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Maximising yield is key to reducing cost per tonne and there are several physical crop performance measures that can help drive improvements.

Many of the benchmarks for a “good” crop are described in the respective AHDB Growth Guides for wheat, barley and oilseed rape -

However Yield Enhancement Network (YEN) research suggests some re-tuning of growth guide benchmarks is required for the highest-yielding crops. The wheat guide for example, is based on an 11 t/ha crop, while the oilseed rape guide targets a 5 t/ha crop.
YEN team leader Roger Sylvester-Bradley of ADAS outlines some of the main physical performance indicators for wheat:

Established plant population

  • Plant density greatly affects crop structure - low populations limit yield if crops don’t compensate through increased tillering, root growth or canopy production
  • Work back from the target yield and heads/m2 to calculate plant population required – take your expectations for tillering capacity into account
  • Be realistic about likely establishment %, tillering capacity and tiller survival when determining optimum sowing rate for individual varieties
  • Plant population is hard to measure beyond the three-leaf stage - focus on shoot counts thereafter.

 Shoot numbers

  • Once tillering begins, shoot numbers are a better indicator of yield potential than plant population
  • Crops with more surviving tillers generally produce more heads and a higher grain yield
  • Optimum tiller number depends on yield potential of the variety and site - work back from target yield and ear number to see how many tillers are required to achieve this.

Ground cover

  • High biomass crops have more green leaf area to maximise light interception and build yield, but too much biomass comes at a cost
  • Measure ground cover using the Green Area Index (GAI) - the ratio of total green area ( to the ground area
  • Aim for GAI of at least 2 by growth stage 31 (first node detectable)
  • GAI 6-7 at flowering is the optimum canopy size for grain production (maximum GAI typically occurs between flag leaf emergence and ear emergence)
  • Extending the period of full green ground cover either side of the normal peak – so earlier in spring (March/April) and later in summer (July/August) – is key to increasing yield.

Ear numbers after flowering

  • Ear number per m2 has the greatest link to final yield
  • Crops can compensate slightly for low ear number by increasing grain size or number per ear, but the impact is not as great as ear density
  • An 11t/ha crop typically has 500 ears/m2, however YEN research shows 15 t/ha crops need nearer 600-700 ears/m2
  • Crop management must be tailored to yield potential.

Oilseed rape
Performance indicators based on AHDB Growth Guide recommendations include:

Plant population

  • Establishing the optimum plant stand and canopy structure is crucial to maximise light interception and seed yield - thick canopies are at greater lodging risk and are likely to reflect more light during flowering
  • Research suggests in ideal situations 25-35 plants/m2 is optimal for highest yield in hybrid and conventional varieties
  • Be realistic about likely establishment when selecting the seed rate to achieve this

Ground cover

  • Manage crops to achieve a target GAI of 3.5 at flowering for optimal canopy structure, light interception and yield
  • Each GAI unit contains around 50kg N/ha. Use this information to optimise top dressing.

Pod/seed number

  • Seed number is critical to final yield and is largely determined in a 19-25 day period after mid-flowering
  • A 5 t/ha oilseed rape crop has around 100,000 seeds/m2
  • The optimum pod number for high seed yield is around 6,000-8,000 pods/m2
  • Crops with excessive pods (10,000/m2) may yield less due to poor light interception.

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