The effect of slurry in the maintenance of the clover component in mixed grass/clover swards
Low input grassland systems depend on cheap fertiliser sources, such as clover or animal manures, to maintain sward productivity. Clover is a poor competitor for phosphate (P2O5) and potash (K2O), a mixed sward will therefore require adequate inputs of these nutrients. Nitrogen (N) leads to the suppression of clover. Recycling of cattle slurry would be followed by small N and P2O5 but large K2O effects. The K2O and P2O5 would be expected to have a beneficial effect on the clover while the N would be detrimental. Two investigations into the balance between these aspects of cattle slurry on clover in a mixed sward were performed. Slurry N led to clover suppression, this effect was strongest following spring applications. K2O had a beneficial effect on the clover, the P2O5 supplied had a small positive effect but was insufficient to fully meet the clover's requirements. There was a suggestion that these beneficial effects were strongest following summer applications. In addition to these fertiliser effects, non nutritional secondary effects often followed slurry with a deleterious action on the clover. These effects were most common following higher rates of slurry and summer applications. A further investigation was performed to establish the effect of varying clover variety and companion grass species on the clover's susceptibility to cattle slurry N and secondary effects and the nature of these effects following pig slurry applications. This revealed that clover's susceptibility to slurry N was inversely related to leaf size. No difference in secondary effects susceptibility arose with different clover varieties or companion grass species. Pig slurry was not accompanied by secondary effects. Slurry applications to mixed swards may therefore have positive and negative nutritional effects on the clover component but non nutritional secondary effects may also act with a deleterious effect on the clover.