By Nicole P. Anderson and Brian C. Donovan, Oregon State University
Since the late 1940s, open-field burning has been used as a widespread practice in grass seed production in the Pacific Northwest. Post-harvest residue management is an important factor in several fine fescues, including creeping red fescue and Chewings fescue, and Kentucky bluegrass seed crops. Open-field burning (Figure 1) has been a vital management tool because of its ability to remove post-harvest residue in grass seed production fields in order to maintain high seed yield and quality (Hardison, 1980; Crowe et al., 1996; Rolston et al., 1997). In the Willamette Valley, seed production of fine fescue seed crops was reduced when grown in the absence of post-harvest residue removal (Chilcote et al., 1980).
Public concern over air quality began in the 1970s and a high priority was placed on research to study alternatives to open-field burning (Canode and Law, 1977). Non-thermal post-harvest residue practices have been successfully developed for other cool-season grasses in the region including perennial ryegrass, tall fescue, and Kentucky bluegrass (Young et al., 1984; Entz et al., 1994; Chastain et al., 1996; Chastain et al., 2000). Unfortunately, there has been less success in finding non-thermal alternatives to open-field burning that do not result in seed yield decreases in fine fescue seed crops, especially as stands age and thatch increases.
Species with a bunch-type growth habit, including perennial ryegrass, tall fescue, and Chewings fescue, have been found to be more tolerant of non-thermal residue management when compared to Kentucky bluegrass and strong creeping red fescue, which display a creeping growth habit (Chastain et al., 2000). Chastain et al. (1996) showed that high seed yield of perennial ryegrass and tall fescue could be achieved with non-thermal management of post-harvest straw and stubble, especially when more than 60% of the straw is removed. In addition, they reported no yield difference from diverse residue management practices on orchardgrass and Chewings fescue in the Willamette Valley. Young et al. (1998a) showed an equivalent seed yield in Chewings fescue between open-field burning and non-thermal management. Figure 2 shows the difference in residue after burning and straw removal.
Chastain et al. (2011) compared seed productivity responses of fine fescue species to residue management and found beneficial effects of open-field burning increased with stand age, resulting in greater seed yields in strong creeping red fescue and Chewings fescue. Burning increased seed yield over non-thermal treatments in strong creeping red fescue by 32 and 84%, in second- and third-year fields, respectively. A study conducted on strong creeping red fescue found open-field burning increased panicles m-2 and spikelets panicle-1 compared to flailing of post-harvest residue, and in turn, resulted in higher seed yields (Zapiola et al., 2014).
Although open-field burning has considerable positive impacts on fine fescue seed production, legislative actions have restricted the total area of seed crops burned in the Willamette Valley each year. More specifically, Oregon Senate Bill 528 ended open-field burning in western Oregon for grass seed crops, except certain “fire-dependent” grass species. The Oregon Department of Agriculture currently regulates open-field burning to 15,000 acres of Chewings fescue, creeping red fescue, and Highland bentgrass seed fields in limited areas of the Willamette Valley each summer (Oregon DEQ, 2022). Fine fescue seed growers are concerned about the future of open-field burning and the ability to sustain an economically viable fine fescue seed industry in Oregon if open-field burning is further restricted.
To address this concern, Oregon State University researchers launched a multi-site multi-year studies to evaluate optimal spring management practices for several fine fescue species grown for seed in non-burned environments. Field trials were conducted over two crop years to examine the effects of spring defoliation and plant growth regulators (PGRs) on seed production characteristics in Chewings fescue and strong creeping red fescue. In addition, the effects of spring nitrogen and PGRs on seed production characteristics were evaluated in two cultivars of Chewings fescue and two cultivars strong creeping red fescue, over a 3-year period in large-scale on-farm trials. The results of this work indicate that growers will not benefit from spring mowing as seed yields were unchanged or decreased with spring defoliation, across multiple timings. Applications of trinexapac-ethyl (TE) PGRs increased seed yields in both species. In strong creeping red fescue, our data indicated that maximum seed yields can be obtained with 45 to 90 kg N ha-1 and 400 g ai TE ha-1. In Chewings fescue, our results suggest that fine fescue seed growers apply 200 g ai TE ha-1, regardless of the spring N rate or stand age.
References
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