’ ryegrass for uptake of 15N‐depleted ammonium nitrate when seeded into dormant bermudagrass (Cynodon dactylon L. pers.). When N was applied in February, ryegrass in pure stand recovered more than two times as much fertilizer N as did clover in pure stand and more than 80% of the fertilizer N when in a mixture with clover. The April application of N resulted in the clover in pure or mixed stand recovering as much or more fertilizer N as did the corresponding ryegrass in pure or mixed stand. Growing clover in mixed stand with ryegrass increased the percentage of the N in the clover derived from N fixation by an average of 23%. Application of fertilizer N reduced the percentage of total N in the clover derived from N fixation by an average of 19%. Total N in the clover from N fixation was either unchanged or reduced when clover was grown with ryegrass and when fertilizer N was applied. Efficiency of fertilizer‐N usage by either plant species ranged from a low of 5 to 70%, depending on timing of application and plant species.