Action:

Calculate seed rate for winterwheat on the basis of targetplant population, expectedestablishment and TGW.

In estimating establishment,consider seedbed conditions,weather at drilling and poten-tial pests and diseases.

Aim for plant populations byearly spring of:

62 plants/m2 for crops sownby late September90 plants/m2 for crops sownby mid-October140 plants/m2 for crops sownby mid-November.

Increase target populationsslightly for crops grown innorthern Britain.

Do not adjust target plantpopulations for differentvarieties.

Only consider re-drilling early-drilled crops if fewer than 30plants/m2 have established.

Optimum winter wheatplant populationTillering capacity

Wheat plants canproduce over 20tillers/plant,particularly whensown early. Resultsdiscussed are based ondata from trials overthree years inHerefordshire (ADASRosemaund). Evenplants of fastdeveloping varietiescontinued to tiller until flag leafemergence if growing conditionswere good (Figure 1).

Any varietal differences in tilleringobserved at normal plantpopulations largely disappeared atlower densities, when there wasless competition between plants.Variety therefore has no effect onoptimum plant population (Table 1).

Plant population andyield

As plant population is reducedtillering does not completelycompensate and ear number/m2

declines.Trial yields were, however,unchanged as shoot numbers fellfrom 600/m2 to 400/m2 because:

green area of individual shootsincreased from 110 cm2/shootto 140 cm2/shoot

grain number/ear increasedfrom about 35 to 50

thousand grain weight (TGW)increased by about 3 g.

Optimum plantpopulation

Sowing date had a major effect onoptimum plant population. Figure2 indicates the following optima:

62 plants/m2 if sown by theend of September

90 plants/m2 if sown by mid-October

Topic Sheet No. 36

Summer 2000

AbbotAvalonBrigadierBusterCadenzaCaxtonChargerConsortDrakeHavenMerciaRialtoRibandSoissonsSpark

Mean

9.28.3

10.49.49.89.19.6

10.410.310.58.3

10.110.38.19.3

9.6

8.88.2

10.19.39.89.09.7

10.510.010.38.39.8

10.28.69.3

9.6

Variety 320 seeds/m2 80 seeds/m2

Table 1. Yields (t/ha) of severalvarieties at two seed rates

20

16

12

8

4

027-Sep 16-Nov 05-Jan 24-Feb 15-Apr 04-Jun 24-Jul 12-Sep

40 seeds/m2

80 seeds/m2

320 seeds/m2

Time course through the season (1998)N

umbe

r of s

hoot

s/pla

nt

Figure 1. Shoot numbers/plant of September-sown wheat, variety Haven

Further information:

Contact: John Spink and Tzehaye Semere,ADAS RosemaundTel: 01432 820444

Debbie Sparkes, University of NottinghamTel: 0115 951 6074

Project Report 234Ongoing project 2249

Summary

Optimum winter wheat plantpopulations/m2 dependcritically on sowing date, notvariety. Seed rates/m2

typically need to be 25% to50% more than plantpopulations/m2, tocompensate for losses.Wheat plants tiller profuselyto compensate for low plantpopulations.

Using low seed rates mayincrease the risk of barepatches but seed cost, lodgingrisk and possibly disease riskincrease at higher rates.Optimum plant populationsare so low that seed rates canbe reduced substantially withlittle risk.

140 plants/m2 if sown bymid-November.

Optimum plant populationat any sowing date is likelyto be slightly higher inScotland and lower insouthern England.This is thesubject of an ongoingproject.

Inevitably some seeds fail toestablish, so seed rates/m2

should normally be 25% to50% higher than optimumplant populations/m2.

Possible savings

Most farmers sow 325-400seeds/m2, depending on localconditions, with a target plantpopulation of 275 plants/m2 inspring. Assuming a seed (includingtreatment) cost of £300/tonneand TGW of 45 g, this wouldmean drilling 170 kg/ha (11

stones/acre), costing £50/ha(£20/acre).

However, 45kg/ha of the sameseed, costing £13.50/ha(£5.40/acre) is sufficient to achievea seed rate of 100 seeds/m2,whichallows for 40% losses to achievethe end of September target plantpopulation.

Optimum winter wheatplant population

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

Topic sheets arefree

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Home-Grown Cereals Authority

Research & DevelopmentCaledonia House223 Pentonville RoadLondon N1 9HY

Tel: 020 7520 3945Fax: 020 7520 3992

TGW

3535

4040

4545

5050

100

2.335

2.640

2.945

3.250

150

3.453

3.960

4.368

4.875

200

4.570

5.180

5.890

6.4100

250

5.688

6.4100

7.2113

8.0125

300

6.8105

7.7120

8.7135

9.6150

350

7.9123

9.0140

10.1158

11.3175

400

9.0140

10.3160

11.6180

12.9200

stones/acrekg/ha

stones/acrekg/ha

stones/acrekg/ha

stones/acrekg/ha

Table 2. Seed size, target seed numberand approximate seed rates needed

seed numbers/m2

160

120

80

40

007-Sep 27-Sep 17-Oct 06-Nov 26-Nov

96/9797/9898/99

Date of sowing

Opt

imum

pla

nt p

opul

atio

n/m

2

Figure 2. Optimum plant populationmainly depends upon sowing date