The effects of strategic nitrogen fertiliser application during the cool season on perennial ryegrass-white clover pastures in the Western Cape Province 3. Clover content
The influence of a single application of fertiliser N (0, 50, 100 and 150 kg N ha-1)applied in either autumn, early winter, late winter, early spring or late spring on the grass-clover balance in a perennial ryegrass-white clover pasture was studied over a three-year period. Responses were measured over two regrowth cycles five and ten weeks after the application of N treatments. Increased fertiliser N rates of up to 100 kg N ha-1 resulted in increasingly lower clover percentages. No differences in clover content were recorded between the 100 and 150 kg N ha-1 application rates five weeks after fertiliser N application. The effect of season of application was inconsistent due mainly to different initial clover contents and differences in environmental conditions amongst years. Partial recovery of clover content was noted at the second regrowth cycle but not to the same levels as at the 0 kg ha-1 treatment combinations. Fertiliser N did not reduce (P>0.05) total clover DM production (kg clover ha-1) over 10 weeks when applied in autumn and early winter. Clover DM yields were, however, reduced (P=0.05) when fertiliser N was applied during early and late spring, excluding 50 kg N ha-1 applied during early spring 2000. The application of 50 kg N ha-1 during the relatively normal rainfall years in 2000 and 2002 did not cause the clover content to drop below 30%. The application of 150 kg N ha-1 resulted in numerous treatment combinations where the clover percentage was less than 30%, the recommended minimum for the pasture to benefit from the clover component.