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Annual ryegrass (Lolium multiflorum Lam.) is a highly productive and high quality cool season forage grown primarily in the southern USA. The annual acreage planted to pastures has increased during the years due to plant breeding improvements such as improved forage and seed yields, increased crown rust resistance (Puccinia coronata Pers. Cda.) and significant gains in winter hardiness. Investment in ryegrass breeding and cultivar development in the southern USA has been minimal, never-the-less advances in the sciences and art of plant breeding have contributed significantly to improvement in the species. Improved cultivars have expanded the ryegrass areas of use northward and west ward into Texas, Oklahoma, Arkansas, and Tennessee, while at the same time greatly reducing the risk of freeze injury.
The management of economic yields of Lolium sp. in grassland agriculture depends on sound knowledge of plant growth and development. Several features of Lolium physiology and morphology play critical roles in growth, development, and plant productivity. For example, the ryegrass seedling has the greatest rate of growth among cultivated cool-season grasses. This feature gives ryegrass an effective competitive edge in crop or pasture establishment. Further development of the seedling gives rise to leaves and tillers. The tiller, branch or shoot on a ryegrass plant, is the fundamental demographic unit of the ryegrass stand. The fate of tillers is the major determinant of productivity in ryegrass plant populations. The growth environment, as affected by both the natural climatic and edaphic conditions and the influence of management practices, can modify the growth and development of ryegrass. Irradiance and temperature are the most important environmental parameters affecting photosynthesis and hence ryegrass growth and development. Soil N status is the largest single nutrient factor affecting ryegrass growth and development. Effective N management is critical for optimum crop or pasture production. The impact of moisture deficit at critical times in seedling development, crop establishment, or regrowth also can be a major factor limiting crop and pasture production. Among Lolium sp., and genotypes within each species, a continuous gradient of floral induction requirements exist. These range from obligate to facultative requirement for short-days (8 h) or low temperatures (0–3°C) or both, to no environmental stimulus required. In Lolium sp., usually day length-temperature floral induction is associated with perennialness, whereas annualness usually requires only genetic induction. These factors, among others, have important implications with regard to seed production.
Annual ryegrass (Lolium multiflorum Lam.) is a popular component of pasture systems in the southeastern USA because it is easy to establish, has high forage quality and is adapted to a wide range of soil types. Nonforage uses include turf, roadside stabilization, and winter cover crop in crop rotations. It is planted in pure stands, mixed with small grains and with clovers (Trifolium sp.) to provide forage during winter and spring. Optimum planting time is September on prepared seedbed or October if overseeded on a warmseason perennial grass in the southeastern USA. Recommended seeding rates are often 28 kg ha−1 in pure stands and 22 kg ha−1 in mixtures with small grains or clover. Under favorable temperature and moisture conditions, annual ryegrass is very responsive to N fertilizer that is split in two to four applications during the growing season. When overseeded on warm-season perennial grasses with clovers a single N application in early winter is often recommended to limit ryegrass competition to the clover. Stocking rate guidelines are 700 kg ha−1 animal weight in winter and 1400 to 2100 kg ha−1 in spring; however, optimum stocking rate will vary with management and climate. Annual ryegrass can be managed for natural reseeding by terminating grazing when seedheads first appear and reducing warm-season grass competition the following autumn by close grazing or light disking. Annual ryegrass is an impressive high-quality forage plant. It can be established without seedbed preparation, grows on a wide range of soil types, persists across a range of environmental conditions, and tolerates intensive use by grazing livestock. Annual ryegrass, also called Italian ryegrass, is indigenous to southern Europe with reports of it being grown in meadows of northern Italy as early as the thirteenth century. It was brought to America in early colonial days (Holt, 1976). Its earliest use for pasture in the southeastern USA is not known. Wheeler and Hill (1957) reported the average annual seed production of common (annual) ryegrass from 1939 to 1945 was 15 million kilograms. It is assumed that a large portion of this seed was shipped to the southeastern USA. At the time of their report they stated that commercial seed production of annual ryegrass in the USA was <25-yr old. This indicates that expanded use of annual ryegrass in the USA probably began in the 1930s.
Annual ryegrass (Lolium multiflorum Lam.) is a high-quality, cool-season forage that responds to soil fertility levels under varying soil, climatic, and management conditions. On high clay-content, tilled soils, N rates up to 448 kg ha−1 applied in increments of 112 kg ha−1 have maintained forage production more uniformly throughout the growing season than a single N application. In a dual-cropping system with bermudagrass [Cynodon dactylon (L.) Pers.], annual ryegrass is seeded later in the fall and has a lower yield potential. Under these conditions, N applied after seedling emergence and again in December, February, and April at rates approximating 70 kg ha−1 at each application has optimized ryegrass production. Rycgrass responds to limestone treatment of acid soils where surface 0- to 15-cm soil pH approximates 5.1 (1:2 soil/water) or lower. Aluminum solubilizes rapidly below pH 5.5 and can be toxic to ryegrass. Acid soils should be limed to maintain pH above 5.5 for production of annual ryegrass and to maintain nutrient use efficiency, especially P use because soil Al and hydroxyaluminum compounds complex this nutrient. The optimum rate of P for maximum ryegrass production in deficient soils is expected to increase as N rates are increased under high yield conditions. Ryegrass increases uptake of K as applied K rates are raised. At 90% of maximum yield, ryegrass removed 180 kg of K ha−1, or 18 kg t−1 of dry forage. Estimates indicate that <2% of the K in forages consumed by cattle in a continuous grazing system is transferred from the pasture as animal tissue K. In alkaline soils, Ca is usually adequate, but is applied as limestone to acid soils. The Ca needs of most classes of cattle can be obtained from annual ryegrass grown on acid soils limed to maintain pH near 6.0. Ryegrass contains lower levels of Mg in late fall and winter, particularly after cold, wet periods and in young regrowth tissue. Concentrations of Mg below 2.0 g kg−1 may cause hypomagnesemic tetany in beef cows during initial stages of lactation. Aluminum depresses Mg uptake while increased plant uptake of P enhances Mg uptake by ryegrass. The soil test for S deficiency levels has generally been inadequate to predict ryegrass response to this nutrient. Ryegrass response to applied S has usually been greatest at high N application rates on sandy, low-organic-matter soils. Ninety percent of maximum ryegrass yield has occurred at a S concentration of 1.2 g kg−1 or at a N/S ratio of 20 in the youngest open leaf.
Immature annual ryegrass (Lolium multiflorum Lam.) can contain levels of digestible nutrients that allow many ruminants to approach their genetic potential for production. This highly nutritious stage of maturity may persist for three or more months before significant declines in digestibility occur; however, nutritional limitations of ryegrass are repeatedly indicated by unpredictably mediocre performance of young animals grazing highly digestible primary growth. These limitations appear related (i) to unfavorable initial adaptations by the ruminal microbial ecosystem to such rapidly digestible forage, (ii) to an inefficient ruminal fermentation and synthesis of microbial protein, and (or) (iii) to reduced forage intake. When suboptimal animal response is related to poor protein use, it may be ameliorated by supplemental feedstuffs and (or) dietary adjuvants that appear to improve efficiency of ruminal protein and energy transformations.
Annual ryegrass (Lolium multiflorum Lam.) planted on a prepared seedbed often provides fall grazing; however, most planted areas of ryegrass are sod-seeded which usually does not provide adequate forage production for continued, uninterrupted grazing in the southeastern USA until late December to mid-February. Rapid forage growth during March to late May often requires frequent increases in stocking density to efficiently use ryegrass pastures. Annual ryegrass is very tolerant of frequent and severe defoliation regimens and often supports 2000 kg ha−1 body weight for a 75 to 100-d period in the spring. On average, individual daily gains for respective animal classes are: suckling calves (Bos taurus), 1.25; stocker calves, 1.05; yearling horses (Equus caballus), 0.80; lambs (Ovis aries), 0.15; and fallow deer (Dama dama), 0.12 kg d−1. Depending upon management and climate, stocker calf gain per unit land area may range from 450 to 900 kg ha−1 from annual ryegrass pastures. Flexible grazing management systems that include variable stocking densities are usually necessary to ensure optimum biological and economic efficiencies.
Perennial ryegrass (Lolium perenne L.) is a temperate, perennial forage grass noted for fast establishment, exceptional quality, and high cool-season productivity. It is folded in the bud, with dark green, glossy, smooth, glabrous, prominently ridged leaf blades. The collar is narrow with small, claw-like auricles and a 0.5- to 2.5-mm thin-membranous, obtuse ligule. Leaf sheaths often are reddish at the base. Flowering culms are 50 to 100 cm with a spike-type inflorescence with 5 to 40 sessile, awnless spikelets positioned edgewise to the rachis. Perennial ryegrass is adapted to mild, wet climates or irrigated regions. It is tolerant of poorly drained soils with a pH range of 5.0 to 8.3. Optimum growth occurs between 20 and 25°C. It is less persistent than other perennial, temperate forage grasses, but because of its high quality is widely used in dairy (Bos taurus) and sheep (Ovis sp.) forage systems; primarily for pasture and silage. Seeding rates vary from 18 to 24 kg ha−1 in pure stands, reduced to 12 to 18 kg ha−1 in mixtures. Depth of planting is 0.5 to 1.25 cm. High levels of fertility are required for high yields and stand persistence. Economical N application levels are in the range of 160 kg N ha−1 yr. Defoliation management during vegetative growth should allow plants to attain a height of 10 to 25 cm prior to grazing but not shorter than 2.5 cm (6 cm for mechanical harvest). When plants enter the reproductive growth phase, clipping or grazing should avoid removal of elevated growing points until boot stage. Currently, lack of persistence and sensitivity to high temperature and drought are the main limitations to expanded use of perennial ryegrass in the USA.
Oregon is the world's major producer of cool-season forage and turf grass seed and a widely recognized center of expertise in seed production. Not surprisingly, nearly all of the annual ryegrass (Lolium multiflorum Lam.) and perennial ryegrass (L. perenne L.) seed in the USA is grown in Oregon. Mild, moist winters, and dry summers favor seed development and harvest, making Oregon's Willamette Valley an ideal place to produce high quality seed. Collectively, this small region produces almost two-thirds of the total USA seed production of cool-season grasses. Most seed produced is of turf-type cultivars. More than 55% of Oregon's production of perennial ryegrass was certified in 1995.