How RHIZA’s satellite imagery can help you during the current fertiliser setback

Since 1st February 2021, all RHIZA customers will have received satellite imagery as part of their chosen package. Uses of this imagery range from crop walking to variable rate applications, and will undoubtedly be invaluable in understanding where best to focus nitrogen spend this spring.

Firstly, it’s important to understand satellite imagery and what it can demonstrate in the field. Both NDVi and GCVi are indexes of vegetative growth (biomass). These types of satellite imagery are calculated from how much infrared and near-infrared light is reflected from a given area – typically the more light reflected, the higher the biomass of that area. However, it is crucial to remember that this doesn’t necessarily guarantee a higher crop biomass as the presence of weeds will also feed into these index readings. NDVi imagery is suitable for assessing crops earlier in their growth phase (autumn through to mid-spring) but after this point this type of imagery can saturate and lose detail in variation. When saturation occurs, the switch is made to GCVi which is more closely related to the chlorophyll levels within the plant. This allows us to see more detail later in the season and is very useful for protein applications in milling wheats.

It is essential to ground-truth satellite imagery to gain an understanding of what each map is illustrating. As previously mentioned, green maps can indicate well-established fields but in other cases, these maps could highlight areas of blackgrass. Many of our customers and agronomists use satellite imagery and contour mobile to aid their crop walking, log any observations and gain a better understanding of the variation within their crops. With fertiliser prices at an all-time high, understanding a field’s potential and addressing crop variation to ensure that spend is distributed appropriately has never been more important.

Variable nitrogen applications will be key in maintaining the break-even ratio of nitrogen applications this spring. After verifying the satellite imagery and assessing crop variation, decisions can be made as to where yield potential lies and how spend should be attributed. With reduced total nitrogen application on some crops, ensuring the optimisation of other areas with potential will secure a reasonable gross margin. Nitrogen inhibiter products such as Liqui-Safe or Enhance will reduce the volatilisation and leaching losses. Coupled with a variable approach, this will ensure that money isn’t spent unnecessarily.

Case Study

Over the past two years, RHIZA have been conducting trials at Agrii’s Digital Technology Farms looking into the benefits of variable rate applications. One series of trials focused on variable rate nitrogen at individual timings and a collective whole VR programme approach. In focusing on the individual timings, trials showed that establishment and weather has a greater influence on tiller numbers than nitrogen loading which is reflected in only 50% of trials showing increased ear numbers when varying the N1/N2 timing. The largest return on investment consistently comes from the N3 application where a “feeding for yield” strategy is employed.

The below case study was carried out on a farm in Essex in Spring 2021. The N1 and N2 timings were applied at a flat rate at the farm standard recommendation.

At the N3 timing, a recommendation for flat rate nitrogen application at 195kg/Ha of Origin 33.5 was updated following the agronomist’s assessment in mid-March that the poorest areas of the field did not warrant the full flat rate. A VR map was built to apply the recommended rate of nitrogen to the higher biomass areas at 195kg/Ha and a reduction to 90kg/Ha on the poorer parts of the field.

This strategy allowed for a much more tailored approach and saw a reduction from 195kg to 142kg average. In doing this, a cost saving of £34/Ha was seen with no detriment to overall yield.

Whilst variable nitrogen is an easy tool for managing inputs in winter crops, nitrogen management in spring crops tends to be more time sensitive. A large proportion of spring crops have the majority of nitrogen applied to the seed bed at the time of sowing with any further applications made at the two-leaf stage, or soon after. At this growth stage, satellite imagery will struggle to pick up canopy variation in a meaningful way. Therefore, to ensure better utilisation of seed bed applications and any top-ups applied, a variable seeding approach will help ensure even establishment and consequently optimise the use of inputs. Up to 4 years of historical satellite imagery can be provided, allowing growers to pick the best representative image to plan from.  

[At the time of writing, the cost of AN was £650/t.]

Coming soon…

In February 2022, RHIZA will unveil exclusive industry-leading satellite imagery, the first of it’s kind in the UK. More information to follow in the new year…

To find out more on how you can realise the best return on your nitrogen spend this spring, contact your local RHIZA account manager or contact info@rhizadigital.co.uk.