Oat (Hitchcock, 1971; McLeod, 1982); cultivated oat (Munz, 1973).

The scientific name is Avena sativa L.; however, cultivated oat is of polyphyletic origin. The common oat varieties used in temperate and mountain areas, including in the U.S.A., were derived from wild oat (Avena fatua L.). Algerian oat and red oat are derived from Avena byzantina K. Koch, whereas a few drought-tolerant varieties are derived from slender oat (Avena barbata) Brot. (Hitchcock, 1971).

The Southern Seedsmen's 1990-91 Directory and Buyers' Guide listed 43 oat varieties as being commercially available. Few varieties of barley or oat are adapted coast to coast (Stoskopf, 1985).

Oat varieties have been changed rapidly in response to development of new strains of pathogens (Coffman, 1977). However, modern oat cultivars show only minor improvements over older varieties. There has been some improvement in root development (Stoskopf, 1985).

'California Red' oat shows a fine growth and is the standard for hay production. However, the fine growth that makes it good for hay also renders it susceptible to lodging and unsuitable for supporting intercropped vetches. It is a late-maturing cultivar, about 13 days later than cv 'Montezuma' (Fred Thomas, pers. comm.).

Cv 'Cayuse' shows coarse growth and 14% higher biomass production on the average than 'California Red.' 'Cayuse' matures in early June, about 20 days after cv 'Montezuma' (Fred Thomas, pers. comm.).

Cv 'Montezuma' matures early, from early to mid-May, with flowering beginning about a month earlier. Fine stems make this variety less suited for intercropping with vetches. Biomass production is about 93% of that of cv 'California Red (Fred Thomas, pers. comm.).'

'Ogle' is a cultivar of oat resistant to barley yellow dwarf virus (Schonbeck, 1988). It shows coarse growth, high biomass production, and is regarded as an early-maturing form of cv 'Cayuse,' maturing ten days after cv 'Montezuma' (Fred Thomas, pers. comm.).

Lemma glabrous; awns straight, often wanting (Munz, 1973).

The wild oat (Avena fatua) seedling has soft, succulent foliage, blade and sheath with very few widely spaced hairs, or if more abundant, these hairs require magnification to be visible; no auricles (ear-like projections) at the base of the leaf; the ligule (collar-like appendage on the inside of the leaf blade) is large, whitish, and pointed (Fischer et al., 1978).

Oat (0.5% outcrossing) and barley (0.2% outcrossing) are mainly self-pollinated (Stoskopf, 1985).

Oat shows moderate resistance to cold (Madson, 1951). Winter forms of oat are not as cold hardy as rye, triticale, wheat (Stoskopf, 1985), or barley (Miller, 1984d). A temperature of -8 degrees Centigrade is required to kill seedlings of oat or barley (Stoskopf, 1985). Miller (1984d) considered that oat is not as drought or cold resistant as barley, rye, or wheat (Miller, 1984d).

Oat grows best in cool, moist climates, yet it is adapted to many climatic extremes. It is an excellent winter cover crop in the South and in areas where winter freezes are not severe (McLeod, 1982).

Oat is susceptible to damage by hot, dry weather that occurs during reproduction (Stoskopf, 1985). The best areas for oat production have relatively cool summers (Coffman, 1977).

In the Northeast, oat is a common late-summer-sown cover crop which winterkills, leaving a protective dead mulch that is easily incorporated in the spring (Schonbeck, 1988).

Oat originated in North Africa, the Near East, and temperate Russia (McLeod, 1982), and the best areas for oat production have relatively cool summers (Coffman, 1977). Few varieties of oat are adapted coast to coast (Stoskopf, 1985). Oat is not as drought or cold resistant as barley, rye, or wheat (Miller, 1984).

The common oat varieties used in temperate and mountain areas, including in the U.S.A., 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.) (Hitchcock, 1971). Munz (1973) mentioned that in California, cultivated oat is an occasional escape from cultivation, and that 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 (Crampton, 1974).

Oat is more tolerant of wet soil conditions than barley, and it requires more moisture than the other small grains (McLeod, 1982). Higher seeding rates of oat or barley may be appropriate where rainfall is heavy (Stoskopf, 1985). In a study at the University of California, Davis, an oat cover crop turned under as green manure depleted soil water by 0.8" in the 0-24" soil stratum; by contrast, 'Lana' woollypod vetch depleted the same stratum by only 0.4" (Stivers and Shennan, 1991).

Jobidon et al. (1989c) tested barley, oat, and wheat-straw mulches as mulches for black spruce (Picea mariana) seedlings in greenhouse trials. The mulches of barley and wheat enhanced foliar phosphorus content, but mulches did not affect mycorrhizal infection or growth of black spruce. All mulches decreased manganese content of the seedlings, however.

Oat can tolerate a soil pH as low as 4.5 (Stoskopf, 1985). Under moderate fertility and drainage, oat tolerates a wider pH range than wheat or barley and has a low lime requirement (McLeod, 1982).

Oat can be grown on loam to heavy soil types (Madson, 1951) and is regarded as not being particular as to soil (Johnny's Selected Seeds, 1983) because it is adapted to many soil types.

Oat is more tolerant of wet soil than is barley. Under moderate fertility and drainage oat tolerates a finer soil texture than does wheat or barley (McLeod, 1982).

Less tolerant than barley. (Fred Thomas, pers. comm.)

All oat species are annual grasses (Crampton, 1974). Oat (0.5% outcrossing) and barley (0.2% outcrossing) are mainly self-pollinated (Stoskopf, 1985). Oat varieties usually have a lower ability to produce tillers than do barley varieties (Stoskopf, 1985). Cereal rye produces more fall and early spring growth than oat (Miller, 1984).

Seeding rates are given as 60 to 90 lbs/acre (McLeod, 1982; Miller et al., 1989) and 80-96 lbs/acre (Johnny's Selected Seeds, 1983). Higher seeding rates of oat or barley may be appropriate where rainfall is heavy (Stoskopf, 1985).

Seeding depth should be 1 inch (McLeod, 1982.), and for barley or oat should be no greater than 5 cm (2 in.) (Stoskopf, 1985). Shallow seeding is possible in areas with high soil moisture and leads to more rapid emergence and lessened incidence of root rot disease (Stoskopf, 1985).

A firm seedbed prevents frost heaving of the plants from the soil during the winter (McLeod, 1982). Barley or oat are usually planted in rows 15 to 20 cm apart (Stoskopf, 1985). Oat can be seeded into the sod of bermuda grass (Miller, 1984).

Sowing can be conducted in the spring or fall (McLeod, 1982). In the northeastern U.S., plant in early fall (Johnny's Selected Seeds, 1983). In California, October to January are recommended (Madson, 1951).

Oat is a grass, and requires no inoculation (R.L. Bugg, pers. comm.).

Oat seed is widely available in the seed trade (R.L. Bugg, pers. comm.).

Oat flowers from April through June, according to Munz (1973). Cultivars vary as to maturation with increasingly late maturation as follows: 'Swan'<'Montezuma'<'Sierra'='California Red'='Curt'<'Cayuse' (Zwer et al., 1984).

Cereal rye matures earlier than oat (Miller, 1984a).

High-yield grain production was as follows (Zwer et al., 1984):

Oat seed remain viable for a relatively long time (McLeod, 1982).

Oat is an erect annual grass (Bugg, pers. comm.). It has moderate to heavy density of growth and shows a succulent growth type (Madson, 1951). Oat varieties usually have a lower ability to produce tillers than do barley varieties (Stoskopf, 1985). Of the cereals, barley and oat have the poorest resistance to lodging (Stoskopf, 1985).

'California Red' oat attained a height of 109.22+/-3.74 (cm, Mean +/- S.E.M.) in Mendocino County, California (Bugg et al., unpublished data). Hitchcock (1971) reported that wild oat (Avena fatua) reached 30-75 cm in height, whereas Munz (1973) reported 30-70 cm for wild oat and 30-60 cm for slender wild oat (Avena barbata). Crampton (1974) listed the height of wild oat (Avena fatua) as ranging from 25-100 cm.

Oat has a fibrous root system (Bugg, pers. comm.).

Kutschera (1960) reported that oat generally roots to a depth of 84-195 cm and wild oat (Avena fatua generally roots to a depth of 91-160 cm.

A temperature of -8 degrees C is required to kill seedlings of oat or barley (Stoskopf, 1985).

Of the cereals, barley and oat have the poorest resistance to lodging (Stoskopf, 1985). Barley is usually more competitive than oat (Stoskopf, 1985).

Mature oat hay has a high C/N ration and decomposes slowly. Seed bed preparation can be hindered by large amounts of oats in a cover crop mix. (Mark Van Horn, pers. comm.)

Oats are harvested with a grain harvester. (Mark Van Horn, pers. comm.)

Oat can be used for hay, pasture, green manure or cover cropping; as a cover crop, oat can provide erosion control, enhance soil life, suppress weeds, and add organic matter (Johnny's Selected Seeds, 1983). Oat can also serve as a temporary or rapidly growing cover crop (McLeod, 1982). Fast-growing annuals such as buckwheat or oat may be used to prepare for transplants or protect soil during short periods when it would otherwise be bare (Gershuny and Smillie, 1986). Two successive cover crops of oat have been used to improve poor soil to the point that it sustains clover; oat can also serve as a temporary or rapidly growing cover crop and is more subject to winter damage than is cereal rye (McLeod, 1982). In the North, late summer and early fall plantings are useful as winter cover (Johnny's Selected Seeds, 1983). Top growth will eventually winter kill but can still serve as a mulch for erosion control (Johnny's Selected Seeds, 1983). The protective dead mulch can is easily incorporated in the spring prior to planting vegetables (Schonbeck, 1988). Oat can be used as a nurse crop in combination with slow-establishing legumes like white and yellow sweet clovers or sourclover which can help reduce weed problems (Bugg, pers. comm.). Oat is usually preferred instead of barley as a companion crop (Stoskopf, 1985). W.T. Lanini (pers. comm.) reported that oat grown as an intercrop suppresses weeds in seeded or established alfalfa.

Oat is used in mixtures with common and hairy vetches, 'Austrian Winter' pea, and bell bean (Bugg, pers. comm.). Inclusion of barley, oat, or rye in a mix of cover crops along with vetches and bell beans appears to reduce infestation by common fiddleneck (Amsinckia intermedia) (Bugg, 1990). Oat is especially suitable intercropped with vetch because oat seed is more easily separable from vetch seed than is barley, cereal rye, or wheat (Duke, 1981). Oat can be used as a nurse crop in combination with slow-establishing legumes like white and yellow sweet clovers or sourclover which can help reduce weed problems (Bugg, pers. comm.). W.T. Lanini reported that oat grown as an intercrop suppresses weeds in seeded or established alfalfa (Cantisano, pers. comm.). Oat is usually preferred over barley as a companion crop; barley is usually more competitive than oat (Stoskopf, 1985). Berseem clover can be grown in combination with white clover, oat, or rye (Duke, 1981).

Oat can be seeded into the sod of bermuda grass (Miller, 1984).

Monocultures of oat (Avena sativa, cv 'Mulga') or triticale yielded more dry matter and digestible organic matter than did bicultures involving common vetch (Vicia sativa) or pea (Pisum sativum). Yields of mixtures did exceed those of monocultures of the relevant legumes. Digestibility and crude protein content were highest in mixtures of peas and triticale. There appears little incentive for farmers to grow mixtures of annual legumes and small-grained cereals for forage production (Droushiotis, 1989).

'California Red' Oat produced 12.775+/-1.410 Mg/ha (Mean +/- S.E.M.) in above-ground dry biomass in Mendocino County, California (Bugg et al., unpublished data). In the same trial, biomasses were 9.88 +/- 1.79 Mg/ha for 'Merced' cereal rye and 12.94 +/- 2.64 Mg/ha for 'U.C. 476' barley; none of the three values was deemed statistically different from the other two in the overall experiment. Nonetheless, Miller (1984), stated that oat does not produce as much dry matter as barley, rye, or wheat, and that cereal rye produces more fall and early spring growth than oat.

Oat, a fibrous-rooted cool-season grass, is sometimes used as a catch crop to retain soil N that otherwise might leach through the profile as nitrate (Bugg, pers. comm.). Mean nitrogen content of oat is 12 lb/a, according to Brinton (1989). In an experiment on rotational cash crops ("break crops") for wheat farmers, fertilizer N requirements were increased by 10 kg/ha following winter oat, decreased by 30 kg/ha following winter rape, winter peas, spring faba beans, or cultivated fallow, and decreased by 40 kg/ha following spring peas (McEwen et al., 1989).

Incorporation of non-legume (high C:N ratio) residues (e.g., corn) led to depression of N availability greater than that for surface residues. N availability was in this order for crop residues: alfalfa > peanut > soybean > oat > sorghum > wheat > corn (Smith and Sharpley, 1990).

Barley, oat, and wheat-straw mulches were tested in field trials in eastern Quebec forest plantations. The mulches reduced soil nitrification, apparently through the production of five phenolic acids. Growth rate and foliar nitrogen content were higher for black-spruce seedlings with mulches. There were no other significant differences in nutrient status (Jobidon et al., 1989b).

Quemada and Cabrera (1995a) reported the following:

These data for residues left on the soil surface reflect the slower breakdown of stems, and the immobilization of N caused by application of materials with high C/N ratios.

Quemada and Cabrera (1995a) also evaluated the relative allocation of carbon to soluble compounds, cellulose, hemicellulose, and lignin, which have profoundly differing rates of decomposition, with the list given in descending order of rate of breakdown. For all three plant species mentioned, stems had much higher concentrations of lignin than did leaves.

Using the CERES-N submodel, Quemada and Cabrera (1995b) further explored the release of N from no-till cover crop residues, deriving decay rate constants from breakdown rates for stems, leaves, and mixtures of both. The constants that best fitted the data were 0.14-day for cellulose; decay rate for lignin was assumed to be 0.00095-day. That is each day, more than 10% of the soluble carbohydrate pool degrades to CO2, about 0.34% of the cellulose pool degrades, and less than 0.1% of the lignin.

Quemada and Cabrera (1995b) in Georgia used the CERES-N model to predict conditions for leaves or stems or 50:50 by dry weight mixtures of crimson clover, cereal rye, oat, and wheat harvested at maturity. All crop residue was cut into 1-cm pieces and placed atop sandy loam soil that had previously been managed without tillage. Incubation was in acrylic plastic cylinders at 35° and 98% RH, for 160 days. The study was replicated three times. Observed N-mineralization was slower than previously reported for incorporated residues:

Humus native to the soil was estimated to mineralize N at 0.00042/day.

Reported C/N ratios were:

Hu et al. (1997) conducted a replicated field study at the Student Experimental Farm (SEF) and the Sustainable Agriculture Farming Systems (SAFS) Project, U.C. Davis, CA. The study compared carbon and nitrogen transformations following cover crop incorporation on organically vs. conventionally managed Yolo sandy loam (at SEF: coarse-loamy, mixed, nonacid, thermic Mollic Xerofluvent) and Reiff sandy loam soil (at SAFS: coarse-loamy, mixed, nonacid, thermic Mollic Xerofluvent) Chemical characteristics for the oat and woollypod vetch harvested on April 14 and used as cover crops were as follows (±S.E.M., where indicated):

Prior to incorporation of cover crops, soil organic N and soil organic C were significantly higher in organically managed than in conventionally managed plots, both at SEF and at SAFS. These differences were lessened or obscured during the 35 days following incorporation. Microbial biomass C was initially greater under organic management at both sites; again, differences were obscured following cover crop incorporation. Cover crop debris buried in litter bags in the SAFS plots showed more rapid disappearance in organic than in conventional plots.

Quemada and Cabrera (1995a) in Georgia found that chemical composition of various winter-annual plants varied in their chemical composition and in their decomposition rates when managed without tillage. In addition, leaves consistently varied from stems in having greater C/N ratios and lignin and cellulose contents (the latter two expressed as g/kg of plant material). Based on CO2 emissions and N mineralized, stems decomposed more slowly than leaves for crimson clover, cereal rye, wheat, and oat.

Wander and Traina (1996a) reported that in the replicate Farming Systems Trial at Rodale Institute Research Center (Kutztown, PA), cover-crop based cash grain production led to significantly higher values than synthetic fertilizer-based cash grain production for the following categories of soil carbon and nitrogen: total C, humic C, humic substance C and N, and light-fraction C and N (all based on g/kg soil).

Oat mean phosphorus content is 2 lb/a, and mean potassium content is 9 lb/a (Brinton, 1989).

In the Northeast, oat is a common late-summer-sown cover crop which winterkills, leaving a protective dead mulch that is easily incorporated in the spring (Schonbeck, 1988).

Hu et al. (1997) conducted a replicated field study at the Student Experimental Farm (SEF) and the Sustainable Agriculture Farming Systems (SAFS) Project, U.C. Davis, CA. The study compared carbon and nitrogen transformations following cover crop incorporation on organically vs. conventionally managed Yolo sandy loam (at SEF: coarse-loamy, mixed, nonacid, thermic Mollic Xerofluvent) and Reiff sandy loam soil (at SAFS: coarse-loamy, mixed, nonacid, thermic Mollic Xerofluvent) Chemical characteristics for the oat and woollypod vetch harvested on April 14 and used as cover crops were as follows (±S.E.M., where indicated):

Prior to incorporation of cover crops, soil organic N and soil organic C were significantly higher in organically managed than in conventionally managed plots, both at SEF and at SAFS. These differences were lessened or obscured during the 35 days following incorporation. Microbial biomass C was initially greater under organic management at both sites; again, differences were obscured following cover crop incorporation. Cover crop debris buried in litter bags in the SAFS plots showed more rapid disappearance in organic than in conventional plots.

Oat is more palatable to livestock than cereal rye, and stock may destroy a cover crop of oat by overgrazing (McLeod, 1982).

Oat harbors various grain aphids (e.g., bird cherry - oat aphid Rhopalosiphum padi and English grain aphid Sitobion avenae) that can attract lady beetles; oat does not host Russian wheat aphid (Bugg, pers. comm.).

Oat varieties have been changed rapidly in response to development of new strains of pathogens (Coffman, 1977). 'Ogle' is a cultivar of oat resistant to barley yellow dwarf virus (Schonbeck, 1988).

Seeding depth for barley or oat should be no greater than 5 cm (2 in.). Shallow seeding is possible in areas with high soil moisture and leads to more rapid emergence and lessened incidence of root rot disease (Stoskopf, 1985).

Winter oat, winter rape, winter peas, and spring faba beans as break crops greatly reduced the incidence of take-all of wheat (Gaeumannomyces graminis) (McEwen et al., 1989).

Inclusion of barley, oat, or rye in a mix of cover crops along with vetches and bell beans appears to reduce infestation by common fiddleneck (Amsinckia intermedia) (Bugg, 1990). Oat can be used as a nurse crop in combination with slow-establishing legumes like white and yellow sweet clovers or sourclover (Duke, 1981). This can help reduce weed problems (Bugg, pers. comm.). W.T. Lanini reported that oat grown as an intercrop suppresses weeds in seeded or established alfalfa (pers. comm.). Oat is usually preferred instead of barley as a companion crop; barley is usually more competitive than oat (Stoskopf, 1985).

Barley, oat, and wheat-straw mulches were tested in eastern Quebec forest plantations of balsam fir/birch. The mulches inhibited red raspberry (Rubus idaeus) and reduced mean weed cover by 41%, apparently through the production of five phenolic acids (Jobidon et al., 1989a).

In a replicated study (r=4) at Blue Heron Vineyard (Fetzer Vineyards), Hopland, Mendocino County, California, cover crops were seeded in late October, 1990; harvest was on May 15-16, 1991. Dominant winter annual weeds were chickweed, shepherds purse, rattail fescue, and annual ryegrass. Weed above-ground dry biomass in plots sown to 'California Red' oat was 0.241+/- 0.083 Mg/ha (Mean +/- S.E.M.) (4.9% of the weed biomass in unseeded control plots). This was not deemed significantly different than the weed biomasses obtained with 'U.C. 476' barley (0.043 +/- 0.043) Mg/ha or 'Merced' cereal rye (0.031 +/- 0.031 Mg/ha). Vegetational cover by oat during early May was 98.75+/-1.25 % Vegetational Cover (Mean +/- S.E.M.) (Bugg et al., unpublished data).