Overwintering of Trifolium repens L. and succeeding growth: Results from acommon protocol carried out at twelve European sites

A common experimental protocol was followed at 12 sites in Europe to study the development of two clover cultivars (AberHerald and Huia) grown in asso ciation with a ryegrass cultivar throughout their annual cycle. The duratio n of the experiment was between 1 and 3 years at each site. Detailed inform ation about the morphogenesis and carbohydrate reserves of white clover dur ing winter and the subsequent productivity of clover plants during the grow ing season was collected. Yield of the companion ryegrass was also measured at several harvests during the growing season and grass tiller density was recorded several Limes during winter, There was wide variation among sites and between years in climatic conditions, in the growth characteristics an d chemical composition of the two cultivars, and in the tiller density of t he ryegrass. The relative performance of the two cultivars varied among sit es but AberHerald generally outperformed Huia, Major changes in plant chara cteristics (morphology, population size. chemical composition, etc,) occurr ed during overwintering. This paper presents a preliminary analysis of the effects of site. clover cultivar and sward age (years) on various plant cha racteristics. It is established that the data provide a unique basis for mo delling the effects of a wide range of environmental conditions and plant p roperties on the performance of white clover in mixed swards. A modelling a pproach that seeks to replace site and year by climatic variables character izing each site by year combination is developed in two companion papers. ( C) 2001 Annals of Botany Company.