What was it all about?

This study, which ran from 2016 to 2019, evaluated how pea yields are affected by plant spacing arrangements, stand density, and individual plant structure. The project team also investigated how water availability at key crop development stages affect overall crop performance. The processing green-pea industry has identified that improved crop establishment practices are a key area to increase yields and profitability.

Detailed field trials were conducted across three production seasons (2016/7, 2017/8 and 2018/9) in northern Tasmania and at the Tasmania Institute of Agriculture (TIA). More than 430 large trial plots were implemented in addition to extensive commercial site surveys and glasshouse trials.

The researchers found out the following:

Plant spacing

Planters used to establish crops are usually based on either 125mm or 200mm inter-row spacings. Field trial comparisons showed that pea returns ($/ha) were on average 7 per cent higher in 125mm row spacings than 200mm rows at the same stand density. Perfect spatial arrangements at equal distances within and between rows demonstrated benefits of up to 20 per cent compared with current practice. Significant investment in precision technology would be required to capture this benefit.

Stand density

Trial results indicated that a stand density of approximately 110 plants per m² is optimal. Slightly higher gross returns can be achieved with higher stand densities, but there is a trade-off between this marginal yield increase and extra seed costs, which make up about one-third of input cost to pea growers.

A survey of commercial seeding equipment used by industry identified significant variability in achieving target stand density and plant spacing within and between rows, with target intra-row spacing achieved less than 50 per cent of the time in most crops. These survey outcomes highlight the importance of maintaining drills, calibrating equipment and soil preparation to achieve consistent planting.

Plant structure

Most peas that contribute to harvested yield arise from the first two nodes to flower on plants. Attempts to modify plant structure and improve harvested yield potential was explored using sub-lethal herbicide doses or physical removal of the apical meristems at key stages. While multiple reproductive branches could be stimulated, the plants appear to adjust resource partitioning and thus the number of peas produced.

Water availability

Field trials investigated the interaction between irrigation pre- and post-flowering and stand density (80, 100, and 120 plants/m²). They demonstrated that appropriate soil water availability to crops both before and after flowering is required to maximise crop performance. Yields generally increased with increasing stand density (from 80 to 120 plants/m²), however not when irrigation was insufficient during flowering, pod set and pod fill.

In this situation, the returns decreased with increasing stand density, highlighting the importance of higher inputs for higher stand density crops throughout the crop lifecycle.

Plant size and health at the time of flowering is a key determinant of yield. A severe water deficit pre-harvest led to shorter plants and low yield that could not be overcome by high levels of irrigation post-flowering.

Recommendations for growers

The project team made the following recommendations for growers to help achieve increased yields:

• Aim to plant in 125mm rows, as narrow rows improve plant health and vigour
• Adopt a target density of 110 plants/m², as higher densities can improve gross returns
• Consistent intra-row spacing improves gross return and maximises the use of seed, with equipment calibration, drill maintenance and soil preparation low-cost ways to optimise establishment
• Reduce water stress by irrigating adequately during the vegetative growth stage, as healthier crops prior to flowering were able to develop and retain more pods
• Irrigate after flowering to produce longer pods with more peas.

ACT NOW

Read more about the research findings in these fact sheets developed by the project team:

• Fact Sheet: Importance of good establishment to maximise processing pea yield
• Fact Sheet: Plant density and green pea returns

You can also read this article Safeguarding the future of the Tasmanian pea industry, published on the AUSVEG website.