Overview
- Most surveyed crops produced substantially more developing seed than was ultimately harvested.
- Pollination remains important, but improving seed set alone is unlikely to close the yield gap.
- Better management of canopy structure, late insect pressure and harvest losses may offer the greatest opportunity to lift realised yield.
Red clover seed crops may be producing considerably more seed than growers ultimately harvest. A survey of 16 commercial crops in Canterbury, New Zealand, found a substantial gap between seed yield potential and realised yield.
The findings suggest that improving pollination alone will not close this gap. For Australian pasture seed growers, they highlight the need to examine canopy management, late-season insect damage and seed losses before and during harvest.
Crops produced more seed than growers harvested
Researchers sampled crops shortly before desiccation, measuring biomass, stems, flowerheads, florets and developing seed. These measurements were used to estimate potential yield and compared with growers' harvested yields.
Realised yields ranged from 200 to 850 kilograms per hectare, averaging 473 kg/ha. Estimated potential yield averaged 790 kg/ha and reached more than 2,000 kg/ha at one site. Most crops therefore harvested considerably less seed than had developed before desiccation.
Pollination was not the only constraint
An average of 60% of florets contained seed, with results ranging from 40% to 80%. This suggests pollination was generally sufficient to establish a reasonable seed crop.
Pollinator management remains important because red clover depends on insect pollination. However, the weak relationships between flower and seed numbers and final yield indicate that other factors may be preventing established seed from reaching the bin.
Focus on late-season losses
Potential constraints include canopy structure, irrigation, forage removal, insect feeding and losses during desiccation, harvest or seed handling. These factors were not directly measured, so their individual effects remain uncertain.
The results nevertheless suggest that late insect damage and harvest losses may be underestimated. Optimising desiccation timing, combine setup and seed handling could offer practical opportunities to retain more yield. Monitoring pests and checking seed losses before, during and behind the harvester may help identify where losses occur.
The study was conducted in New Zealand and provides a benchmark rather than a management prescription. Australian research is needed to determine whether similar yield gaps occur under local cultivars, pests, pollinators and harvest systems.
