The effect of sward height on responses of mini-swards of perennial ryegrass/white clover to slurry application

The influence of sward height at the time of slurry application on sward responses to slurry was investigated using perennial ryegrass ( Lolium perenne )/white clover ( Trifolium repens ) mini-swards under greenhouse conditions. Pig slurry, cattle slurry and a fertilizer control were applied either to: swards cut 1 d before slurry application to heights of 2, 4 or 8 cm (CH2, CH4 or CH8); or to swards cut to 4 cm with regrowth intervals of 1, 4 or 8 d before slurry application (RI1, RI4 and RI8). Scorch, smother and growth of marked clover stolons and grass tillers were monitored after slurry application. Dry-matter yields of both species were recorded over two harvests. Electrolyte leakage from leaves was used to assess leaf damage. Both slurries increased leakage, which was greatest from clover leaves, with biggest increases caused by pig slurry. Yield responses to slurry application varied with plant species and sward height. Reduced grass growth after slurry application to long swards (CH8, RI4, RI8) was probably caused by greater smother. In short swards (CH2), grass leaf growth was not depressed following slurry application but grass yields were reduced. Ammonia volatilization losses may have been greater in both long and short swards, contributing to yield reductions. Yield responses to slurry were greatest in swards cut to 4 cm, 1 d before application.