ENHANCED ROOT NODULATION OF SUBTERRANEAN CLOVER (TRIFOLIUM-SUBTERRANEUM) BY RHIZOBIUM-LEGUMINOSARIUM BIOVAR TRIFOLII IN THE PRESENCE OF THE EARTHWORM APORRECTODEA-TRAPEZOIDES (LUMBRICIDAE)

In a greenhouse study, the effect of the earthworm Aporrectodea trapezoides on root nodulation in seedlings of subterranean clover (Trifolium subterraneum) was examined in the presence and absence of added Rhizobium leguminosarium biovar trifolii (strain NA30). When R. trifolii NA30 was inoculated into dung and placed on the soil surface, the total number of root nodules was five times greater (P<0.001) in the presence of earthworms than without earthworms and the number of nodules on the primary root of the plants 2-8 cm below the soil surface was 4 to 6 times greater (P<0.001) in the presence of earthworms. The additional nodulation did not affect plant growth or foliar N. When NA 30 was dispersed through the soil at the beginning of the experiment, the presence of earthworms did not influence the level of root nodulation. The presence of earthworms increased root dry weight by 20-30%, plant top weight by up to 125% (P<0.001), and foliar N by 5-25% (P<0.001). Surface-applied dung increased the dry weight of plant tops (2- to 3-fold, P< 0.001) but did not affect the concentration of foliar N (P<0.005).