Trials currently underway on brassica crops have shown that variable-rate nitrogen management will only be of benefit if nitrogen is the main cause of variability in the crop canopy.
Trials carried out to date as part of AHDB's GREATsoils programme have not shown evidence that variable-rate nitrogen applications increase marketable yield or produce a more consistent crop size. The variability in crop canopy, measured by a drone, is likely caused by other soil or crop factors. Growers should consider the following:
Crop type - Crops with a high nitrogen requirement and where the majority of the nitrogen is applied to the growing crop are most likely to benefit from variable-rate application.
Field variability - The optimum rate is more likely to vary in fields where there is variation in soil type or texture.
Sensors - Canopy-sensing technology includes satellite imagery, tractor-mounted sensors and drones, each with different costs and benefits.
Decision-making - There are algorithms to calculate nitrogen application rates for some combinable crops but growers must decide by how much to vary the rate for others.
Measuring results - Consider how to decide whether varying the application rate has been successful. Split field comparisons may be useful.
A series of events about the GREATsoils programme are planned for 2017. For details, see horticulture.ahdb.org.uk.
For details on all AHDB Horticulture activity, see horticulture.ahdb.org.uk.