Keywords: fertiliser spreading, fertiliser spread patterns, spinning disc, SP rating, wind tunnel tests, fertiliser flow characteristics.

The uniformity of fertilisers applied to arable crops has important implications for crop performance. A key component in the process of applying the fertiliser is the control of mean application rate and the uniformity of distribution across the treated swath. Because the physical properties of the fertiliser influence the performance of the spreader, test procedures (SP) and an indoor test rig based on a spinning disc spreader were developed. This paper describes recent developments in the procedures, including the use of standardised radial distribution patterns to determine compliance with the SP test, the analysis of flow onto the spinning disc, and investigations relating to particle shatter. Improvements in the rig to reduce particle-particle interaction and errors due to particle bounce are also described.

Compound and blended materials, as well as segregating during storage, handling, and in the spreading mechanism, can segregate in flight. A series of tests were carried out in a wind tunnel using a hopper to distribute material with a honeycomb sampling array positioned downwind to collect material. Mixtures and compounds with varying particle density were assessed. Although the results showed some effects due to particle bounce, the results with materials of known density were in reasonable agreement with theoretical analyses, thereby confirming the approach taken. It may therefore be possible to extend the existing test procedures to include nutrient segregation in flight and extend the range of products covered by the SP scheme.

Prof P C H Miller and Dr C S Parkin, Silsoe Research Institute, Wrest Park, Silsoe, Bedfordshire MK45 4HS, UK.

20 pages, 11 figures, 1 table, 15 references.