Seed Dormancy & Germination
BARLEY DORMANCY & GERMINATION
Cultivated barley is a grass that may be either a winter or spring annual. Barley growth can be divided into a number of stages: germination, seedling development, tillering, stem elongation, heading (ear emergence), flowering and ripening.
The duration of each of barley’s developmental stages can vary widely. Growth rate depends on the weather, water supply, soil fertility
the degree of competition with other plants, the presence of pests and diseases, and the time of planting. Initially the growth is slow while the plant’s seedlings establish and the tillers form. Total time to maturity will depend on variety, location and planting date.
When a seed is unable to actually germinate, even when conditions are most favourable, that is known as dormancy.
BARLEY PLANTS AT SUCCESSIVE STAGES OF GROWTH
Dormancy of the barley grain is typically imposed by the seed-covering structures known as lemma, palea, pericarp and seed coat.
Primary dormancy is intrinsic; whereas secondary dormancy arises as a result of external factors such as water sensitivity, where germination is reduced under excessive moisture conditions.
While low dormancy is desirable in malting barley, too little dormancy can lead to pre-germination or pre-harvest sprouting, where germination of the grain begins on the mother plant in rainy conditions before harvest.
Both pre-germination and pre-harvest sprouting trigger the hydrolysis of the endosperm and can have adverse effects on the yield, malting quality and storage life of the grain.
In addition to the influence of barley variety, dormancy varies with grain maturity and with the conditions during ripening, harvest and storage. Freshly harvested grain is the most dormant, and dormancy declines as the grain ripens. Cool, moist conditions during ripening encourage the expression of dormancy, while low dormancy is generally associated with high temperatures, short days, low moisture and high nitrogen levels.
In the natural environment, the release of seed dormancy is promoted by factors including after-ripening (exposure of the seed to hot, dry conditions) and stratification (imbibition of water at low temperature).
In cultivation practices, dormancy is commonly relieved by after-ripening, which is achieved by storing the grain after harvest in warm temperatures and low humidity. Seed coat-imposed dormancy in barley may last between a few weeks to 9 months in dry storage. In contrast, storing grain in cold and moist conditions can hold on to dormancy. Barley seeds have been known to stay dormant for 3 years at 2°C under high humidity.
Shed grain may exhibit more prolonged dormancy than grain kept in dry storage. This is possibly because the wet periods following harvest encourage the retention of dormancy, so that self-sown grain often germinates just before the following crop.
The malting process requires barley grains to germinate rapidly and uniformly – by at least 50% in 1–2 days and by 95–100% after 3 days. Maltsters do this in a controlled manner, steeping the grain to increase the moisture content.
Exposure to periods of rain interspersed with dry conditions may encourage germination in grains on the soil surface. On the other hand, deep cultivation soon after harvest encourages dormancy by placing the grain in a cool, moist environment.
While low temperatures during grain development can induce deeper dormancy, low temperatures during germination can break dormancy of freshly harvested seeds.
Germination can occur at temperatures between 5°C and 38°C, with 29°C being optimal. Successful germination also requires both water and oxygen. The process begins with the grain absorbing moisture and swelling, and the rate of grain imbibition increases rapidly with increasing temperature.
Soil type and condition, including the pH level, can also affect the natural germination of barley seeds. Deep cultivation in certain soil types can prevent emergence by encouraging prolonged dormancy in seeds as a result of low oxygen availability. By delaying germination, deep burial can reduce the viability of shed seeds.
FRESHLY HARVESTED BARLEY FROM JOHN ROWES FARM