Step-by-step guide
1. Measure the amount of nitrogen in the crop
Measure and calculate canopy size in terms of Green Area Index (GAI). GAI is the ratio of green tissue to ground area, and it can be measured by visual assessment (reference photos can be found on the HGCA website)
Multiply the GAI by 50kg nitrogen per hectare, and enter this figure as the amount of crop canopy nitrogen. For example, if the crop has a GAI of 1.5, enter 75 as the amount of crop canopy nitrogen (1.5 x 50 = 75)
2. Measure the amount of nitrogen in the soil
Soil mineral nitrogen is best measured directly using systems such as the GrowHow N-Min analysis. An estimate can also be made based on a combination of previous cropping, soil type and overwinter rainfall using RB209 or PLANET software.
3. Decide on your target yield
This will affect the amount of nitrogen that is required.
4. Tick if you are using manufactured fertiliser
The uptake of manufactured nitrogen is 60%, so this needs to be taken into account.
A key element of the Sigma Team is the discussion around calculating optimum fertiliser recommendations, which is not always easy. GrowHow's unique N-Min & N-Calc service has been used within the Sigma Team to calculate growers' nutrient requirements: follow this link to find out more.
5. Enter your crop’s anticipated mid-flowering date
This will affect the timing and number of nitrogen applications.
6. Enter the number of applications
The calculator will work out the timing for your applications based on the crop’s ability to take up and use the nitrogen you apply.
7. Click the ‘Calculate’ button
You will be provided with a recommendation (that you can print) based on the information you have entered.
If you wish to change any of the information that you provided, simply enter the new details and click 'Calculate' to get a new recommendation.
This calculator is intended as a tool for managing canopy development and no consideration is included of what management might be used to extend canopy duration.
Useful links
Nitrogen Fertiliser Recommendations (Defra)
Nitrate Vulnerable Zones (Defra)
Web-based interactive map which brings together geographic information on key environmental schemes and designations in one place
Environmental issues and their interaction with Scottish agriculture
GAI assessment tool
Defra helpline: 0845 345 1302
An independent confidential telephone and email helpline is now available to answer technical queries from farmers, growers and advisers. Lines are open 7am to 7pm Monday to Friday and will be charged at a local rate.
Disclaimer
This calculator has been developed as a tool to help inform nitrogen application decisions, and Syngenta Seeds Ltd cannot accept any liability arising out of or in connection with the use of this tool. Any recommendation is given as a guide only. You should work with your agronomist when calculating N rates and timings, taking into consideration the fertility of the field. All applications should be carried out following best practice and working within any relevant legislation/regulations that may apply (see Defra link above for NVZs).
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