AS> Vol.6 No.10, October 2015

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Paul W. Bartholomew

USDA-ARS Grazinglands Research Laboratory, El Reno, OK, USA.

Use of individual plants as experimental units may be necessary when resources are limited, but inter-plant variation risks obscuring differences among treatments. Experiments were undertaken to measure the effects of seed size on seedling size and response to applied nitrogen of annual ryegrass (Lolium multiflorum L.) harvested six or nine weeks after emergence. In two series of experiments, shoot and root dry weights of seedlings increased respectively at means of 53 - 61 and 29 - 30 mg·mg^-1 increase in mean seed weight. Between the largest and smallest seed sizes used in this study, there was 83% difference in shoot weight at harvest six weeks after emergence and 22% difference with harvest nine weeks after emergence. Nitrogen (N) application, in comparison, increased shoot dry weights by averages of 69% and 77% with harvests at six or nine weeks, respectively. Dry mass response to N application was similar across seed size categories in shoots or roots. A mean 30% of total seedling-N was retained in roots. Nitrogen utilization efficiency for shoot growth (increase in shoot growth per unit increase in shoot N capture) ranged from 64 mg·mg^-1 with harvest six weeks after emergence to 114 mg·mg^-1 with harvest at nine weeks after emergence. Delay in seedling harvest from six to nine weeks post-emergence and use of closely-graded seed can reduce variation in individual seedling size and contribute to reduction in random variation in small-scale experiments.

Seed Size, Seedling Growth, Lolium multiflorum

Bartholomew, P. (2015) Seed Size Effects on Early Seedling Growth and Response to Applied Nitrogen in Annual Ryegrass (Lolium multiflorum L.). Agricultural Sciences, 6, 1232-1238. doi: 10.4236/as.2015.610118.