OREGON STATE UNIVERSITY
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Oat is a small grain, annual, cool-season grass species used for both grain and forage. It is the least winter hardy species of the small grains. It is commonly planted in the spring and used primarily as a silage or hay crop. Sometimes it is used as pasture. Oat is often used in companion seedings with legumes, especially alfalfa. Straw, after grain harvest, is often used as forage.
Oat’s growth habit is bunched with numerous tillers. It is an annual plant, typically planted as a summer annual.
Global and USA Suitability
Oat originated in North Africa, the Near East, and temperate Russia. The best areas for oat production have relatively cool summers. Few varieties of oat are adapted coast to coast. Oat is not as drought or cold resistant as barley, rye, or wheat. [UC-Davis oat publication]
Oat is a cool-season annual grasses. It is more winter-sensitive than other small grains. Winterkills in Hardiness Zone 6 and colder and much of Zone 7. Optimum growth temperature is between 68 and 70°F (20-21 °C). Growth and development are substantially reduced at temperatures above 82 to 86°F (28-30 °C). Most oat production is in areas where annual precipitation is between 18 and 53 inches (450-1350 mm), especially in areas where March to August precipitation is greater than 18 inches (450 cm).
pH: Spring and winter types: tolerant of strongly acid to moderately alkaline soils (5.1-8.4).
Aluminum: Somewhat tolerant of Aluminum (persisted at 1–2 ppm Al3+ and pH 4.0).
Soil Drainage: Spring types: Well-suited to well-drained and moderately well-drained soils; Winter types: well-suited to excessively drained to moderately well-drained soils; tolerates only brief flooding (3-6 days).
Flooding: tolerates only brief flooding (3-6 days)
Salinity: Moderately tolerant, 3–6 dS/m (millimhos/cm).
Based on literature and expert oat specialist counsel, climatic and soil tolerances were compiled. Nine maps were created for oat, one for each of 3 climate factors and one for each of the soil factors, one combined climate factors map, one combined soil factors map, and a map for all of the factors combined. This allows for each factor to be examined and addressed to improve suitability through management. Small images of maps are provided below, with larger maps linked by clicking. For spring oat, all factors except for Tmin values would be the same.
USA Production Areas
In 2022, the production of oats in the U.S. amounted to approximately 57.66 million bushels, over a 40 percent increase from the production in 2021.
The following maps were provided by the USDA National Agricultural Statistic Service: USDA - National Agricultural Statistics Service - Charts and Maps - County Maps - Oats: Planted Acreage by County https://www.nass.usda.gov/Charts_and_Maps/Crops_County/ot-pl.php.
Production Profile
Oat is a cool-season grass with optimum growth rates between 64 and 68 ̊F (18-20 ̊C).
The sigmoidal growth curve of plant height vs days after planting of oat is illustrated in a Kansas State University publication: http://courses.missouristate.edu/WestonWalker/AGA375_Forages/Forage%20Mgmt/References/2Forages/4Annual/2Cool
Winter oat can be planted early into cool soils [~40 ̊F (4.4 ̊C)] and can be harvested for forage in 58-65 days. Winter oat is planted in late summer or early autumn, growing sufficiently for light grazing before growth stops due to low temperatures. Spring harvest at the soft-dough to dough stage is early enough to allow a double-cropping system with corn, sorghum, or other warm-season annual grasses.
Irrigation Requirements
Adequate soil moisture during germination and early seedling growth is important for cool-season annuals planted for forage. When managed as a grazing or hay crop, emphasis should be focused on meeting the plant’s water needs during rapid growth stages (see Figure 7 of this web link: https://extensionpublications.unl.edu/assets/html/g2012/build/g2012.htm).
Even moderate water stress during vegetative stages is likely to reduce yield, although it may lead to improved forage quality.
Note: Irrigation needs during August and early September can be relatively high, reducing water-use efficiency, especially when compared to spring-planted systems.
The common oat varieties used in temperate and mountain areas were derived from wild oat (Avena fatua L.). Algerian oat and red oat varieties are derived from Avena byzantina K. Koch, whereas a few drought-tolerant varieties are derived from slender oat (Avena barbata Brot.). Slender wild oat (Avena barbata Brot.) is a common weed in waste fields and open slopes, whereas wild oat (Avena fatua L.) is a common weed of waste and cultivated areas. Wild oat does best on rich soils, whereas slender wild oat is tolerant of a variety of soils. [UC-Davis Oat publication]
Oat cultivars are classified on the basis of maturity rating (early, mid, or late-season) and projected use (grain or forage type). A mid-season cultivar will mature more rapidly than a very late-season cultivar, regardless of growing season (spring or fall), or planting date within season. Two other characteristics of oat cultivars are important. First, cultivars selected specifically for production of forage generally exhibit much slower maturation characteristics than grain-type cultivars. Secondly, oat has a long-day photoperiod requirement for flowering that is disrupted by a late-summer planting date. As a result, the maturation rate for all cultivars is generally much slower in the fall, and differences among cultivars of diverse maturity classes tend to be more separated. See http://ipm.ucanr.edu/PMG/r730000411.html; https://smallgrains.ucdavis.edu/cereal_files/OatCvDescLJ11.pdf
As the oat plant matures through its growth stages, forage yield increases and feeding value decreases. When harvested for silage or hay, very high quality forage is obtained when it is harvested in the boot stage, with higher yields when harvested later (mild or dough stage of the grain).
Nitrate poisoning, grass tetany, and bloat are antiquality issues of concern.
Nitrate (NO3-) accumulates in plant tissue because of luxuriant uptake of soil N when plant metabolism of N is slow or stopped. This condition is promoted by cool temperature, drought, or other physiological stress that slows growth (Wright and Davison, 1964; Adv. Agron. 16:197-247). Plant nitrate is not toxic to animals but is reduced to nitrite (NO2-) in the rumen which causes methemoglobinemia that may lead to acute poisoning of animals. Non-ruminants, such as horses, are also subject to methemoglobinemia, however, at higher consumed concentrations.
Nitrate is the most common form of nitrogen in soil solution. Plants need nitrogen to make amino acids and proteins which results in plant growth and increased yields, however, excessive applications of N fertilizers can result in appreciable amounts of nitrate accumulation. For silage, ensiling more than 30 days, may entirely or partially degrade the nitrate concentration. Nevertheless, high nitrate level forages should be checked before feeding by submitting samples to an accredited forage lab. Farm workers can develop Silo-Filler’s disease from inhaling nitric and nitrous oxides emitted from fermenting forages containing high N concentrations. Ensure good air ventilation to reduce the health hazard.
Livestock suffering from methemoglobin poisoning, will have brownish-colored blood and brownish discoloration to the nonpigmented areas of skin and mucous membranes. Clinical signs include staggering, rapid pulse, frequent urination, and labored breathing followed by collapse, coma and death. Sub-lethal toxicity, which is primarily unrecognized in livestock, includes early-term abortions in pregnant females. This can also manifest as open cows or ewes at calving and lambing.
Plants with < 0.44% dry matter nitrate are considered safe. Forages containing 3,400 to 4,500 mg N/g as nitrate should be considered potentially toxic and should be mixed with safer feeds prior to use.
Hypomagnesemia (grass tetany) is a magnesium (Mg) deficiency of ruminants associated with their grazing of cool-season grasses during spring. It occurs in all classes of cattle and sheep, but is most prevalent among older females early in their lactation. Magnesium must be supplied daily because it is excreted in urine and milk. Symptoms are nervousness, twitching and staggering, collapsing, and convulsions that may cause death.
Vegetative and early jointing stage cereal grains, like other lush growing pastures, may have a low Mg content. Many factors affect Mg concentration and availability to livestock. The principal factor is high potassium (K) which negatively affects soil Mg uptake by plants and animal absorption and low calcium (Ca) levels. Forage Mg levels greater than 0.2 percent (2.0 mg/g) and a milliequivalent ratio of less than 2.2 for K/(Ca+Mg) are considered safe.
Grass tetany often occurs when the crop has received large amounts of water (from spring rains or irrigation) and has been heavily fertilized with N and K because soil Mg is leached by water and K is preferentially absorbed in early spring. Agronomic practices to increase forage Mg include splitting applications of N and K fertilizers, liming acid soils with dolomitic limestone, spraying Mg on herbage, or choosing cultivars higher in Mg. Mg can be supplemented to livestock by applying Mg fertilizer to pasture, providing other higher Mg-containing forages (e.g. legumes), adding Mg to drinking water, providing stock salt-mineral, molasses licks, or other energy sources to reduce the incidence.
Although usually associated with legume grazing, cereal grain pastures can cause frothy bloat. Pasture bloat is caused by rapid release of cell contents of succulent, immature forage during rumen fermentation. The material has a rapid rate of cell rupture, releasing the soluble proteins and fermentable carbohydrates. Soluble proteins are foaming agents, causing the formation of a stable foam in the rumen. This prevents eructation (belching) of rumen gases formed by the fermentation.
Bloat typically happens on lush pastures, with low dry matter and fiber content, and high protein and soluble nitrogen fractions. These conditions may occur in autumn or early spring. To prevent bloat, hungry cattle should be supplemented with more fibrous forages. Low concentrations of Ca may make bloat more likely by reducing rumen motility. High levels of soluble protein are also associated with increased occurrence of bloat.
Bloat can be controlled by feeding antifoaming agents such as poloxalen (Bloat Guard) or laurenth-23.
Journal and Agric. Exp. Stn. Publications
Textbook Publication