Submitted to: Agricultural Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/22/2015
Publication Date: N/A
Interpretive Summary: Nitrogen is an essential plant nutrient that farmers regularly apply to pastures to promote grass production for animal feeding. Nitrogen use represents a significant component of production costs of grass grown for hay or grazing. For both economic and environmental reasons, it is important that nitrogen applied to pastures be captured by plants and effectively used to produce animal feedstuff. Unfortunately, even with best management practices, the amount of nitrogen recovered in pastures is often 50% or less of that applied and this represents at best a significant waste of resources and at worst a potential for degrading water and air quality. Selective breeding for grasses that offer improved capture and utilization of applied nitrogen is one possible way to improve resource use and avoid environmental damage. The range of variability in these characteristics is, however, largely unexplored. In an exploratory study individual seedlings from 19 lines of annual ryegrass and 15 lines of tall fescue were grown in a greenhouse to provide an evaluation of variability in nitrogen uptake and utilization efficiencies existing within these commonly used species of forage grasses. There were differences in nitrogen uptake among accessions, but these differences were closely linked to root size. There were also differences among accessions in nitrogen utilization by roots and shoots, and these differences were not strongly linked to differences in dry mass yield, suggesting that although improvement in dry mass yield is an important objective for plant breeders it will not necessarily lead to improved nitrogen use efficiency. The results of these small-scale trials should be followed up with a more extensive evaluation of the nitrogen use efficiency in available germplasm.
Technical Abstract: Efficient use of nitrogen (N) applied to grassland is important, both for ensuring economic viability of N use and to minimize the amount of unrecovered N that is susceptible to loss from the agricultural system to the broader environment. Comparison was made of N uptake efficiency and of utilization efficiency of that captured N by roots and shoots of accessions and cultivars of annual ryegrass (Lolium multiflorum L.) or of tall fescue (Schedonorus phoenix (Scop.) Holub). Nitrogen uptake was closely and positively correlated with root and seedling-total dry mass (DM). There were significant differences in N uptake among accessions, but these were essentially a reflection of differences in seedling mass. The root mass and N uptake relation was similar in annual ryegrass and tall fescue. At harvest nine weeks after emergence, N contained in roots represented, on average, 34 and 27% of total seedling N in annual ryegrass and tall fescue, respectively. There were significant differences among accessions in shoot or root N utilization efficiency but there was no close relation of DM yield with N utilization efficiency. Although commercial cultivars ranked highly in DM yield, N uptake and N utilization, several unimproved accessions offered similar performance. In spite of the limited scope of this study, there was evidence of segregation of N uptake and N utilization characteristics in annual ryegrass and tall fescue that may justify more extensive investigation of within-species variability in response to applied N.