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The Variable Rate Seed myth


We introduced variable rate seed over 15 years ago and the benefits, including that of a yield increase of 4.2% over flat rate drilling, are well documented.

However, every now and then I come across individuals who think that doing variable rate seed avoids the need for variable rate applications of nitrogen. This is a myth.

Where did the myth come from?

Often the myth is perpetuated by scenarios where the advisor may not have a variable rate nitrogen solution to offer, or in instances where there is simply a lack of understanding about how the two practices complement one another.

The easiest way to understand this is to think about what you are managing with each technique: 

​Technique Objective
Variable rate seed ​ Manage plant counts in each part of the field to ensure a sufficient crop that meets yield potential.
Variable rate nitrogen​ Supply the crop with the right amount of nitrogen in each part of the field to ensure optimum return on inputs.

If we think about the statements above we can see that the two techniques are each managing very different issues.Variable rate seed will deal with areas of the field that enter the main growing period with fewer plants due to increased winter losses.Alongside this, underlying differences in soil nitrogen supply to the crop and variation in plant uptake will still need managing if yield is going to be optimised.

The yield benefit of variable rate nitrogen is 4.6% on its own, variable rate seed (as stated above) gives a yield benefit of 4.2%.Used together, a cumulative benefit of between 8 and 12% has been measured.

One explanation for the confusion around doing both techniques together is that they are both methods of CANOPY MANAGEMENT. While true, on their own they are only part of a much bigger picture.

Crop establishment – controlled by autumn and winter conditions

  • Moisture content of soil at cultivation and drilling influences seedbed quality
  • Soil temperature controls germination and emergence
  • Pest (slug) numbers influenced by breeding conditions in previous season
  • Severe (cold) winter can reduce tillers, leaves and plant numbers.

Nitrogen supply – influenced by overwinter rainfall and spring temperatures

  • High/low winter rainfall leads to high/low N losses = less N left for spring growth
  • Warm winter temps = high N mineralisation = higher N losses through leaching or crop uptake
  • Warm spring temps = higher early N supply
  • Cold Spring temps = reduced early N supply

Depending on crop prices, both services offer an annual return of over £50 per hectare.

Speak to us

For help with calculating the benefit of using variable rate seed and nitrogen on your farm, please get in touch. We can provide you with archive data to demonstrate historic variations in your fields and this is crucial for implementing effective strategies going forward.

Simon Parrington

SOYL Commerical Director

Frontrunner - 22nd March 2019
Frontrunner - 15th March 2019

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Wednesday, 21 October 2020

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