Thomas Wilkinson
The below article aims to provide tips on a few key parameters to help learn how to drill and establish winter cereals.
Seed rates:
Seed rate (kg/ha) = [Target plants (per m²) x Thousand Grain Weight (g)] / % Establishment
In 20 out of the 25 seed rate experiments done by ADAS on wheat sown in late September/early October, the economic optimum plant population was between 70 and 170 plants/m2. However, targeting a spring plant population in the region of 200 plants/m2 for this drilling window provides insurance against unpredictable factors without creating an excessive risk of lodging. Higher plant populations may be required if an additional objective is to outcompete black-grass.
The benchmark target spring population in two-row winter barley is about 300 plants/m2, with a lower recommended plant population recommended for hybrid barley.
The percentage plant establishment needs to be estimated depending on each individual situation. Establishment decreases from around 70% for sowings in September to less than 50% for sowings in November or later, and on average, establishment on sandy soils is 90% compared with 65% on loams and clays. If using farm saved seed or unused seed from last year then you should test the germination and take this into account when estimating expected % establishment.
Sowing date:
Following the early completion of harvest this year there is potential to sow cereal crops early. This is assuming there is enough moisture in the soil, and rain forecast, to allow the full process of germination and establishment to take place, and the soil is not too strong to allow drilling/cultivations. If sowing early, there are several factors to consider. The target plant population of early sown crops is lower because the plants have more time to produce compensatory tillers. For each week drilling is brought forward, the target plant population can be reduced by 12 plants/m2. ADAS seed rate trials sown during the last week of September in England had an average optimum plant population of 148 plants/m2. Note there have not been any ADAS seed rate trials sown before 20th September, so there is a lack of evidence about optimum plant numbers for crops sown in the first half of September. Careful consideration should be given to sowing varieties with a low lodging resistance before the end of September due to the high potential risk of lodging. Sowing a crop one week earlier will reduce the effective varietal lodging resistance score by 0.5 points. In general varieties with slow early development are better suited for early drilling.
For winter cereals, it will take around 150 °C days from drilling to emergence. This is equivalent to about 11 days in September, 15 days in October or 26 days in November.
The window for sowing winter barley is narrower than for winter wheat because barley has a low vernalisation requirement, which makes it less suited to very early sowing. Also, yields decline more for late sown barley than wheat because it is less able to compensate for reduced tillering by producing more grains per ear. This is because each spikelet of two-row barley only contains one fertile floret and six-row barley has three fertile florets per spikelet. This contrasts with wheat spikelets which contain up to nine potentially fertile florets (three to five usually forming viable grains). For this reason barley yield is generally driven by shoot number.
North vs south
High optimal plant populations are observed more frequently at more northerly latitudes. This is because the colder temperatures mean there is less time for compensatory tillering between planting and the start of stem extension. ADAS analysis has suggested that seed rate should be increased by 11-28 seeds/m2 per increase in each degree of latitude. It is likely that higher seed rates will also be required on high altitude sites, again because cooler temperatures limit compensatory tillering.
Rotational position
In second and subsequent wheat positions optimal plant populations are 30–40 plants/m2 lower that in first wheats, due to take-all having a greater yield impact on high compared to low plant populations. This is partly due to closer proximity of plant roots which increases the risk of take-all disease spread from plant to plant. If take-all is controlled by a seed treatment in second and later position wheats the optimal plant populations are only 20-25 plants/m2 lower than for first wheats.
Variable seed rates
ADAS tramline trials comparing variable seed rates against flat rates have shown they do have the potential to increase yield where the field average seed rate is close to the economic optimum. However, in situations where the field average seed rate is above the optimum, it is unlikely that there will be a yield advantage. Where super-optimal seed rates are normally used it is possible for gross margin to be improved by reducing seed costs.
| ACTION • Use known thousand grain weights, reliable germination rates and your best estimate of % establishment to calculate seed rates. • Establish an extra 50 plants/m2 for each month drilling is delayed to compensate for reduced tillering. • Remember the drilling window for winter barley is narrower than for winter wheat, with barley yields declining more rapidly than wheat when sown late. • Be aware that in second and subsequent wheat positions optimal plant populations are 30–40 plants/m2 lower that for first wheats. • Remember that if high seed rates are normally used, which may be above the economic optimum, varying seed rates will have a limited effect on yield but may improve gross margin by reducing seed costs. |