Thomas G. Chastain
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 the fine fescues.
There are three primary residue management methods practiced by Oregon’s grass seed growers:
1. Thermal. This method includes fire-based straw and stubble removal and includes field burning with full straw load in place on the field (open-field burning) and propane burning. In some instances, straw is removed from the field and burned in stacks. Field burning has been an effective, economical and controversial method of crop residue removal and pest control in grass seed crops for more than 50 years.
2. Clean non-thermal. This method is based on straw removal by baling, and removal from the field. Stubble reduction following straw removal with a flail mower may or may not be employed. Straw removed from grass seed fields is used for animal feed, especially for export markets, as well as other products. The straw removed from seed fields has potential for use a feedstock for the production of ethanol biofuel.
3. Full straw load. This method involves no straw removal as the straw is allowed to decompose in the field. Straw length may be reduced by flail mower and/or by combine straw chopper. The straw composts in place in the seed field thereby improving several beneficial characteristics of the soil.
Crops residues are managed in grass seed fields for control of certain diseases and weeds, to stimulate seed yield in some species of grasses, to remove large volumes of straw and stubble that might interfere with crop management operations, and to recycle nutrients in grass seed fields. A broad range of grass species are grown for seed production in Oregon – these species differ markedly in their seed yield response to post-harvest residue management.
Perennial ryegrass, Tall fescue, and Orchardgrass
Perennial ryegrass, tall fescue, and orchardgrass are the predominant perennial grass seed crop species grown in Western Oregon – some form of clean non-thermal or full straw load management works best for these crops. A recent OSU publication summarizes the results of these field studies with these crops and adds new insights on how grass seed crop residue management influences nutrients and nutrient management decisions.
The publication can be obtained by following the link below:
Postharvest Residue Management for Grass Seed Production in Western Oregon EM 9051
Fine Fescues
Three closely related species of Festuca exhibiting fine leaf texture are commercially important turfgrasses and are known collectively as the fine fescues. These species are Chewings fescue (CF)[F. rubra L. subsp. fallax (Thuill.) Nyman], strong creeping red fescue (strong CRF)(F. rubra L. subsp. rubra), and slender creeping red fescue (slender CRF)[F. rubra L. var. littoralis (Vasey)]. While fine fescue species are morphologically similar in many characteristics, strong CRF and slender CRF produce rhizomes, but CF does not.
Our studies have shown that retaining a full straw load on the three fine fescue species produces reduced seed yields. In 2nd year stands, burning increased seed yield in all strong CRF cultivars, but caused mixed responses in CF and slender CRF cultivars. In other words, in some cultivars of CF and slender CRF, burning increased seed yield while in others it did not. Burning increased seed yield in 3rd year stands in all CF and strong CRF cultivars, but reduced yield by 9% in slender CRF. Slender CRF is sensitive to thermal management especially in weaker, older stands. Burning increased seed yield over non-thermal treatment in strong CRF by 32% and by 84%, in 2nd and 3rd year stands, respectively. Beneficial effects of burning increased with stand age, resulting in greater seed yields in fine fescue species except slender CRF. Clean non-thermal management can be economically employed early in the life of the stand in CF and at all stand ages in slender CRF, but not in strong CRF.
Post-harvest residue management recommendations for growers of fine fescue seed crops need to be species-specific and stand age specific within the group (CF, slender CRF, strong CRF) rather than broadly across the group as had been done in the past. Differences among cultivars within these species need to be considered as well.
The following articles have more detailed information on post-harvest management in fine fescue seed crops:
Kentucky Bluegrass
Kentucky bluegrass is an important grass seed crop grown in the central and northeastern portions of Oregon. Kentucky bluegrass is like the fine fescue seed crops in that it is intolerant of a full-straw load and will produce poor seed yields over the life of the stand if straw is not removed. Removal of stubble is also important – removing too little stubble reduces seed yield in Kentucky bluegrass and other seed crops that produce rhizomes.
More information on residue management in Kentucky bluegrass seed crops can be found here:
