Environmental effects, in particular of rainfall, on the digestibility of dry mature subterranean clover

Abstract

In vitro dry matter digestibility (DMD) was determined in dry mature subterranean clover (Trifolium subterraneum L.) from a field survey and from 2 field experiments. From the survey, the range in DMD between sites for individual cultivars was 9 percentage units (45-54%) through to 25 percentage units (35-60%). Differences in pattern of end-of-season rainfall over 3 years (experiment 2) resulted in changes in DMD ranging from 4 to 11 percentage units for the 4 genotypes examined. The 3 instances of midsummer rains were followed by decreases of 5-16 percentage units in DMD (experiments 1 and 2). The greatest range in DMD found in our study was 29 percentage units (37-66%). In the 2 cases of genotype x environment interaction (1 in each experiment) the key factors appeared to be genotype flowering (or senescence) time together with end-of-season rainfall pattern. Genetic differences can be caused by 'haying off effects with late genotypes, and by marked leaching effects with early genotypes due to prolonged or intense end-of-season rains. Such effects are likely to override most intrinsic genetic differences other than those due to flowering time. We suggest that environmental effects on DMD are sufficiently large and important to warrant further detailed study, and that an adequate understanding of such effects is needed for appropriate management practices (e.g. supplementary feeding) and for the identification of genotype differences.