Field pea: crop management and production

Paddock selection

When selecting a paddock in which to grow field pea you need to consider the following points:

Soil type

Field pea can be successfully grown on a wide range of soil types, but prefer sandy loams or heavier, and pH (measured in CaCl₂) above 5.0. Duplex soils with neutral to alkaline subsoils are suitable if they do not become waterlogged, although the sandy surface may pose an unacceptable erosion risk after harvest. Field pea does not tolerate salinity or waterlogging well, so avoid soils where these are likely.

Blackspot risk

This is largely determined by the rotational history of the paddock, and of surrounding paddocks. Choose paddocks that have not grown field peas for at least three years, and go no closer than 500 metres (m) to paddocks that grew field peas in the previous year. It is preferable to be at least 50m downwind of two and three year old stubbles, but no separation is necessary upwind of these older stubbles.

Surface condition

This has important implications for ease of harvest and soil erosion after harvest. Avoid paddocks with a rough or uneven surface that will be difficult to follow closely with the header front and avoid paddocks with stones or stumps that could be picked up by the header. These can cause considerable damage if they pass through the threshing drum. Some obstacles are acceptable if they are buried by rolling post-sowing. Avoid paddocks with loose surface soil if it will be exposed to strong winds after harvest.

Herbicide residues

Field pea is sensitive to residues of sulfonylurea herbicides that may have been applied to a preceding cereal crop, so avoid paddocks where this will be a problem. Residues are likely to be greater on alkaline soils, and after a dry growing season and a dry summer. Sulfonylurea herbicides also differ in their breakdown rates. Information on persistence and safe withholding periods is given on the herbicide label and should be consulted.

Weed population

Field pea is not a strong competitor with weeds, so the best paddocks will have low weed burdens, especially of broadleaf weeds. However, remember that the ability to plant late means that some cultural weed control is usually possible and that there is a greater range of post-emergent herbicides available for use in field pea than in other pulse crops.

Frost risk

Frost during early pod filling can cause devastating yield losses in field pea. Avoid paddocks with a high probability of frost from 1-3 weeks after flowering.

Sowing window

Choosing when to sow field pea requires a compromise between being early enough to avoid end of season drought and late enough to avoid bad blackspot infection. Since other crops, such as wheat, lupins and canola, benefit much more from early sowing, field pea should be sown after these sowing crops is complete. It is unlikely then that field pea will be sown too early and the important question will be how late is it safe to sow field pea?

Data from Department of Agriculture and Food, Western Australia trials suggest that, while best results will be obtained sowing around the beginning of June, or perhaps a little earlier in low rainfall areas, sowing is safe until the end of June in most parts of the state. Sowing should cease earlier in low rainfall areas north of the Great Eastern Highway: where there is 100 millimetres (mm) or more of water stored in the soil, sowing can safely continue until 15 June, but should cease on 1 June if there is less. Stored soil water makes little difference south of the Great Eastern Highway.

Inoculation

Field pea, being a legume, has the capacity to derive its nitrogen requirements from the atmosphere but, in order to do this it must be inoculated with Rhizobium bacteria that will form nodules on the crop's roots. Field pea should be inoculated with Group E inoculum before sowing, irrespective of whether the paddock has grown field pea before.

This is because the field pea Rhizobium does not survive well in Western Australian soils. Field pea can also be inoculated with Group F inoculum, although remember that the Rhizobium strains in the two groups may not always be equally effective on peas. Achieving good nodulation is crucial to growing a good crop, so take care to inoculate properly. Slurry inoculation is the best way to ensure a well nodulated crop.

Sow seed within three days of inoculation, as the inoculum has only a limited life span on dry seed. Fungicide seed dressings will further reduce the life span of the inoculum so, as seed dressings have little value in preventing disease in WA; their use is not recommended.

Granular inoculum is now available and can be applied to the soil separately in much the same way as fertiliser. This provides increased flexibility at sowing as it removes the need to inoculate within three days of sowing and will make achieving good nodulation compatible with fungicide seed dressings, should these ever become worthwhile in WA.

Sowing rate and depth

Sow sufficient seed to establish 45 plants/m for conventional-leaved varieties and 55 plants/m for semi-leafless varieties. The necessary sowing rate will depend on germination percentage and seed size.

At these sowing rates yield is usually fairly unresponsive to changes in density. However, dense crops compete better with weeds and feed better when harvesting, so resist the temptation to reduce sowing rates.

Field peas grow well in conventionally spaced rows (18-25 centimetres (cm)). Limited research in the 1990s showed no adverse effects on yield of planting in rows as wide as 36cm, but poorer standing ability (with a conventional-leaved prostrate cultivar) was observed, and consequently more difficulty harvesting.

For this reason, wider rows are not recommended for field peas. Standing ability in semi-leafless cultivars is likely to be impaired in wide rows too, since plants will experience less support from their neighbours than in narrow rows.

Levelling the paddock

Trouble-free harvesting requires an even soil surface and this is best achieved by rolling. This is most important for prostrate cultivars, but applies also to semi-erect cultivars because these will lodge under some circumstances.

Use either steel or rubber-tyred rollers. Heavy steel rollers do a better job leveling heavier soil types, especially the larger ridges left by no-till seeding, and pushing small stones and sticks into the ground. However, they have a greater tendency than rubber-tyred rollers to smear and seal the soil surface if it is moist.

It may be necessary to wait for the soil surface to dry after seeding before rolling with a steel roller where a rubber-tyred roller could follow directly behind the seeder. Less pressure is required to knock down ridges on sandy soils and on them rubber-tyred rollers are just as effective as steel rollers.

Roll is best done straight after sowing, as long as the soil surface is not too moist. However, field peas can be rolled after emergence, when it is best between the three and 10 node stages.

Rolling earlier risks damaging emerging seedlings and older plants are usually too tall to recover completely from being knocked down in the rolling operation. Don't roll for two weeks before or after applying post-emergent herbicides, as the stress of rolling will predispose the crop to damage from these herbicides. Rolling emerged crops is best done in the afternoon, as then the plants are more flexible and less likely to be damaged.

Harvesting

Many thousands of hectares of semi leafless field peas are harvested trouble free each year as new Kaspa type varieties together with grower experience and recent machinery innovations and modifications, have solved the majority of harvesting difficulties.

Semi-leafless Kaspa type field pea varieties like PBA Gunyah, Twilight and Wharton have a substantially improved structure for harvesting compared with the old trailing types such as Dunwa or Parafield. In most conditions the Kaspa types will stand better at harvest than trailing type varieties.

Nevertheless, for ease of harvest, particularly in circumstances where semi-leafless peas may lodge, it is important to prepare paddocks prior to, and after sowing to ensure a clean level paddock for harvest. Some semi-leafless peas including PBA Gunyah, Twilight and Wharton have a sugar pod trait that reduces pod shatter.

The combination of reduced lodging, improved pod height and reduced pod shatter available in semi-leafless lines like PBA Gunyah, Twilight and Wharton results in lower losses in the paddock and a cleaner sample. In Kaspa type field peas like cereals may be harvested above ground level, even where it has lodged.

This is because most pods are formed near the top of the plant. Even the most efficient harvesters cannot overcome poor planning. Successful field pea harvesting begins at the end of the previous season through good paddock selection and stubble handling. Decisions made at sowing and spraying of the field pea crop are also important.

Probably the most important step in reducing harvesting difficulties is to select a paddock with a low weed burden, particularly broad-leaved weeds and which is relatively even and free of stones, sticks and large soil clods. Broadleaf weeds such as wild radish and mustard decrease yield by competition and increase harvest losses.

Rolling, which levels the paddock and pushes small rocks and sticks into the soil is the second most important step. See Levelling the paddock. The moisture receival standard for field peas is 14.0%. The crop can be safely harvested at 16% moisture and if left in a stack the seed will dry out naturally. Harvesting at 14-16% moisture will have no effect on seed viability and the grain will be less prone to mechanical damage during handling.

Field peas can lose seed moisture rapidly and will be more prone to damage below 12% moisture. Therefore do not delay the harvest of seed crops any longer than necessary. Semi-leafless field pea varieties which have the ‘sugar pod’ trait have been found to be best harvested in warm conditions. In cool damp weather the vine can be hard to thresh and choppers and spreader efficiency is reduced.

Harvester settings will depend on crop foliage and seed moisture, but the following table and the header operator's manual may be a useful starting guide.

Drum or rotor speed should be kept to a minimum without significantly reducing the harvesting capacity. As a guide, to reduce pulse seed damage the peripheral speed of the drum should not be greater than 12 metres per second (20-30 metres per second for cereals). Harvesters have a range of drum or rotor diameters so this will have to be checked in order to start at around the correct rotational speed.

Grain handling and storage

Once field peas are harvested they should be handled as few times, and as gently, as possible. This is because they are very fragile, and the mechanical damage caused by augering, for example, can reduce germination percentage.