Response of simple grass-white clover and multi-species pastures to gibberellic acid or nitrogen fertiliser in autumn

Herbage dry matter (DM) production, botanical composition and nutritive value of pastures were measured in response to the application of 24 g/ha gibberellic acid (GA; 60 g ProGibb (R)/ha) and 50 kg N/ha nitrogen fertiliser (N; 106 kg urea/ha) in autumn. Responses were compared for simple two species grass (perennial ryegrass or tall fescue)-white clover pastures and multi-species pastures where herbs (chicory and plantain), legumes (red clover and lucerne) and prairie grass were sown with the simple mixtures. Four weeks after application, the increase in DM yield averaged across pasture mixtures relative to untreated plots was 273, 104, and 493 kg DM/ha for GA alone, N fertiliser alone, and GA and N combined, respectively. Application of GA increased the white clover percentage in all pastures except simple tall fescue pastures. The percentage of herbs in multi species pastures was increased by application of N but not GA. Crude protein concentration was decreased by GA application in all pastures except simple ryegrass pastures. The results from this study show that it is important to consider the botanical composition of pastures when determining the effect of GA on DM yield and nutritive value.