Nitrogen management is a crucial issue in terms of environmental and economical efficiency for winter wheat husbandry. Precision Agriculture in particular Remote Sensing, has been used to determine the variability of the crop. However, to be able to apply the required rate of nitrogen, the calibration of the data with the crop characteristics is critical. Satellite, airborne and ground based platforms are possible to use. Despite the presence of some commercial applications of the satellite and airborne techniques, the ground based systems offer advantages in terms of availability. The most common passive ground based remote sensing system in Europe is the Yara N sensor which has limitations in poor light conditions. Active sensors, using their own energy sources, are now available in the market e.g. the Crop Circle (Holland Scientific) and the Yara N sensor ALS. The aim of this work was to evaluate the active and passive ground based remote sensing systems for canopy nitrogen management in winter wheat. The work was divided into three sub-experiments. Two were conducted in Wilstead (UK) in 2005 and 2006, with the objective to determine the relationship between sensors output (NDVI) and crop (wheat) characteristics during the growing season and to evaluate their application in field management of winter wheat. The field experiment carried out in Oponice (Slovakia) in 2006 assessed three different management strategies (the real time, near real time and traditional nitrogen management). The results showed that both the active and the passive sensors determine the variability in shoot numbers and total nitrogen content of plants particularly in the early growth stages. The application of Nitrogen using these sensors in the UK saved 15kg N/ha (UK). The nitrogen saved in Slovakia was small (1.5 kg/ha). Use of the sensors enabled a reduction in nitrogen without a negative influence on yield, which increased the Nitrogen use efficiency. In addition to this there were potential environmental benefits through a 52% reduction of the residual Nitrogen in the soil in the UK. In Slovakia there was no significant overall reduction in the total nitrogen used; however, a different application rates was applied to 80% of the field. The overall cost of production in Slovakia using the sensors was increased by 5%. The cost of sensing in the UK was £11/ha which could be offset by the 15 kgN/ha reduction and a potential small increase of yield by 1%
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