Later maturing cultivars and increased ability to apply irrigation have led to
inquiries by producers about proper irrigation management in tall fescue (Festuca
arundinacea Schreb.) seed crops. The literature reveals little information about
irrigation of perennial grass seed crops in general, and none about tall fescue in
particular. Willamette Valley producers need research-based information on which to
base irrigation management decisions.
A field study was established near Corvallis, Oregon on a Woodburn silt loam
soil (fine-silty, mixed, mesic, Aquultic Argixeroll) to study the effect of spring
irrigation on six cultivars of tall fescue. Dryland conditions were compared to (1)
irrigation to fill the profile to field capacity (238 mm) at anthesis and (2) irrigation to
maintain water deficit ≤ 50 n-rn-i below field capacity until the beginning of seed fill.
Soil water was monitored with time domain reflectometry (TDR) at 15-cm increments
to a depth of 60 cm. Data from the experiment were used to calculate reproductive
efficiency (RE), harvest index (HI) and water use efficiency (WUE).
The 2003 growing season was wet during the first half and dry during the
second half, while the 2004 season was characterized by alternating moist and dry
periods. Both irrigation treatments received 78 mm of water in 2003. In 2004,
treatments received 112 and 172 mm of water for the single application and
maintained application, respectively. Responses did not differ between the two
irrigated treatments. In both years, an interaction existed between irrigation and
cultivar for yield but not for seed number and weight. In 2003, yields were increased
by 13 to 39% over non-irrigated yields, depending on cultivar. 'Barrington' and
'Bingo' showed the strongest response to irrigation. 'Velocity' was not responsive to
irrigation in 2004, though the remaining cultivars exhibited a positive yield response
(14%). Seed weight across cultivars increased with irrigation in 2003 and 2004. Seed
number increased with irrigation in 2003 but not 2004.
Potential yield, tiller and panicle characteristics, RE, HI and WUE were not
affected by irrigation but were cultivar dependant. Average RE was greater in 2004
(3 1%) than in 2003 (19%). Harvest indices ranged from 0.05 to 0.19. Water use
efficiency ranged from 2.92 to 9.92 kg ha⁻¹ mm⁻¹, averaging 6.21 kg ha⁻¹ mm⁻¹.
In general, the reduction of water deficit stress during seed fill increases tall
fescue yield due to increases in seed weight and number. However, level of response
depended on cultivar and climatic conditions during the growing season. Irrigation in
the present study would have been profitable for Willamette Valley producers.
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