Pea

2.2. PULSES

Pulses are leguminous species with seeds of relatively big size and high protein content.

All of them belong to Fabaceae/Leguminosae.

2.2.1. Pea (Pisum sativum L.)

Pea is one of the oldest cultivated plants in the world, it was domesticated the same time as cereals. The growing area is 6,593,926.47 ha for dry and 2,266,368.61 ha for green pea.

The global production is 9,830,015.66 tons for dry and 18,490,919.89 tons for green pea (FAO, 2012). For human consumption, the immature (green) peas (or the tender pod in snow peas) are used as a vegetable, fresh, frozen or canned, while varieties of field peas are grown to produce dry peas (green or yellow split pea shelled from the matured pod).

Fodder pea (mostly varieties of Pisum sativum L. ssp. arvense /L./ POIR.) has a multipurpose use in livestock nutrition (green fodder, grain, silage etc.). However, compared to non-legumes, its yields are very variable and advancement in this field is very slow. Being high N-fixers, field peas produce abundant vining forage and contribute to short-term soil conditioning. Succulent stems break down easily and are a quick source of available N. Field peas grow rapidly in the cool, moist weather as winter annuals and as early-sown summer annuals.

Further benefits of field pea growing:

– Bountiful biomass. Under a long, cool, moist season during their vegetative stages, winter peas produce more than 5.8 t/ha dry matter, even when planted in spring in colder climates.

– Nitrogen source. As Rhizobium bacteria living in symbiosis with pulses are able to 'fix' nitrogen, field peas are top N producers, yielding from 100 to 170 kg N/ha, and at times up to 350 kg N/ha.

– Rotational effects. Pulse crops (grain legumes such as field peas, faba beans and lentils) improve sustainability of dryland crop rotations by providing disease suppression, better tilth and other enhancements to soil quality.

– Quick growing. Rapid spring growth helps peas out compete weeds and make an N contribution in time for summer cash crops in some areas.

– Forage booster. Field peas grown with barley, oat, triticale or wheat provide excellent livestock forage. Peas slightly improve forage yield, but significantly boost protein and relative feed value of small grain hay.

– Long-term bloomer. The purple and white blossoms of field peas are an early and extended source of nectar for honeybees.

Botanical characteristics

Field pea is an annual, cool-season, pulse crop. It has a taproot system of mediocre strength. There are two main types of field pea regarding growth habit. One type is an aggressive climbing variety and the other is a bush or dwarf type. Field pea stems grow from 60 to 100 cm (in the case of forage peas up to 150-200 cm) in length. Each leaf has a branched tendril at its tip and one to three pairs of leaflets. Most varieties of field pea produce white (P.s. ssp. hortense) (Figure 19) or reddish-purple (P.s. ssp. arvense) (Figure 20) flowers. Field pea stems (or vines) are prostrate at maturity. The pods contain from four to nine seeds and may be up to 8-10 cm in length.

Fodder pea grown for grain has high protein content (20-25%). The seed color is often green or yellow like at those produced for human consumption (P.s. ssp. hortense) but it can be dark brownish or mottled (P.s. ssp. arvense), too. The 1000 seed weight is 100-300 g.

57 Forage peas are usually leafy genotypes of high protein and carotene content. They have reddish-purple flowers, grains are usually colorful, purple or brownish (P.s. ssp. arvense).

Seeds are usually smaller (1000 seed weight 70-120 g) than those of the yellow or green varieties.

Figure 19 Field pea

Figure 20 Fodder pea

Pea has several convarieties, the most importants being:

- Round peas (P. sativum L. convar. sativum) – The surface of the ripe seeds is smooth (Figure 21 left). Seed coat can be easily removed (dehulling) thus split peas are produced.

Round peas lose tenderness quickly. They are usually utilized after cooking. For other purposes harvesting at early stages of ripening is necessary.

- Wrinkled peas (P. sativum L. convar. medullare Alef.) – The surface of the ripe seeds is wrinkled (Figure 21 right). Wrinkled peas convert a low proportion of their sugar content into starch. The sugar level builds up inside the pea (6-9%, almost 100% sucrose), so they taste sweeter than the round ones. They cannot be dehulled. Wrinkled peas are utilized fresh, canned or deep-frozen.

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- Snow peas (P. sativum L. convar. axiphium Alef.) – Their pods are free from parchment (hard endoderm), they feature flat pods that are sweet and edible (a.k.a. sugar peas). The seeds are very tiny, can be eaten fresh or cooked, traditional in stir-fry. They are called snap peas when they have plump and rounded edible pods instead of flat ones. It tends to be very sweet, and can be eaten raw or cooked.

Figure 21 Round (left) and wrinkled (right) peas

According to the extended BBCH-scale, pea has the following principal phenological growth stages:

0: Germination 1: Leaf development

3: Stem elongation (main shoot) 5: Inflorescence emergence 6: Flowering

7: Development of fruit 8: Ripening of fruit and seed 9: Senescence

The germination of pea is hypogeal (cotyledons remain below ground). Pea is a self-pollinating, long-day plant. Pods mature from the lowest flowering node upwards. At (over)ripening pea is prone to pod shattering and seed drop.

Its center of origin is Central Asia, the Near East, Abyssinia and the Mediterranean. Pea belongs to the family Fabaceae/Leguminosae and it is a diploid species (2n=14).

Pea is rich in protein (22-24%) and minerals. Carbohydrate content is 50-55%, fat content is 1.3-1.6%. It is rich in vitamins B1, B2 and C.

Environmental requirements

Peas are not heat-demanding crops. They germinate at 4.4 °C and at 2-3 leaves stage they tolerate some grades of frost. Overwintering forage peas are winter-hardy (-15-20 °C). The maximum temperature at vegetative growing is 12-14 ° C, at flowering- ripening 18-20 ° C. Pea has a moderate water requirement (200-250 mm), its transpiration coefficient being 300-500. It utilizes water relatively well but it is sensitive for drought at early stages of development and in the reproductive stage from flowering to pod set.

Peas are crops of the better wheat soils rich in lime (pH 6.5-8).

59 Cultivation

Its best and most common fore- and aftercrops are cereals. Other suitable forecrops are crucifers, flax and row crops fertilized with manure (e.g. potato, sugar beet). Rotation is 3-4 yars. Pulses and legumes as well as other crops harvested late and leaving root and stem residues must be avoided as forecrops. Pea itself is an excellent forecrop for most non-relative crops. Tillage resembles those described for spring crops. Seedbed levelling is essential in order to reduce losses at harvesting. Basic fertilization and sowing data can be found in Tables 29 and 30, respectively. Among pulses peas have the highest demand for calcium. Irrigation is needed especially for green pea: 30-40 mm in rotation of 14 days.

Table 29 Nutrient requirement of pea

Nutrient uptake to 1 ton of grain and by-product

dry pea N: 60 kg/t P₂O₅: 17 kg/t K₂O: 35 kg/t CaO: 32 kg/t MgO: 6 kg/t green pea N: 19 kg/t P2O5: 6 kg/t K2O: 15 kg/t CaO: 10 kg/t MgO: 2 kg/t fodder pea N: 35-45 kg/t P₂O₅: 10-15 kg/t K₂O: 15-25 kg/t CaO: 10 kg/t MgO: 2 kg/t

Table 30 Sowing data of fodder pea Sowing date:

- dry pea - green pea

- autumn pea

25. February-31. March

25. February-10. April (in 10 day periods and/or with varieties of different growing period or based on

effective heat units) 15-30. September

Row distance: 12-15.2 cm

Sowing depth: 5-8 cm

Seed rate:

- grain (dry) - green

0.8-1 million seeds/ha (late to early varieties) 1.2-1.5 million seeds/ha (late to early varieties)

yielding: 70-80%

150-300 kg/ha

1000 seed weight: 150-300 g

Diseases

Septoria leaf spot (Septoria pisi), Sclerotinia crown rot, Fusarium root rot as well as seed rot and blights of the stem, leaf or pod, Ascochyta blight (Ascochyta pisi), Pseudomonas pisi, Sclerotinia minor, Sclerotinia trifoliorum, PMV, PEMV

Pests

Heterodera goettingiana, Otiorrhynchus ligustici, Sitonia spp., pea aphid (Acyrtosiphon pisum), lima-bean pod borer (Etiella zinckenella), pea weevil (Bruchus pisorum)

Harvesting Green peas

The most important quality aspect is tenderness. It is determined by finometer (F°), on the field and by tenderometer (T°), in the processing factory: T° = 3*(F° - 3). Fresh pea loses tenderness quickly (3-5 F°/day, in case of threshed seeds even 1 F°/hour) thus it must be

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delivered in the cold store in 4 hours. Optimal harvesting at 35-50 (45-50) F°. Too early harvesting results in the damage of seeds. Green pea is harvested by a pea harvester (pod stripper/combine). Its yield is 5-8 t/ha.

Dry and fodder peas

For grain food or feed, peas must be harvested by a specifically modified cereal combine at full ripening (16-18% moisture content) when leaves are dry, pods are yellow, seeds are hard. Combine must be equipped with a floating flexible cutter platform. If harvested by the inderect way (e.g. in the case of weedy fields or heterogenous ripening) cut plants are left on the field for post-ripening followed by threshing by a combine. Its grain yield is 3-5 t/ha.

For green forage or haylage, it can be mown at flowering according to the livestock’s demand. Its green mass is 20-35 t/ha.

Field peas for hay should be harvested when most of the pods are well formed. Harvesting can be performed by using a mower with lifting guards and a windrow attachment to handle the sprawling vines.