Optimum Winter Wheat Plant Population (HGCA Topic Sheet No.36)

Optimum Winter Wheat Plant Population

TS No.36
Summer
2000



Action:

  • Calculate seed rate for winter wheat on the basis of target plant population, expected establishment and TGW.
  • In estimating establishment, consider seedbed conditions, weather at drilling and potential pests and diseases.
  • Aim for plant populations by early spring of:
    • 62 plants/m2 for crops sown by late September
    • 90 plants/m2 for crops sown by mid-October
    • 140 plants/m2 for crops sown by mid-November.
  • Increase target populations slightly for crops grown in northern Britain.
  • Do not adjust target plant populations for different varieties.
  • Only consider re-drilling early-drilled crops if fewer than 30 plants/m2 have established.

Tillering capacity

Wheat plants can produce over 20 tillers/plant, particularly when sown early. Results discussed are based on data from trials over three years in Herefordshire (ADAS Rosemaund). Even plants of fast developing varieties continued to tiller until flag leaf emergence if growing conditions were good (Figure 1).

Any varietal differences in tillering observed at normal plant populations largely disappeared at lower densities, when there was less competition between plants. Variety therefore has no effect on optimum plant population (Table 1).

Plant population and yield

As plant population is reduced tillering does not completely compensate and ear number/m2 declines.Trial yields were, however, unchanged as shoot numbers fell from 600/m2 to 400/m2 because:

  • green area of individual shoots increased from 110 cm2/shoot to 140 cm2/shoot
  • grain number/ear increased from about 35 to 50
  • thousand grain weight (TGW) increased by about 3 g.

Optimum plant population

Sowing date had a major effect on optimum plant population. Figure 2 indicates the following optima:

  • 62 plants/m2 if sown by the end of September
  • 90 plants/m2 if sown by mid-October
  • 140 plants/m2 if sown by mid-November.

Optimum plant population at any sowing date is likely to be slightly higher in Scotland and lower in southern England. This is the subject of an ongoing project.

Inevitably some seeds fail to establish, so seed rates/m2 should normally be 25% to 50% higher than optimum plant populations/m2.

Possible savings

Most farmers sow 325-400 seeds/m2, depending on local conditions, with a target plant population of 275 plants/m2 in spring. Assuming a seed (including treatment) cost of 300/tonne and TGW of 45 g, this would mean drilling 170 kg/ha (11 stones/acre), costing 50/ha (20/acre).

However, 45kg/ha of the same seed, costing 13.50/ha (5.40/acre) is sufficient to achieve a seed rate of 100 seeds/m2, which allows for 40% losses to achieve the end of September target plant population.

Summary

Optimum winter wheat plant populations/m2 depend critically on sowing date, not variety. Seed rates/m2 typically need to be 25% to 50% more than plant populations/m2, to compensate for losses. Wheat plants tiller profusely to compensate for low plant populations.

Using low seed rates may increase the risk of bare patches but seed cost, lodging risk and possibly disease risk increase at higher rates. Optimum plant populations are so low that seed rates can be reduced substantially with little risk.

Further information:

Contact: John Spink and Tzehaye Semere,
ADAS Rosemaund
Tel: 01432 820444

Debbie Sparkes, University of Nottingham
Tel: 0115 951 6074

Project Report 234
Ongoing project 2249


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The Home-Grown Cereals Authority (HGCA) has provided funding for this project but has not conducted the research or written this report.While the authors have worked on the best information available to them, neither the HGCA nor the authors shall in any event be liable for any loss, damage or injury howsoever suffered directly or indirectly in relation to the report or the research on which it is based.

Reference herein to trade names and proprietary products without stating that they are protected does not imply they may be regarded as unprotected and thus free for general use. No endorsement of named products is intended, nor is any criticism implied of other alternative, but unnamed products.

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