Rationale for Mixed Ammonium Nitrate – Urea Fertilisers and Assessment of Granular Products

Keyords: Ammonium nitrate, Urea, Mixed fertiliser, Grassland.

Nitrogen may be supplied in nitrate, ammonium or amide forms. Each has characteristic advantages and disadvantages but no single form is optimum under all conditions. This provides a rationale for a fertiliser containing multiple forms of nitrogen.

A granular fertiliser has been assessed which provides urea, ammonium and nitrate nitrogen. The fertiliser consists of two components – one containing urea and dolomite, the other containing ammonium nitrate, ammonium sulphate and dolomite. Thus, the fertiliser also provides sulphur and magnesium as supplementary ingredients.

The efficacy of this fertiliser has been assessed in field experiments on grassland and with selected arable crops. Comparisons with urea and calcium ammonium nitrate (CAN) have led to the general conclusion that the new formulation offers advantages in efficacy as a grassland fertiliser and is as good as CAN on the arable crops which were tested.

The fertiliser has also been subjected to a range of tests concerning spreading and storage properties. Spreading properties have been shown to be satisfactory but some problems of caking have been encountered in long term storage tests and further work is required to improve storage properties.

¹⁵N has been used to study the mode of action of the new formulation. It has been shown that an interaction can occur between ammonium nitrate and urea in terms of nitrogen uptake efficiency by ryegrass from a mixed ammonium nitrate/urea source. This feature may help to explain differences in efficacy which were seen in comparisons of the new fertiliser with CAN and urea in the field experiments.

M Kerry Garrett, Department of Agriculture, Belfast, Northern Ireland, UK.

36 Pages, 10 Figures, 11 Tables, 39 Refs.