Author
 |
Bartholomew, Paul |
|
Submitted to: Agricultural Sciences
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 9/17/2015 Publication Date: 10/28/2015 Citation: Bartholomew, P.W. 2015. Seed size effects on early seedling growth and response to applied nitrogen in annual ryegrass (Lolium multiflorum L.). Agricultural Sciences. 1232-1238. Interpretive Summary: Often it is convenient, or necessary because of seed or other resource limitations, to conduct plant-related experiments with single plants as the experimental unit. The downside of this is that the natural variability among plants within a population may obscure any effects of treatments that are tested by the experiment. Conventionally, problems of variability in experiments are mitigated by increased replication, or repetition of treatments, but where there are resource constraints use of increased numbers of plants may not be feasible. Ideally plants within an experiment should be as uniform as possible, but uniformity may be difficult to measure before a plant is harvested. Experiments were undertaken with annual ryegrass, a common forage species, to determine whether seed size selection at the beginning of an experiment would enhance the uniformity of plants produced. There was a clear effect of seed size on seedling growth. At harvest nine weeks after emergence, seedlings from large seeds were 22% larger than those from the smallest seed size categories. There was no effect of seed size on seedling growth response to applied nitrogen. Closely-graded seed can be used to improve uniformity of plants for experimental use and will allow greater precision and reduce resource requirement in small-scale experiments. Technical Abstract: 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. |
