132 Chen et al. Sektion Futterqualität und Pflanzenbestand Root growth of ryegrass-white clover swards depends on sward age S. Chen, R. Loges, F. Taube University of Kiel, Institute for Crop Science and Plant Breeding, 24118 Kiel, Germany schen@gfo.uni-kiel.de 1 Introduction How the root system, the quantity as well as quality, differs among sward ages seldom received at- tention. It was assumed that the root system of older sward is likely to be more efficient, whereas better rooting characteristics of resown sward was expected either to perform a better yield in dry years or to have greater uptake / growth hence reducing nitrate leaching; but direct observation among sward ages is scant. Earlier study found that the sward age has close relation in soil N avail- ability in leys, which gives rise to difficulty in distinguishing sward age effect from the effect of N where ferilizer is added. The specialty in ryegrass-clover swards is that N addition will decrease the proportion of clover, who inherently had no response in terms of SRL, root production and root C/N ratio, which are all lower compared with that of perennial ryegrass [3], hence the effect of sward age and N would be confounded by the alternation in sward composition. After renovation of grass- land, applying organic N manure not only improved sward establishment and root standing biomass but also increase soil total C and total N compared with mineral fertilizer. On the other hand, grass- lands treated with slurry are also associated with increased respiration as well as fastened SOM mineralization involving the C/N and SRL [5], indicating the contribution of improved root stand- ing biomass to long-term C sequestration is limited due to alternation in the root quality. Interaction of sward age and fertilizer (if exists) may alter the sward composition which drives the C and N cycle in grasslands in an indirect way and the quantity and quality (e.g. chemical and mor- phological traits) of roots in a direct way, hence being a driving factor altering decomposition in the litter-soil continuum. In present work, we tested how root growth pattern (quanitative and qualita- tive parameters) responses to different sward ages and slurry level in concern with sward composi- tion. 2 Material and methods Two years’ field experiment was performed in managed perennial ryegrass (Lolium perenne L.) – white clover (Trifolium repens L.) swards (4 defoliation per year) nearby Kiel to investigate effect of sward age (1-, 2-, 5-years’ old sward and permanent grassland control, referred as Y1, Y2, Y5 and PG then) and cattle slurry (0 or 240 kg N ha -1 y -1 , referred as N0 and N1 then) on root growth. Total root production was estimated by accumulative root biomass in 4 sequential ingrowth core sets [1] in all swards with special concern of specific root length (SRL, m g -1 ) and root in-season turnover which was calculated as difference between BNPP and retained root biomass in a long- term ingrowth-core in Y1 and Y5 to evaluating fine root lifespan. Belowground biomass (BGB) as well as sward composition (classified into grass, clover and herbs) were observed at each defolia- tion day. Results was first examined in respect to sward age, slurry and sampling dates in three-way ANOVA; while no interaction of sampling date with other factors the annual weighted means of pa- rameters were compared in two-way ANOVA. Experimental year was considered as random effect