Annual rainfall can be tabulated as calendar year (January –December) or crop year (September – August), but given the seasonal distribution of rainfall in the summer dry, winter wet climate of western Oregon, crop year precipitation is more relevant with regard to crop production and is considered here. The wet cycle in our Mediterranean climate begins in autumn and ends in spring so crop year precipitation better captures the seasonal nature of our region’s rainfall patterns (Fig. 1).
The efficacy of post-harvest fall irrigation (mid-August until the end of September) in perennial ryegrass and tall fescue is an important question for Willamette Valley seed producers. We conducted research to determine whether irrigation in this period is beneficial for these seed crops.
Some of the perennial ryegrass work was done in the very dry years of the early 1990s. Those years were as dry as our current three-year drought in western Oregon. What we found was that in two cultivars of perennial ryegrass, there was no effect of 2 inches of irrigation water in August and September on seed yield over a three-year period.
The late summer and early fall period has long been thought to be critical for regrowth of the grass seed crops after harvest and for the following year’s seed yield. Extremely dry conditions during this period in the Willamette Valley can reduce stands and crop regrowth in both seed crops. There is good evidence from our research that irrigation does improve the appearance of the stand (number of tillers and stand cover) going into the winter.
In a second set of trials, post-harvest irrigation was applied (5 inches) in three years in perennial ryegrass and in tall fescue from 2010 through 2012. This was compared with no irrigation. Weather conditions ranged from very dry to very wet in fall in the study years. Our results clearly indicate that there was no effect of this irrigation on seed yield in perennial ryegrass and tall fescue.
Our investigations suggest that while early fall irrigation increases tiller production and may enhance stand persistence under Willamette Valley conditions, there were no beneficial effects of fall irrigation on seed yield in perennial ryegrass and tall fescue even under dry conditions. The soil at our Hyslop Farm research site 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.
So what about other soils? If tall fescue or perennial ryegrass is grown on a light textured soil with poorer water holding capacity and high drainage such as soils that have high sand content and low clay content, then we cannot rule out the possibility that irrigation might be beneficial for stand persistence especially in areas that have gravel bars. But it is not known whether irrigation in these soils is beneficial for seed yield.
Nearly 200 delegates and other attendees recently participated in the 8th International Herbage Seed Conference hosted on the Lanzhou University campus in Lanzhou, China. The vice governor of the Gansu Provincial government as well as other dignitaries were present for the opening ceremonies of the conference, and were an indication of the importance of herbage seed in China.
The conference featured addresses delivered by dynamic speakers, interesting poster sessions, and tours, including a post-conference visit to the Hexi corridor. Delegates were treated to the gracious hospitality of our hosts and excellent local food.
Upcoming IHSG conferences will be held in Argentina in 2017, and in Oregon USA in 2019.
The stubble and straw remaining in grass seed fields after harvesting seed is known as residue. Post-harvest residue burning has been justified on the basis of pest control and stimulation of seed yield. Public concern over air quality and the potential for adverse health impacts on the region’s residents has necessitated the identification of alternative residue management practices. Oregon legislation (SB 528) has, in effect, ended the practice of field burning in the western part of the state for most species except for fine fescue seed crops.
The big concern in the region continues to be the persistent drought and high temperatures that have prevailed throughout May and June. These months are very important for grass seed yields because two important processes take place during the period: pollination and seed filling.
Drought and heat both can adversely affect pollination and subsequent seed filling. The lack of water as a result of drought means that the movement of sugars into the seed is impeded, and thus, are not available for filling of the seed’s endosperm tissues with starch. Heat can have direct effects on enzymes that are involved in seed filling. Consequently, seed yield can be reduced by both reduction in seed weight (light seed) and seed number (aborted seed).
Average temperatures for June (+4.5°F above the long-term average) at Corvallis were the 2nd warmest since 1948 with 1992 having the warmest June in that period. May was 2.2°F above the average. Rainfall in May and June was also very low with the combined rainfall the 3rd lowest since the mid 1970s. The lowest combined May and June rainfall was recorded on 1992. This year’s drought and heat bears a strong resemblance to 1992.
Seed yields of perennial ryegrass were reduced by 11% in 1992 and tall fescue experienced a 14.5% loss in yield in that year. By contrast, a large number of seed growers are reporting greater losses in seed yield of these crops this year even though the drought and heat have not been as severe in 2015 as they were in 1992.
For more information on this still developing story, see the following article in the Capital Press:
A group of young New Zealand farmers visited the Willamette Valley as well as other parts of Oregon recently. This group is known as the Arable Y and is organized by the Foundation for Arable Research in New Zealand. A young farmer from Tasmania, Australia also accompanied the group during its stay in Oregon.
I had the pleasure of addressing this group in 2013 at their meeting in Ashburton, New Zealand, so it was really nice to see them make the trip to Oregon. And it was likewise pleasurable to have the opportunity to tell them about Oregon’s seed production research programs during their visit here. One of our farmer hosts during the visit, Jon Iverson, experienced New Zealand seed production for himself in an farm internship while a student at Oregon State. Another of our department’s recent graduates was in New Zealand on an internship at the time that I made my address there and made acquaintances with the group during his stay in the country. This type of exchange is beneficial for all involved.
A big thank you is owed to James VanLeeuwen, a mid-Willamette Valley farmer who was involved in planning and logistics for the visit as well as the other farmers and seed industry partners that participated.