Effects of earthworm inoculation upon the root growth of direct drilled cereals.
Normal field populations of deep-burrowing or shallow-working earthworms were inoculated into small plots that had been sterilized with dichloropropane-dichloropropene on a site that had been directly drilled with cereals for 6 successive yr. Inoculation with deep-burrowing spp. (Lumbricus terrestris and Allolobophora longa) significantly increased barley plant populations and the wt. and depth of roots and the ht. and amount of foliage. Most of the straw debris on the soil surface was incorporated into the soil in the earthworm-inoculated plots, compared with very little in plots with no earthworms. Yield was also increased significantly by earthworm inoculation. In box experiments comparing the influence of natural and simulated earthworm burrows on root growth it was shown that, although the provision of channels for roots to grow was important, the improved root growth was also partially due to the lining of the burrows with more available nutrients than the surrounding soil. Other experiments demonstrated that the N from dead earthworms was insufficient to account for increased root growth. Ways of encouraging the build-up of earthworm populations in direct drilled land are discussed.