Variable Nitrogen Application Based on Crop Sensing

Keywords: Variable rate technology, Remote sensing, N-fertilisation, Sensor, Spatially variable nitrogen, On-line sensor, Real time sensing

Although nitrogen (N) is the most interesting nutrient for spatially variable application with the highest economic and environmental potential, other nutrients (P, K and lime) are in the forefront of precision farming. The reason for this is that appropriate methods are still missing, which can correctly and quickly predict the N fertiliser requirement at the required high resolution and cost efficiency. For cost reasons, deep soil sampling on a grid basis is not regarded as a realistic approach for site-specific N management. Plant monitoring or sensing is seen as the future method to determine the crop’s N demand on a spatial basis. This is because, direct or indirect measurement of crop’s N status has the advantage that the actual plant-available N from the soil is indicated, whereas soil analysis measures an N potential which is thereafter influenced by several factors which affect final plant availability.

In 1987 Hydro Agri started to develop instant in-field methods to determine N fertiliser rate. Methods which were investigated started with the Nitrate Sap Test, the Hydro PrecisioN-Tester (PNT) and the PrecisioN-Sensor (PNS), a recently released system for tractor-mounted crop sensing. PNT and PNS indirectly determine the N fertiliser demand based on chlorophyll measurement by transmittance and reflectance respectively, and are calibrated in field trials for cereals.

The PNT, which is a small handy device used for field-specific uniform N application, has been shown to have a good performance regarding yield, grain quality and environment, and is already recommended in governmental-funded environmental programs. The PNS, a tractor-based remote sensing system, allows real-time spatially variable N application. Using the PNS, a large variation of the N rate required in a single field between 0 to 120 kg N/ha for the second N dressing for winter wheat has been found. Yield advantages were determined by comparison to uniform N application at the same N rate. Further advantages of spatially variable N application according to crop needs are: reduced Nmin content after harvest, higher and more uniform grain protein, less lodging, uniform ripening and reduced fungal infection.

J. Wollring, S. Reusch and C. Karlsson, Hydro Agri Deutschland GmbH, Hanninghof 35, D-48249 Dülmen, Germany.

28 pages,19 figures, 12 refs.