Estimating Crop Biomass And Nitrogen Uptake Using Cropspectm, A Newly Developed Active Crop-canopy Reflectance Sensor
1J. Vollmar, 2S. Reusch, 2J. Jasper, 2A. Link
1. FarmLogs
2. Yara International, Research Centre Hanninghof, Duelmen, Germany
In-season variable rate nitrogen fertilizer application needs efficient determination of the nitrogen nutrition status of crops with high spatial and temporal resolution. A suitable approach to get this information fast and at low cost is proximal sensing of the light that is reflected from the crop canopy.
CropSpecTM is an active vehicle mounted crop canopy sensor. Using pulsed laser diodes as light source, the sensor is designed to look at the crop at an oblique view from a height of up to 4 meters in order to enable a large footprint for accurate measurements in various crops.
The objective of the research presented in this paper was to assess the agronomic performance of this newly developed sensor, i.e. the accuracy of biomass and N uptake estimations that can be achieved when using the instrument in different arable crops. Field experiments with increasing nitrogen rates have been conducted during the 2009 growing season in winter wheat, winter barley, spring barley, oats, oilseed rape and corn. Crop canopy reflectance was measured in frequent intervals throughout the main growing season (4 to 10 measurement dates per crop). Destructive plant biomass samples were taken at the measurement dates in order to determine the actual biomass growth, N concentration and N uptake of the crop. Sensor readings were related to these crop parameters, crop specific calibration functions were derived, and the capacity to predict the actual crop biomass and N uptake was investigated. The impact of different varieties and seed densities on the prediction quality was investigated in the winter barley and corn trials. Those were set up as multi-factorial experiments, with three varieties and two seed densities in winter barley and three seed densities in corn.
