Thomas G. Chastain

Research conducted at Hyslop Farm has shown that spring irrigation in tall fescue and perennial ryegrass can increase seed yield.  The soil at Hyslop Farm is a medium textured soil (Woodburn silt loam) that is typical of many places in the valley where tall fescue and perennial ryegrass seed crops are grown.  This soil is deep and has good water holding capacity.

Tall fescue seed yield responses to spring irrigation varied among the cultivars tested.  Increased number of seed in tall fescue was most responsible for the seed yield improvement observed with spring irrigation.   Strategic timing of spring irrigation to support seed filling was more important for increasing seed yield than season-long irrigation.  Spring irrigation increased seed yield up to 39%.  First years stands of stands of tall fescue averaged 28% increase in seed yield with spring irrigation while second year stands averaged 11% increased yield.

Table 1. Spring irrigation effects on seed yield in perennial ryegrass

In three of the four years it was too wet to apply multiple irrigations in the spring in perennial ryegrass, only single irrigations were made and they were timed to coincide with flowering and to support seed filling (Table 1).  In Year 2, a single application increased seed yield by 11.5% while multiple irrigations through the spring, seed yield increases averaged 21.7%.  The normal rainfall at Hyslop Farm during the April-May period is 5.83 inches, so only 1 in 4 years was near or below average rainfall.  It was clear that seed yield of perennial ryegrass was increased even in springs with wetter than normal rainfall.  Drier springs may require more frequent irrigations, and the single irrigation timed at flowering might not be sufficient.  Rainfall during the April-June period is less than the 5.83 inch average 60.5% of the time, so a grower should see yield responses to irrigation more times than not on a medium textured soil.

So what about other soils?  If tall fescue or perennial ryegrass is grown on heavier textured soils such as those with high clay contents, a seed yield response to irrigation might be limited to dry springs because of the high water holding capacity of the soil.  A single irrigation timed at flowering might not be enough for a light textured soil with poorer water holding capacity and high drainage such as soils that have high sand content and low clay content.  These soils might need additional early season irrigation prior to flowering especially in years when rainfall is low in April and early May.  This was the case in England and in New Zealand when perennial ryegrass seed crops were grown in trials on light textured soils with less in the way of water holding capacity.  Fields that have gravel bars usually need additional irrigation.

All 7 cultivars of perennial ryegrass tested responded to spring irrigation with increased seed yield.  Seed yield increases attributable to spring irrigation were the result of increased seed number and seed weight, but seed yield was not substantially affected by the expression of other seed yield components.