The performance of a white clover based dairy system in comparison with a grass/fertiliser-N system. I. Botanical composition and sward utilisation

The performance of a white clover based dairy system in comparison with a g rass/fertiliser-N system was studied during three years. Mixed swards of pe rennial ryegrass and white clover were established successfully through res eeding or sodseeding. Both systems had 59 dairy cows and a milk quota of 45 0 tonnes per year. The allocated areas of 41 ha for the grass/clover system and 34 ha for the grass/fertiliser-N system were based on an expected yiel d difference of 15 to 20% in favour of the grass/fertiliser-N swards. The g rassland management consisted of a rotational grazing system with one to th ree silage cuts per paddock, depending on herbage growth. The average white clover ground cover was 31, 30 and 26% in the three subsequent years, but with a large variation between seasons and paddocks. Season, clover variety and sward age x clover variety explained 28% of the variance in clover cov er, but 72% remained unexplained. Grass/clover and grass/fertiliser-N sward s received 69 and 275 kg N ha(-1) year(-1), respectively, including the ino rganic N from applied cattle slurry, but excluding animal excreta during gr azing. The average annual net DM yield from grass/fertiliser-N swards was 1 0.8 t ha(-1) and from grass/clover swards 10.1 t ha(-1). The yield differen ce occurred mainly in spring, but was smaller than expected, causing a rela tive silage surplus for the grass/clover system. The OMD of grass/clover wa s slightly, but consistently, higher than that of grass-only, while the CP concentration of grass/clover was consistently higher from July onwards. It is concluded that mixed swards of perennial ryegrass and white clover can function as a sound basis to produce good quality herbage for a dairy syste m.