The Importance of Variable Seed Rates for Arable Crops

In this episode, we are talking to Sam Fordham, head of technical for RHIZA.

Today we are taking about variable seed rates for combinable crops, Sam suggests this is the most important input to vary.

But as we look towards the main autumn sowing period, we consider what the key principles and benefits are for the grower. 

What Is Variable Rate Seed?

Sam Fordham:
Variable seed rate isn’t a new concept. It’s been in the precision farming industry for about ten years. The technology used to implement it has been around for a while, but our understanding of what we’re trying to achieve with it has evolved. Initially, farmers wanted an even crop and yield map, but now we’re using seed rates to manipulate crops early on, setting them up for better performance in the spring.

What Is a Base Seed Rate?

Sam Fordham:
A base rate is the number of seeds you plan to plant per square meter, based on the field’s conditions, the crop type, and the variety being used. For example, you might decide on 350 seeds per square meter as a base rate for a particular field. However, depending on the soil type, rotation, and other factors, farmers often vary that rate across different parts of the farm.

What Is the Principle of Variable Seed Rates?

Sam Fordham:
Variable seed rates allow farmers to adjust the base rate within a field. Instead of treating the whole field uniformly, you recognise that different areas within a field may require different seed densities. The goal is to optimise crop establishment and ensure the crop is set up well for the spring.

How Many Farmers Are Adopting Variable Seed Rates?

Sam Fordham:
Surprisingly, not as many as you might think. While most farmers change their seed rate at a field level, only around 40% of UK cereal acreage uses variable seed rates within fields. That’s likely an overestimate too.

Why Drill With Variable Seed Rates?

Sam Fordham:
The key objective is to ensure the crop enters winter in the best possible condition. Establishment rates vary depending on soil type, so variable seed rates help even out these differences. This ensures that when spring arrives, the crop can support the yield you’re expecting without being held back by limiting factors.

What Are the Risks of Not Using Variable Seed Rates?

Sam Fordham:
If you don’t use variable seed rates, you risk having uneven plant populations in the spring. For example, heavier soils may need higher seed rates to reach the desired plant density. If you don’t have enough plants in the ground, it’s hard to reach that target population in spring, which can lead to yield loss.

How Important Is Getting the Seed Rate Right?

Sam Fordham:
It’s crucial. Seed is the first input, and if you don’t get it right, nothing else will matter. Although seed is relatively cheap compared to fertilisers and crop protection products, it’s the foundation of the crop. Farmers should consider being more liberal with seed in certain areas to ensure they’re not under-utilising more expensive inputs later in the season.

Does Variable Seeding Work for Other Arable Crops?

Sam Fordham:
Yes, it works across all combined arable crops. Whether it’s wheat, oilseed rape, or even beans, the principle remains the same. You adjust the base rate by a percentage, depending on the crop and soil conditions, to optimise plant population density.

How Can Farmers Start Using Variable Seed Rates?

Sam Fordham:
There are multiple ways to adopt variable seed rates. While having GPS-equipped tractors and drills is ideal, you can still manually adjust seed rates on the go if your drill has radar ground speed. You can also use satellite imagery to understand where establishment issues occur and adjust accordingly.

How Does the Contour Platform Help With Variable Seeding?

Sam Fordham:
Contour is a tool that helps farmers turn satellite imagery into actionable seed plans. You can set your base rates and then adjust them based on different areas of the field, such as headlands or spots prone to establishment issues. The tool creates job sheets and seed orders, helping farmers distribute seed more effectively across their fields.

Has the Recent Dry Summer Revealed More Data From Satellite Maps?

Sam Fordham:
Yes, dry summers reveal a lot about soil type changes within fields. We use two types of satellite imagery—NDVI and GCP—and GCP really comes into its own in late-season drought conditions. These maps help identify areas that need attention, either through soil sampling or direct seed rate adjustments.

Why Should Farmers Adopt Variable Seeding?

Sam Fordham:
Variable seeding allows farmers to set their crops up for success from the start. With commodity prices at record highs and input costs increasing, farmers need to maximise crop output. By eliminating limiting factors early on, it becomes easier to manage crops throughout the season and achieve higher yields.

What Is Your Top Tip for Farmers?

Sam Fordham:
Look at the data you already have. Yield maps and satellite imagery are great tools to identify limiting factors in your fields. From there, speak to someone who can help guide you on how to use variable seed rates to maximise your crop’s potential.