Description:    Signals for determining rates for site-specific nitrogen fertilisation can be obtained via different sensors. Optical systems that record the nitrogen supply status of the plant via the reflected sunlight have been widely validated. In particular, ground based systems like the YARA N-Sensor have been put into practice. However, such sensors have disadvantages as they only record a small part of the crop population to the left and right of the tramline. This disadvantage is overcome by data obtained from the air (aircraft) or space (satellite). In the study presented, three systems—ground, aerial and space—were compared; of particular interest were data from the RapidEye-System, which has delivered data since 2009. The comparison showed that if the (well suited) Red Edge Inflection Point (REIP) has to be calculated for the determination of the site-specific amount of N-fertiliser, then the system based on satellite imagery would not be suitable for determining N-rates. In addition, the delivered data were shifted by 35 m and had to be corrected. The aerial system also delivered spatially shifted data, however the REIP can be calculated without a problem. Upon considering the costs and the weather dependant availability of the data, the ground based system was most suitable, despite its disadvantage of providing an incomplete crop recording; the aerial system, however, provides a good alternative if its costs can be reduced. The space system would be a good alternative if it were able to deliver all four wavelength ranges that are necessary for the REIP. Content Type Journal Article Pages 1-16 DOI 10.1007/s11119-012-9278-1 Authors P. Wagner, Agribusiness and Farm Management Group, Martin-Luther-University Halle-Wittenberg, Karl-Freiherr-von-Fritsch-Straße 4, 06099 Halle, Germany K. Hank, Agribusiness and Farm Management Group, Martin-Luther-University Halle-Wittenberg, Karl-Freiherr-von-Fritsch-Straße 4, 06099 Halle, Germany Journal Precision Agriculture Online ISSN 1573-1618 Print ISSN 1385-2256