The response of mini-swards of perennial ryegrass/white clover to simulated rainfall following slurry application

Perennial ryegrass/white clover mini-swards were used to determine whether sward responses to slurry were modified by subsequent simulated rainfall (SR). Combinations of two SR volume rates (6.5 and 13 mm), three SR timings (3, 24 and 48 h after slurry application) and two slurry types (cattle, pig) were compared with a fertilizer control (no SR). Scorch, smother and growth of marked stolons and tillers were monitored after slurry application and yields of both species were recorded. Slurry coverage of plastic squares indicated that smother may be greater on horizontally orientated leaves (clover). Reduced grass leaf growth and numbers of clover growing points in the week following slurry application were attributed mainly to smother, and possibly other phytotoxic effects of slurry. Reasons for the superior clover growth with cattle slurry are unknown, although its higher P and K content may have contributed. Timing of rainfall is important in influencing sward responses to slurry application. Results suggest that application of slurry may be most beneficial when it immediately precedes rainfall and that longer intervals between slurry application and rainfall reduce grass and clover growth through either greater ammonia loss or slurry negative effects.