Production of reactive oxygen species in the lumen of the colon, a process that is influenced by nutritional factors, may be important in the etiology of colorectal cancer. Because research on humans in support of this hypothesis is lacking, the objective of this study was to measure the effect of different dietary compositions on the in vitro oxygen radical production in human feces. Over a period of 12 d, seven healthy subjects received a diet rich in fat (50%) and meat and poor in dietary fiber. After a period of 1 wk, they received a vegetarian diet poor in fat (20%) and rich in dietary fiber. At the end of each study period, feces were collected and analyzed for in vitro oxygen radical production with dimethylsulfoxide as the free radical scavenger. The mean hydroxyl radical production was 13 times greater in feces of subjects when they consumed the diet rich in fat and poor in dietary fiber [52.7 +/- 29.5 micromol/(g feces x h)] than when they consumed the diet poor in fat and rich in dietary fiber [3.9 +/- 3.9 micromol/(g feces x h); P < 0.05]. This difference was associated with a 42% higher fecal iron concentration when they consumed the first diet (7.0 +/- 19.2 micromol/g feces) than when they consumed the second (4.9 +/- 1.9 micromol/g feces; P < 0.05). The results of this study confirm that diets high in fat and meat and low in fiber markedly increase the potential for hydroxyl radical formation in the feces, which in turn may contribute to an enhanced risk of colorectal cancer.

It has widely been observed that the effect of elevating atmospheric CO 2 concentrations on rice productivity depends largely on soil N availabilities. However, the responses of ammonia volatilization from flooded paddy soil that is an important pathway of N loss and thus affecting fertilizer N availability to concomitant increases in atmospheric CO 2 and temperature has rarely been studied. In this paper, we first report the interactive effect of elevated CO2 and temperature on ammonia volatilization from rice paddy soils applied with urea. Urea labeled with 15 N was used to quantitatively estimate the contribution of applied urea-N to total ammonia volatilization. This study was conducted using Temperature Gradient Chambers (TGCs) with two CO2 levels [ambient CO2 (AC), 383 ppmv and elevated CO2 (EC), 645 ppmv] as whole-plot treatment (main treatment) and two temperature levels [ambient temperature (AT), 25.7℃ and elevated temperature (ET), 27.8℃] as split-plot treatments (sub-treatment) with triplicates. Elevated temperature increased ammonia volatilization probably due to a shift of chemical equilibrium toward NH3 production via enhanced hydrolysis of urea to NH 3 of which rate is dependent on temperature. Meanwhile, elevated CO 2 decreased ammonia volatilization and that could be attributed to increased rhizosphere biomass that assimilates NH4 + otherwise being lost via volatilization. Such opposite effects of elevated temperature and CO 2 resulted in the accumulated amount of ammonia volatilization in the order of ACET>ACAT>ECET>ECAT. The pattern of ammonia volatilization from applied urea-15 N as affected by treatments was very similar to that of total ammonia volatilization. Our results suggest that elevated CO2 has the potential to decrease ammonia volatilization from paddy soils applied with urea, but the effect could partially be offset when air temperature rises concomitantly.

Lim SS and Jung JW contributed equally (Co-first authors)Decomposition of compost applied to soils is affected basically by its biological stability; but, many other chemical properties of the compost may also influence compost organic-C mineralization. This study was conducted to investigate the principal substrate quality factors of composts that determine C mineralization of compost with similar stability degree (SD). Three composts samples with similar SD but different chemical properties such as pH, C/N, K 2 SO 4 -extractable C, and molar ratio of NH 4 + to NO 3 -were mixed with an acid loamy soil and CO 2 emission was monitored during the laboratory incubation for 100 days. Temporal pattern of cumulative compost organic-C mineralization expressed as % of total organic C (C % TOC ) followed double exponential first order kinetics model and the C % TOC ranged from 4.8 to 11.8% at the end of incubation. The pattern of C % TOC among the composts was not coincident with the SD pattern (40.1 to 58.6%) of the composts; e.g. compost with the lowest SD resulted in the least C % TOC and vice versa. This result indicates that SD of compost can not serve as a concrete predictor of compost mineralization as SD is subject not only to maturity of compost but also to characteristics of co-composting materials such as rice hull (low SD) and sawdust (high SD). Meanwhile, such pattern of C % TOC collaborated with pH, C/N, K 2 SO 4 -extractable C, and molar ratio of NH 4 + to NO 3 -of the composts that are regarded as chemical indices of the progress of composting. Therefore, for better prediction of compost mineralization in soils, it is necessary to consider both SD and other chemical indices (pH, C/N, and molar ratio of NH 4 + to NO 3 -).

BACKGROUND:Mathematical model such as GLEAMS have been developed and successfully applied to upland fields to estimate the level of pesticide residues in soil. But, the GLEAMS model rarely applied to the Korean conditions. METHODS AND RESULTS: To evaluate pesticide transport in soil residue using the GLEAMS model from pepper plot, Alachlor, Endosulfan, Cypermethrin and Fenvalerate were applied for standard and double rate. Soil sampling was conducted and decaying patterns of pesticides were investigated. Observed climate data such as temperature and irrigation amount were used for hydrology simulation. The observed pesticide residue data of 2008 were used for parameter calibration, and validation of GLEAMS model was conducted with observed data of 2009. After calibration, the K oc (Organic carbon distribution coefficient) and WSHFRC (Washoff fraction) parameters were identified as key parameters. The simulated concentrations of the pesticides except Fenvalerate were sensitive to K oc parameter. Overall, soil residue concentrations of Alachlor, Cypermethrin and Fenvalerate were fairly simulated compared to those of

No abstract