한국환경농학회지제27권제1 호 (2008) Korean Journal of Environmental Agriculture Vol. 27, No. 1, pp. 66-71 연구보문 논토양에서석탄회와석고의혼합제를활용한인산유출저감 이용복 1) 이슬비 2) 오주환 2) 이창훈 3) 홍창오 2) 김필주 2,4)* 1) 농업과학기술원, 2) 경상대학교대학원응용생명과학부, 3) 작물과학원영남농업연구소, 4) 경상대학교농업생명과학원 (2008년 2월 15 일접수, 2008년 3월 26 일수리) Effects of Fly Ash and Gypsum Mixture on Reducing Phosphorus Loss from Paddy Soil Yong Bok Lee 1), Seul Bi Lee 2),JuHwanOh 2), Chang Hoon Lee 3), Chang Oh Hong 2),andPilJooKim 2,4)* ( 1) National Institute of Agricultural Science & Technology, RDA, Suwon, 441-707, South Korea, 2) Division of Applied Life Science (BK21 Program), Gyeongsang National University, Jinju, 660-701, South Korea, 3) Yeongnam Agricultural Research Institute, National Institute of Crop Science, Milyang, South Korea, 4) Institute of Agriculture and Life Science, Gyeongsang National University, Jinju, 660-701, South Korea) ABSTRACT: Phosphorus transfer from agricultural soils to surface waters is an important environmental issue. Fly ash and phospho-gypsum which are industrial by-product were investigated as a means of reducing dissolved phosphorus in arable soil. To determine the optimum mixing ratio of fly ash (FA) and phospho-gypsum (PG) for reducing dissolved reactive P (DRP) in soil, various mixture ratio of FA and PG were mixed with two soil. The DRP content and ph in soils were analysed after 3 weeks incubation under flooding condition. Although DRP content in soils was significantly decreased by FA-PG mixture compared with control, there were no significant difference among the FA and PG mixture ratio of 75:25, 50:50, and 25:75. The mixture of 75% FA and 25% PG was selected for field test. A field experiment was carried out to evaluate the reducing DRP content in paddy soil to which 0 (NPK), 20 (FG 20), 40 (FG 40), and 60 (FG 60) Mg ha -1 of the mixture were applied. The DRP content was reduced by 31% at the application rate of 60 Mg ha -1. In contrast to deceasing DRP, Ca-P content increased significantly with the mixture application rate. After rice harvesting, available SiO 2, P, and exchangeable Ca content in soil increased significantly with application rate due to high content of Si, P, and Ca in the mixture. Mixtures of fly ash and gypsum should reduce P loss from paddy soil and increase soil fertility. Key Words: Fly ash, phospho-gypsum, dissolved reactive phosphorus 서 농경지인산관리는농업생산과환경에큰영향을미친다. 농경지에인산함량이적정수준이하일때는작물수량을감소시키지만, 과량축적되어있을때는강우나관개에의해주변수계로이동되어부영양화의원인물질로작용한다 1,2). 농경지인산은토양침식에의한입자형태 (particulate form) 와수용성형태(dissolved form) 로유출되지만, 이중약 80% 는수용성형태로유출된다 3). 우리나라농경지토양은 1960년대후반복합비료의본격 론 * 연락저자 : Tel: +82-55-751-5466 Fax: +82-55-757-0178 E-mail: pjkim@gsnu.ac.kr 적인공급과다수확정책에의한비료시용량증가와 1980년대이후축산농가의가축사육량증가에의한축분의다량시용으로토양내인산이과량집적되어새로운농업환경문제로대두되고있다 4). 특히, 2012년가축분의해양투기가전면금지되고, 현재가축분의농경지활용을장려하고있는상황에서농경지로부터인산유출은심화될전망이다. 따라서농경지인산유출저감에대한연구의필요성은절실히요구되고있지만국내에서이에대한연구는활발히수행되지않고있다. 인산은 Al, Ca, Fe와쉽게화학적침전물을형성하여용해도가감소된다 5,6). 이러한인산의특성을이용해서 iron oxides, steel wool, metallic iron particles과같은다양한제재들이수용성인산을제거하기위해연구되어지고있다 7-9). 그리고농경지인산유출에많은영향을미치는가축분에서수용성 66
석탄회-석고혼합제처리에의한농경지인산유출저감 67 인산을제거하기위해 alum을첨가하기도한다. 그러나이들제재들은인산을제거하는데국한되어있고, 다른농업적이점 이없기때문에광범위한농경지에사용하기는적당하지않다. 산업부산물인석탄회(fly ash) 는농경지토양의물리 화학성개선을위한개량제로서많은연구가수행되어졌다 11-13). 특히, 석탄회에많이함유되어있는규산은벼수량증대에중요한역할을하는성분이다. 그리고최근에석탄회가토양중수용성인산을칼슘과침전물을형성하여인산유출을저감시킨다는보고가있으며, 석탄회에의한수용성인산제거효율은석탄회에포함된칼슘의함량에의해서결정된다 14,15). 그러나국내에서생산되는석탄회는인산- 칼슘의불용성화합물을형성하여수용성인산을저감하는데필요한칼슘의함량이대단히낮다. 인광석으로부터인산을생산하는과정에서생성되는부산물인인산석고는칼슘을다량함유하고있으므로석탄회에부족한칼슘을공급하기적합한제재이다. 따라서본연구에서는농경지인산유출저감을위한석탄회와석고의적정혼합비를실내시험을통해서선발하여그적용가능성을논토양에서평가하였다. 재료및방법 석탄회와인산석고의적정혼합비율농경지토양에서인산유출저감을위한석탄회 -인산석고의적정혼합비율을선발하고저항온시험을실시하였다. 공시재료인석탄회는경남하동에위치한화력발전소에서생성된것이고, 인산석고는전남여수에위치한남해화학에서인광석으로부터인산을생산하는과정에서생성된부산물이다. 석탄회와석고의 ph는각각 10.1과 3.0 이었다 (Table 1). 실내시험에이용된토양은양질사토(LS) 와미사질양토 (SiL) 의두가지논토양이다. 양질사토는 ph가 6.1, 유효인산함량이 258 mg kg -1 이었고, 미사질양토는 ph가 6.3, 유효인산함량이 57 mg kg -1 이었다. 석탄회와석고를각각 100:0, 75:25, 50:50, 25:75, 0:100 혼합한혼합제 4 Mg ha -1 해당량을 1kg의논토양과썩어서 25 에서담수조건으로 3 주간항온후토양의 ph와 dissolved reactive phosphorus (DRP) 를분석하였다 16). Table 1. Chemical properties of fly ash and gypsum used in the experiment Parameter ph (1:5, H 2O) Total CaO (g kg -1 ) Phosphorus (mg kg -1 ) Total P Avaliable P Avaliable SiO 2 (mg kg -1 ) SD, standard deviation 10) Fly ash Gypsum Mean SD Mean SD 10.1 26.2 767 576 1,134 0.2 3.2 21 27 107 3.0 286 134 70 12 0.1 12 11 4 2 현장적용시험 항온시험에서선발된석탄회와인산석고 (75:25, wt wt -1 ) 혼합제를각각 0 (NPK), 20 (FG 20), 40 (FG 40), 60 (FG 60) Mg ha -1 을논토양에처리하여현장적용가능성을평가하였다. 논토양의이화학적특성은 Table 2에서보는바와같다. 처리별혼합제는벼이앙 15일전에처리하여 15 cm 깊이로경운하였다. 그리고 1998년 6월 5일화산벼를 15 x 30 cm 간격으로이앙하여동년 10월 5 일수확하였다. 각시험구면적은 10 m 2 로난괴법 3 반복으로실시하였다. 모든처리구에 N-P 2O 5-K 2 O를 120-48-80 kg ha -1 시비하였으며, 이때질소는 3 번, 칼륨은 2 번분시하였고, 인산은전량기비로시비하였다. 토양의이화학적특성및인산분획토양시료는표토 (0-15 cm) 를채취하여풍건후 2 mm 체로친후분석용시료로이용하였다. 토양의이화학적특성중 ph (1:5), 유기물, 치환성양이온 (1N-NH 4OAc, ph 7.0), 유효규산및유효인산은농촌진흥청토양분석법에준하여분석하였다 17). Dissolved reactive phosphorus(drp) 는토양5g을증류수 25mL과30분간진탕한후토양용액을 0.45 μm여과지에여과하여 Ascrobic acid 환원법으로측정 하였다 16). 그리고수확후토양의Ca-P, Al-P 및Fe-P 함량를분석하였다 18). 결과및고찰 농경지인산유출저감에가장적합한석탄회- 석고의혼합비를선발하기위해실시한항온시험에서 ph 변화는 figure 1 에서보는바와같다. 항온 3주후토양의 ph는두 토양모두에서석탄회단독처리구가가장높았으며, 석고단독처리구에서가장낮았다. 이는석탄회와석고의자체의강 알칼리와강산성에서기인된것으로판단된다. 그리고두토 양모두에서석탄회에석고의혼합비가증가함에따라토양 ph 는감소하였으며, 석탄회 -석고 25:75과 50:50 혼합제는무처리구보다 ph 가낮았다. 따라서석고단독및석탄회 -석 Table 2. Physical and chemical properties of the soils used in the field tests before the experiment. ph (1:5, H 2O) Organic matter (g kg -1 ) Total N (g kg -1 ) Available P 2O 5 (mg kg -1 ) Available SiO 2 (mg kg -1 ) Ex. cations (cmol c kg -1 ) Ca Mg K SD, standard deviation Mean 5.7 20.2 1.4 76 68 3.49 0.61 0.55 SD 0.1 1.1 0.1 7 8 0.21 0.02 0.10
68 이용복 이슬비 오주환 이창훈 홍창오 김필주 7.0 LS 7.5 SiL ph (1:5 H 2 O) 6.5 6.0 ph 6.0 in the control ph (1:5 H 2 O) 7.0 6.5 ph 6.3 in the control 5.5 6.0 Fig. 1. Effect of fly ash (FA) and phospho-gypsum (PG) mixture ratio on soil ph after 3 weeks incubation at 25. DRP (mg kg -1 ) 3.0 2.0 1.0 LS 1.97 mg P kg -1 in the control DRP (mg kg -1 ) 1.0 0.8 0.6 0.4 0.2 SiL 0.28 mg P kg -1 in the control 0.0 0.0 Fig. 2. Effect of fly ash (FA) and phospho-gypsum (PG) mixture ratio on reduction of dissolved reactive phosphorus (DRP) in soil. after 3 weeks incubation at 25. 고 25:75 및 50:50 혼합비는토양을산성화시킬가능성이 있어농경지시용은적합하지않는것으로판단된다. 농경지인산유출량은토양중 DRP 함량에적접적인영향을받는다 19). 본연구에서석탄회석고혼합제처리후토양 - 중 DRP 함량은석탄회와석고의혼합비에따라서큰차이를 보였다 (Fig. 2). 석탄회- 석고 75:25 처리구의 DRP 함량은 LS와 SiL에서각각 0.58, 0.09 mg P kg -1 으로무처리구에비해크게감소되었다. 두토양모두에서석탄회- 석고 25:75 및 50:50 처리구와석고단독처리구의토양중 DRP 함량은무처리구보다현저히감소되었지만, 석탄회-석고 75:25 처리구와는큰차이가없었다. 따라서농경지인산유출저감을위한적합한석탄회: 석고혼합비를 75:25 (wt wt -1 ) 로선발하고현장검정시험을실시하였다. 석탄회단독처리구의 DRP 함량은 LS와 SiL에서각각 2.44, 0.32 mg P kg -1 으로무처리구보다높았다. 이러한결과는본연구이용된석탄회의칼슘함량 (CaO 2.6%) 이낮기때문인것으로사료된다. 석탄회는화력발전소에서원료로이용하는석탄의종류와회처리방법에따라서그구성분이크게달라진다.Chen등 20) 의보고에의하면 15가지석탄회의 CaO 함량은 2-22% 사이에분포하고있었으며, CaO DRP (mg kg -1 ) 4.0 3.0 2.0 1.0 0.0 7/5 8/5 9/5 10/5 Sampling date (Month/day) NPK FG 20 FG 40 FG 60 Fig. 3. Change of dissolved reactive phosphorus (DRP) in surface soil during rice cultivation. 함량이 2-3% 인것은용액중인산제거에효과가없는것으로보고하였다. 그리고 Cheung 과Venkitachalam 21) 은석탄회를통한수용성인산제거의주작용은 Ca와침전에의한것이라고보고하였다. 벼재배기간동안석탄회석고혼합제시용으로토양중 - DRP 함량은삼요소구에비해현저히감소되었다 (Fig. 3).
석탄회-석고혼합제처리에의한농경지인산유출저감 69 혼합제처리 45 일후 (7월 5 일), 혼합제 20, 40, 60 Mg ha -1 처리구에서삼요소(NPK) 처리구에비해각각 18, 22, 31% 의 DRP 함량이감소효과가있었으며, 이러한경향은벼생 육전기간에걸쳐지속되었다. 석탄회처리에의한수용성인산의고정화율은석탄회에포함된 CaO와 CaSO 4 함량에의해서결정된다 20). 본연구에서도혼합제처리량증가에따라서토양중 DRP 함량은감소되었다. 수확후토양중 Ca-P 함량은혼합제 20, 40, 60 Mg ha -1 처리구에각각 54.8, 64.2, 68.5 mg kg -1 으로 NPK 처리구 51.3 mg kg -1 에비해현저히증가되었다 (Fig. 4). 그리고 Al-P 함량도혼합제 20, 40, 60 Mg ha -1 처리로 NPK 처리구에비해증가되었다. 그러나 Fe-P 함량은처리간에차이가없었다. 토양중인산의형태별분포는인산질비료의종류, 토양광물의종류및토양 ph에의존적인것으로잘알려져있다. 그리고산성토양에서는 Fe-P 및 Al-P가주로존재하 22) 고염기성토양에서는 Ca-P 가주로존재한다. Elrashidi 등은석탄회를처리에의한수용인산의저감기작은불용성칼슘화합물을형성하는것과석탄회에포함된 Al-hydroxides 에흡착되는것이라고보고하였다. Tsitouridou와 Georgiou 23) 는칼슘함량이다른세가지석탄회의인산제거효과비교에서인산제거의주반응은흡착과침전이라고하였다. 그리고 Phosphorus (mg kg -1 ) 160 140 120 100 80 60 40 20 0 NPK FG 20 FG 40 FG 60 Ca-P Al-P Fe-P Phosphorus fraction Fig. 4. Changes of extractable phosphorus fraction in surface soil after rice harvest. Dou 등 15) 은 anthracite fly ash는비록 ph가높지만칼슘함량이 5% 로낮아서수용성인산저감에는효과가없다고보고하였다. 본연구에서혼합제 20, 40, 60 Mg ha -1 시용후토양 ph는각각 6.0, 6.2, 6.2로 NPK 처리구 5.8 보다높았다. 따라서석탄회-석고혼합제시용에의한 DRP 감소는강알리의석탄회에의한토양pH 상승효과와석고를통해서공급된칼슘과침전반응이라고판단된다. 혼합제시용에의해서수확후토양의 ph는 NPK 처리구에비해증가되었다 (Table 3). 그리고혼합제시용은토양중유효규산, 유효인산, 치환성칼슘함량을증가시켰다. 특히, 유효규산의함량은혼합제 20, 40, 60 Mg ha -1 처리구에서각각 145, 198, 246 mg kg -1 으로 NPK 처리구 59 mg kg -1 에비해현저한증가를보였다. 규산은벼재배에있어수량을증가시키고, 도복을방지하며, 병에대한저항성을증가시키는것으로잘알려져있다 24,25). 요 농경지인산유출저감을위한석탄회- 석고의적정혼합비를실내시험을통해서선발하고이를논토양에서적용가능성을평가하였다. 석탄회- 석고혼합제시용은두토양(LS, SiL) 에서토양중 dissolved reactive P (DRP) 함량을현저히감소시켰다. 그러나석탄회- 석고혼합비 75:25, 50:50 및 25:75 처리간에토양중 DRP 감소효과는큰차이가없었다. 따라서석탄회- 석고 75:25 혼합제 0, 20, 40, 60 Mg ha -1 를논토양에시용하여벼재배기간동안 DRP 함량과수확후형태별인산함량변화를조사하였다. 혼합제시용량증가에따라서토양중DRP 함량은감소하였으나, 수확후토양중 Ca-P 함량은혼합제시용량증가에따라서증가되었다. 그리고혼합제시용량증가에따라서토양중유효인산, 유효규산및치환성칼슘함량이현저히증가되었다. 따라서석탄회-석고혼합제는토양중인산의용해도를감소시켜농경지로부터인산유출을저감시킴과동시에토양비옥도증진에우수한제재로평가되었다. 약 Table 3. Chemical properties of surface soil after rice harvest. ph (1:5 with H 2O) Organic Matter (g kg -1 ) Available P 2O 5 (mg kg -1 ) Available SiO 2 (mg kg -1 ) Ex. cations (cmolc kg -1 ) Ca Mg K NPK FG20 FG40 FG60 LSD 0.05 5.8 28.6 78 59 3.40 0.63 0.40 6.0 28.4 89 145 5.48 0.89 0.34 6.2 31.0 106 198 7.12 0.79 0.32 6.2 29.8 112 256 8.96 0.76 0.35 0.3 ns 17 22 1.21 ns ns ns means not significant within LSD 0.05
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