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BACKGROUND: With increasing public awareness to environment-friendly agriculture, many efforts have been run to develop organic farming technologies in Korea as of late 90s. The objective of this study was to investigate the effects of different organic farming practices on soil chemical properties and water quality in paddy fields. METHODS AND RESULTS: Total nitrogen (TN) and total phosphorus (TP) were monitored for a two-year period (2006 to 2007) from the study organic paddy fields located in Wan-ju, Jeonbuk Province in Korea. TN and TP of organic paddy water were gradually increased for 2~3 weeks after organic manure application and then gra- dually decreased afterward. The overall variation of TP in the paddy fields was much greater than that of TN. The phosphorus content in organic paddy field appeared to increase with the organic farming period. CONCLUSION(s): This indicates that long-term organic farming is likely to cause phosphorus accumulation in soils and increase vulnerability to rainfall runoff. Thus, appropriate phosphorus management needs to be imple- mented, particularly, to reduce excessive phosphorus supply owing to nitrogen-based determination of organic manure application amount.

Energy efficiency and nutrient balance are good methods for environmental assessment of the environmentally-friendly agriculture. The objectives of this study were 1) to estimate the energy efficiency and nutrient balance of the organic rice farming, and 2) to suggest a solution to improvement the energy efficiency and nutrient balance. The set of estimation was performed at the organic rice farming area (8.9 ha) in Wanju-gun during the paddy cultivation period from 2006 to 2007. The organic farming complex consists of four weeding methods using 1) duck, 2) apple snail, 3) duck and apple snail and 4) hands and machinery. Results from this estimation should that the organic rice farming area was less efficient than conventional rice farming. The efficiency of organic farming area in 2006 was higher than in 2007. For the calculation of the nutrient balance, the N, P and K contents of input materials (cattle manure, milk vetch, mixed oilcake, rice bran, rice straw and barley straw) and output (farm products) were analysed. Annual environmental loads of N, P2O5 and K2O were estimated at 4.4 kg/10a, 13.8 kg/10a and 14.5 kg/10a, respectively. Cattle manure had the largest portion among the inputs items and nutrient concentration of cattle manure was high. Thus energy efficiency and nutrient balance depend on cattle manure input. Therefore it is necessary to control the manure input to improve the efficiency of organic rice farming.

This study was conducted to identify the characteristics of non-point pollutants discharge in a small agricultural watershed during farming season. for this purpose, the Neoungchon watershed in Goesangun was selected as a typical agricultural area. Runoff and water quality data in the stream, the domestic sewage and the precipitation of the watershed were analyzed periodically from June 1 to November 6 in 2004 and pollutant loads were estimated. As a result the mean concentrations of BOD, SS, TN and TP in the stream were 3.0, 76.7, 8.7, 0.16 mg/L in rainy season and 2.4, 10.0, 3.5, 0.11 mg/L in dry season respectively. Daily discharge of non-point pollutant occurred above of 95% in rainy period. Measured pollutant loads in the watershed were of T-N and of T-P, within the range of other research results. Effluent loads based on guideline of total pollutant to stream management of MOE (Ministry of Environment) were less than delivery loads since the guideline could not reflect the agricultural practices, geomorphic and meteorological characteristics in an agricultural watershed.

A prototype surface flow constructed wetland was built in the upstream area of reclaimed tidal lands to improve the water quality of Lake Sihwa by treating severely polluted stream water. In this study, a tracer test using rhodamine-WT was performed to investigate the flow characteristics and to quantify the observed hydraulic residence time (HRT) for a high-lying cell in the Banwol wetland of the Sihwa constructed wetland. The tracer test indicated that even if flow was mainly observed in the open water area of the Banwol wetland, water flowed continuously in the vegetative area and there was no dead zone. The calculated HRT (51.3 hrs), calculated by dividing the wetland volume by the wetland inflow, exceeded the observed HRT (38.7 hrs), since the short-circuiting of flux resulting from irregular topography and vegetation was not reflected in the calculated HRT. The exit tracer concentration curves were reproduced well by both the plug flow with dispersion and tanks-in-series models, indicating that the performance of the Banwol wetland can be estimated accurately using these models.