- Introduction of later maturing cultivars of perennial ryegrass (Lolium perenne
L.) places more seed production fields in a period of drought common to Oregon
during vital stages of reproductive development. During these stages, the final yield of
the crop is largely determined by the number of seeds set, and the development of
individual seed weight. There is belief that water deficit during these periods may
drastically reduce yield, which could be eliminated with properly timed spring
irrigation. Therefore, this study was undertaken to (i) determine crop water use and
water use efficiency of both irrigated and non-irrigated perennial ryegrass cultivars,
(ii) observe any water use differences as a result of cultivar differences in perennial
ryegrass, (iii) compare seed yield and seed yield components of different cultivars
within irrigated and non-irrigated treatments, and (iv) determine appropriate timing
and amount of irrigation to apply if it is revealed that irrigation enhances yield.
A linear irrigation system was used to apply irrigation to six cultivars of
perennial ryegrass in the crop years 2003 and 2004. In 2003 from 1 March to 25 July,
285 mm of water was consumed by non-irrigated plants, 365 mm when soil profile
was filled once prior to peak anthesis, and 388 mm when soil moisture was maintained within 50 mm of field capacity to peak anthesis. In 2004 from 1 March to 8 July, nonirrigated
plants consumed 279 mm of water, 353 mm from treatment to fill soil profile
once, and 482 mm from treatment that maintained soil moisture up to peak anthesis.
No statistical difference was observed in water use efficiency between treatments in
2003. In 2004 an interaction was observed between cultivars and irrigation, thus
cultivars responded differently to irrigation. Contrasts revealed that cultivars
responded differently with respect to water use efficiency.
In 2003, irrigation to maintain soil moisture resulted in a 27% increase in yield,
18% due to an increase in seed number, and 8% due to an increase in seed weight.
Irrigation to fill profile once resulted in a 21% increase in yield, 14% due to an
increase in seed number, and 6% due to an increase in seed weight. In 2004 a cultivar
by irrigation interaction was observed for total yield, seed weight, and seed number.
Seed yield was increased by irrigation in all cultivars.
In 2003, irrigation to maintain soil moisture began 3 June and corresponded
with the beginning of anthesis, and proceeded to peak anthesis, 11 June. No rainfall
was received during this period, or the period of seed fill which followed. In 2004
irrigation to maintain soil moisture began 29 April, and continued to peak anthesis, 4
June. Irrigation to fill profile once occurred between 3 June and 7 June in 2003, and
between 31 May and 4 June in 2004. In 2004 significant rainfall occurred after peak
anthesis during the period of seed fill. Data from both years suggest that irrigation to
alleviate water deficit from the onset of anthesis through peak anthesis provides the
plant with sufficient water to increase individual seed weight and seed set, thus
improving overall yield.