Prota 1: Cereals and pulses/Céréales et légumes secs
Sp. pl. 1: 79 (1753).
2n = 42
Oat, oats, common oat (En). Avoine, avoine cultivée (Fr). Aveia, aveia-amarela (Po).
Origin and geographic distribution
Avena sativa is only known in cultivation and its exact origin is unclear. Oat was not cultivated as early as wheat and barley and probably it persisted as a weed in fields of these cereals for centuries before it was taken into cultivation. Oat seeds have been found in 4000-year-old remains in Egypt, but these were probably from weeds and not from cultivated oat. The oldest known cultivated oat remains were found in caves in Switzerland that date back to around 1000 BC. Avena sativa probably evolved in central or northern Europe from wild Avena sterilis L. germplasm from south-western Asia. Nowadays oat is extensively cultivated in northern temperate regions, mainly in Europe and North America. In tropical Africa it is mainly grown in Ethiopia and Kenya. It is also cultivated in South Africa, Morocco, Algeria and Tunisia.
Oat has been used as food and fodder since ancient times. Oat grain is an ingredient in a wide range of food products including breakfast cereals, porridge, cookies, breads and muffins, crackers and snacks, beverages, meat extenders and baby foods. Oat grain is considered to have potential as a source of good edible oil. In Ethiopia oat is made into ‘injera’ (pancake-like bread), ‘tella’ (local beer) and other products. In industrialized countries oat grain mainly finds application as animal feed, especially for horses, but also for cattle, sheep, turkeys and other animals. The green plant is good forage; it makes good hay and silage or is grazed by animals. The straw too is used as forage, e.g. in Ethiopia, where it also serves as bedding for livestock, fuel and roofing material for traditional houses. Also in Kenya oat is used as food and as fodder. A field sown for grain production can be used for grazing if rains are inadequate; on the other hand fields are sometimes grazed to delay grain development.
In Australia oat is planted for sand binding on dunes. An important industrial utilization is the use of oat hulls for the production of furfural and other furan compounds, utilized in the production of fungicides, disinfectants and preservatives. Oat products also find application in the cosmetic industry as talc replacements and in skin care products. Oat flour has anti-oxidant properties and has been used for food conservation, but it has largely been replaced by synthetic chemicals.
Production and international trade
According to FAO statistics the average world oat grain production in 1999–2003 amounted to about 25.9 million t/year from 12.7 million ha. The main producing countries are the Russian Federation (5.8 million t/year in 1999–2003, from 3.8 million ha), Canada (3.3 million t/year from 1.4 million ha) and the United States (2.0 million t/year from 0.9 million ha). The average oat grain production in sub-Sahara Africa in 1998–2003 has been estimated at 55,000 t/year from 53,000 ha, almost entirely from Ethiopia (50,000 t/year from 49,000 ha) and Kenya (3500 t/year from 3400 ha) and small amounts from Zimbabwe.
Due to the decline of oat as animal feed, partly as a result of the mechanization of agriculture and decreased importance of workhorses, world production steadily declined from about 50 million t/year (from about 35 million ha) in the early 1960s to about 26 million t/year (from about 13 million ha) in the early 2000s. In the same period the production in sub-Sahara Africa increased from about 20,000 t/year to about 55,000 t/year.
The largest part of the oat production is consumed locally, with about 2.5 million t/year entering international trade in 1998–2002. Canada (1.2 million t/year), Sweden (450,000 t/year) and Finland (360,000 t/year) are the largest exporters; the United States (1.7 million t/year) the largest importer. International trade in oat in tropical Africa is insignificant.
The composition of oat grain per 100 g edible portion is: water 8.2 g, energy 1628 kJ (389 kcal), protein 16.9 g, fat 6.9 g, carbohydrate 66.3 g, dietary fibre 10.6 g, Ca 54 mg, Mg 177 mg, P 523 mg, Fe 4.7 mg, Zn 4.0 mg, vitamin A 0 IU, thiamin 0.76 mg, riboflavin 0.14 mg, niacin 0.96 mg, vitamin B6 0.12 mg, folate 56 μg and ascorbic acid 0 mg. The essential amino acid composition per 100 g edible portion is: tryptophan 234 mg, lysine 701 mg, methionine 312 mg, phenylalanine 895 mg, threonine 575 mg, valine 937 mg, leucine 1284 mg and isoleucine 694 mg. The principal fatty acids are per 100 g edible portion: linoleic acid 2424 mg, oleic acid 2165 mg, palmitic acid 1034 mg and linolenic acid 111 mg (USDA, 2004). Compared to other cereals, oat has a high protein content and a good amino acid profile, with a high level of lysine. The fat content is also higher than that of other cereals, with a high proportion of unsaturated fatty acids. Starch contents of 43–61% have been recorded. The amylose content of the starch is 11–34%. Starch granules are irregular to polygonal in shape with an average diameter of (3.8–)7.0–7.8(–10.5) μm.
The soluble fibre in oat bran is believed to reduce blood cholesterol in humans, due to the presence of β-glucan. Oat has shown hypoglycaemic activity and beneficial effects on gastro-intestinal functions. Oat bran seems to protect against dental caries. Compounds contributing to the antioxidant properties of oat flour include glyceryl esters of hydroxycinnamic acid, ferulic acid and caffeic acids. Oat seems to be tolerated by most coeliac patients, although concerns remain.
The unhulled ground grain is highly acceptable for ruminants and horses. Hulled and ground oat grain is usually fed to pigs and poultry. Oat green forage, hay and silage is highly palatable to ruminants. In Kenya the crude protein content of oat plants (on dry matter basis) declined from 20.2% for 50 cm-tall plants to 8.1% at full flowering, with the in-vitro protein digestibility declining from 84.9% to 46.7%. The crude fibre content increased from 23.3% to 28.1%, the carbohydrate content from 42.0% to 56.0%, the ash content decreased from 11.5% to 5.4%, and the ether-extract from 3.7% to 2.4%. Straw in Kenya contained on dry matter basis: 5.3% crude protein, 38.0% crude fibre, 10.2% ash, 1.4% ether extract and 45.1% N-free extract.
Erect annual grass up to 2 m tall, with a fibrous root system; stems (culms) solitary or tufted, smooth or scabrous beneath the inflorescence. Leaves alternate, simple; leaf sheath long and loose, rounded on the back; ligule blunt, membranous, 3–5 mm long; blade linear, flat, 10–45 cm × 0.3–1.5(–2) cm. Inflorescence a terminal panicle 15–30(–40) cm long, loose and open or contracted. Spikelet slender-stalked, pendulous, 1.5–3.5 cm long, usually 2–3-flowered, with the uppermost florets reduced, non-shattering; glumes almost equal, narrowly elliptical-oblong, sharply acute, several-veined; lemma 1–2.5 cm long, more or less truncate or minutely 2– 4-toothed, awn present or absent, glabrous or sparsely hairy around the awn insertion; palea slightly shorter than lemma; stamens 3; ovary superior, villous, with 2 laterally exserted stigmas. Fruit a caryopsis (grain), 0.5–1 cm long, narrow, with nearly parallel sides, hairy, grooved lengthwise on the face, tightly enclosed by lemma and palea.
Other botanical information
Avena comprises about 30 species, which are diploid (2n = 14), tetraploid (2n = 28) or hexaploid (2n = 42). All hexaploid Avena species belong to section Avena. The hexaploids Avena sativa, Avena byzantina C.Koch (red oat), Avena fatua L. and Avena sterilis L. are interfertile. Avena byzantina is closely related to Avena sativa and possibly derived through selection from the latter. Some authors include Avena byzantina in Avena sativa. Avena byzantina is cultivated mainly in southern Europe. In tropical Africa it has been grown experimentally in Kenya and has been recorded as a weed in Tanzania. It has naturalized in South Africa, where it is found in disturbed locations and on roadsides. Avena fatua and Avena sterilis are important weeds of cereals, e.g. in Europe, Ethiopia and Kenya, and differ from Avena sativa in their shattering spikelets and hairy lemmas. The tetraploid Avena abyssinica Hochst. can be distinguished from Avena sativa by the two bristles at its lemma tip.
Avena sativa is variable, which is reflected in elaborate infraspecific classifications, mainly based on inflorescence and lemma characteristics.
Growth and development
Oat seeds start to germinate 7 days after sowing. Seedlings start tillering 35–45 days after sowing. Up to 12 leaves are produced per stem. The time from sowing to flowering depends on sowing time, e.g. in north-western Europe it is 100 days for spring-sown crops to 270 days for autumn-sown crops. Oat is largely self-pollinated with up to 1% outcrossing. The time from flowering to harvesting is about 60 days in north-western Europe. The total crop duration is 3–6 months in Ethiopia and Kenya, and 6–11 months in temperate regions. Shattered seeds remain viable in the soil for a long time, which may result in weedy growth in subsequent crops.
Oat is mostly grown under cool and moist conditions in cool-temperate regions, mainly as spring-sown and to some extent autumn-sown crop. In tropical Africa it is mostly grown in mid- to high-altitude areas (1600–3000 m altitude), with an annual rainfall over 800 mm and minimum and maximum air temperatures of 6°C and 24°C, respectively. In Ethiopia it is usually grown at 2700–3000 m altitude. Oat is not as sensitive to frost as wheat. When moisture is not limiting it also performs well in warmer, humid mid-altitude tropical environments. Oat needs more water than any other cereal except rice. It is generally a quantitative long-day plant, but differences in photoperiod-sensitivity exist among cultivars, with particularly strong responses in northern European cultivars. Vernalization responses have also been recorded.
Oat thrives on a wide range of soil types, as long as drainage is sufficient. It grows on soils that are sandy, low in fertility, or highly acidic (as low as pH 4.5), but it performs best on well-drained, fertile, loamy soils.
Propagation and planting
Oat is propagated by seed. The 1000-seed weight is 22–37 g. Seeds 2–3 months old normally have more than 85% germination. Oat seeds kept under natural cold conditions in the highlands of Ethiopia still germinated after 15 years of storage. Under tropical highland conditions, the seeds are broadcast or drilled (row spacing 15–20 cm) at a recommended rate of 60–120 kg/ha, with drilled crops and crops intended for grain production at the lower end of the range. In Kenya oat is normally sown with a wheat drill in rows 20–25 cm apart, at a seed rate of 60–80 kg/ha. In the high-altitude tropics, oat is usually sown at the onset of the rainy season. When grown for forage, oat is sometimes grown mixed with vetches (Vicia spp.) or pea (Pisum sativum L.).
The vigorous growth of oat seedlings and the release of allelopathic compounds depress weed growth. Hand-weeding (usually once) and application of broadleaf herbicides such as 2,4-D may be used for weed control. In Ethiopia farmers do not weed their oat fields. Oat fields are seldom fertilized in tropical Africa, although the crop responds well to application of NPK. In the Ethiopian highlands the general recommendation is to apply 18–23 kg N and 20–30 kg P per ha at sowing, and 35–46 kg N per ha top-dressing at tillering. Oat is grown in rotation with barley, wheat, faba bean, pea and sometimes with fallow or a green manure. Allelopathic compounds can hinder the growth of subsequent crops, if they are sown within about 3 weeks after the harvest of oat. In Kenya an oat crop may be grazed 1–2 times, before it is allowed to mature as a grain crop. Alternatives are 2–4 grazings of a crop in a season, 2 grazings followed by use as a hay crop, or 1–2 grazings followed by a hay crop and a grazing. Oat can be grazed within 6–8 weeks after sowing.
Diseases and pests
Leaf (crown) rust (Puccinia coronata f.sp. avenae) and stem rust (Puccinia graminis f.sp. avenae) are the most important diseases of oat. Systemic fungicides such as triazoles and morpholines are effective in controlling them, but this is seldom economical. The use of cultivars resistant to rust is recommended. Septoria leaf spot (Septoria avenae), barley yellow dwarf virus (BYDV, also called ‘red leaf’), halo blight (Pseudomonas coronafaciens), loose smut (Ustilago avenae) and covered smut (Ustilago hordei) are other common diseases of oat.
Major pests include grasshoppers, army worms and cut worms. Various aphid species are vectors of BYDV. At later stages of maturity birds and rats are important pests. Weevils (Sitophilus granarius) and some other beetles attack stored oat grain.
In Africa oat is harvested manually by sickle or scythe, for forage normally after heading, and for grain when the seed is in the hard dough stage, which is normally at the end of the rainy season. The harvest is left in the field for sun-drying and is subsequently threshed (grain crop) or piled (forage crop). A mechanized combine can be utilized for harvesting large-scale grain oat crops or a mower for forage oat crops. When oat straw is needed for roofing, the panicle is harvested by sickle for grain, after which the remaining stubble is harvested by sickle or scythe at ground level.
The world average grain yield of oat is about 2 t/ha with straw yields of about 5.5 t/ha. As the result of threshing is not a naked grain, the hull (lemma and palea) generally accounts for 25–35% of the total grain weight. The average oat grain yield in Ethiopia and Kenya is about 1 t/ha. When oat is harvested for green fodder, hay or silage the dry matter yield is 4–15 t/ha.
Handling after harvest
Oat grain should be dried to a moisture content of 12–14% before storage, with a storage temperature below 20°C. In industrialized countries oat grain processing generally involves cleaning, drying (to partially inactivate lipolytic enzymes which would result in rancidity), hulling, cutting, steaming (to complete inactivation of lipolytic enzymes) and flaking or milling. The cheapest way of conserving oat forage is hay making. In areas where hay making is difficult, oat can be made into silage, either alone or mixed with legumes.
Large Avena sativa germplasm collections are maintained in the United States (National Small Grains Germplasm Research Facility, USDA-ARS, Aberdeen, Idaho, 10,000 accessions), the Russian Federation (N.I. Vavilov All-Russian Scientific Research Institute of Plant Industry, St. Petersburg, 8800 accessions), Canada (Soil and Crops Research and Development Centre, Sainte-Foy, Quebec, 7500 accessions) and Kenya (National Genebank of Kenya, Crop Plant Genetic Resources Centre, KARI, Kikuyu, 3700 accessions). A total of 656 accessions are kept at ICARDA (Syria) and ILRI (Ethiopia). About 835 oat accessions (mostly from Europe, United States and Ethiopia) are available at the EARO (Ethiopian Agricultural Research Organization) Holetta Research Centre in Ethiopia. Oat seeds show orthodox seed storage behaviour.
The major objectives in oat breeding are improved grain and forage yields. The development of cultivars resistant to fungal and viral diseases, especially crown and stem rusts, is important too. Sources of resistance to crown rust are found in wild Avena species, especially Avena sterilis. Modern techniques of breeding have resulted in improved cultivars with desirable traits such as resistance to diseases, high yield, huskless (‘naked’) grains, white-coloured large grain, and high contents of protein and oil in the grain. Molecular marker maps have been constructed and a genetic transformation system has been developed that allows the insertion of foreign genes into oat using particle bombardment. In tropical Africa there are small-scale breeding activities in Ethiopia and Kenya, mainly focusing on resistance to diseases and increased forage and grain yields. In Ethiopia and Kenya farmers are mainly interested in dual-purpose cultivars.
Due to its tolerance to poor soil fertility and to frost, its low requirements of external inputs such as fertilizers, and its dual-purpose character (food and fodder), oat has favourable prospects in the highlands of tropical Africa, especially for resource-poor farmers. On a worldwide scale, oat also has potential for pharmaceutical and cosmetic uses.
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Correct citation of this article:
Assefa, G., 2006. Avena sativa L. In: Brink, M. & Belay, G. (Editors). PROTA 1: Cereals and pulses/Céréales et légumes secs. [CD-Rom]. PROTA, Wageningen, Netherlands.
1, part of stem with leaf; 2, inflorescence.
Redrawn and adapted by Iskak Syamsudin
crop at grain-filling stage
detail of flowers