Keyords: Ammonium nitrate, Urea, Mixed fertilizer, 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 fertilizer containing multiple forms of nitrogen.

A granular fertilizer has been assessed which provides urea, ammonium and nitrate nitrogen. The fertilizer consists of two components - one containing urea and dolomite, the other containing ammonium nitrate, ammonium sulfate and dolomite. Thus, the fertilizer also provides sulfur and magnesium as supplementary ingredients.

The efficacy of this fertilizer 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 fertilizer and is as good as CAN on the arable crops which were tested.

The fertilizer 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 fertilizer 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.