- Seed yield in perennial ryegrass is the product of yield components
that develop during the life of the plant. Crop yield potential is
defined by the number of fertile tillers, spikelets per spike, and
florets per spikelet. It has been shown that perennial ryegrass
realizes only a small percentage of the potential as harvested seed, and
is an inherently poor seed producer as cultivars have been selected
primarily for vegetative production or desirable turf characteristics.
The Willamette Valley of Oregon produces nearly all of the
perennial ryegrass seed grown in the United States. Environmental
conditions during plant growth control potential yield development and
the efficiency with which it is used. To increase the efficiency of
seed production, it is important to understand the effects specialized
cultural management techniques have in this producing region.
In these studies on perennial ryegrass, the effects of varying the
amount and time of spring applied nitrogen (N), and the effects of the
plant growth retardant paclobutrazol were investigated under field
conditions using the cultivar Pennfine. In addition, the influence of
high levels of early spring N, combined with growth retardant use was
Increased tiller densities, the result of higher N level, can
result in a greater seed yield potential. However, as tiller densities
become greater, the components of seed yield on individual tillers
become smaller. In addition, earlier and more severe lodging result in
greater tiller mortality and harvest dry weight losses. Split spring
applications totaling 120 to 150 kg N ha⁻¹ appeared to provide a better
balance between compensating yield components, while maintaining an
economic seed yield.
Spring application of paclobutrazol delayed the onset and severity
of lodging, resulting in an increased number of fertile tillers in the
stand, and a greater number of potential seed sites per unit area.
Earlier dates of application had a greater effect in reducing lodging in
1983, but no difference was observed between two spring growth stages in
1984. Reduced lodging appears to enhance seed set, resulting in a
greater number of seeds recovered at harvest and a higher floret site
utilization (FSU). Harvest index was also increased with paclobutrazol.
Application of paclobutrazol significantly increased seed yield, a
result of improved seed recovery due to more seeds per spike. However,
the increased yield potential resulting from higher N rate was not
recovered by application of paclobutrazol where severe lodging
conditions occurred prior to the completion of seed filling. Under more
normal environmental conditions, 120 kg N ha⁻¹, followed with a growth
retardant application, had a significantly greater seed yield than the