The improvement of centrifugal fertiliser spreaders for precision application control

Keywords: fertiliser, global navigation satellite system, disc spreaders, variable rate, section control.

Since the early 1990s there has been a growing concern about environmental implications associated with the use of fertilisers. In Europe, over 90% of granular fertiliser is distributed using centrifugal spreaders of the spinning disc type. The reasons for the popularity of centrifugal fertiliser spreaders include their affordable price, easy maintenance and a large working width of up to

54 m currently. However, the performance of centrifugal fertiliser spreaders is highly dependent on the properties of the fertiliser particles. This results in large differences in spread patterns, depending on the fertiliser type as well as the prevailing weather conditions (e.g. air humidity, wind). This dependency currently requires extensive experimental calibration of the spreader for each type of fertiliser. The end user understanding and correct use of centrifugal fertiliser spreaders have historically been encouraged by the use of spread charts and manuals derived from standardised certification of spreader technologies. Developments in spreader testing facilities have allowed manufacturers to identify the factors influencing spreading pattern and rapidly run reproducible tests. This had also led to an acceleration of technical development, providing farmers with greater choice and the potential to improve accuracy of spreading in the field and achieve better utilisation of fertiliser. This paper reviews recently introduced technologies and the results of relevant research on centrifugal fertiliser spreaders.

The development of technologies based on global navigation satellite systems (GNSS) and remote sensing/machine vision have provided an opportunity to exploit the variability of spatial and boundary characteristics that exists for agricultural fields. Manufacturers of agricultural machinery have responded with the development of variable rate technology (VRT) and section control for centrifugal fertiliser spreaders. As providers of farm management information systems (FMIS) continue to refine the management resolution strategies, it is essential for the end user to understand the performance characteristics of the GNSS and machine vision based control systems assembled from typical components for such control systems. In the past, a framework for the development of new standards for characterising and reporting the performance of VRT and section control has been suggested. Also, a revision of the EN 13739 standard has been suggested for the evaluation of transport delays and application pattern deviations. These suggestions demand new solutions for test platforms. During recent years, technologies such as the monitoring of solid fertiliser application patterns in three dimensional space, and re-radiating systems that provide re-radiation of the GNSS signals indoors, have been introduced. This paper reviews these technologies and discusses the practical relevance of certified tests of variable rate and section control systems based on GNSS, in relation to the need to improve end user achievement of even fertiliser distribution at sub-field level.

Michael Nørremark, Aarhus University, Faculty of Science and Technology, Department of Engineering, Aarhus, Denmark.

Mogens Nielsen, Yara Danmark Gødning A/S, Fredericia, Denmark.

Krister Persson, Aarhus University, Faculty of Science and Technology, Department of Engineering, Aarhus, Denmark.

34 pages, 9 figures, 55 references