More accuracy with seed rates can lead to better establishment in variably drilled crops – with higher yields being the main aim.
Seed establishment across different soil types, even in the same field, can be highly variable and growers should consider, rotation, soil health, nutrition, establishment method and a host of other variables, according to agronomy company, Farmacy.
Achieving higher yields is all about having enough plants, ears per square metre and creating and maintaining that crop biomass to push for the higher yields, pointed out David Howard, its technical manager. “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.”
Even though plants can tiller well at lower seed rates, that only goes so far, as every variety is genetically programmed tiller differently, and tillering is highly dependent on good conditions throughout the growing cycle, he argued.
“We know that soil type has the biggest impact on establishment, however, working out variable seed rate calculations 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,” he said.
Guessing is just not good enough: “If you use typical low seed rates on a light sandy soil, without knowing what your establishment percentage is, then you risk never having the number of plants needed in the spring.
"You have to get out there and work out the establishment rate by counting the number of plants/m2 and build up a picture over three or four years, which can increase yields. The difference in ear number between the lowest and highest establishment percentages in our trials given standard grain no and TGW equates to 1-1.5t/ha,” he added.
Looking specifically at the impact of seed rates on varieties with different growth habits, Hutchinsons created a series of establishment trials at Little Ponton, in Lincolnshire. In this, 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 inter-plant competition increased, rooting was compromised, and uptake of water and nutrients, therefore, limited – Little Ponton is a shallow light soil site.”
“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,” said Mr Howard.
“LG Sundance 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 howed very little loss of tillers between March and April by comparison to KWs Siskin."
“Ear length is a good indicator of stress, so this can start to tell us when the seed rate is too high so in a separate trial, we also looked at how seed rate influences ear number and length," added Mr Howard.
"We drilled KWS Silverstone in three separates 2ha blocks at different seed rates of 250, 350 and 450 seeds/m2. We found that the optimum seed rate for ear length and ear count for this site was between 350-375 seeds/m2 – again confirming that higher seed rates are not necessarily the optimum.”
“Sites where access to water or nutrition can be challenging, it can be hard to support high plant populations as competition for resources outweighs plant potential. This confirms that 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,” said Mr Howard.
Each field had its own characteristics that will determine the best seed rate from variety, previous cropping, rotation, nutrition etc - “It's about finding out what this is by looking at the ears and overall establishment percentage, he said.
Sowing methods also influence establishment: “As 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," he added.
“So, whilst inter-row competition is reduced, competition between plants in the row is increased and may be way too high.”