초록 ▼

Ⅳ. 연구개발 결과 및 활용에 대한 건의
1. 연구결과
가. 농지배수의 측정 및 분석
1) 연구대상지역으로 경기도 여주군 가남면의 약 10ha의 지하수 관개지역과 충청북도 청원 옥산면의 약 40ha의 하천수 관개지역이다. 이 두 지역을 선정하여 필지단위와 광역단위로 각각 측정하였다.
2) 수위측정은 유입구 지역과 유출구 지역을 선정하고 자동수위계로 연속 측정을 하였다. 실측을 통한 수위측정자료와 유속계로 측정한 유속, 단면자료를 이용하여 유량으로 환산 후 수위-유량의 회귀관계식을 도출하여 수위에 따른 유량을 산

Ⅳ. 연구개발 결과 및 활용에 대한 건의
1. 연구결과
가. 농지배수의 측정 및 분석
1) 연구대상지역으로 경기도 여주군 가남면의 약 10ha의 지하수 관개지역과 충청북도 청원 옥산면의 약 40ha의 하천수 관개지역이다. 이 두 지역을 선정하여 필지단위와 광역단위로 각각 측정하였다.
2) 수위측정은 유입구 지역과 유출구 지역을 선정하고 자동수위계로 연속 측정을 하였다. 실측을 통한 수위측정자료와 유속계로 측정한 유속, 단면자료를 이용하여 유량으로 환산 후 수위-유량의 회귀관계식을 도출하여 수위에 따른 유량을 산정하였다.
3) 수질측정은 평상시, 강우기, 관개기, 비관개기 등으로 구분하고 월 2회 이상 측정하였고, 지표유출이 발생하는 강우시에는 강우초기부터 끝까지 시간대별로 실측(관개기 위주로 연 3회 이상)하였으며, 수질분석항목은 COD, T-N, T-P, EC, pH, 온도 등을 Standard Methods에 따라 분석하였다.
4) 웨어 및 수위계를 설치하여 논에서의 관개유입량과 농지배수량을 측정하였으며, 침투계를 이용하여 침투량을 실측하였고, 증발산량은 Pennman법을 이용하여 추정하였다.
5) 시비조건의 차(저감시비구, 표준시비구, 과잉시비구)에 따른 3개의 시험구에서 각각 유출량과 작물흡수량, 작물생장 및 수확량을 비교 분석하였다. 또한 각 시험구별 작물의 건조중량과 영양물질 함유율을 곱하여 작물 흡수율량을 산정하였다.
6) 용수와 강수의 수량 및 수질 측정을 통하여 유입부하량을 산정하였으며, 침투수와 지표배수의 수량 및 수질 측정을 통하여 유출부하량을 산정하였다.
다. 농지배수 관리 및 처리기법 개발
1) 자연정화방법에 의한 수질개선사례 조사와 오수처리, 비점원오염처리, 오염하천정화, 농지배수처리의 수질개선사례를 조사하였고, 현장실험을 통한 인공습지와 저류지, 정화논에서 적용가능한 자연정화방법들을 비교 분석하였다.
2) 소요면적의 이론적 설계방법과 기존시설의 자료를 응용한 경험적 설계방법을 이용하여 자연정화시설의 설계인자를 도출과 모형화를 시도하였으며, 농지배수처리에 최적인 식물을 선정하고, 자연정화 조성시 식물식재 및 조기 안정화방법을 연구하였다.
3) 자연정화시설의 처리효과를 유지하기 위한 관리 방법을 연구하였으며, 유지관리를 최소화시킬 수 있는 저기술형 운영방법을 연구하였다.
4) 인공습지와 저류지, 정화논의 연계관리 시스템을 연구하였으며 현장 실험의 결과를 이용하여 처리시스템을 연구하였으며, 저기술형으로서 유지관리를 최소화시킬 수 있는 자연정화시설을 선정하였다.
5) 시비량감소, 물꼬 높이 조절, 담수심 조절에 따른 관리기법을 현장실험을 통하여 연구하였으며, 유지관리를 최소화 시킬 수 있는 관리방법을 제시하였다.
6) 농지배수 모형화를 위한 모형을 개발하였으며, 논에서의 수문 및 수질예측을 위해 개발된 모형의 적용성을 필지논을 대상으로 검토하였다.
2. 연구결과의 활용방안
가. 농지배수 관리기법 개발
1) 농업비점원오염 관리대책에 정책자료 제공
2) 친환경적 농지배수관리기술의 농가보급
3) 합리적인 물과 영양물질수지 분석기법의 제공으로 농업생산성 증대
4) 농업비점원오염 연구 방법 확립
5) 효과적인 농업용수 관리방안 제시
나. 농지배수 처리기법 개발
1) 충분한 현장측정자료는 다른 농업환경정책에 기초자료 제공
2) 농업비점원오염의 자연정화처리기법 제공
3) 저류지 및 인공습지 등의 설계 및 시공 방법 보급
4) 유사한 다른 비점원오염 방지시설에의 적용
5) 논에서 오염배출 및 정화기능의 정확한 파악

Abstract ▼

IV. RESULTS AND APPLICABILITY
1. Water Balance
a. Following the initial irrigation, the ponded water depth varied over time with natural precipitation and irrigation, except during two fertilization periods for tillering (May and June) and at panicle initiation (July).
b. Water was forced t

IV. RESULTS AND APPLICABILITY
1. Water Balance
a. Following the initial irrigation, the ponded water depth varied over time with natural precipitation and irrigation, except during two fertilization periods for tillering (May and June) and at panicle initiation (July).
b. Water was forced to drain through weirs during the fertilization periods.
Generally, water inflow was supplied by irrigation for the first month, and thereafter the water level was maintained by rainfall and by drainage water from upper paddy fields.
c. Ponded water depth was not recorded after September because there was no significant rainfall or surface drainage.
d. The surface drainage occurred mainly during times of high rainfall and when there was forced drainage for culturing practices. The landscape at the experimental site has a gentle slope, and paddy fields are developed in cascade terraces. This allows drainage water from upper paddy fields to flow into the treatment plots and drain to the lower paddy fields successively.
e. Total water inflow to the paddy plots ranged from 1,180-1,920mm in groundwater irrigation area and 1,130-1,170mm in surface water irrigation area. Abut 45-60% of inflow was supplied by rainfall, and the remaining was from irrigation and upper paddy fields in about equal amounts.
f. Total water outflow was closely balanced to the total water inflow,And showing 1,160-1,900mm and 1,100-1,210mm for groundwater and surface water irrigation area, respectively. Where surface drainage and evapotranspiration removed the most water and deep percolation was relatively small.
g. The water balance in paddy fields depended predominantly on rainfall during the growing season, however, the rainfall received was less than that required for paddy rice culture. These results partly explain the importance of timely irrigation for rice production, as well as for total water requirement.
2. Nutrient Balance
a. When considering the overall mass balance for nutrients, among the three treatments, the SF (standard fertilization) treatment generally had a close balance between inputs and outputs, the EF (excessive fertilization) treatment had a nutrient surplus, and the RF (reduced fertilization) treatment had a deficit.
b. Rice yield was correlated with fertilization rate, implying that within the range of treatments considered, the harvest might be increased by adding fertilizer at rates above the standard practice. There was an apparent difference in the dry weight of leaf, shoot, and root, according to the change in fertilization rate. However, the dry weight of grain per plot displayed little difference among them. This indicates that a higher fertilization rate does not necessarily assure greater grain production.
c. Monthly variations of T-P and T-N input and output also occurred.
Most of the T-P input was supplied by fertilization at transplanting, and a small portion was supplied by irrigation. The T-N input was mainly supplied by the three applications of fertilizer. In addition, significant amounts of nutrients were supplied by precipitation and from the upper paddy field, and groundwater irrigation did not contribute much to the nutrient loading because of its relatively good water quality.
d. Although most of the nutrient output was attributed to plant uptake, nutrient loss by surface drainage was substantial, at about 10 % for T-N and 7 % for T-P. Nutrient loss by deep percolation was negligible.
3. Nutrient Net Outflow
a. Net outflow of T-N and T-P has trends of increasing with rainfall amount; this is most apparent for T-N. Generally, T-N net outflow tends to be negative when rainfall is less than 800 mm during the growing season, which implies that paddy fields can work as water purifying systems, rather than as pollutant discharging systems, as long as rainfall is relatively low. This is encouraging because annual rainfall is about 1,200 mm in Korea, and amounts below 800 mm during the growing season (May to October) are not unusual. Therefore, Korean paddy field might be classified as a landscape with the potential to purify water, from the perspective of T-N removal. This is contrary to the general idea that paddy rice cultivation always contributes significant amounts of nutrients to receiving water systems.
b. The data on T-P net outflow also demonstrates a similar pattern with T-N. Overall nutrient net outflow in Korean paddy fields increases as rainfall increases, therefore, the paddy field could be used in a beneficial manner to retain nutrients, rather than discharging them, as long as rainfall does not exceeding 800 mm during the growing period.
4. Applicability
a. Surface drainage constituted about half the total water loss surpassing evapotranspiration. Saving water by limiting inflow could be a possible strategy to reduce surface drainage, if rice production is not significantly affected. Less water inflow, however, needs careful field management because rainfall does not necessarily meet the water requirements for rice culture, and very accurate and timely water delivery would be required.
b. Raising the drainage weir height in diked rice fields can increase rainwater storage by reducing excess flow from the field and reducing rainfall excess through surface drainage. The weir height in this study varied, but was maintained at 10 cm most of the time, and it could be raised further to save rainwater and reduce surface overflow if necessary.
c. The other factor to be considered in reducing surface drainage is the irrigation practice for rice culture. Much of the surface drainage during the study period occurred for culturing purposes. Because forced midsummer drainage has been practiced mainly for fertilization, overall surface drainage could be reduced significantly with a minimized forced drain practice.
d. An important reason for reducing surface drainage water is the reduction of non-point source nutrient loading to receiving water bodies. In many countries, including Korea, water quality problems in rural areas are thought to be attributable largely to excessive fertilization and the resulting agricultural runoff. Nutrient loading from paddy fields occurs where the outflow water carries nutrients. Thus, reducing surface drainage water can reduce nutrient loading proportionally.
e. The fertilization rate itself did not affect nutrient loss by surface drainage. Therefore, paddy fields with even higher fertilization rates may be able to reduce nutrient loading substantially by minimizing surface drainage water outflow, mainly by water saving-irrigation and higher dike.
f. Considering the discussion above, water-saving irrigation, raising the drainage weir height in diked rice fields, and minimizing forced surface drainage are suggested as management measures to reduce nutrient loading from paddy fields. The possible benefits might include: 1) reduced irrigation water use and more efficient water resource allocation; 2) increased storage of rainwater with resulting flood prevention and groundwater recharge effects; and 3) reduced nutrient loss, i.e., reduced nutrient loading and fewer water quality problems.
g. These practices are suggested to reduce surface drainage outflow. They could save water and protect downstream water quality. However, deviation from standard practices might affect the rice yield and further investigations are recommended.
h. Wetland system demonstrated high performance in reducing nutrient concentration even in low concentration range such as agricultural drainage and impaired stream waters. It is also a cost effective and low-technology water purification system using natural resources, and provides ancillary beneficial habitats for wildlife with little maintenance efforts.
i. Pond system showed less effective than wetland system in nutrient removal, but it is expected to remove SS in heavy rainfall event.
Therefore, pond-wetland combined system is recommended to treat nonpoint source pollution loading from paddy fields.
j. Purifying paddy was the most effective for nutrient removal of agricultural drainage loading and it can also provide substantial biomass (rice) production. In contrast to the general viewpoint, rice culture in paddy fields may be beneficial from a water quality perspective. Paddy fields could retain nutrients within the system as well as produce rice unless rainfall is extreme.