Floret fertility and seed yield in selected perennial ryegrass cultivars as affected by time and rate of nitrogen (N) application Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/jh343x03c

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  • To increase efficiency of seed production, it is important to understand the effects of nitrogen (N) fertilizer rate and time of application. In particular, the effects on floret fertility should be examined since only a small proportion of florets actually produce harvestable seed. For these reasons, experiments were conducted in the field in 1981 and 1982 to study the effect of rate and time of nitrogen application at different growth stages on potential and actual seed yield and floret fertility. Specific effects of nitrogen on rate of floret filling in the top, intermediate and the bottom locations of the spike were observed. Two cultivars of perennial ryegrass were used in this study: Linn, an early maturing forage cultivar and Pennfine, which is a later maturing turf-type cultivar. Different nitrogen rates were applied at the vegetative phase, during spikelet initiation phase and at both stages. Nitrogen application increased the seed yield potential by increasing the number of fertile tillers per unit area and/or number of florets per spikelet. Nitrogen rate and time of application had no effect on floret fertility. Floret fertility percentage in all treatments were initially about 61%, but by final harvest had decreased to 20-32%. This reduction was likely due to loss of light seed during har vesting and cleaning. There was a slightly lower floret fer tility in the top compared with the intermediate and bottom location of the spike, but this was not affected by nitrogen rate or timing. Linn cultivar showed a higher rate of floret filling than the Pennfine; however, nitrogen rate and time of application showed no effect on rate of floret filling. Seed yield was affected by nitrogen application only in 1981, due to lodging, excessive vegetative tillering, and yield com ponent compensation. Results in this study do not support the hypothesis that management practices should be aimed at increasing head size rather than head numbers.
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