Influence of Biochar and Earthworms on Plant Growth, Fusarium Crown and Root Rot, and Mycorrhizal Colonization of Asparagus

Biochar and earthworms were two treatments examined alone and in combination for their influence on increasing asparagus root health in old asparagus soils by reducing Fusarium crown and root rot (FCRR) and increasing colonization by vesicular arbuscular mycorrhizae (VAM). Earthworms (Lumbricus terrestris) were added to pots filled with soil infested with the pathogenic Fusarium spp. and planted with asparagus. Earthworm activity was associated with a 66% increase in root weight and a 50% reduction in FCRR disease. When biochar, a fine-grained activated charcoal, was added to pots at 0, 1.6, and 3.2% (w/w), planted to asparagus, and then drenched with a mixture of the inhibitory allelochemicals (caffeic, coumaric, and ferulic acids), root weights increased and FCRR disease ratings declined with increasing rates of biochar. The allelochemicals alone did not affect plant growth or FCRR, but reduced VAM colonization. However, biochar reduced the negative effect of the allelochemicals on VAM. A series of studies examined the combination of earthworms and biochar in soils heavily amended with dried asparagus residues. When these treated soils were later planted to asparagus, no interactions were observed between biochar and earthworms on growth or FCRR. In autoclaved soils, biochar reduced root weights. Earthworms were not effective in the studies possibly due to the high rate of residues added. The beneficial effects of both treatments appear to directly influence the pathogenic and beneficial microbes, their interactions with each other, and with the allelochemicals and plants roots, possibly by interrupting signals between roots and microbes.