EFFECT OF MIXED CROPPING ON THE NITROGEN NUTRITION AND GROWTH OF PERENNIAL RYEGRASS AND WHITE CLOVER

The nitrogen nutrition of cut white clover and perennial ryegrass mono cultures and mixtures sown in adjacent rows was studied during 2 sprin g regrowths, with and without a nitrogenous fertilizer supply, using t he nitrogen dilution curve method. Ryegrass shoot biomass per row and shoot nitrogen concentration increased in the mixture compared with th e monoculture. For a similar ryegrass shoot biomass, the nitrogen conc entration was higher in the mixed than in the pure ryegrass. Perennial ryegrass shoot nitrogen levels increased significantly in the mixture , but this effect was weaker after nitrogen fertilization. A sub-trial where clover and grass shoots and roots were separated by vertical pa rtitons, or mixed, indicated a significant increase in the nitrogen nu trition level of ryegrass at the final cut, due to root interaction be tween both species. The decline in leaf nitrogen concentration of whit e clover during regrowth was partly due to a decline in the lamina/pet iole ratio. Furthermore, when the sward total leaf biomass increased, clover lamina nitrogen concentration declined according to a power fun ction. At a given total leaf biomass, clover lamina, nitrogen concentr ation was not significantly affected by association with ryegrass. Nev ertheless, the clover content of the mixed sward was negatively correl ated with ryegrass nitrogen nutrition level.