Effect of earthworm surface casts upon maize growth

Ground soil and earthworm surface casts of known chemical composition were mixed at cast to soil ratios of 0:100, 20:80, 40:60, 60:40, 80:20 and 100:0 . Maize(Zea mays) was grown in 10 kg of each mixture in a pot experiment. E ach treatment was replicated live times. The maize was harvested at 70 days after planting and numbers of standing and green leaves and dry mass of ab oveground biomass were recorded. The percentage of casts in the mixture had no significant effect upon numbers of leaves. Aboveground plant dry mass w as significantly affected (P < 0.0001) by cast:soil ratio and had a logarit hmic (P < 0.0001, r(2) = 0.55 at 1, 23 d.f) positive response to cast perce ntage in the mixture at 20% and above. Aboveground biomass in the 60% cast mixture was twice that in the 100% soil. Yet total amounts in the 60% cast mixture of exchangeable Ca2+, Mg2+, K+ and total N were respectively 1.36, 1.48, 1.13 and 1.35 times those in 100% soil. Nutrients in ground casts mig ht be more available to plants than those from soil.