High Yield Grass Seed Production and Water Quality Protection Handbook

Residue Management

The management of straw and stubble after seed harvest is an essential component of perennial grass seed production and is a determining factor in seed yield. Three approaches to residue management in perennial grass seed crops have evolved: thermal, clean nonthermal and full straw load. Following is the definition of each approach and examples of common practices.

Common practices

I. Thermal - Fire-based residue removal and stubble management systems.

Full straw load + Open field burn
Full straw load + Open field burn + propane burn
Bale + Open field burn
Bale + Propane burner

II. Clean Nonthermal - Primary straw removal by baling, various methods of secondary removal to achieve a clean field. Stubble management may or may not be employed.

Bale
Bale + flail (various types)
Bale + flail + rake (various types) + remove (various methods)
Bale + reclip (with swather) + remove with loafer
Bale + vacuum
Bale + remove by rake, vacuum, loafer, etc. + compost (off field)

III. Full Straw Load - No straw removal, straw composts in place on field. Stubble height is reduced by flail mower.

Flail (1 to 3X) with various flails
Flail (1 to 3X) with various flails + partial removal of straw on grass crowns by rake, drags (farm drags, chain-link fence, etc.)
Flail (1X) after combine straw chopper

Seed yields are dependent on residue management technique and stand age, and vary among species. Species with a bunch-type growth habit (tall fescue, orchardgrass, perennial ryegrass) are more tolerant of residue management without straw removal and are readily amenable to clean nonthermal techniques. Unlike other bunch-type species, Chewings fescue does not tolerate much straw. Orchardgrass seed yield is equally responsive to any of the residue management possibilities. Clean nonthermal management is more difficult in species with a creeping-type growth habit (Kentucky bluegrass, dryland bentgrass) and these species do not tolerate a full straw load. Creeping red fescue can only be managed with fire in order to avoid significant seed yield reductions after the first production year. Hard fescue and creeping bentgrass yields can be reduced when nonthermal management practices are used.

Thermal management

Field burning provides disease control, especially diseases of the seed including blind seed and ergot, but not foliar diseases. Weed control is aided by field burning as fire destroys volunteer crop seed, weed seed and weed plants. In creeping red fescue, field burning has a direct stimulative influence on seed yield, but this is not observed in other species. Burning also recycles several important nutrients to the soil, including potassium and phosphorus, but not nitrogen.

Growers in the Willamette Valley have largely adopted non-thermal alternatives as burning has been on the decline for nearly two decades. Normally, field burning is practiced with the full straw load (i.e. without any straw removal). However, in central Oregon, field burning is done after straw removal by baling.

Clean nonthermal management

Economical, clean, nonthermal management has been made possible by the development of an off-farm straw removal and handling industry. Straw farmers are independent operators that bale and remove straw after seed harvest, although some grass seed producers bale their own straw after harvest. The straw is stored or shipped to bale compressor facilities where its bulk is reduced for export to international straw markets. Currently, more than 500,000 tons of Oregon grass seed straw enters this export market destined primarily for use in Japan and Korea. In addition, some grass seed crop straw is used locally for animal feed.

Baling removes most (75 percent or more) of the straw remaining after harvest. Stubble management by flail mowers or rotary mowers often follows baling. Perennial ryegrass and tall fescue seed yields are best maintained over the life of the stand when at least 60 percent of the residue is removed. High seed yield can be maintained in Kentucky bluegrass without open-field burning when straw removal is thorough and stubble height is reduced to less than 1.5 inches prior to crop regrowth. Chewings fescue and dryland bentgrass have consistently responded to clean nonthermal management with seed yields equal to burning, while creeping red fescue has not. Managing residues without open-field burning does not reduce seed purity or germination.

Full-straw management

Baling removes most (75% of more) of
straw that remains after harvest.

Stubble management by flail chopping
can help stimulate crop regrowth when
straw is baled following harvest.

Figure 1. Grass seed production
acreage and field burning acreage
in the Willamette Valley.

Management of residue without removal by baling has become a common practice in the southern Willamette Valley. This form of residue management is commonly known as full-straw management. Several forms of chopping a full straw load in place have evolved as seed growers sought low cost residue management alternatives. Full-straw management is a reasonable alternative tool that allows producers to forego baling when straw might not meet quality standards. Moreover, some growers object to the potential loss of important plant nutrients when straw is removed by baling and instead desire the benefits of nutrient cycling associated with the decomposition of the straw. Other growers have used the full straw load as a mulch to aid in the suppression of troublesome weeds.

Full-straw management can be a profitable practice for grass seed production, but this practice is not without risks. Careful consideration of these risks must be weighed before adoption of full-straw management. The following factors are known to affect seed yield of grasses grown under full-straw management: species, cultivar and stand age. The best yield results have been obtained with orchardgrass followed by tall fescue and perennial ryegrass. Some cultivars of tall fescue and perennial ryegrass are more tolerant of full straw loads than are others.

Summary and recommendations

Several factors should be considered when selecting a residue management technique for grass seed production. These include:

Species - Need to choose the best approach for the species depending on their inherent tolerance to the presence of straw and stubble after harvest.
Cultivar - Some variation in performance among cultivars with the various residue management approaches has been noted.
Stand age - Older stands tend to be more susceptible to environmental stress. Old stands are more susceptible to loss of stand when burned or when full straw load management is used.
Location of field - Fields located near housing developments or major roads are more difficult locations to burn - or to generate dust from nonthermal techniques.
Weed and/or disease pressure - Volunteer weed contamination problems make burning or clean nonthermal management the best choice, whereas annual bluegrass might be better controlled in a full straw load system.
Economics and risk tolerance - Seed growers need to choose the residue management method that best fits the economic productivity of their farming enterprise while minimizing the potential risk of seed yield loss. Under each of the approaches to residue management noted earlier, there are several different but often equally effective means of attaining the desired level of stubble and straw removal. Other methods of removing straw and stubble in grass seed fields in addition to those listed may be effective and economical.

Tom Chastain and Bill Young; Oregon State University Extension Service