Physical Qualities of Fertilisers and Variable Rate Spreading – Interactions

Variable rate spreading of mineral fertilisers have been introduced during the last 5 few years to make it possible to reduce the used amount of fertiliser on each single field and farm. A second aim of doing variable rate spreading is to utilise a limited amount of fertiliser in a better way.

Keywords: Fertiliser spreading, variable rate, precision agriculture, fertiliser spreaders, fertiliser quality

Different technical solutions are on market based on more or less advanced methods for flow regulation of the mineral fertiliser distributors. The available technique seems to perform well when talking of regulating along the direction of travel. Across the field – transversal to direction of travel the distribution must be expected to be unsatisfactory.

All types of centrifugal spreaders, that are the most common types of fertiliser distributors in Europe, are more or less depending on correct setting of all parameters on the machine in order to be able to perform a even distribution across the tramlines. Basically all distributors are able to perform good spread patterns for certain fertilisers and flow rates but normally the settings have to be changed by the flow rate.

When doing variable rate spreading big changes in application rates may occur from one tramline to an other. If demands for different application rates are recognised a gentle change from level to level must be optimal. Gentle change from one fertiliser level to an other can only be achieved if the spreading pattern is triangular independent of the flow of fertiliser through the spreader.

Trials have shown that from no combination of fertiliser and distributor it has been possible to keep a optimum spread pattern independingly of the flow rate. Spread patterns change by the flow rate. Analyses of spread patterns from single discs show dependency of flow rate for all types of distributors but when simulations are made of total spread pattern from both discs it seems that spreader of centre line type are less sensitive to changes in flow rate than off centre types

In recent trials in which 5 fertilisers with different physical characteristics have been used

their are seen no clear relation between fertiliser and changes in spread pattern.

The trials have shown that if the goal of gentle change from one fertiliser level to and other transversal to travelling direction shall be reached the technology have to be developed in a way that the distributors can be regulated on more parameters (wane position, drop point, inclination etc.) than only the flow rate that is what can be done today. The regulation of more parameters must be individually adapted for the different types of fertilisers.

Krister Persson, Danish Institute of Agricultural Sciences, Research Centre Bygholm, Box 536, DK-8700 Horsens, Denmark.

28 pages, 4 tables, 17 figures, 8 refs.