Three pedons were surveyed to clarify chemical properties and mineralogical characteristics of tea garden soils in the Cheju Island, Korea. The results are as follows: 1) Soil color of the soils in the Cheju Island were black or brownish black. The gravel contents of the soils in the three pedon were very high (10-70%), and the soil textures were sandy loam. 2) All three pedons surveyed were classified into Andosols, which had dark colored and high humic A horizons, the phosphate absorption coefficients of 1500 or more and large amounts of acid oxalate extractable Al and Fe (Al_o and Fe_o). 3) The soil pH (H_2O) under the tree crown were lower than those in the inter-row. The exchangeable Al were high in the soil under the tree crown, reflecting low pH of those soils. Furthermore, the exchangeable cation was low in the soil under the tree crown, because of the strong leaching and the lacking of dolomite application. 4) It was estimated that the tea garden soils in the Cheju Island contain not only allophane but also chrolite, 2:1-2:1:1 intergraded minerals and 1:1 type clay mineral by X-ray diffraction analysis.

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To identify anthropogenic sources of nitrogen in the shallow groundwaters used in the Noda City, Chiba Prefecture, stable isotope composition of nitrogen (δ^<15>N) and sulfur (δ^<34>S) as well as the nitrate concentration in twenty-one groundwaters from wells in the fields were determined. The high proportion of Cl^-+SO_4^<2->+NO_3^- in the total anion concentration suggests strong influence of human activities on the groundwater quality. Groundwaters with high NO_3^--N concentrations (>15.0mg-N L^<-1>) were mainly found in the farm land area. The δ^<15>N values of the main fertilizers used in the studied area (-1.4 to +4.3‰) and those of the domestic detergents (-2.9 to +3.6‰) were similar, making the distinction of NO_3^- derived from the two sources difficult. The δ^<15>N values of NO_3^- in the groundwaters ranged from +2.5 to +10.3‰. Low δ^<15>N values of groundwater NO_3^- in the farm land area suggest that the NO_3^- contamination was caused by farming with ammonium-containing fertilizers and compost, and by domestic sewage. In the Noda area including the residential districts, groundwater samples were strongly contaminated by domestic pollutants. As the δ^<34>S values of chemical fertilizers and domestic detergents used in the studied area were also similar (ranging from -2.7 to -0.4‰ and from -4.2 to -0.7‰, respectively), it was difficult to distinguish these sources using δ^<34>S values. The δ^<34>S values of sulfate in the groundwaters were mostly in the range from +1.1 to +7.8‰, and suggest that the contaminant sulfur was also originated from chemical fertilizers, and domestic sewage and compost. These results demonstrate that simultaneous analysis of δ^<34>S and δ^<15>N is very useful for reliable estimation of the origin of NO_3^- in groundwater.

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The dynamics of nitrogen and carbon in the field with continuous application of sewage sludge compost since 1978 were investigated using ^<15>N and ^<13>C natural abundance techniques. Barley (Hordeum vulgare L.) and corn (Zea mays L.) have been grown in an Andsol field in winter and summer, respectively, with composts or chemical fertilizers. Based on the analysis of natural abundances of nitrogen and carbon isotopes in crops and soils, following three were concluded. (1) A part of the sewage sludge compost applied to the field was quickly decomposed and mineralized during the early short period, and the other part was remained in the soil for a long time and slowly decomposed and mineralized. By application of the sewage sludge composts, the δ^<15>N values of the soil were increased while the δ^<13>C values were decreased. (2) The nitrogen mineralized from the sewage sludge compost was absorbed first to leaves and finally allocated to the ears. The carbon dioxide derived from the sewage sludge compost was significantly fixed into barley but not into corn by leaf photosynthesis of CO_2 near the soil surface. (3) The organic carbon from the sewage sludge left in soil was estimated to be 35-44% of soil organic carbon after continuous application of sewage sludge compost for 26 years.

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A series of field experiments was conducted to test whether nitrogen (N) supplied as compost or as chemical fertilizer similarly affected the quality of Japanese radish and sweet corn. Cattle manure compost (C/N=8.4-10.4) was applied at rates of 0, 2 and 4kg m^<-2> and chemical fertilizer N at two (sweet corn) or three (Japanese radish) levels from 0 to 12g N m^<-2> as ammonium sulfate. Soil nitrate N increased slowly from the date of compost application in the plots that received only compost, but increased rapidly after application of chemical fertilizers. In a bare fallow area the average value of soil nitrate N (in the plow layer) throughout the plant growing season was 22mg kg^<-1> dry soil in the plot of 4kg m^<-2> compost, 40mg kg^<-1> dry soil in the plot of 12g N m^<-2> chemical fertilizer, and 51mg kg^<-1> dry soil in the plot of 4kg m^<-2> compost+12g N m^<-2> chemical fertilizer. Soil nitrate N was integrated and divided by the number of days from the date of application to harvest and compared with the amount of N uptake by sweet corn; they were positively correlated irrespective of N source. This may indicate that the amount of N uptake was determined primarily by the amount of nitrate N supplied by compost in addition to chemical fertilizer. Sugar content of Japanese radish and sweet corn, and the content of ascorbic acid of Japanese radish, decreased with increased N uptake. Plant products of all plots were harvested on the same day; those products that had received compost as the N source had lower sugar and ascorbic acid contents than those that received chemical fertilizer only, even though the N uptake was same. However, the suitable harvest time for sweet corn was the time when the grain had the highest sugar content, and this advanced with increased compost application. The relationship between sugar content and N uptake was the same irrespective of N source, when compared at the suitable harvest time for each treatment. So we concluded that the sugar content was determined by the amount of nitrogen uptake regardless of the N source (compost application or chemical fertilizer application). The suitable harvest time for radish may be determined by root weight. It is considered that the quality of radish was better to be compared at the time when radish in each treatment had the same size.

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