Abstract
Slurries with different chemical characteristics were applied to the soil packed in Wagner pots. Used slurries were untreated cow manure slurry, aerated slurry, and anaerobically digested slurry. Plots treated with compost and chemical fertilizers were also installed for the control. The ratio of humic substances to the total carbon was higher in the order of digested slurry > aerated slurry, untreated slurry ≫ compost. These materials were mixed in the upper 9cm of the soil in the pots, while the amounts of carbon contained in these materials were adjusted to the same amount. Three consentive crops of Brassica campestris subsp. napus var. komatsuna were grown in these pots. Application of slurries increased the organic matter contents and CEC of the soil, as did compost. The number of fungi colonies and the weight of crop roots also increased remarkably due to the slurry application. The application of slurry also increased remarkably the amount of macro aggregate (> 250μm) in the soil, and the amount was larger in the order of digested slurry > aerated slurry > untreated slurry > compost. When macro-aggregate was disaggregated, both the particulate organic matter fraction (> 53μm) and mineral-associated organic matter fraction (< 53μm) increased in the slurry-treated plots, while the increase in the mineral-associated organic matter fraction was tremendous. The distribution of carbon among aggregates with different sizes revealed that the carbon was accumulated in the mineral-associated organic matter fraction in the macro-aggregates in the slurry applied plots, which was presumed to be due to the contribution of fine humic substances in the slurry. On the other hand, when compost was applied to soil, only the weight and carbon contents of particulate organic matter fraction in the macro-aggregate increased, but this did not lead to the formation of macro-aggregate. Weights of crop roots and the numbers of fungi colonies both showed positive correlations with the amount of macro-aggregate. Application of slurries also brought about the decrease in soil bulk density, and the increase in porosity for gravitational water and saturated permeability. As shown above, the application of slurries improved physico-chemical characteristics of soils, which was caused by the increase in mineral-associated organic matter fraction due to the humic substances contained in the slurries as well as due to the formation of macro-aggregates, due to the increase in the number of fungi colonies and the weights of crop roots. These mechanisms were different from the mechanism estimated in the case of compost application.
