Spring Barley Seeding Rate to Achieve Optimum Plant Population

Barley needs plants – How to achieve the optimum plant population for yield.

It goes without saying that when we grow cereal crops, we want as much grain produced per square metre as possible. One of the critical factors in achieving this is the establishment of the optimum number of plants per square metre. The old adage “well sown is half grown” owes its origin to this thought process.
Those who regularly manage winter wheat, winter oilseed rape and to some extent oats will know just how these crops can adapt to compensate for lower plant numbers and still produce an adequate yield. These crops compensate by changing their canopy structure to produce more tillers and larger ears in the case of winter wheat and more branches in the case of oilseed rape. They can also set more seeds and redirect nutrients to fill larger seeds where space allows.
Barley however both winter and spring is different. Barley is quite limited in how it can produce a good yield when plant numbers are compromised. Barley can and will tiller where plants are missing but it cannot compensate with grain number and grain size like wheat. In other words, a high yielding crop of barley needs plants….

What are optimum plant numbers for maximum yield in spring barley?

Trials have shown that 300 plants/m2 for spring barley emerging in March/ early April is around optimum. As the planting date moves later (mid – end of April), this optimum moves a bit higher to approx. 310-320 plants/m2 due to lack of time for tillering.

How do we calculate a seed rate to establish our target plant population?

To calculate the target seed rate, we need to know the seed size (TGW in grams) and make an estimate on what rate of plant establishment we will achieve in the field. TGW will be printed on all Goldcrop supplied seed so that is the easy bit taken care of.
Estimating the establishment rate in field takes a bit more thought. A certain percentage of the seeds in a bag will not grow (certified seed must be at least 85% germination by law). In addition, a certain number of seeds will be lost in the field. Most treated certified spring barley seed will be between 90 & 100% germination. In good planting conditions, one can expect to lose at least 8-10% of seeds in field before emergence. Therefore, it is reasonable to expect to achieve 85% establishment (seed germination and field losses combined) when planting certified spring barley seed in good conditions. Losses can be quite a bit higher if the seed quality or seed bed quality is sub-optimum. I have even observed that soil type can have an impact on establishment rates with shaley soils rarely achieving 90% establishment due to coulter bounce when planting and seeds being covered by small stones. In general, my experience is that plant establishment rates in field are rarely as high as we would like due to an underestimation of in field seed losses. The practice of doing plant counts once the crop has emerged can be useful in getting a feel for what establishment rates you are achieving on your own soil type and will give you confidence in deciding seed rates in future years.

Seed Rate Calculation Formula

Seed rate (Kg/Ha) = Target Population (Plants/m2) x TGW (g)
bbbbbbbbbbbbbbbbbbbbbbEstablishment Rate (%)

Example of the seed rate calculation

Target plant population = 300 plants/m2
Seed TGW = 54 grams
Estimated establishment rate (combination of seed germination rate & in field loss) = 85%

300 x 54 = 190kg/Ha (12 stone/acre)
85

Note: allowance should be made where planting barley in very fertile situations such as after long term grass or on peaty soils. High plant numbers in such fertile locations can further increase lodging pressure and it may be advisable to reduce the target plant population.

Proof of the pudding…

In 2011, I decided to conduct a seed rate trial on winter barley. I had read about the requirement to have adequate plant numbers in barley to achieve high yields, I had my doubts as I had regularly seen the great tillering ability of winter barley and felt that it could probably compensate for low plant numbers by tillering.
Two varieties (Cassia and Saffron) were planted in plots at the Goldcrop trial site in Shanagarry to achieve 4 different plant populations in the case of each variety.
The results were illuminating and confirmed to me the limit of barley to compensate for lower plant numbers.

Variety	Target Plant Population (Plants/m2)	Yield (T/Ha at 15%mc)
Saffron	220	9.1
Saffron	250	8.8
Saffron	300	9.9
Saffron	350	9.0
Cassia	200	9.5
Cassia	250	10.0
Cassia	300	10.5
Cassia	350	9.8

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Article by John Dunne, Goldcrop Ltd.