When it comes to crop performance, your seed rate is a critical factor to success. Variability across different soil types and even within the same fields can be extensive, and the results can often mean an inconsistent crop.

It’s a delicate balance to strike though - too few seeds and you risk excessive tillering, delayed maturity, increased weed pressure, and underutilised yield potential. Too many, and you may face higher input costs, increased lodging and reduced grain quality due to overcrowding.

So, what’s the sweet spot and how do you get there?

The goal: optimal plant population

Achieving a uniform and optimal plant population across the field is key to maximising the best of light, water and nutrients - and ultimately, yield. But it’s more than just increasing or decreasing the number of seeds drilled. Every seed has the potential to become a productive plant, yet many factors influence whether it actually does.

Soil type: a key influencer

One of the most critical and often underestimated factors is soil type. Heavier soils with high clay content tend to produce cloddy seedbeds. As a result, there can be poor soil-to-seed contact which can hinder germination and emergence, leading to patchy establishment. These soils also retain more moisture and stay cooler, which can reduce seed vigour and increase losses from pests like slugs.

On the flip side, lighter soils typically break down more easily, creating a fine tilth that promotes excellent seed contact. This leads to better germination, stronger emergence, and more consistent crop stands.

Tailoring seed rates to soil conditions

Understanding the variability within your fields is essential. A one-size-fits-all approach to drilling doesn’t work - instead, it’s important to assess soil types and anticipate potential losses to calculate the correct seed rate for each zone. This is where variable rate seed comes into its own, allowing you to easily make precise adjustments that reflect real field conditions.

Variable rate seed is not just a technical upgrade either, but rather a strategic move towards optimised, sustainable, resilient crop production. By aligning seed rates with your soil’s characteristics and expected plant losses, you can set the stage for healthier crops, better yields, and a more efficient use of inputs overall.

How does variable rate seed technology work?

·         Step 1: EMI (conductivity) survey

·         Step 2: Ground-truthing of EMI maps

An electrical conductivity – or EMI - survey is firstly carried out by our precision team, which is a non-intrusive method for assessing a soil’s physical properties.

During this process, an electrical conductivity meter sends an electrical current into the soil and measures its ability to conduct it. As water is a good conductor and clay soils hold more moisture, the amount of clay and sand content can be directly related to the values measured by the meter, giving a clear picture of where a soil’s physical characteristics change across the field. Other attributes such as stone content and soil depth can also affect the EMI values.

Our research has shown the direct relationship between clod size, seedbed quality and conductivity (see graph above).

During this survey, we collect EMI values every few metres across the field and a map of spatial variation is created.

The next step is to assign an establishment rate (percentage of seeds that successfully grow) to each soil zone identified by the survey. Typically, heavy clays have a 60% establishment rate, medium soils 70-75% and light soils anything up to 90%.

At Frontier, our precision specialists use a unique database of establishment measurements based on plant counts to help assign these values. Plant counts are taken across a range of soil types related to not only clay content but stone content and landscape position too, helping to build up a large dataset of establishment values across a range of soil types.

The establishment percentage can then be matched to the soil survey classification to make an accurate map of how establishment values vary across a field.

Once the establishment zones have been designated, the final bespoke, variable seed rate map can be made easily in our MyFarm platform, either by yourself or with support from our applications team.

Maps can be made using the kg/ha, seed/m² or plants/m² options. The simplest method is to choose a kg/ha value, which will be assigned to the mean establishment rate for the field, adjusted up for lower establishment and down for higher establishment.

The option of seeds/m² will assign the default seed number to the average establishment percentage and then calculate the kg/ha for each zone using the thousand grain weight (TGW) for the seed batch.

The plants/m² option uses the optimum or target population figure. Each establishment percentage will be used to calculate the seed rate against the target plant number. For example, if the target is 200 plants/ m² and establishment is 60%, then 333 seeds would be required. The TGW value can then be used to calculate the kg/ha needed.

Evidence-based technology

Our precision services team carries out extensive trials to assess the benefits of variable rate seed against uniform seed rates.

Examples of some of this research are shown below, comparing variable rate seed vs. flate rate seed with winter wheat where a clear benefit is shown:

How can this approach support a yield increase?

Achieving the optimum number of plants/m² gives the best possible chance of obtaining optimum yield.

The graph below shows a field that ranges from light to heavy soils and demonstrates how close to optimum the plant numbers are across the field after the use of variable rate drilling technology. Much of the flat rate-drilled field is well below the target population of 190 plants/m² and this will result in lower yields.

You can read more about how variable rate technology has supported one of our growers, Rob Deane, in this Farmers Weekly article from KUHN Farm Machinery.

A walk-through of the tool in our MyFarm platform is also available below from precision services applications team leader, James Wyllie.

Creating your own seed rate trials

By using variable rate drilling equipment, a simple trial can be set up to create plots of different seed rates to help determine the optimum figures for your field. Using a GPS yield map, the average yields for each plot can be measured and the seed rate that gives the highest yield can be identified.

The below maps show a variable rate plan for oilseed rape including trial plots (kg/ha) on three different soil types.

Over time, you can create trials in different seasons to establish the correct rate in relation to weather conditions and drilling dates across the farm.

As well as your own seed rate plans, these trials also can be easily created and automated through MyFarm, with support always on hand from your local precision area manager.

Late drilling winter wheat?

More advice and technical guidance can also be found in this recent article from national technical manager for seed, Kirsty Richards.

If you have any further questions about the benefits of variable rate seed or require any technical advice, contact us on 0800 227 445 or email us at info@frontierag.co.uk.