Factors Affecting the Performance of Seedlings and Ramets of Invading Grasses in an Established Ryegrass Sward

(1) Seeds and two-tiller ramets of Poa trivialis L., P. annua L., Agrostis stolonifera L. and Festuca rubra L. were planted into an established sward of Lolium perenne L. in both autumn and spring. Two levels of each of N and PK were applied to the sward. (2) Seedling mortality was greatest during the summer. Seedling survival after 1 year (spring planting) or 18 months (autumn planting) ranged from 0.4% to 38.5%, depending on species, sowing date and N level. Fertilizer N and spring-sowing both reduced survival in F. rubra and P. trivialis, but not in A. stolonifera or P. annua. (3) About 70% of surviving seedlings were small (2-10 mg) and grew little during the experiment. Fertilizer N and autumn sowing, especially in combination, increased the size of F. rubra and P. trivialis seedlings (c. 35 mg), but PK had no effect. (4) Ramet survival (21-95%) was much greater than seedling survival. As in the case of seedlings, fertilizer N and spring-sowing reduced ramet survival. (5) Surviving ramets were much larger (25-650 mg) than seedlings (2-40 mg). As in the case of seedlings, autumn planting and N application increased ramet weight, but PK fertilizer decreased it. (6) Differences between species in plant survival and plant size are discussed in the context of changes in the botanical composition of sown swards with age and management.