At a recent open day at the Farmacy Harleston demonstration site in Norfolk, hosted by Lewis Partners, there was much discussion around the benefits and agronomic challenges associated with using higher seed rates for wheat when pushing for higher yields.
“Through the work in the Yield Enhancement Network (YEN), we know that achieving higher yields is all about having enough plants and ears per square metre, and creating and maintaining that crop biomass to push for the higher yields," said David Howard, Farmacy Technical Manager.
“Even though plants can tiller well at lower seed rates, that only goes so far as, genetically, every variety is programmed to tiller differently and tillering is highly dependent on good conditions throughout the growing cycle.
“As seen this year, tiller initiation was good, but lack of rainfall caused high tiller loss later in the season. In many cases, targeting low seed rates and high tillering will not match the benefit of having the optimum number of seeds from the outset.
“Growers know that soil type has the biggest impact on establishment, however calculating variable seed rate for a soil type alone can be a rough science.
“If you start with the incorrect basic rate, adjusting this by 10 or 20% is not going to make the difference that is needed.
“Establishment across soil types can be so variable and should consider rotation, soil health, nutrition, establishment method and a host of other variables.
“As agronomists and growers we need to understand how we can manipulate the crop to achieve this through seed rates, nutrition etc. on different soil types and the impact of varietal differences in growth habit.”
Guessing is just not good enough, said Mr Howard - highlighting, for example, that low seed rates on a light, sandy soil without knowing your establishment percentage runs the risk of not achieving the number of plants needed in the spring.
“You have to get out there in the spring and work out the establishment rate by counting the number of plants/m2 and build up a picture over 3-4 years and this can mean big differences in yields," he says.
“The difference in ear number between the lowest and highest establishment percentages in our trials given standard grain numbers and thousand grain weight (TGW) equates to 1-1.5t/ha."
Looking specifically at the impact of seed rates on varieties with different growth habits, Hutchinsons established a series of establishment trials at Little Ponton in Lincolnshire, designed the answer the question: if a variety is high tillering, is less seed needed for optimum plant ear counts and vice versa?
Mr Howard adds: “As every variety tillers differently they are much more unpredictable than having more seeds there from the outset."
In the trial, the wheat variety LG Sundance, which has a high tiller retention growth habit was compared to the more standard tillering variety, KWS Siskin.
Both varieties were drilled at four different rates from 150 seeds/m2 up to 450 seeds/m2 in 100 seeds/m2 increments, and then the green area index and ear numbers were measured.
"We found that the tiller number for KWS Siskin was fairly static all the way up to 350 seeds/m2.This is most likely because, as interplant competition increased, rooting was compromised and uptake of water and nutrients therefore limited – Little Ponton is a shallow, light soil site,” says Mr Howard.
“However at 450 seed/m2 the significant increase in plants meant that even when tillers were lost due to competition for resources, it still had enough plants to make up for it.
“That said, it equated to the same tiller number as 350 seeds/m2 of LG Sundance, which responded well to higher seed rates and tiller number increased with each increase in seed rate-performing best at 450 seeds/m2 producing more ears and a greater green area index.
“Interestingly, as the dry weather took hold, its genetic tillering potential came to the fore and showed very little loss of tillers between March and April by comparison to KWS Siskin."
Ear length is a good indicator of stress and can tell growers when the seed rate is too high, so in a separate trial, they looked at how seed rate influences ear number and length. KWS Silverstone was sown in three separate 2ha blocks at different seed rates of 250, 350 and 450 seeds/m2.
The trials found that the optimum seed rate for ear length and ear count for this site was between 350-375 seeds/m2 – confirming that higher seed rates are not necessarily the optimum.
“Sites where access to water or nutrition can be challenging find it hard to support high plant populations as competition for resources outweighs plant potential," Mr Howard adds.
“In order to get the optimum ear counts and crop biomass, and eventually higher yields, variable seed rates cannot be calculated on soil type alone.”
Every field will have its own characteristics that will determine the best seed rate: such as variety, previous cropping, rotation, nutrition - growers need to find out what this is by looking at the ears and overall establishment percentage.
He pointed out that as establishment methods can influence establishment and many growers move to low soil disturbance systems that drill in wider rows, seed rates become even more important, particularly where they are already quite high as, effectively, you have the same amount of seed going down half the number of coulters.
“So whilst inter-row competition is reduced, competition between plants in the row is increased and may be way too high," Mr Howard adds.
Using field mapping service Omnia, it is possible to input all of your field information to create the most accurate variable rate map possible, bringing about a more even establishment, according to Nick Strelczuk, Hutchinsons Precision Technology Specialist.
Maps can be created with Omnia for all of the necessary field and crop data and then matched to a target plant population for that variety, creating a detailed variable drilling plan.
“In the validation trials last year, we compared variably drilled wheat alongside a farm standard rate on spilt fields and taking them to yield. The work proved that using Omnia Precision Agronomy can increase yields by an average of 0.6t/ha, worth £99/ha (based on wheat at 165/t)”, Mr Strelczuk adds.
“We anticipate similar results from the 20 winter wheat and spring barley validation trials in the ground this year, ranging from Scotland to Kent. “So far, it’s very clear to see the variably drilled plots are much more uniform and even in terms of tiller and ear numbers. If we work on the YEN promise of more biomass and ear numbers leading to higher yields, its certainly looking hopeful for a good harvest result.”