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Pisum sativum L. |
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Leguminosae Common names Forage pea, field pea. |
Authors:
Dr. John Frame
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Description Rapid-growing, glabrous annual with angular or roundish hollow stems covered with a waxy bloom. In leafy types, leaves consist of one or more pairs of opposite leaflets borne on petioles together with several pairs of tendrils (which are essentially modified leaves) and a single or compound terminal tendril. Leaflets broad and ovate with distinct ribs, and slightly toothed or entire. The two (pseudo) stipules at the base of the leaf are also ovate but much larger than the leaflets. In semi-leafless types the leaflets are replaced by tendrils but the stipules are still present while in leafless types the leaflets are also replaced by tendrils but the stipules are stunted. The two leafless types have better standing ability than the leafy types. The plants are tap-rooted, l m or more in depth, with numerous lateral roots. On each plant, inflorescences comprising one or two self-fertile flowers are borne on the end of axillary peduncles. Flower colour differs according to cultivar with white, pink, lavender, blue and purple represented. Pods containing several seeds, flattened when young but becoming roundish later, are dehiscent along two sides. Seeds range in colour from dun to brown and may be mottled. Distribution In the recent past the field pea was mainly used as a leguminous constituent in cereal/legume mixtures grown for arable silage (and this is still the main purpose for which it is used). Following breeding efforts in Europe, forage pea cultivars were developed which gave high yields of forage, 6-8 t/ha DM, circa 100 days after sowing when pure-sown (Flengmark, 1973). These forage cultivars have been increasingly used in Europe and other temperate areas e.g. north-central USA, though their use as short-term ‘catch’ crops is still secondary to their use in arable silage mixtures. Forage peas can also be grown in the tropics at high altitudes and as a cool-season (winter) crop in some regions with hot dry summers. Forage peas, and other legumes such as red clover, are being increasingly used in organic farming to supply a bulky, protein-rich crop. Characteristics Upright growth form with tangled vegetation, though late-maturing types are more prostrate than early-maturing types. Growth period of 12-18 weeks depending upon cultivar. In temperate areas, most vigorous growth from spring-sowing. Lodging can occur with increasing maturity, particularly under wet conditions. Generally grows best between 100C and 200C. Place in rotation Can be included anywhere in a rotation. A spring-sown crop provides entry for a late-summer/early autumn grass sow-out, a winter cereal or a forage brassica catch crop (Whytock and Frame, 1985a). In very favourable areas there may be a chance of growing a second crop of forage peas in the same year, particularly if an early-maturing cultivar is sown. To avoid the risk of disease build-up, e.g. Sclerotinia stem rot (Sclerotinia trifoliorum) peas should not be grown on the same land more often than one year in five. Season of growth In temperate areas, spring/early summer for early-sown crops, summer/autumn for later-sown crops. Grown in winter when grown as a cool-season crop in warm, temperate areas. Drought tolerance Intolerant of drought which has a particularly adverse effect on production if it occurs at flowering. Soil requirements Requires free-draining soils since intolerant of waterlogging. Sandy or medium-loam, moderately fertile soils are particularly suitable. Soil pH 6.0 to 7.0 but not overlimed since this will result in manganese deficiency (marsh spot) especially organic soils. Rhizobial relationships Rhizobial inoculation of seed was beneficial to nodulation, plant growth and nitrogen fixation on acid soils where peas had not been previously grown (Sparrow et al., 1993). Land preparation for sowing Well-cultivated, fine but firm seed bed required to promote rapid root and plant development. Over-compaction must be avoided. Sowing depth and soil cover Ideally drilled at 7.5 cm depth on a level seed-bed so that after soil consolidation by rolling, seeds are at 3 to 5 cm depth. Drill rows are usually 15-20 cm apart. Sowing time and rate Spring sowing optimal when soil temperature has reached 7-80C. Risk of drought with summer sowing. Winterhardy types can be sown in autumn in winter-mild areas, e.g. southern Europe. Seed rates are variable, being influenced by seed size (and cost of seeds), but 100-125 kg/ha is typical. A target plant population for pure-sown stands is 70-80 plants/m2. Pure-sown peas can be undersown with a grass seed mixture where leafless or semi-leafless peas are used since they have better standing ability and allow more light penetration to the base of the stand than leafy cultivars. However, it is much more common to undersow arable silage, e.g. using 40-60 kg/ha peas plus 60-100 kg/ha spring barley (Whytock and Frame, 1985b); vetches (Vicia sativa) may also be included at 10-30 kg/ha. Forage pea/triticale mixtures may also be used. Number of seeds per kg 2700 to 4500. Seed treatment before sowing A fungicide seed dressing is advisable to prevent ‘damping-off’ of seedlings by Pythium spp. Nutrient requirements The main requirement is for phosphate and potash application at rates dependent on the soil P and K status; on fertile soils, dressings of 25-50 kg/ha each of P2O5 and K2O are typical. If broadcast, fertilizer requires to be incorporated into the soil, or if drilled, placed near the seeds, because of the limited root development of peas. However, seeds should not be in contact with fertilizer because of the risk of scorch damage to the seedlings. A ‘starter’ dressing of 25 kg N/ha is sometimes applied to encourage rapid initial growth. For arable silage, 60-80 kg N/ha and 40-50 kg/ha each of P2O5 and K2O are typical rates for soils of moderate fertility status. Ability to compete with weeds Initially poor especially in cold springs, but competitive once full canopy achieved. Tolerance of herbicides Tolerates ‘legume-safe’ herbicides such as MCPB. Herbicide choice determined by cultivar since there is variation in leaf wax among cultivars. Seedling vigour Strong. Vigour of growth Vigorous growth towards maturity particularly when sown in early season. Nitrogen-fixing ability Estimates vary but usually amounts up to 70 kg N/ha cited (La Rue and Patterson, 1981). However, Kucey (1989) recorded 117 kg N/ha in western Canada.Using a total N difference method (N yield of peas minus N yield of non-N-fixing crops), Sparrow et al., (1993) reported amounts of 130-150 kg N/ha in Alaska, USA. Dry matter yields Yields up to 9 t/ha DM, equivalent to circa 50 t/ha fresh material, obtainable in the UK. Optimal yield is when crop flowering and lower pods fully formed though still at the flat pod stage (12-18 weeks dependent on maturity type). Delay beyond this stage gives little further increase in yield because of senescence of lower stem and leaves. In the UK, Fraser et al. (2000) obtained 5.39 t/ha DM at 10 weeks, 6.17 t/ha at 12 weeks and 5.60 at 14 weeks with cv. Magnus. Yields of 4.5-6.0 t/ha DM were recorded in Cyprus (Papastylianou, 1990). In Alaska the DM yields were 4-9 t/ha on neutral soils and 3-5 t/ha on acid soils, rhizobial seed inoculation being beneficial on acid soils where peas not grown before (Sparrow et al., 1993). In other work there, peas yielded 2.5 t/ha at flowering and 7 t/ha at mature pod stage (Brundage et al., 1979). At two sites in Alberta, Canada pea monocultures yielded 6.18-6.55 t/ha DM while in cereal/pea mixtures total yields ranged between 4.53 and 12.30 t/ha DM with pea contributions of 38-86% (Berkenkamp and Meeres, 1987). Suitability for silage Suitable for ensiling which is the main use for pure-sown stands. To avoid soil contamination when cutting, the stubble height has to be 10 cm above ground level and the cut swath left unturned. An alternative to wilting is to spray a desiccant and after about ten days, harvest directly with a forage harvester preferably fitted with a reel and a side knife to make a clean-cut swath. Wilting to 25-30% DM, short chopping, addition of an effective additive, good consolidation and airtight sealing are all required to ensure high-quality silage. Inoculation by Lactobacillus plantarum at ensiling beneficially decreased pH and ammonia N production, and increased lactate and water-soluble carbohydrate contents compared with uninoculated material (Fraser et al., 2000). The crop can be ensiled in clamps or in big bales. Feeding value Valuable source of protein. A typical analysis of the cut material prior to ensiling is: crude protein, 16-20%; DOMD, i.e. proportion of digestible organic matter in the dry matter 60-65%; and metabolizable energy (ME), 10.0-10.5 MJ/kg DM. Delay in harvesting beyond the flat pod stage results in reduced digestibility and overall feeding value. Conversely, earlier harvesting gives a high-quality forage but at the expense of production. Arable silage will generally have lower crude protein (10-14%), DOMD (58-63%) and ME (9.0-10.0) though these values can be higher depending on the pea cultivar chosen and its contribution but also on the cereal species and cultivar, particularly its straw length, a long length being advantageous. Acceptability Highly acceptable forage with good intake characteristics. Growing lambs of 9-10 months old had a daily intake of 58 g/kg LW0.75 compared with 44 g for a medium-quality grass silage, though less than lucerne (71g) of equivalent digestibility (Fraser et al., 2000). Wether sheep consumed 61.3-73.0 g/kg LW0.75 of freshly cut forage peas but intake of pea silage was less at 55.2-66.5 g/kg LW0.75 (Kirilov, 1997). Anti-quality factors Possible risk of bloat when grazed but risk is probably lessened by the presence in the forage of condensed tannins the levels of which can vary appreciably. Grazing Can be grazed by a range of livestock, e.g. dairy cows. Should be strip-grazed to avoid wastage. Zero grazing is possible but avoidance of soil contamination of the forage when cutting is important. Cultivars Many cultivars are available ranging from early- to late-maturing and from leafy to leafless. In temperate areas most are for spring sowing but some winterhardy cultivars for sowing with winter cereals have been developed too. Certain cultivars bred for harvesting as grain peas for human or animal consumption are also suitable for sowing pure or in mixture with cereals for arable silage. Some typical cultivars used in Europe are Magnus, Setchey, Solara, Sponsor, Athos, Baccara, Nitoche, Rif and Gracia. Some other examples are Trapper and Austria (Canada) and Mega (New Zealand). Diseases The main threat is ‘damping-off’ of seedlings but this is controllable by a fungicide seed dressing. The use of certified disease-free seed will prevent other seedling diseases such as foot rots (Fusarium spp. and Ascochyta spp.). Also, the chosen cultivars should be resistant to Fusarium wilt (Fusarium oxysporum f.sp. pisi) and downy mildew (Peronospora viciae) since there are no effective fungicide treatments available. Pests The most significant pests are pigeons and rooks which may be particularly troublesome at sowing or seedling emergence. The pea and bean weevil (Sitona lineatus) and aphids (Acyrthosiphon pisum) are potentially damaging pests (Sheldrick et al., 1995). Main attributes Short-term catch crop. High forage yield in relatively short growth period. High nutritive value. Protein-rich. Highly acceptable feed for different classes of stock. Good intake characteristics. Main shortcomings Not highly suited to grassland-dominant areas on account of short-term nature and need to plough up grassland, though suited to grassland-arable rotations. Links
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