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CROPPING SYSTEMS

Residue Management of Perennial Ryegrass and Tall Fescue Seed Crops

^a Dep. of Crop and Soil Science, Oregon State Univ., Corvallis, OR 97331-3002 USA

william.c.young{at}orst.edu

Received for publication October 16, 1996.

	ABSTRACT

TOP NOTES ABSTRACT INTRODUCTION Materials and methods Results Discussion REFERENCES

 
Regulations on open-field burning have forced grass seed growers to adopt alternatives for postharvest residue management. Experiments were conducted on fields established by grass seed producers in western Oregon to compare effects of (i) mechanical straw removal and flail-chopping the stubble (flail-chop), (ii) mechanical straw removal and propane-burning the stubble (propane-burn), and (iii) open-field burning the residue (open-burn) on seed yield the following year. Treatments were tested on three consecutive crop years of perennial ryegrass (Lolium perenne L. cv. Regal and Pleasure) and tall fescue (Festuca arundinacea Schreb. cv. Martin and Rebel II). Seed yield components were measured to identify the components through which treatments affect yield. Treatments did not affect seed yield of Regal perennial ryegrass and Martin tall fescue in any crop year. Third-crop seed yield of Pleasure perennial ryegrass was 15% higher for the open-burn than for the flail-chop treatment; fourth-crop seed yield was 12% higher for the open-burn treatment than for either flail-chop or propane-burn. Across years, seed yields of Rebel II tall fescue for propane-burn and open-burn treatments were 8 and 12% greater, respectively, than for flail-chop. Where seed yields were affected, differences among treatments were through changes in seed number per unit area (seeds m^-2), but seed weight was relatively stable. Treatments did not affect the number of fertile tillers in any cultivar. Variations in seed number were apparently due to treatment effects on the number of seeds set per tiller. We conclude that the need for postharvest residue burning in perennial ryegrass and tall fescue is cultivar specific. Mechanical residue removal is apparently as effective as open-field burning for maintaining high seed yields in some cultivars of these grasses.

	INTRODUCTION

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POSTHARVEST BURNING

of grass seed crop residue started in Oregon during the 1940s to control seed diseases in perennial ryegrass (Hardison, 1976). Compared with mechanical methods of residue removal, burning the postharvest residue effectively and relatively inexpensively removes residue from grass seed fields, and increases seed yield of most cool-season perennial grasses the following year (Chilcote et al., 1980). Grass seed growers in western Oregon have been searching for alternatives to residue burning because of increased restrictions on open-field burning to prevent air pollution.

Using different cultivars on grower's fields, Pumphrey (1965) found that red fescue (Festuca rubra L.) seed yield was the same when the residue was completely removed by mowing the stubble and raking all residue as when the residue was burned. Mechanical removal of the residue is also as effective as burning for seed production of `Pennlate' orchardgrass (Dactylis glomerata L.) and `Newport' Kentucky bluegrass (Poa pratensis L.) (Canode, 1972). However, Hickey and Ensign (1983) found that seed yields of many Kentucky bluegrass cultivars were higher when the residue was burned than when the stubble was mechanically removed to 25 mm. Other research (Chilcote et al., 1980; Canode and Law, 1978) also indicated that red fescue seed yield is higher when the residue is burned than when the stubble is flail-chopped close to the soil surface and all residue removed. Similarly, seed yield of smooth bromegrass (Bromus inermis Leyss.) and crested wheatgrass [Agropyron desertorum (Fisch. ex Link) Schult.] was greater when the residue was burned than when it was mechanically removed (Canode and Law, 1978). Young et al. (1998) reported that mechanical removal of postharvest residue maintained seed yield of `Center' Chewing's fescue (Festuca rubra L. subsp. commutata Gaudin) similar to that with open-burn, but open-burn was required to achieve maximum seed yield in `Cindy' creeping red fescue (Festuca rubra L. subsp. rubra Smith).

Limited information is available on the effects of different residue removal methods on seed yield of perennial ryegrass and tall fescue. Earlier work in Oregon (Chilcote et al., 1980) indicated that seed yield of these grasses is higher when the residue is burned than when it is mechanically removed. Close clipping of stubble (25 mm height) and removing the residue maintains seed yields similar to those with burning in Newport Kentucky bluegrass and `Encota' Chewing's-type fescue, but not in `Manhattan' perennial ryegrass (Young et al., 1984).

Currently, there are numerous combinations of nonthermal postharvest residue management systems for perennial grasses (Young et al., 1994). In general, more complete residue removal enhances seed yield (Chilcote et al., 1983). Besides open-field burning, another thermal method for postharvest residue management is the use of a propane flamer to burn the residue after the straw has been baled and removed from the field (Chilcote and Youngberg, 1975). Emission of pollutants may be less with this method, because most residue is removed before burning (Chilcote and Youngberg, 1975). Our objective was to determine if baling the straw and flail-chopping the stubble, or baling the straw and propane-burning the stubble of perennial ryegrass and tall fescue is as effective for seed production in the following years as is open-field burning postharvest residue. Effects of residue management on yield components were measured to determine which are most affected by residue management methods.

	Materials and methods

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Four sites were selected in fields near Corvallis, OR, where perennial ryegrass cv. Regal (Site 1) and cv. Pleasure (Site 2) or tall fescue cv. Martin (Site 3) and cv. Rebel II (Site 4) were established by cooperating commercial seed producers. Tall fescue sites were established in the fall of 1986, and mowed through the summer of 1987; the first seed was harvested in the summer of 1988. Perennial ryegrass fields were established in the fall of 1987 and seed was harvested in the summer of 1988. Soil for Sites 1, 2, and 3 was Dayton silt loam (fine, smectitic, mesic Typic Albaqualf), and for Site 4 it was Woodburn silt loam (fine-silty, mixed, mesic Aquultic Argixeroll). Row spacing was 0.25 m for Regal, 0.3 m for Pleasure, and 0.5 m for both tall fescue cultivars. All cultivars were seeded at 6 kg ha^-1. Broadleaf weeds were controlled by applications of a tank mix of 2,4-D [(2,4-dichlorophenoxy)acetic acid] low volatile ester at 0.56 kg a.i. ha^-1 plus dicamba (3,6-dichloro-2-methoxybenzoic acid) at 0.28 kg a.i. ha^-1 in January of the establishment year. Following harvest of all seed crops, 34 kg N ha^-1 as (NH₄)₂SO₄ was applied in fall and 112 kg N ha^-1 as urea was applied in late winter.

Residue management treatments were: (i) straw residue removed and stubble flail-chopped (flail-chop), (ii) straw residue removed and stubble propane-burned (propane-burn), and (iii) residue and stubble open-burned with full straw load (open-burn). For flail-chop treatment, straw was baled and removed after seed harvest and the stubble was flail-chopped to a height of 70 mm, with the debris left on the ground. For propane-burn treatment, straw was baled and removed and the stubble was burned with a commercial propane flamer (Chilcote and Youngberg, 1975) traveling at 5 km h^-1. For open-burn treatment, straw was first removed and its dry weight was recorded, then the straw was returned to the plots, spread uniformly, and set on fire. Each plot (7 by 30 m) was randomly selected across the field, and the experiment was arranged in four randomized complete blocks. A 7- by 7-m area was randomly selected in each plot for yield component measurements. The same treatments were applied to each plot every year, and yield and yield component were measured on the second, third, and the fourth seed crops during the summers of 1989, 1990, and 1991, respectively. Open-burning the first-year residue of Rebel II tall fescue considerably reduced the second-year stand, probably because of exceptionally high straw dry weight and dry conditions prior to burning. Therefore, the experiment for that year was terminated and was resumed after harvesting the second seed crop.

Peak anthesis was determined by examining fertile tillers in the field when anther exsertion began, and was defined as the time when 70% of randomly selected fertile tillers had exserted anthers. The number of total and fertile tillers at peak anthesis was determined by cutting all aboveground plant material from two randomly selected 0.1-m² quadrats in each plot. The number of spikelets per inflorescence was counted on 10 randomly selected fully emerged tillers at maturity. Floret number per spikelet was determined by counting the florets in all positions at the bottom, middle, and top of a subsample of four randomly selected inflorescences. The mean number of florets per spikelet from all positions was taken as the number of florets per spikelet. The number of floret sites per unit area (m²) was calculated by multiplying the mean number of florets per inflorescence by the number of fertile tillers per unit area at anthesis. Floret sites per unit area represent the number of empty florets as well as filled florets at maturity.

Seed yield was determined by harvesting a 1- by 6-m section from the middle of each plot using a small-plot harvester incorporating a sickle bar cutter and draper designed for bagging harvested biomass. Plots were harvested when seed moisture content was about 400 g kg^-1. The harvested material was air-dried for 2 wk and then placed in a forced-air dryer at 35°C for 12 h prior to threshing with a belt thresher. Total dry weight of the harvested materials was recorded before threshing, and straw weight was calculated by subtracting seed weight from harvested biomass. Weight per seed was calculated based on 1000-seed weight. The number of seeds per unit area achieved at harvest was calculated by dividing the total seed yield by weight per seed.

Data combined over years were analyzed as a factorial design, and main effects of treatments and their interaction with years were evaluated. When treatment x year interactions were not significant, data were analyzed across years as randomized complete block design and means were compared using Fisher's protected LSD. Correlations of seed yield with yield components were determined within each year.

	Results

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Residue management treatments did not affect Regal perennial ryegrass seed yield, but florets per spikelet and floret sites per unit area were affected (Table 1) . The number of florets per spikelet in Regal was lower for propane-burn than open-burn (Table 2) . The number of floret sites per unit area was lower for propane-burn than the other two treatments. Treatments did not affect the numbers of tillers and seeds produced per unit area (Table 1).

	Discussion

TOP NOTES ABSTRACT INTRODUCTION Materials and methods Results Discussion REFERENCES

The number of years that postharvest treatments are applied should also be considered when investigating residue management effects on seed yield of grasses. Young et al. (1984) reported that seed yield of Manhattan perennial ryegrass decreased in the year immediately following mechanical removal of the residue compared with open-field burning, but that seed yield of Newport Kentucky bluegrass was maintained for two years and declined in the third year when stubble was close-clipped or flail-chopped.

Reducing volunteer seedlings in the subsequent crop is another reason that producers of Certified grass seed in western Oregon burn postharvest residue. It is difficult to selectively remove volunteers of the same species from a grass seed crop by using herbicides. Burning the residue after a grass crop is harvested helps to destroy most of the seeds on the soil surface and reduces the number of volunteer seedlings in following crops. However, recent work indicates that, with proper herbicide treatments, seed certification standards for perennial ryegrass (Mueller-Warrant et al., 1994) and tall fescue (Mueller-Warrant et al., 1995) can be met without field burning.

Straw disposal has been another advantage for burning postharvest residue. Until recently, grass seed straw has had little or no market value and straw disposal has been a major challenge for grass seed growers. However, a market for grass seed straw has been emerging in western Oregon, which makes alternatives to open-field burning more attractive to the growers (Oregon Econ. Dev. Dep., 1991).

Strong yield component compensation in all the cultivars made it difficult to determine the yield component that most closely affected the seed yield as a result of residue management practices. Chilcote et al. (1980, 1983) attributed seed yield improvements of many grasses after postharvest residue burning to increases in the number of fertile tillers produced. In contrast, when straw burning improved seed yield in our study, the increased yield was not associated with increased number of fertile tillers, but was correlated with increased straw weight and increased number of seeds per unit area. Burning the residue increased the number of seeds produced per fertile tiller. Because treatments did not affect the number of floret sites per fertile tiller, burning probably improved floret site utilization. Burning apparently resulted in fewer but heavier fertile tillers, which bore more seeds than in unburned plants.

The radiation environment at the plant base, especially variations in the red/far-red ratio, dramatically affect tiller dynamics and reproductive development of cool-season grasses (Casal et al., 1985, 1987). In perennial ryegrass, the majority of inflorescences at harvest are borne on tillers that appear during the previous late summer and autumn (Ryle, 1964; Hill and Watkin, 1975). The degree to which postharvest residue of grass seed crops is removed can affect the radiation environment at the plant base. Understanding how methods of straw removal affect light quality and quantity at the plant base during summer and autumn months might help to determine responses of grasses to postharvest residue management.Oregon Economic Development Department and the Oregon Department of Agriculture. 1991

	NOTES

TOP NOTES ABSTRACT INTRODUCTION Materials and methods Results Discussion REFERENCES

 
Contribution from the Oregon Agric. Exp. Stn., Tech. Paper No. 11058.

	REFERENCES

TOP NOTES ABSTRACT INTRODUCTION Materials and methods Results Discussion REFERENCES

 

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• Casal J.J., Deregibus V.A., Sanchez R.A. Variation in tiller dynamics and morphology in Lolium multiflorum Lam. vegetative and reproductive plants as affected by differences in red/far-red irradiation. Ann. Bot. (London) 1985;56:553-559.[Abstract/Free Full Text]
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• Chilcote, D.O., and H.W. Youngberg. 1975. Propane flamer burning of grass seed field stubble. Prog. Rep. Ext/ACS 8, Agric. Exp. Stn. Oregon State Univ., Corvallis.
• Chilcote, D.O., H.W. Youngberg, P.C. Stanwood, and S. Kim. 1980. Post-harvest residue burning effects on perennial grass development and seed yield. p. 91–103. In P.D. Hebblethwaite (ed.) Proc. Easter School in Agric. Sci., 28th, Univ. of Nottingham. 1978. Butterworth, London.
• Chilcote, D.O., H.W. Youngberg, and W.C. Young III. 1983. Post-harvest residue burning as a management tool in grass-seed production. p. 254–257. In J.A. Smith and V.W. Hays (ed.) Proc. Int. Grassl. Congr., 14th, Lexington, KY. 15–24 June 1981. Westview Press, Boulder, CO.
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• Mueller-Warrant G.W., Young W.C., III, Mellbye M.E. Influence of residue removal method and herbicides on perennial ryegrass seed production: I. Weed control. Agron. J. 1994;86:677-684.[Abstract/Free Full Text]
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