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Ear formation, grain development and crop ripening in wheat
Capacity for grain filling is set by grain number per unit area and the storage capacity of each grain. Satisfying the capacity depends on photosynthesis, as well as the redistribution of stem reserves.
Grain filling capacity
Ear development
Benchmark: 18 days from flag leaf to ear emergence
Varietal influence: High
- Ears are initiated during the foundation phase
- Spikelet initiation is completed as stem extension starts (GS31)
- Floret initiation and development proceed until flowering
The number of potentially fertile florets depends on assimilate supplies to the ear, particularly during booting, and is affected by shoot numbers. At shoot numbers of over 400/m2, mutual shading results in fewer grains in each ear.
Grain number
Benchmark: 48 grains/ear – 22,000 grains/m2
Varietal influence: High (grains/ear)
Other influences: Shoot numbers, pests
The benchmark for grain number per ear is 48. With 460 surviving fertile shoots/m2, this gives 22,000 grains/m2.
The number of grains on each ear depends on the number of fertile spikelets on the rachis (the central ‘stem’ of the ear). Compared to barley, wheat is relatively flexible, with spikelets containing up to nine fertile florets.
Cool, bright conditions – especially, one or two weeks before flowering – can prolong or enhance the ear formation period and increase grain number per ear. However, inclement weather at flowering, such as heavy rain, heat or drought, can impair pollination and reduce the number of fertilised florets.
Varieties with smaller culm leaves tend to have more shoots/m2 and fewer grains/ear. Breadmaking varieties tend to have fewer grains/ear.
Some insects, such as orange blossom midge, can reduce grain numbers and feed on developing grains.
Ear weight at flowering
Benchmark: 420 mg/ear (dry weight)
Varietal influence: High
Other influences: Photosynthesis during the construction phase
Ear weight increases rapidly during booting. By flowering, the benchmark dry ear weight is 420 mg/ear, comprising glumes, rachis and florets – weights remain similar throughout grain filling and become the chaff at harvest. As a result, ear weight at flowering multiplied by fertile ear number per unit area can indicate yield potential.
Photosynthesis in the ear contributes significantly to grain growth. The benchmark final ear weight at harvest is 2.8 g, 15% of which is chaff.
In wheat, yield variation due to region, soil type and early crop management is more strongly related to grain number rather than the weight of each grain.
Grain filling and ripening
Benchmark: 43 mg dry matter per grain in 45 days from flowering to 26 July
Varietal influence: Medium
Other influences: Water availability, disease
Grain filling starts when flowering is complete and continues until grain reaches about 45% moisture.
Grains accumulate more water than dry matter for about four weeks after flowering, when water content is at its maximum. Water enables cells first to divide, then expand. Severe drought or disease can significantly reduce grain size.
As water uptake stops, dry matter accumulation accelerates. Rapid dry weight growth continues with starch and protein deposition in expanded grain cells – these are supplied by both photosynthesis and redistribution of reserves.
Suboptimal photosynthesis during the first two or three weeks of grain growth reduces the cell number and potential weight of each grain.
The benchmark period from flowering until maximum/final dry weight (the grain filling period) is 45 days. However, this varies considerably – it can be 28 days in severe drought conditions.
The benchmark weight/grain is 43 mg dry matter, which equates to a ‘thousand grain weight’ of 50 g at 15% moisture.
Varietal differences in average grain weight are shown in the AHDB Recommended List.
Canopy survival during grain filling
Benchmark: GAI <2 after maximum grain weight achieved
Varietal influence: Medium
Other influences: N supply, foliar disease
Canopies start to senesce rapidly from GS71, about nine days after flowering. Most remaining greenness is lost just after grain weight reaches its maximum.
High nitrogen uptake, fungicide use or cool, moist weather all tend to delay senescence. Crops at northerly latitudes generally have high grain weight, because cooler temperatures prolong grain filling. Hot weather reduces grain weight by shortening the period of grain growth, even in bright and moist conditions. Grain weight is also reduced by leaf or root disease, pest infestation or early lodging.
Note: No further grain filling occurs once grain moisture is below 45%, at around GS87, so yield cannot be affected by any treatment applied at or after this stage.
Ripening
Benchmark: 45 to 20% moisture content in two weeks
Varietal influence: Low
Other influences: Lodging
After grain filling, moisture content provides the best indication of ripening until grains are dry enough to harvest. On average, grain takes about two weeks to dry, from 45 to 20% moisture. Frequent rain re-wets grain and slows moisture loss, especially at low moisture contents. Lodged crops dry slowly.
Glyphosate products may be used pre-harvest on a range of crops to control weeds, aid harvesting and help protect grain quality (particularly in wet harvests) and food safety.
Pre-harvest glyphosate use in cereals and oilseed rape
How to measure grain filling, moisture and ripening
Grain filling period*: The number of days between GS65 and when the gain reaches 45% moisture content.
Grain moisture: Thresh grain from around 20 representative ears, weigh the sample, dry the sample (at 80–100°C) until no further weight loss and weigh again.
Moisture content: 100 - (grain dry weight ÷ sampled grain weight) x 100.
Grain ripening period: The number of days from 45 to 20% moisture content.
*If a grain sample is taken at the end of the grain filling period, the dried and weighed grain can then be counted and divided by the number of grains to determine the dry matter per grain.
General growth benchmarks during flowering and grain development
How to use benchmarks to assess cereal growth
GS59 |
6 June |
Ear completely emerged |
Fertile |
495/m2
|
Little further shoot death occurs |
N uptake |
230 kg/ha |
36 kg N/ha per unit GAI |
GAI |
6.4 |
GAI is falling from its maximum of 6.9 in late May |
Above-ground dry weight |
11.4 t/ha |
Growth may slow if flowering is delayed |
Height to collar |
53 cm |
Five internodes extend |
GS61 |
11 June |
Start of flowering |
Fertile shoots |
460/m2
|
150 additional infertile shoots/m2 remain until harvest |
Roots |
1.0 t/ha; 31 km/m2
|
Sufficient for full moisture capture to 70 cm depth. Deepest roots reach to ~1.5 m. Maximum root system size reached |
N uptake |
248 kg/ha |
Only 30 kg/ha further uptake occurs |
GAI |
6.3 |
Canopy senescence is slow |
Above-ground dry weight |
12.1 t/ha |
About two-thirds of final dry weight |
Growth rate |
0.18 t/ha/day |
During most of the production phase (GS61 to GS87) |
Height to collar |
69 cm |
Little further extension occurs |
Stem dry weight |
7.1 t/ha |
33% is soluble, giving 2.3 t/ha for redistribution |
Ears |
1.9 t/ha |
Ears have 48 grain sites after flowering. Each ear weighs 420 mg (dry) both now and as chaff at harvest |
GS71 |
20 June |
Grain watery ripe |
GAI |
5.7 |
Rapid senescence now starts |
Stem dry weight |
7.6 t/ha |
Now at its maximum. Rapid redistribution of soluble reserves begins at GS73 |
Above-ground dry weight |
13.7 t/ha |
All further increase occurs in the grain |
GS87 |
29 July |
Grain at ‘hard dough’ |
GAI |
1.3 |
All greenness will be lost in the next few days |
Above-ground dry weight |
19.6 t/ha |
About 1.2 t/ha is subsequently lost, mainly from the straw |
Grain filling |
Lasts 45 days |
Grain filling stopped at about 45% moisture, about 3 days before GS87 |
Harvest ripe |
9 August |
Grain ‘harvest ripe’ |
Ears (fertile shoots) |
460/m2
|
At least 400 shoots/m2 |
N uptake |
279 kg/ha |
68% of final crop N is in grain (32% in chaff, straw and stubble) |
Above-ground dry weight |
18.4 t/ha |
51% grain (10% chaff, the rest as straw and stubble) |
Straw dry weight |
7.3 t/ha |
Includes stems and leaves; only 0.2 t/ha soluble sugars remains |
Chaff dry weight |
2.0 t/ha |
Chaff is 420 mg/ear |
Grain weight |
50 mg at 15% moisture |
Specific weight 78 kg/hl |
Grain protein |
11.5% (dry basis) |
Calculated as 2.0% N x 5.7 |
Grain yield |
11.0 t/ha at 15% moisture |
Shedding losses are 0.03t/ha |
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