Establishment of California oatgrass from seed can be problematic as the result of delayed germination and variable seed dormancy, as well as moderately slow seedling development combined with early competition from other species. Difficulties with reseeding Danthonia species were reported in the early to mid 1900’s when interest grew in reintroducing native perennial grasses on depleted or weedy grazing lands in California (Laude 1949).
Seed dormancy and germination: Evidence suggests the variable seed dormancy in California oatgrass is the result of either single or double (combined) dormancy. The dormancy may be variants of seed coat imposed dormancy, physiological (embryo) or both. Moreover, the amount and possibly the type of dormancy can vary among populations of California oatgrass (Trask and Pyke 1998). It may also depend on crop year or seed lot (Laude 1949) within the same population because climatic conditions during seed development can influence the expression of seed dormancy. Furthermore, the length of time and conditions during storage may affect seed dormancy of grasses like California oatgrass by influencing after ripening (Simpson 1990). Amme (2008) reports that fresh seed or seed that is sown and watered immediately after collection can germinate readily at a high percentage. In contrast, germination is delayed after a period storage, suggesting that dormancy can deepen over time.
Field observations indicate dormancy will also vary among seeds within the same seed lot of California oatgrass. In some years at Corvallis, Oregon, both fall seeding of fields and fall sowing of containers resulted in a portion of seedlings emerging within three weeks, while additional seedlings emerged as early as March in each of the following two springs (Darris per. obs.). Others report more continuous but prolonged germination and emergence periods. Some variability in the dormancy and germination in mechanically harvested lots may be due in part to aggressive seed combining and conditioning/cleaning processes. In these instances some dehulling (ie. hulling or separating the caryopsis or kernel from the lemma and palea), may occur and the seed coat (pericarp) is inadvertently scarified or nicked on some seeds and not others.
Given the variable dormancy in California oatgrass seed, many methods have been used for improving germination with varying success. No treatment may be needed (Emery 1988, Dyer 2001) and direct sowing with untreated dry seed resulted in 60% germination in 21 days for Young (2001).
Mechanical abrasion or “injury” with coarse sand paper or brush machines in the process of dehulling, acid scarification, or puncturing of the seed coat alone have improved germination by reducing seed coat imposed dormancy. However, mechanical scarification can be difficult to achieve without unwanted damage to the seed. In a study done by the Corvallis Plant Materials Center (PMC) (unpublished data) germination was greatly reduced by using a huller-scarifier (brush machine) to dehull and simultaneously scarify seed alone or in combination with prechilling (cold moist stratification) treatments. The mechanical procedure was far too aggressive and caused excessive damage to the seed and therefore significantly lower germination. This supports Laude (1949) who indicated mechanical scarification to weaken the seed coat did not appear feasible due to the protruding embryo being in an exposed position resulting in embryo injury.
An alternative physical means of scarification may be the use of an oat huller to condition the seed. It appears to dehull more gently and reduce breakage to the ends of the seed compared to a huller-scarifier (Darris pers. obs.). Further testing is needed to confirm if this machine can simultaneously dehull and effectively scarify the seed coat to get good germination without resorting to acid treatment.
In one greenhouse study, inflorescence (terminal) seed treated for 15 minutes with concentrated sulfuric acid (sp. gr. 1.84) as a means of scarification resulted in faster and higher seedling emergence for all 16 populations after 4 weeks, and for all but 4 populations after 16 weeks (Laude 1949). The acid both dehulled the seed and etched the seed coat. However, 15 minutes seemed too severe for cleistogenes. For terminal seed, 15 minutes of acid treatment gave the best results in the field (8-20% seedling emergence), 30 to 45 minutes gave the best results in a germinator (81% germination), and 20 minutes resulted in the highest emergence (19-27%) in a greenhouse. In contrast, 5 to 10 minutes gave the best results for cleistogenes in the field (4% emergence) and greenhouse (10% emergence), while 10 to 15 minute treatments were best in the germinator (71-81% germination). In all cases, performance declined for acid treatments beyond these time frames. This work underscores the fact that different results can occur between controlled environments and field conditions and between the two seed types of California oatgrass. It also demonstrates the importance of recommending the best treatments found in field tests for field use (Laude 1949).
It would appear dormancy reduction in these trials was primarily the result of injury to or weakening of the seed coat and not dehulling (Laude 1949). Glumes or the seed covering formed by lemma and palea (the seed “hull”) can create seed dormancy in grasses (Simpson 1990) apart from the coat itself. However, whether in a germinator, greenhouse, or field and regardless of seed type, both untreated seed with lemma and palea intact and dehulled seed barely germinated while dehulled seed nicked with a scalpel showed a substantial improvement in percent germination and emergence. The author considers nicking the seed and acid treatment to be akin for the necessary purpose of weakening the seed coat.
The seed coat imposed dormancy in California oatgrass may or may not be a form of physical dormancy (seed coat constraint on moisture imbibition). Laude (1949) found that dehulled but unscarified seed and acid scarified seed both adsorbed moisture similarly. As a result, the author suggests the dormancy is caused by restricted gas exchange or mechanical constraints and not the prevention of moisture uptake. However, based on structural characteristics of grass seed coats, Simpson (1990) argues that rate or specific location of moisture uptake by the seed rather than gas exchange can be explanations. This suggests the possibility of California oatgrass seed possessing a variant of “physical” dormancy but further investigation is needed.
For reducing physiological dormancy, a solution of potassium nitrate (KNO3) or moist prechilling (cold moist stratification) alone have improved germination, as has giberellic acid (GA3) in combination with seed scarification, KNO3 plus scarification, or prechilling. Improvement with a combination of chemical and physical treatments supports the notion that California oatgrass can have complex or combined dormancy. Dobrenz and Beetle (1966) found that for both chasmogamic and cleistogamic seed, germination was similar and did not occur without blotters being soaked with KNO3. Results were 0% germination for controls and 10% germination using a solution of 0.2 % KNO3. In a study with four populations having 0 to 91% initial dormancy, a combination of seed scarification (by dehulling and rubbing seeds/caryopses between course sandpaper) and GA3 (300 ppm or 0.03%) improved cumulative germination to over 80% in all but one seed lot, while breaking over 90% of the dormancy. KNO3 only enhanced germination in combination with scarification and GA3 (Task and Pyke 1998). In a pilot study to enhance germination Trask (1996) found GA3 (400 ppm) alone to be the most successful treatment regardless of whether the seed was scarified or not. A combination of light, a 20/25°C (68/77°F) night/day temperature regime, and seven week prechill is suggested by Chirco and Turner (1986-2007). Unpublished work by the Corvallis PMC on two populations of California oatgrass demonstrated that moist prechilling of both inflorescence seed and cleistogenes at 5°C (39°F) for 45 to 90 days was effective in significantly improving germination as recorded for the first 28 days in a germinator.
Other practitioners indicate improved germination with 30 days of moist prechilling at 3-4°C (37-39°F) in combination with manual removal of the hull (Keeley 2000), 12 to 13 weeks of cold moist stratification alone, or simple fall sowing (Boyer 2007a). From personal communication with Jebb (1995), Rose et al. (1998) report California oatgrass does better with a one to three day soak in running water followed by three months of cold moist stratification at 1-5°C (34-41°F). Guerrant and Raven (1995) achieved good germination with cold stratification at 5°C (41°F) for six weeks followed by warm stratification for six weeks using 16 hour days at 20°C (68°F) and 8 hour nights at 10°C (50°F). Knapp and Rice (1994) found seed viability and germination varied among populations. They had “high” germination rates by squeezing the caryopsis out from the glumes and lemmas, pre-treating with 400 ppm GA3, and cold moist stratifying for 2-3 weeks at 4°C (39°F). In successful field applications using fall sown seed, it may not be clear whether germination was enhanced by cold moist stratification over winter, or weakening of the seed coat by soil influences, or both.
Finally, Maslovat (2001) reported that California oatgrass required light to germinate and associates this trait with natural regeneration after disturbance. However, for the Corvallis PMC some seed germinated in the dark, suggesting light may not always be necessary.
Summary: California oatgrass seed can be nondormant, for example when “fresh”, or commonly possess one or more types of dormancy that need to be overcome for germination to occur. The kind or amount of treatment(s) required, if any, may be specific to population, crop year, seed lot, seed type, storage conditions, or age of seed. The Association of Official Seed Analysts (Aosa) has not set official rules for testing the germination of California oatgrass. Nevertheless, for many seed lots the most practical method to improve germination without resorting to chemical enhancements is cold moist stratification. This can be done by fall seeding or moist prechilling in a controlled environment for 21-120 days. For other seed lots, dehulling/scarification of the seed will greatly improve germination if the seed coat can be scratched, nicked, or eroded without undue injury to the embryo. Manual methods to remove the caryopsis from the hull (squeezing out the caryopsis, rolling seed between rubber mats) along with the use of sandpaper or scalpels to weaken the surface are not practical on a large scale. A mechanical means is needed for large seed lots but a brush machine appears to be too aggressive. Gentler mechanical means of dehulling and scarifying, such as the use of an oat huller, needs further evaluation. Acid scarification requires special safety precautions but merits consideration. Finally, in some cases a combination of both stratification and scarification may prove to be the most effective way of reducing dormancy.
Natural establishment: Maslovat (2001) examined and described factors influencing natural and assisted establishment of California oatgrass in Garry oak ecosystems of Southwest British Columbia. Characteristics of this grass suggest it is an important colonizer following disturbances such as fire. While a modest seed producer, its seed dormancy and need for light to germinate help create a persistent seed bank (Maslovat 2001). The seed often remains viable in the ground for years. Stands can be resurrected from this latent seed by mowing or other disturbances (Amme 2003).
Seedling recruitment appears aided by retention of shallow litter or moss and variable microtopography, especially minor depressions and grooves that favor higher moisture storage. Deeper litter, often exacerbated by long term fire suppression, may act as an impediment to root penetration and seedling emergence. However, raking of the soil to completely remove litter and clippings can reduce seed germination and establishment on some sites (Maslovat 2001).
The awns found on unprocessed seeds of California oatgrass presumably improve dispersal by attaching to passing animals. In addition, the same awns are hygroscopic (bend and straighten with wetting and drying), a trait implicated in natural seed burial. They may also assist in seed migration and selection of more favorable microsites (Maslovat 2001).
Site preparation: Keys to establishing California oatgrass for revegetation and other goals are preplant weed control and proper seedbed preparation. Starting situations can vary greatly, calling for site specific strategies. Among the most difficult cases are abandoned fields and other areas dominated by exotic weeds that have an extensive weed seed bank built up in the soil. One option for site preparation is to fallow the area for one to three years with repeated tillage operations following each flush of new weeds in order to reduce the weed seed bank prior to sowing. A nonselective herbicide (usually glyphosate) can be used in combination with the tillage (Darris 2003, Campbell 2004, Stromberg et al. 2002, Stromberg and Kephart 2003). Others suggest the weed seeds are usually too numerous and better addressed with minimal soil disturbance and two years of herbicide application followed by planting with a no-till drill (Boyer 2007b).
In restoring oak savanna or other grassland habitats, plowing or other major tillage operations are not recommended next to existing desirable native trees and shrubs, on sites that already have some native plant diversity or rare plants, or before ground nesting birds have completed their nesting cycle (Campbell 2004). In order to preserve native perennial grasses already on site, herbicides are a poor choice where weedy annual grasses are a problem because (except for fine fescues) the chemicals used to control one group also control the other (McClaran 1981). Such sites or inclusions are better candidates for interseeding, no-till drilling, or transplanting.
Besides tillage and herbicides, other site preparation methods include burning, grazing, mowing, soil solarization or combinations thereof (Campbell 2004, Rodgers 1981, Kephart and Amme 1992). Where permitted, burning can be a good choice for site preparation depending on existing conditions (Campbell 2004, Rogers 1981).
Seed testing: Given the potential for highly variable seed dormancy, it is strongly recommended that all seed lots of California oatgrass be given a TZ (tetrazolium chloride) test to determine total viability along with a germination test before purchasing and planting. The difference between the two tests will give an estimate of the percent dormant seed. If dormancy is low, special stratification or scarification treatments are unnecessary. If dormancy is high, pure live seeding rate calculations need to be based on total seed viability and not percent germination.
Direct seeding: Direct sowing of California oatgrass in the Pacific Northwest USA is usually best in late summer or fall (August-October) to naturally stratify the seed over winter (Maslovat 2001), assuming high dormancy in the seed lot. However, seeding date may be extended into the early winter (November) if site conditions have low risk of disturbance after seeding and the time outdoors remains long enough for natural stratification to occur (cool moist conditions may be required for up to 4 months). Emergence in milder winter growing climes typically occurs in late February and March (Boyer 2007b). Late winter or spring sowing with dormant seed can also result in germination the following March (Maslovat 2001), but seed losses from predation, erosion, weed competition, natural mortality, or other factors are potentially greater due to the lengthier period of inactivity. Spring planting may work equally well in some regions if seed is primarily nondormant or cold moist stratified or scarified in advance.
On occasion, de-awing of California oatgrass seed may be needed to facilitate movement through certain seeding machinery. However, Maslovat (2001) describes the ecological importance of the awn and states “restoration of this species will only be successful if the disaspores [seeds] remain awned”. Despite this pronouncement, germination of some seed lots benefit from dehulling/scarifying and substantial awn removal cannot be prevented during mechanical or acid conditioning.
The most successful stands of California oatgrass are usually achieved by drilling, no-till drilling, or broadcasting the seed alone rather than in a mix. As with natural establishment, very shallow soil coverage (0.6 cm or 0.25 in or less) is critical because of the light requirement. Broadcast seeding may additionally benefit from irregular surfaces. Mixing the species with nondormant seed of fast establishing grasses or forbs, native or otherwise, can lead to poor establishment because quicker germinating species will occupy the space first. To achieve a more natural appearance in prairie restoration, California oatgrass can be sown alone in irregular patches within more favorable soil inclusions then surrounded by a variety of higher diversity plantings. This is similar to the mosaic seeding approach described by Campbell (2004). Plant diversity can also be achieved afterwards by over seeding new stands the following spring or fall with forbs and/or other native grasses that have nondormant seed. Some restoration practitioners suggest seeding forbs a year before the grasses for improved species richness, as native forbs are more able to establish without grass competition (Clark and Wilson 2005). However, California oatgrass may be an exception and could be sown with forbs because of its seed dormancy.
For California oatgrass to be sown in a mixture, the most viable options may be (1) combining it with species that have similar seed dormancy, (2) using it with low rates of a less competitive, more diminutive species or short-lived plants useful for winter cover, or (3) both. Species for the first option could include Columbia needlegrass (Achnatherum nelsonii) or Lemmon’s needlegrass (Achnatherum lemmonii). Choices for the second option include slender hairgrass (Deschampsia elongata) (Boyer 2007b, Darris 2003) which only lives 1 to 3 years, or better yet, annual hairgrass (Deschampsia danthonioides). However, both native hairgrasses establish readily when fall sown and should be limited to 0.5 kg/ha (~1/2 lb/ac) in a mix with California oatgrass. They are also prolific re-seeders.
It is reported that California oatgrass has anywhere from 198,000 to 363,000 seeds/kg (90,000-165,000 seeds/lb) (Wrysinski 2004, Heritage Seedlings 2007, Darris and Lambert 2000, Guerrant and Raven 1995). The number probably depends on the degree of physical seed conditioning, genetics, and growing conditions at the time of seed formation. Dehulled and de-awned seed lots will be in the high end of the range. Each 1 kg of pure live seed (PLS) sown per ha will result in 20-37 live seeds/m2 (1 lb PLS/ac results in about 2-4 live seeds/ft2). Sown alone, suggested seeding rates for drilling are 10-16 PLS kg/ha (9-15 PLS lbs/ac), depending on goals and site conditions. Rates are high because of unpredictability and should be doubled for broadcast seeding.
Amendments: A starter fertilizer is usually not recommended for slow establishing native grasses like California oatgrass as it encourages excessive weed competition. A covering of mulch such as a thin layer of native straw, hydromulch, or erosion blanket is particularly useful on steeper banks. For improved stability, the straw can be crimped into the soil or covered with a netting (Kephart and Amme 1992) such as jute.
Weed control: Guidelines for the use of a number of herbicides for controlling weeds in native grass plantings in California are outlined by Drewitz and Anderson (2003). Pesticide labels vary by state and change over time, so the most current, local information must be reviewed and followed. Seed dormancy in California oatgrass can be put to good use. Sowing monotypic stands allows for fall and early winter germinating weeds to be controlled with glyphosate or other nonselective herbicide before the oatgrass seedlings emerge (Boyer 2007b, Darris 2003). After emergence and early growth of the California oatgrass, broadleaf weeds can further be controlled with a selective broadleaf herbicide applied at the right stage (Peachy et al. 2007). Mowing over the top of the oatgrass seedlings is a good alternative to control taller weeds, as is wicking with an herbicide, especially before the weeds go to seed. Timely, controlled grazing may also be beneficial for weed control in newer stands.
Transplanting: Some practitioners have had more establishment success using transplanted seedlings instead of seed (Suttle and Thornsen 2007, Buisson et al. 2004, Angelo 2005, McClaran 1981). Reasons can include low germination rates and slow seedling and plant development the first year limiting the species ability to compete with weeds and other plants. Container grown seedlings are well suited to smaller projects. Initial costs are higher per acre, but site preparation requirements can be less and establishment risks lower compared to direct seeding. If a “sod” appearance is desired, a grid spacing of 12-15 cm (5-6 in) may be needed. Amme (2003) suggests a good “turf” of California oatgrass can be established with a spacing of 20-25 cm (8-10 in).
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