Sweet vernal grass
Anthoxanthum odoratum (Schröter, 1888)
BOTANY
Annual grass growing in bunches, or perennial with short, thin rhizomes and numerous young shoots.
Culms are up to 50 cm high, slim, smooth and glabrous.
Leaf blades adaxially greenish-grey and matt, undersurface greenish-yellow, shiny, on fully developed plants rolled up to a pipe undersurface out.
Leaf sheaths with margins not connate as far as base, round, grooved, scabrous, glabrous or pilose, bunches of long hairs at the aperture.
Ligules form a 2-8 mm long, membranous fringe.
Inflorescence a panicle, 0.5-8 cm long, up to 2 cm wide, ovoid to oblong, dense, contracted, multiflowered, usually tawny.
Spikelet with two infertile, stunted florets with a fertile, laterally contracted. Above glume divided, in ripeness abscission of three florets in one unit, while glume stays adnate.
SUITABILITY FOR RESTORATION
In the Alps this European species grows in hilly, montane and subalpine zones. Because of its early flowering period and ripeness, advancing to sites desiccating in summer is possible. This species grows on soil that is free of groundwater, and on almost any meadow land. As a result of its low growth, it prefers meadows.
Apart from rocks and rough debris the plant grows on almost any moist to semiarid soil with a low to intermediate nutrient supply and a pH between 3.2 and 6.5.
This is an all-purpose grass in montane and subalpine sites, excellent for filling gaps thanks to the early ripeness of seeds and high seed production, its low biomass growth and low nutrient requirements. The grass is highly resistant to exhaust gases.
SEEDS
Lemma of lower awned florets often apically glabrous with broad, membranous, white margins. Lemma of upper fertile florets at least on margins (often dorsally and the entire upper half) with short, stiff, patulous bristly hairs, often long cilia.
Seeds
Glume oblong-elliptic, contracted, auburn, with long, shaggy, auburn hair; hairs pointing up; tips of glumes light yellow, translucent, membranous, glabrous, rounded. Awns of lower glumes 7-8 mm long, emerging from a little above the base, knee-high (same height as tip of glume), tightly contorted, black-brown, then thinner and lighter, tip of awn is whitish-yellow.
Inflorescence a panicle, 1.5-2 mm long, 0.6-0.8 mm wide and 0.3-0.5 mm thick, ovate-acuminate, can easily be squeezed out at glumes. Lemma smooth, auburn, shiny; palea finely scabrous, matt. Fruit 1-1.5 mm long, 0.5-0.7 mm wide, 0.3 mm thick, ovate-acuminate, tawny, matt.
Thousand seed weight: 0.5-0.6 g.
REQUIREMENTS
(soil and climate)
Light soil that is permeable and free of groundwater with a pH between 5.5 and 7.0 is suitable for seed production of sweet vernal grass. Propagation is not successful on compact, flat, waterlogged soil.
CULTIVATION
Sweet vernal grass needs a wellprepared, flat, fine seedbed. Seeds have a sufficient seed flow and are therefore suitable for all common seeding systems. Cultivation is possible by open sowing as well as under a cover crop. When using cover crops (e.g. summer cereals or linseed), it is important to have a light cover crop population because sweet vernal grass is not very tolerant to shade. Open sowing can be undertaken until the end of June or the beginning of July. Sufficient water supply is important.
Seed rate: 7-9 kg/ha are sufficient for good germination and optimal conditions for seed emergence.
Row spacing: 12-15 cm. Depending on the construction of the sower, broadcast sowing (e.g. by removing the sowing tubes) is also possible.
FERTILIZATION
Phosphorus and potassium: an intermediate supply of phosphorus and potassium is usually sufficient for propagation to develop successfully. Should additional fertilization be required, 20 tonnes/ha of well-decomposed manure is recommended in autumn.
Nitrogen: main application of nitrogen should be carried out early in autumn in order to facilitate tillering and the development of spermatophors. Mineral fertilization might prove necessary on poor soil and in dry weather in spring, in the event of bad nitrogen mobilization. Sweet vernal grass develops quickly in spring. Later fertilization at a disadvantageous stage of development (blossom, ripeness) facilitates the growth of leaves only and inhibits compact ripeness.
MAINTENANCE AND WEED CONTROL
In the year of cultivation any maintenance has to be carried out with great care. Straw of the cover crop has to be removed and the stubbles cut.
Effective weed control in the first year is the basis for a population that is free of weeds and has a high crop yield.
As for most grasses the following guidelines apply. Before sowing, only contact herbicides should be used, up to three days before the beginning of sowing. Hormone-type and broad-spectrum herbicides should generally not be used until the species has reached the three leaf stage. Note that the herbicides listed in Table 3 are not registered for use in seed cultivation in some countries.
Inflorescence
Especially when cultivated in lowlands or in humid weather, sweet vernal grass is very sensitive to rust and leaf diseases.
Application of fungicides: (usage and dose as in grain cultivation) may, therefore, already be necessary in late summer of the first year or specifically after the first harvest. Note the instructions for the use of herbicides given in the introduction.
Cutting in autumn is only necessary for high growth. Sweet vernal grass is resistant to snow mould and low temperatures in winter. Especially with high rust infestation, cutting in late summer or in spring of the first harvest year might be useful or even necessary.
Because of early ripeness, competition with weeds may be very high in the summer of the first harvest year. Selective weed control with wick and total herbicides (e.g. Glyphosate) is possible because of different growth heights.
HARVEST AND YIELDS
Resistance to lodging: high.
Shattering tendency: very high.
Ripeness: seeds assume a typical brown colour. Panicles change colour to golden yellow, similar to straw. Seeds ripen one after the other from the apex down to the base. Defining the optimal time of ripeness is extremely difficult.
Ripening period: very early, in warm regions in the middle of May, in cooler regions in the last week of May to the beginning of June. There are important differences between ecotypes. A more compact ripeness can be achieved by appropriate selection.
Harvesting technique: because of the plant’s high shattering tendency, direct threshing is recommended. The rotational speed of the threshing drum should be low to avoid dehusking of seeds. Seeds as well as chaff in the sieve should be checked several times while threshing.
Seed propagation stand
Settings of the threshing concave: generally close; the drier the seeds, the wider the setting in order to prevent seed damage.
Crop yields: crop yields can vary greatly, between 50 and 250 kg/ha. As for all site-specific species, specialized knowledge and several years of experience are necessary to obtain optimal, stable crop yields.
Only two harvesting years are possible because of the intensive maintenance required.
Site-specific grasses and herbs - Seed production and use for restoration of mountain 13
