Evaluation of Evapotranspiration in Different Paddy Soils Using Weighable Lysimeter Before Flooding Stage 511 Introduction 전세계적으로물공급량의 70% 가농업용수로사용되고있

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1 Korean J. Soil Sci. Fert. Vol.51, No.4, pp , 2018 Korean Journal of Soil Science and Fertilizer Article pissn : eissn : Evaluation of Evapotranspiration in Different Paddy Soils Using Weighable Lysimeter Before Flooding Stage Dong-Jin Kim, Kyung-hwa Han, Yong-seon Zhang, Hee-rae Cho, Seon-ah Hwang, Jung-hun Ok*, Kum-Sik Choi, and Jung-soon Choi Division of Soil and Fertilizer, National Institute of Agricultural Sciences, Rural Development Administration, Wanju, Jeonbuk 55365, Korea *Corresponding author: okjh@korea.kr A B S T R A C T Received: September 30, 2018 Revised: November 28, 2018 Accepted: November 29, 2018 Water is closely linked to agricultural productivity and is an essential resource for agriculture. Climate change and drought are causing water scarcity, and that has an enormous impact on agricultural productivity. Efficient water management methods are needed to prepare for water shortages. The lysimeter is well known as a facility for precisely measuring water and nutrient movement in the soil. Therefore, this study was conducted to investigate the evapotranspiration of different paddy soils using weighable lysimeter and to evaluate the relationship between the evapotranspiration estimated by weighable lysimeter and the reference evapotranspiration estimated by FAO Penman-Monteith equation and Hargreaves equation. This study was performed in lysimeter facility located at the National Institute of Agricultural Sciences, Rural Development Administration, and used lysimeter weight values and meteorological data measured from 1st January to 30th April in The daily evapotranspiration estimated by the lysimeter was ET LY, the reference evapotranspiration estimated by FAO Penman-Monteith equation was ET PM, and the reference evapotranspiration estimated by Hargreaves equation was ET HS. ET LY showed that loam (L) was higher than that of sandy loam (SL) and silty clay loam (SiCL). The accumulated evapotranspiration from 1st January to 30th April in 2018 was in the order of L (235 mm) > SL (231 mm) > SiCL (192 mm). Solar radiation showed a higher coefficient of determination (R 2 ) than mean temperature in the correlation between the meteorological data and ET LY. The relationship between ET LY and ET HS showed a relatively low coefficient of determination, whereas the coefficient of determination in the relationship between ET LY and ET PM showed relatively high fitness for SiCL (0.631), L (0.860) and SL (0.884). Precise measurement and management of soil moisture using lysimeter are expected to be possible. Keywords: Evapotranspiration, FAO Penman-Monteith equation, Hargreaves equation, Lysimeter, Paddy soil, Water scarcity The coefficient of determination (R 2 ) and linear equation between the ET LY and ET PM /ET HS estimated by the regression equation. Soil ET LY -ET PM ET LY -ET HS Linear equation R 2 Linear equation R 2 Silty clay loam y=0.853x y=0.535x Loam y=1.179x y=0.793x Sandy loam y=1.237x y=0.841x ET LY, evapotranspiration estimated by weighable lysimeter; ET PM, reference evapotranspiration estimated by FAO Penman-Monteith equation (Allen et al., 1998); ET HS, reference evapotranspiration estimated by Hargreaves equation (Hargreaves and Samani, 1985). C The Korean Society of Soil Science and Fertilizer. This is an Open Access article distributed under the terms of the Creative Commons Attribution Non- Commercial License ( which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

2 Evaluation of Evapotranspiration in Different Paddy Soils Using Weighable Lysimeter Before Flooding Stage 511 Introduction 전세계적으로물공급량의 70% 가농업용수로사용되고있으며, 물은농업에있어매우중요한자원이다 (UNESCO, 2001; Chartzoulakis and Bertaki, 2015; Saccon, 2018). 국내에서는수자원중농업용수의비율이 62% 를차지하고있다 (MOLIT, 2011). 전세계적으로기후변화는가뭄등의물부족을야기하고있으며, 물부족은농업환경을위협하고있다 (Pereira et al., 2002; Hanjra and Qureshi, 2010; Vargas-Amelin and Pindado, 2014). 농업분야에서는물부족대비를위해다양한물관리방안연구가진행되고있다. 관개수절약을위한논토양의투수량산출 (Chae and Kim, 2001), 지역별봄배추의관개기준설정 (Eom et al., 2010), 시설재배오이의적정관개시점평가 (Jeon et al., 2010) 등의연구결과가보고된바있으며, 농업에서는물절약을위한물관리방법이중요한수단이다. 농업환경에서효율적인물관리를위해서는기상조건, 기준증발산량등의기본자료가필요하다. 기준작물증발산량 (reference crop evapotranspiration, ET 0 ) 은수분부족이없는조건에서잔디등기준작물의증산과토양표면의증발을합한값이다 (Allen et al., 1998). ET 0 를산정하는다양한공식중 FAO Penman-Monteith (FAO P-M) 공식 (Allen et al., 1998) 이활용도가가장높고, 여러학자들에의해서 FAO P-M 공식의우수성이입증된바있다 (Jensen et al., 1990; Cai et al., 2007; Pereira et al., 2015). 국내에서는 Yoo et al. (2007) 이 FAO P-M 공식과빈도분석법을이용하여 10년빈도한발에대한기준증발산량을산정한바있다. Rim (2008a) 은 FAO P-M 공식을이용하여월별및연별기준증발산량추세를분석하였다. Lee and Cho (2011) 은일조시간과 FAO P-M 공식을적용하여우리나라 20개지점의기준증발산량을추정하였다. FAO P-M 공식에비해 Hargreaves 공식은기본기상자료만있으면비교적간단히기준증발산량을산정할수있다 (Hargreaves and Samani, 1985). 그러나 Moon et al. (2013) 은 Hargreaves 공식을이용할경우지역적기후특성에따라기준증발산량이과소또는과대산정될수있음을제시하였고, FAO P-M 공식과비교하여국내 71 개지점에대한지역별매개변수추정을통해수정된 Hargreaves 공식을제안하였다. Lee et al. (2008) 은경기만유역에서기상자료의결측또는부족지역에대하여 Hargreaves 공식의매개변수를추정하였다. Lee and Park (2008) 은국내 23개지점의 년동안의기상자료를토대로 Hargreaves 공식의보정계수를산정한바있다. 최근농업환경에서물절약을위한정밀한물이동측정이요구되고있으며, 이러한토양수분이동의정밀한측정을위하여교란되지않은자연상태토양을중량식라이시미터로측정되는연구가활발히진행되고있다 (Meißner et al., 2010). Kim et al. (2010) 은지하수위조절라이시미터에서보리, 밀, 조의수분이용효율을평가한바있고, Seo et al. (2016) 은중량식라이시미터를이용하여동절기동안논토양의물수지를평가하였다. 또한 Lee et al. (2017) 은라이시미터를이용한물관리방법에따른콩재배지에서양분용탈및흡수특성을조사하였고, Seo et al. (2017) 은중량식라이시미터를이용하여토성이다른토양에서토양수분함량추정모델적용을위한토양수분특성곡선을평가한바있다. 증발산량을산정하는것은효율적물관리를위한필수기초자료라할수있다. 따라서본연구에서는중량식라이시미터를이용하여토성이다른논토양의증발산량을조사하고, 증량식라이시미터를이용하여산출한증발산량과 FAO Penman-Monteith 및 Hargreaves 공식을이용하여산출한기준증발산량간관계적합도를평가하였다. 조사된결과는정밀한농업용수관리를위한기초자료로제공하고자하였다. Materials and Methods 연구지점및라이시미터구성 본연구는전라북도완주군농촌진흥청국립농업과학원 (National Institute of

512 Korean Journal of Soil Science and Fertilizer Vol. 51, No. 4, 2018 Agricultural Sciences, NAS) 토양수분이동실험동내의중량식라이시미터 (weighable lysimeter) 시설을이용하여수행하였다.

3 512 Korean Journal of Soil Science and Fertilizer Vol. 51, No. 4, 2018 Agricultural Sciences, NAS) 토양수분이동실험동내의중량식라이시미터 (weighable lysimeter) 시설을이용하여수행하였다. 연구지점은해발 33 m, 북위 35 49'29'', 동경 '46'' 에위치하고있다. 중량식라이시미터는자연토양구조그대로의교란되지않은토양을이용하였으며, 표면적 1 m 2, 깊이 1.5 m이다. 라이시미터를이용하여측정된데이터는 1시간단위로 data logger (UGTLog, UGT, Germanay) 에자동수집되었다. 라이시미터의구성은 Fig. 1과같다. 본라이시미터시설은 Seo et al. (2016) 과 Seo et al. (2017) 의연구에서사용된바있다. Fig. 1. The cross-sectional design of a weighable lysimeter (a: weighable monolithic lysimeter; b: load cells with 10 g accuracy; c: drainage measurement device; d: sensors for measurements of soil condition such as soil water tension, soil water moisture, temperature, and electrical conductivity; e: groundwater control device; f: automatic data logger; g: surface runoff measurement tool) (Seo et al., 2016; Seo et al., 2017). 시험토양및기상측정본연구에서는미사질식양토 (silty clay loam, SiCL), 양토 (loam, L), 사양토 (sandy loam, SL) 세종류의비교란논토양을사용하였다. 미사질식양토 ( 부용통 ) 는전라북도익산지역에서, 양토 ( 강서통 ) 와사양토 ( 강서통 ) 는전주지역에서각각채취하였다. 각토양의물리적특성은깊이별로토양입자분포 (particle size distribution) 와용적밀도 (bulk density) 를분석하였다. 토양입자분포는 Gee and Bauder (1986) 의비중계법을이용하여입자분포비율을산정한후미국농무부 (United States Department of Agriculture, USDA) 의토성삼각표 (soil texture triangle) 를이용하여토성을결정하였다. 용적밀도는 Blake and Hartge (1986) 의코아법을이용하였다. 시험토양의물리적특성은 Table 1과같고, 본시험토양은 Seo et al. (2017) 의연구에서사용된바있다. 시험에사용된기상자료는국립농업과학원중량식라이시미터시설에설치된기상정보시스템 (Weather Information System, WIS, STA Co., Korea) 으로측정하였다. 담수전비경작기간동안논토양의증발산량산정을위하여 2018년 01월 01월부터 2018년 04월 30일까지자료를활용하였다.

4 Evaluation of Evapotranspiration in Different Paddy Soils Using Weighable Lysimeter Before Flooding Stage 513 Table 1. Physical properties of soils used in this study. Soil Soil depth Bulk density Particle size distribution Sand Silt Clay Soil texture cm Mg m % Silty clay loam Silty clay SiCL Silty clay Silty clay loam Silty clay loam Loam Loam L Loam Loam Loamy sand Sand Sandy loam Sandy loam SL Loam Sandy loam Sandy loam Sandy loam SiCL, L, and SL are indicated silty clay loam, loam, and sandy loam in soil texture, respectively. 증발산량산정증발산량은 2018년 01월 01일부터 2018년 04월 30일까지수집된라이시미터자료와기상정보시스템자료를이용하여산정하였다. 본연구에서는라이시미터를활용한증발산량 (evapotranspiration, ET LY ), Allen et al. (1998) 이제안한 FAO (Food and Agriculture Organization of the United Nations) Penman-Monteith 공식에따른기준증발산량 (reference evapotranspiration, ET PM ), Hagreaves and Samani (1985) 가제안한 Hargreaves 공식에따른기준증발산량 (reference evapotranspiration, ET HS ) 을산정하였다. 라이시미터를활용한 ET LY 산출공식은 Klammler and Fank (2014) 가제안한방법을따랐으며, 그공식은 Eq. 1과같다. ET LY = P+I-D-R (Eq. 1) 여기서, ET LY 는증발산량 (mm day -1 ), P는강우량 (mm day -1 ), I는관개량 (mm day -1 ), D는지하배수량 (mm day -1 ), R 은지표유출량 (mm day -1 ) 이다. 일자마다누적된증발산량은누적증발산량 (accumulated evapotranspiration, ET A ) 으로하였다. ET PM 산정을위한 FAO Penman-Monteith 공식은 Eq. 2와같다. (Eq. 2)

5 514 Korean Journal of Soil Science and Fertilizer Vol. 51, No. 4, 2018 ET PM 는기준증발산량 (mm day -1 ), Δ는포화수증기압과온도곡선기울기 (kpa C -1 ), γ는건습계상수 (kpa C -1 ), u 2 는지상 2m 높이에서의풍속 (m s -1 ), R n 은이용가능복사열 (MJ m -2 day -1 ), G는토양열유동밀도 (MJ m -2 day -1 ), T 는일평균온도 ( C), e s 는포화수증기압 (kpa), e a 는실제수증기압 (kpa) 이다. ET HS 산정을위한 Hargreaves 공식은 Eq. 3과같다. max min (Eq. 3) ET HS 는기준증발산량 (mm d -1 ), K ET 는 Hargreaves and Samani (1985) 가미국캘리포니아주데이비스의 8년간기상자료를이용하여산정한값으로 이기본값이다. R a 는대기권밖의복사에너지를증발산량단위 (mm day -1 ) 로환산한값이며, 위도 (latitude) 와줄리안데이 (Julian day) 로계산할수있다. T max 는일최고온도 ( C) 과 T min 은일최저온도 ( C) 이다. 통계분석기상자료 ( 평균온도, 일사량 ) 와라이시미터를활용하여산정한증발산량 (ET LY ) 간관계, 대중적기준증발산량공식으로산정된 ET PM (FAO Penman-Monteith equation) 및 ET HS (Hargreaves equation) 와 ET LY 간관계의적합도를평가하기위하여회귀분석 (regression analysis) 을실시하였다. 회귀식의결정계수 (coefficient of determination, R 2 ) 는 SigmaPlot (SigmaPlot 10.0, Systat Software Inc., USA) 을이용하여산출하였다. Results and Discussion 기상자료분석및기준증발산량 (ET LY ) 기상정보시스템으로부터얻어진 2018년 01월 01일에서 2018년 04 월 30일까지의평균온도, 일사량, 강우량을 Fig. 2에나타내었다. 1월과 2월은강한추위로인하여영하온도를기록하는날이빈번하였으며, 3월부터서서히영상온도를회복하였다. 강우가발생한일자에는낮은일사량을보였으며, 평균온도증가와함께 3월부터일사량이서서히증가하였다. 이기간동안 10 mm이상강우를 11차례기록하였다. 라이시미터를이용하여산출한증발산량 (evapotranspiration, ET LY ) 과그누적증발산량 (accumulated evapotranspiration, ET A ) 은 Fig. 3과같다. ET LY 는양토 (L) 가대체적으로높게나타났으며미사질식양토 (SiCL) 는낮게나타났다. 미사질식양토 (SiCL), 양토 (L), 사양토 (SL) 의 ET LY 경향은비슷하였으며, 영상기온으로회복된 3월부터 ET LY 가증가하였다. 2018년 1월 1일부터 2018년 4월 30일까지의 ET A 는 ET LY 의결과가반영되어 L (235 mm) > SL (231 mm) > SiCL (192 mm) 순서로나타났다. 다만 1월 30일시점으로 SL과 SiCL의 ET A 순위가역전되었다 (Fig. 3). SiCL의높은점토함량으로수분보유력이높아증발량이낮은것으로보인다. Seo et al. (2017) 의연구에서도점토함량이높은토양이높은수분보유력을보였다. 또한 ET LY 가증가하기시작한 3월은영상온도회복으로잡초가발생하였으며 (Fig. 4), 잡초피복이증산량증가에영향을준것으로보인다. L의잡초피복도가상대적으로높았으며 (Fig. 4), 이는 L의증산량증가로이어져 ET LY 가높아진것으로보인다. L의낮은점토함량은증발량을증대시키고높은잡초피복도는증산량을증대시켜 L의증발산량이높은것으로추정된다. Anapalli et al. (2016) 는라이시미터를이용한연구에서옥수수생육발달에따라바이오매스와엽면적이증가할수록증발산량이증가함을보고하였다.

6 Evaluation of Evapotranspiration in Different Paddy Soils Using Weighable Lysimeter Before Flooding Stage 515 Fig. 2. Daily variation of weather factors in the study site from 1st January to 30th April in SiCL, L, and SL are indicated silty clay loam, loam, and sandy loam in soil texture, respectively. Fig. 3. Changes in daily evapotranspiration (ET LY ) and accumulated evapotranspiration (ET A ) estimated by weighable lysimeter from 1st January to 30th April in 2018.

516 Korean Journal of Soil Science and Fertilizer Vol. 51, No. 4, 2018 SiCL, L, and SL are indicated silty clay loam, loam, and sandy loam in soil texture, respectively. Fig. 4. State of different paddy soils before flooding stage from January to April in 2018.

2) 증발산량에 영향을 준 것으로 보인다. 평균온도 및 일사량을 ETLY와 회귀분석하여 결정계수 (coefficient of determination, R2)를 산출한 결과, 평균온도와 토양별 ETLY 의 R2는 SiCL (0.257), L (0.392), SL (0.416)로 낮게 나타난 반면, 일사량과 토양별 ETLY의 R2는 SiCL (0.

7 516 Korean Journal of Soil Science and Fertilizer Vol. 51, No. 4, 2018 SiCL, L, and SL are indicated silty clay loam, loam, and sandy loam in soil texture, respectively. Fig. 4. State of different paddy soils before flooding stage from January to April in 기상과 증발산량 (ETLY) 관계 2018년 01월 01일부터 2018년 04월 30일까지 강우량과 증발산량 (ETLY)을 비 교한 결과는 Fig. 5와 같다. 강우가 발생된 일자에는 미사질식양토 (SiCL), 양토 (L), 사양토 (SL) 모두 ETLY가 매우 낮았다. 강우가 발생된 일자는 일사량이 급격히 감소하여 (Fig. 2) 증발산량에 영향을 준 것으로 보인다. 평균온도 및 일사량을 ETLY와 회귀분석하여 결정계수 (coefficient of determination, R2)를 산출한 결과, 평균온도와 토양별 ETLY 의 R2는 SiCL (0.257), L (0.392), SL (0.416)로 낮게 나타난 반면, 일사량과 토양별 ETLY의 R2는 SiCL (0.654), L (0.819), SL (0.798)로 높게 나타났다 (Fig. 6). 평균온도보다는 일사량이 ETLY에 보다 많은 영향을 준 것으로 볼 수 있 다. 또한 강우가 발생된 일자에 일사량이 급격히 감소하여 ETLY가 낮아진 것과 동일하게 해석할 수 있다. Lee et al. (2012)은 라이시미터 관측 증발산량과 일사량이 높은 상관성 (R2=0.889)이 있음을 확인한 바 있다.

8 Evaluation of Evapotranspiration in Different Paddy Soils Using Weighable Lysimeter Before Flooding Stage 517 SiCL, L, and SL are indicated silty clay loam, loam, and sandy loam in soil texture, respectively. ET LY, evapotranspiration estimated by weighable lysimeter. Fig. 5. Comparison of rainfall and daily evapotranspiration (ET LY ) in different paddy soils from 1st January to 30th April in 증발산량과기준증발산량의관계기준증발산량산정을위하여 FAO Penman-Monteith (FAO P-M) 공식 (Allen et al., 1998) 및 Hargreaves 공식 (Hargreaves and Samani, 1985) 을사용하였고, 라이시미터를이용하여증발산량을산정하였다. 각각의기준증발산량및증발산량을 ET PM, ET HS, ET LY 라하였으며, 상호간적합도평가를위한회귀분석을실시하여결정계수 (coefficient of determination, R 2 ) 를산출하였다. ET PM 과 ET HS 간기울기는 (y=1.204x+0.264), R 2 는 0.887으로높은적합도를나타내었다 (data not shown). Rim (2008b) 의증발산량산정방법

9 518 Korean Journal of Soil Science and Fertilizer Vol. 51, No. 4, 2018 SiCL, L, and SL are indicated silty clay loam, loam, and sandy loam in soil texture, respectively. Fig. 6. Correlation between the mean temperature/solar radiation and daily evapotranspiration (ET LY ) using regression equations. 들간비교에서전국 21개지역을조사한결과 Hargreaves 공식이 FAO P-M 공식과유사함을밝힌바있다. 또한 Yoon and Choi (2018) 의기준증발산량공식별비교에서대구, 부산, 서울지역의 FAO P-M 공식과 Hargreaves 공식간 R 2 값이각각 0.983, 0.972, 0.867로상관성이높게나타났다. ET PM 과토양별 ET LY 간관계, ET HS 와토양별 ET LY 간관계를 Fig. 7에나타내었다. ET PM -ET LY (SiCL) 의기울기 (0.853) 는 1보다작으나 1에가깝고, R 2 는 0.631이다. ET PM -ET LY (L) 의기울기 (1.179) 는 1보다크나 1에가깝고, R 2 는0.860이다. ET PM -ET LY (SL) 또한기울기 (1.237) 는 1보다크나 1에가깝고, R 2 는 0.884이다. ET PM 과 ET LY 간관계는비교적높은적합도를나타내었다. ET PM -ET LY 간적합도가높은것은 FAO P-M 공식의우수성 (Jensen et al., 1990; Cai et al., 2007; Pereira et al., 2015) 으로설명이가능하다. ET HS -ET LY 간관계의 R 2 는 SiCL (0.407), L (0.638), SL (0.669) 로서비교적낮은적합도를나타내었다. Yoon and Choi (2018) 는기상자료결측과산정에따라기준증발산량을비교평가한결과, Hargreaves 공식은지역특성을고려한계수보정이필요함을언급하였다. 그러나 ET HS 가 ET PM 과비교적높은상관성이있으므로 Hargreaves

10 Evaluation of Evapotranspiration in Different Paddy Soils Using Weighable Lysimeter Before Flooding Stage 519 공식의적절한보정계수산정이이루어진다면간편한기준증발산량추정이가능할것으로판단된다. 더욱이라이시미터를이용하여산정된증발산량은 FAO P-M 공식에높은적합도를나타내어라이시미터를이용한증발산량의정밀한측정이가능할것으로기대된다. 이를통해재배지토양의정밀한수분관리가가능할것으로생각된다. SiCL, L, and SL are indicated silty clay loam, loam, and sandy loam in soil texture, respectively. ETLY, evapotranspiration estimated by weighable lysimeter; ETPM, reference evapotranspiration estimated by FAO Penman-Monteith equation (Allen et al., 1998); ETHS, reference evapotranspiration estimated by Hargreaves equation (Hargreaves and Samani, 1985). Fig. 7. Correlation between the ET PM /ET HS and ET LY using regression equations.

11 520 Korean Journal of Soil Science and Fertilizer Vol. 51, No. 4, 2018 Conclusions 본연구에서는중량식라이시미터를이용하여담수전비경작기간동안토성이서로다른논토양의증발산량을산정하였다. 그리고산정된증발산량과기상인자의관계성을조사하였고, 대중적으로사용되는 FAO Penman-Monteith 공식및 Hargreaves 공식을이용하여산정된기준증발산량과라이시미터를이용하여산정된증발산량간관계를조사하여적합도를평가하였다. 평균온도보다일사량이라이시미터를이용하여산정된증발산량과높은관계성이있는것으로나타났으며, 강우발생은일사량에영향을주어증발산량에도영향을주었다. 라이시미터를이용하여산정된증발산량은우수성이검증된 FAO Penman-Monteith 공식으로산정된기준증발산량과높은적합도를나타내었다. 따라서라이시미터를이용한토양수분의정밀한측정이가능하며정밀한토양수분관리가가능한만큼물절약형작물재배기술개발이가능할것으로판단된다. Acknowledgement This study was financially supported by a grant from the research project (No. PJ ) of National Institute of Agricultural Sciences, Rural Development Administration, Republic of Korea. References Allen, R.G., L.S. Pereira, D. Raes, and M. Smith FAO irrigation and drainage paper, No. 56, Crop evapotranspiration: guidelines for computing crop water requirements. Food and Agriculture Organization of the United Nations, Rome, Italy. Anapalli, S.S., L.R. Ahuja, P.H. Gowda, L. Ma, G. Marek, S.R. Evett, and T.A. Howell Simulation of crop evapotranspiration and crop coefficients with data in weighing lysimeters. Agric. Water Manag. 177: Blake, G.R. and K.H. Hartge Bulk density in methods of soil analysis. In: A. Klute (ed.). Method of soil analysis. Part 1. (2nd edition). American Society of Agronomy, Madison, Wisconsin, USA. Chae, J.C. and S.W. Kim Effect of soil texture on rice growth and paddy soil percolation under lysimeter condition. Korean J. Crop Sci. 46: Chartzoulakis, K. and M. Bertaki Sustainable water management in agriculture under climate change. Agric. Agric. Sci. Procedia 4: Eom, K.C., P.K. Jung, M.H. Koh, S.H. Kim, S.Y. Yoo, S.H. Park, S.O. Hur, and S.K. Ha Water saving irrigation manual of spring chinese cabbage. Korean J. Soil Sci. Fert. 43(6): Gee, G.W. and J.W. Bauder Particle size analysis. In: A. Klute (ed.). Method of soil analysis. Part 1. (2nd edition). American Society of Agronomy, Madison, Wisconsin, USA. Hanjra, M.A. and M.E. Qureshi Global water crisis and future food security in an era of climate change. Food Policy 35: Hargreaves, G.H. and Z.A. Samani Reference crop evapotranspiration from temperature. Am. Soc. Agric. Eng. 1(2): Jensen, M.E., R.D. Burman, and R.G. Allen Evapotranspiration and irrigation water requirements. American Society of Civil Engineers Manuals and Reports on Engineering. Practice No. 70. American Society of Civil Engineers, New York, USA.

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05서찬양(521~529)ok Korean Journal of Remote Sensing, Vol.28, No.5, 2012, pp.521~529 http://dx.doi.org/10.7780/kjrs.2012.28.5.5 Spatial Estimation of Priestley-Taylor Based Potential Evapotranspiration Using MODIS Imageries: