Thomas G. Chastain
Field trials conducted in the Willamette Valley showed that crop water use from April 1st through seed harvest in perennial ryegrass seed crops was 10.5 inches on a medium textured soil (silt loam). Crop water use in tall fescue during the same period was 10.1 inches on the same soil type. A perennial ryegrass or tall fescue seed field will need a combination of water stored in the profile over winter and irrigation to meet this water use for best seed yields especially if rainfall is short of this 10.1 to 10.5 inch total.
Spring rainfall at Corvallis averages 5.8 inches, but the crop water use need exceeds 10 inches on a medium textured soil. Our results indicate that a single irrigation (over a few days) of 3.7 inches timed at early flowering (BBCH 60) resulted in a seed yield increase of 16% in perennial ryegrass. However, the highest perennial ryegrass seed yield increase of 25% was made possible with multiple irrigations (total irrigation water = 6.5 inches) timed between spike emergence (BBCH 50) and peak flowering (BBCH 65).
Unlike perennial ryegrass, tall fescue seed yield was increased by 19% with a single spring irrigation (over a few days) of 3.7 inches timed to coincide with flowering (BBCH 60-65). No further increases in tall fescue seed yield were observed with multiple irrigations totaling 6.8 inches.
What about water use and irrigation needs in light textured well-drained soils (sand, sandy loam) or heavy textured soil (clay)? In New Zealand, water use in perennial ryegrass seed crops on a light textured soil was 12 inches over the same spring period. Less water is stored in a light textured soil so more irrigation was needed than in a medium textured soil. Maximum seed yield increase in perennial ryegrass was 26% in a light textured soil in New Zealand with 8 inches of total water applied over the season. More irrigation (8 inches vs. 6.5 inches) was needed to provide essentially the same result in a light textured soil than in a medium textured soil. Less irrigation will be needed if the spring rainfall is high or if the soil is heavy textured.
The current conditions suggest that less water might be needed this year with heavy rainfall in March and average rainfall in April. Current crop year precipitation through the end of April is much greater than average (over 47 inches to date) and greater than the 2014-15 crop year where drought conditions prevailed in the spring. But as the previous post indicated, temperatures are much above normal this spring thereby advancing growth and development of the crop.