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We conducted a pot trial to investigate the effects of soil cadmium (Cd) content, soil pH, soil type and soil chloride (Cl -) content on Cd uptake by garland chrysanthemum (Chrysanthemum coronarium cv. Kiwame-Cyuba) to improve predictions of plant Cd uptake. We concluded that predictions of plant Cd uptake should involve the following two procedures: (i) predicting the Cd concentration of the soil solution as a function of the chemical properties of the soil, (ii) predicting plant Cd uptake as a function of the Cd concentration in the soil solution. A unique hyperbolic relationship was observed between plant Cd uptake and total Cd concentration in the soil solution. The relationship was independent of soil type, soil Cd content and salinity treatment, and was explained by:where U Cd represents plant Cd uptake, [Cd T ] represents the total Cd concentration of the soil solution, and V p , V max and K m are constants. The Cd adsorption kinetics were investigated using the "monodentate coordination model," which enabled Cd 2+ activity in the soil solution to be explained by: log(Cd 2+ ) = log K mon + log Q Cd -pHlog C Cd , where K mon represents the equilibrium constant of Cd adsorption, (Cd 2+ ) represents Cd 2+ activity, Q cd represents the amount of Cd adsorbed, and C Cd represents the Cd adsorption capacity. The total Cd concentration in the soil solution showed a linear correlation with the Clconcentration in the soil solution. The effect of Clsalinity on the total Cd concentration in the soil solution was attributed to the formation of a cadmium-chloride complex (CdCl + ). For a more robust prediction of plant Cd uptake, there is a clear need for a simple method that can simultaneously determine the soil Cd concentration, the coefficient constant for Cd adsorption and the Cd adsorption capacity of the soil.

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The denitrification enzyme activity (DEA) and dissolved organic carbon (DOC) concentration in soil from the plow layer to a depth of 5 m were measured in an Andisol upland field to which several types of organic matter had been continuously applied for 20 years. The DEA was measured using the acetylene inhibition method. The DEA values at the plow layer were 0.15-0.16 mmol N kg -1 per day in the chemical fertilizer plots. Higher DEA values were detected in all the plots to which organic matter had been applied: 0.19 mmol N kg -1 per day in the rice straw manure plot and 0.81 mmol N kg -1 per day in the pig dung plot. In contrast, lower DEA values were detected in the non-nitrogen and non-fertilizer plots, that is, 0.02 and 0.03 mmol N kg -1 per day, respectively. The DEA values correlated with total organic carbon (TOC) values, total nitrogen (T-N) values, nitrogen mineralization rate, and available P measured using the Bray No.2 test; a highly significant correlation coefficient was obtained for the DOC (pH 5.5-6.0) calibrated with pH-DOC relations. In all plots examined, the plow layers showed the highest DEA values, and these dropped abruptly between depths of 0.5 and 1.0 m. At depths lower than 1.0 m, the DEA ranged from 10 -4 to 10 -5 mmol N kg -1 per day in all plots despite remarkable differences in DEA in the plow layers among plots. These observations suggested that the application of organic matter enhances the organic carbon content and DEA values in the plow layer, the extent of which is largely influenced by the variety and quantity of the applied organic matter. However, the properties of the applied organic matter did not influence the organic carbon contents or the DEA values at the subsurface. Furthermore, our investigations confirmed that subsurface denitrification did not substantially decrease the nitrate concentration during downward infiltration.