Korean J. Soil Sci. Fert. Vol.51, No.4, pp.499-509, 2018 Korean Journal of Soil Science and Fertilizer Short communication https://doi.org/10.7745/kjssf.2018.51.4.499 pissn : 0367-6315 eissn : 2288-2162 Effects of Agro-machine Operating Period on Soil Physical Properties in Upland Fields Hee-Rae Cho and Kyung-Hwa Han* Soil and Fertilizer Division, National Institute of Agricultural Sciences, RDA, Wanju 55365, Korea *Corresponding author: bearthink@korea.kr A B S T R A C T Received: September 28, 2018 Revised: November 5, 2018 Accepted: November 12, 2018 The subsoil compaction by heavy agro-machine is an ongoing cumulative process and threat in sustainable agriculture, especially exchange land use. The knowledge concerning the effects of agro-machine on soil physical properties in upland is necessary in arable soil management. The purpose of this study is to assess soil physical properties by heavy agro-machine operating period in upland. The choice of target soils was based on soil series, which preferentially have larger area in Korean upland field, including ranking 1 st to 29 th. Investigated sites of chosen soil series were designated at mainly distributed area of them. The soil physical properties include plow pan depth, bulk density, soil hardness and saturated hydraulic conductivity. From the investigation, soils with heavy agro-machine longer than 10 years, showed higher plow pan thickness, bulk density and hardness, and shallower surface soil depth than soils with heavy agro-machine shorter than 9 yrs. The value of plow pan thickness, bulk density, hardness, and surface soil depth is 19.8 cm, 1.54 Mg m -3, 21.8 mm and 16.9 cm in front one and 15.2 cm, 1.48 Mg m -3, 19.3 mm and 18.1 cm in back one. Especially fine silty and heavy clayey upland soils had an increase of plow pan thickness and decrease of saturated hydraulic conductivity by longer use of heavy agro-machine when classified by different soil textural families and upland soil types. Therefore, periodic improvement of physical properties is needed for upland soil management in the long-term point of view. Keywords: Agro-machine, Soil physical properties, Subsoil compaction, Hydraulic conductivity, Plow pan The change in physical properties of upland soils as increase of heavy agro-machine use period. Items Depth Years with heavy agro-machine <9 (A) >10 (B) Ratio (B/A) Average years 8 13 1.58 Surface soil depth (cm) 18.1 ± 2.1 a 16.9 ± 1.7 b 0.93 Plowing depth (cm) 13.5 ± 1.5 ns 13.0 ± 1.2 ns 0.96 Plow pan thickness (cm) 15.2 ± 4.2 b 19.8 ± 4.5 a 1.30 Bulk density (Mg m -3 ) top 1.24 ± 0.12 b 1.34 ± 0.12 a 1.08 sub 1.48 ± 0.09 b 1.54 ± 0.08 a 1.04 Porosity (%) top 53.4 ± 4.2 a 49.3 ± 4.7 b 0.93 sub 44.2 ± 3.5 a 42.0 ± 3.1 b 0.95 Hardness (mm) top 10.3 ± 2.6 b 12.7 ± 2.5 a 1.23 sub 19.3 ± 3.1 b 21.8 ± 3.0 a 1.13 Data are means±standard deviation. Different letters in the same row indicate significant difference according to t-test (p<0.05). 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 (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
500 Korean Journal of Soil Science and Fertilizer Vol. 51, No. 4, 2018 Introduction 최근대형농기계사용증대와논, 밭을시설재배지로의농지지목변경증가로농경지의토양물리적특성변화가심화되고있다. 통계청농업면적조사자료 (2018) 에따르면 2017년기준시설재배작물면적의 84% 가밭으로 2000년이후꾸준히증가하고있으며, 2017 기준트랙터보유대수는 21만 6천대로 2003년부터 2017년까지트랙터는 37% 증가하였고이중 60마력이상의대형트랙터는두배이상증가하였다. 토양구조는물과공기의흐름에영향을주기때문에물관리에매우중요한중요한요인중하나이다. 특히시설재배지는비가림환경으로재배시기가다양하고일년에여러작기의영농이이루어지기때문에시설재배지의물관리는밭에비하여어려우며경반층형성및토양투수성이중요한관리인자가된다. 지목변경이잦은현대농업에서기계적다짐에의한밭토양물리성변화에실태파악이중요하다. 대형농기계사용은깊이의토양층에압력을가하고횟수를거듭할수록경반층 (plow pan) 의두께가증가한다 (Shierlaw and Alston, 1984). 농기계운행은토양구조와토양내공극의양, 분포및공극연결성에영향을주어 (Schaffer et al., 2007) 토양이단단해지거나물빠짐이느려지는등의문제를발생하게할수있다. Seo et al. (2016) 은사양토에서쟁기바닥층에서물의하향이동이제한되고전토층의물의하향이동을결정하게된다고언급하였다. 이는작물의생육에영향을끼치게되며기계적저항이증가하거나 (Unger and Kaspar, 1994) 산소공급의감소로 (Czyz, 2004) 인해작물의뿌리뻗음이제한되고 (Cook et al., 1996) 결과적으로생산성에영향을주게된다 (Letey 1985; Saqib et al., 2004). 완두뿌리뻗음은경도가증가할수록감소하여생육에제한을주는한계산중식경도가 24 mm 라고보고되었다 (Jo et al., 1977). 사과과원에서경반층이토심 40 cm 이내에나타날때사과수량이약 36% 감소하였다고보고되었다 (Kim and Jo, 1998). 특히심토의다짐 (subsoil compaction) 은일단한번발생하면구조가회복되기어렵고영구적이라는점에서심각한문제가된다 (Akker and Canarache, 2001; Horn and Fleige, 2009). 단기적으로는표토의다짐의피해가더빨리나타나지만, 장기적으로는다짐이누적되고복원이쉽지않으며일부는영향이지속적으로나타나는심토의다짐이더심각하다 (Alakukku, 2000; Voorhees, 2000). 지금까지다짐에대한물리성변화및작물생육에의영향을분석한많은연구가있었지만, 농기계사용연차에따른물리성변화에대한연구는많지않다. 본연구에서는농기계사용연차가증가함에따라대형농기계사용연차에따른밭의심토물리성변화를분석하여농기계에대한영향을평가하였다. Materials and Methods 조사대상및토양속성조사우리나라대표적인밭토양의물리성을조사하기위해제주도를제외한분포면적이넓은토양통 29개를택하여조사지역을선정하였다 (Table 1). 2007년부터 2008년까지각지역에서농기계사용연차 9년이하인곳과 10년이상인곳을선택하여 64지점을조사하였다. 조사대상에서석력함량 35% 이상인석력토는제외하였다. 토양통분포면적, 밭토양유형및토성속 (soil textural families) 등은한국토양총설 (NIAST, 1992) 및 Taxonomical classification of Korean soils (NIAST, 2000) 을참고하였다. 토양물리성조사밭의토양물리성으로관입저항, 경반층특성, 표토심, 경운심, 밭의표토와심토에대한용적밀도, 공극률, 산중식경도, 심토포화수리전도도등을조사하였으며, 표토와심토의토양시료는경운깊이를기준으로채취하였다. 관입저항, 경반층이나타나는최소와최대깊이, 두께는토양관입저항계 (Penetrologger, Eijkelkamp,
Effects of Agro-machine Operating Period on Soil Physical Properties in Upland Fields 501 Table 1. Investigated soils of characterizing physical properties for upland soils. Soil textural family Soil series Investigated points Togye (Typic Quartzipsamments) 2 Sandy Nagdong (Typic Quartzipsamments) 2 Haeri (Typic Quartzipsamments) 2 Hwabong (Typic Quartzipsamments) 2 Sangju (Coarse loamy, Dystric Fluventic Eutrudepts) 2 Jigog (Coarse loamy, Typic Dystrudepts) 4 Jungdong (Coarse loamy, Typic Udifluvents) 2 Coarse loamy Noegog (Coarse loamy, Fluvaquentic Dystrudepts) 2 Seongsan (Coarse loamy, Typic Dystrudepts) 2 Deogcheon (Coarse loamy over sandy skeletal, Typic Udifluvents) 2 Gwacheon (Coarse loamy, Dystric Fluventic Eutrudepts) 2 Bonryang (Coarse loamy over sandy, Typic Udifluvents) 2 Weongog (Fine loamy, Fluventic Dystrudepts) 2 Daegog (Fine loamy, Fluvaquentic Dystrudepts) 2 Yonggye (Fine loamy, Typic Dystrudepts) 2 Fine loamy Ugog (Fine loamy, Typic Dystrudepts) 2 Baegsan (Fine loamy, Dystric Fluventic Eutrudepts) 2 Banho (Fine loamy, Dystric Fluventic Eutrudepts) 4 Bugog (Fine loamy, Typic Fragiudalfs) 2 Anryong (Fine loamy, Typic Hapludalfs) 2 Fine silty Ihyeon (Fine silty over coarse silty, Dystric Fluventic Eutrudepts) 4 Yeongog (Fine silty, Aquic Fragiudalfs) 2 Gopyeong (Fine, Typic Hapludalfs) 2 Bancheon (Fine, Typic Hapludalfs) 2 Pogog (Fine, Aquic Fragiudalfs) 2 Clayey Uji (Fine, Typic Hapludalfs) 2 Jangpa (Fine, Typic Hapludalfs) 2 Bansan (Fine, Humic Hapludults) 2 Pyeongan (Fine, Typic Hapludalfs) 2 Holland) 를이용하여측정하였다. 산중식 (Yamanaka) 경도는토양경도계 (Strength of spring 78.4 N/40 mm, cone angle 25, 20', Japan) 로측정하였다. 용적밀도와공극률은 100 cm 3 코어시료를채취하여건토중량법으로분석하였고, 심토의포화수리전도도는채취한코어를수조에서포화시킨후정수위법및변수위법으로측정하였다 (NAS, 2017). 정수위법계산식 (Eq. 1) Q : 투수량 (cm 3 /hr)
502 Korean Journal of Soil Science and Fertilizer Vol. 51, No. 4, 2018 L : 토주길이 (cm) A : 토주의단면적 (cm 2 ) : 수두차 (cm) : t C에서의물의점성계수 (Centipoise) : 25 C 표준상태에서의물의점성계수 (Centipoise) : 25 C 표준상태에서의수리전도도 (cm/hr) 변수위법계산식 log (Eq. 2) : 수관의직경 (cm) : 토주의직경 (cm) : 토주길이 (cm) : 초기수위, : 시간경과후수위 (cm) 통계처리농기계사용연차 9년이하와 10년이상의두그룹으로나누어연차에따른토양물리적특성을비교하되, t-test로통계적유의성을검정하였다. 토성속별로그룹을나누어토양물리적특성을비교하였는데, GLM으로검정후 Duncan s Multiple Range test를이용하여유의성을검정하였다. 농기계사용연차에따른용적밀도, 경반층두께및경도간에관계를회귀분석하였다. 통계분석은 SAS 통계프로그램을이용하였으며 5% 에서통계적유의성을검정하였다 (SAS, ver. 9.2, Cary, NC). Results and Discussion 농기계사용연차에따른밭토양물리성변화 Cho 등 (2016) 에의하면밭토양물리성개량기준을심토용적밀도가사양토 1.55 Mg m -3, 양토 1.50 Mg m -3, 미사질식양토 1.45 Mg m -3 미만으로보고하였고, 이에근거하여심토용적 Fig. 1. Distribution of subsoil bulk density according to years with heavy agro-machine. Bulk density distribution classified by value of 1.5 Mg m -3
Effects of Agro-machine Operating Period on Soil Physical Properties in Upland Fields 503 Table 2. The change in physical properties of upland soils as increase of heavy agro-machine use period. Items Depth Years with heavy agro-machine <9 (A) >10 (B) Ratio (B/A) Average years 8 13 1.58 Surface soil depth (cm) 18.1 ± 2.1 a 16.9 ± 1.7 b 0.93 Plowing depth (cm) 13.5 ± 1.5 ns 13.0 ± 1.2 ns 0.96 Plow pan thickness (cm) 15.2 ± 4.2 b 19.8 ± 4.5 a 1.30 Bulk density (Mg m -3 ) Porosity (%) top 1.24 ± 0.12 b 1.34 ± 0.12 a 1.08 sub 1.48 ± 0.09 b 1.54 ± 0.08 a 1.04 top 53.4 ± 4.2 a 49.3 ± 4.7 b 0.93 sub 44.2 ± 3.5 a 42.0 ± 3.1 b 0.95 top 10.3 ± 2.6 b 12.7 ± 2.5 a 1.23 Hardness (mm) sub 19.3 ± 3.1 b 21.8 ± 3.0 a 1.13 Data are means±standard deviation. Different letters in the same row indicate significant difference according to t-test (p<0.05). 밀도 1.5 Mg m -3 미만인지점과이상인지점의분포를농기계사용연차에따라분석하였다 (Fig. 1) 농기계사용연차 10-12 년범위에서 1.5 Mg m -3 미만지점이 5%, 1.5 Mg m -3 이상지점이 19% 로 10년이상에서 1.5 Mg m -3 를초과하는지점이보다많아졌다. 따라서 10년차를기준으로다짐이심화되었음을판단하였고, 9년이하인지점과 10년이상인지점을기준으로그룹으로나누어토양물리성을분석하였다. 10년이상인밭은 9년이하밭에비해경반층두께, 용적밀도, 경도가증가하였고공극률과표토심이감소하였으며, 경운심은통계적으로유의한차이가없었다 (Table 2). 경반층두께는 15.2 cm에서 19.8 cm로증가하였는데, 농기계운행횟수증가에따른경반층두께가증가한다는것과일치하는결과였다 (Shierlaw and Alston, 1984). 용적밀도는표토 1.24 Mg m -3 에서 1.34 Mg m -3, 심토 1.48 Mg m -3 에서 1.54 Mg m -3 로, 산중식경도는표토 10.3 mm에서 12.7 mm, 심토 19.3 mm에서 21.8 mm로증가하였으며, 표토심은 18.1 cm 에서 16.9 cm로감소하였다. 농기계사용연차가증가함에따라심토는더단단해져용적밀도가증가하는것으로판단되었다. 농기계사용으로증가된용적밀도와경도는작물생육에영향을미칠수있다. 토양다짐에따른경도및용적밀도증가로완두와대맥뿌리신장속도및분포비율이감소하였으며 (Jo et al., 1977; Jo et al., 1983), 밭에서는야마나까경도가 23-24 mm 이상이되면근군발달이아주불량해진다고보고되었다 (Jo et al., 1977). 일본에서는화산회, 사질, 양질, 점질등의토양및과채, 엽채, 단근채, 장근채등의작물로나누어적정경도를 18-24 mm 이하로제시한다 (Japan soil association, 1986). 토성속에따른경반층두께, 용적밀도, 경도토성속별로분류하여토성속에따른경반층두께, 심토용적밀도, 심토경도평균치를비교하였다 (Table 3). 토성속별비교에서는경반층두께는통계적유의성이나타나지않았고, 심토용적밀도는사양질이 1.56 Mg m -3 로높고미사식양질 1.46 Mg m -3, 식질 1.47 Mg m -3 로낮았으며, 심토경도는미사식양질 22.9 mm로가장높고, 사질에서 17.6 mm로가장낮았다. 토성속별로사용연차에따른심토용적밀도를회귀분석하였다 (Fig. 2). 토성속별로농기계사용연차에따른심토용적밀도회귀분석에서는어떤그룹에서도통계적유의성을보이지않았다. 용적밀도는입경분포, 유기물함량, 토양깊이, 경운등의특성에따라달라진다. 토성별로는사양토 1.19-1.67 Mg m -3, 양토 1.19-1.96 Mg m -3, 미사토 1.19-1.53 Mg m -3, 식토 0.92-1.32 Mg m -3 범위를갖는다 (Hartge et al., 2016). 토성속별용적밀도에서는차이가있었지만농기계사
504 Korean Journal of Soil Science and Fertilizer Vol. 51, No. 4, 2018 Table 3. The plow pan thickness, subsoil bulk density and subsoil hardness of upland soil classified by soil textural families. Soil textural family Plow pan thickness (cm) Subsoil bulk density (Mg m -3 ) Subsoil hardness (mm) Sandy 16.3 ± 3.1 a 1.52 ± 0.05 ab 17.6 ± 1.9 c Coarse loamy 18.9 ± 5.8 a 1.56 ± 0.08 a 20.2 ± 2.0 b Fine loamy 16.8 ± 4.3 a 1.50 ± 0.10 ab 21.4 ± 2.0 ab Fine silty 15.7 ± 5.1 a 1.46 ± 0.07 b 22.9 ± 3.0 a Clayey 18.4 ± 4.2 a 1.47 ± 0.09 b 22.0 ± 2.7 ab Data are means±standard deviation. Different letters in the same column indicate significant difference according to Ducan s multiple range test (p<0.05). Fig. 2. The subsoil bulk density as increase of heavy agro-machine use period in different soil textural families. 용연차에따라용적밀도변화는뚜렷하게나타나지않았는데, 농기계에의해다짐이되나용적밀도에대한입자의영향이큰것으로판단된다. Keller and Hakansson (2010) 은기계적다짐에의한용적밀도변화에대해입경분포에따라달라지며, 점토함량 29.3% 일때최대치가된다고발표하였다. 다른토양연구자들도다짐에의한토양의기계적특성변화는점토함량의범위에따라달라진다고설명하였다 (Larson et al., 1980; Lebert and Horn, 1991; Smith et al., 1997; Imhoff et al., 2004). 기계적다짐에의한영향이거의없는사질을제외하고토성속별로농기계사용연차에따른심토경도및경반
Effects of Agro-machine Operating Period on Soil Physical Properties in Upland Fields 505 Fig. 3. The plow pan thickness and hardness of subsoil as increase of heavy agro-machine use period in different soil textural families. 층두께의관계를분석하였다 (Fig. 3). 농기계사용연차에따라식양질에서경도가증가하였으며, 미사식양질에서경반층의두께가증가하였고, 이외에는유의하지않았다. 농기계사용에따른다짐의영향이심토점토함량 18-35% 에서뚜렷한것을볼수있었다. 일반적으로입자가작은토양이입자가큰토양보다다짐이잘일어나며, 점토함량이 30% 이하에서는점토함량이증가함에따라압축지수 (compression index) 가증가한다 (Larson et al., 1980; Imhoff et al., 2004). 점토함량에따라농기계사용연차에대한경반층형성정도가달라지며, 특히미사식양질토양이취약하다는것을알수있었다. 밭유형별관입저항특성과포화수리전도도밭유형별로농기계사용연차 9년이하밭과 10년이상밭의관입저항과포화수리전도도를비교하였다 (Fig. 4). 대형농기계사용연차에따라관입저항의증가가나타났는데사질밭 (sandy textured) 과중점밭 (heavy clayey) 에서더뚜렷하였다. 농기계사용연차 10년이상의밭에서경반층출현깊이가사질밭에서는 20 cm 이하에서나타났으며, 중점밭에서는 10 cm 이하에서나타나사질밭과중점밭에서경반층출현깊이가현저히낮아지는것을볼수있었다. Raper (2005) 의결과에서도농기계하중에의한관입저항의증가가토심 30cm까지뚜렷이나타났다. Kim and Jo (1998) 은사과과원의경우경반층이 40 cm 이하출현시사과수량이 36% 감소하였다고보고하였다. 포화수리전도도또한농기계사용연차 10년이상밭에서급격히감소되었는데, 중점밭의경우 9년이하밭일때 1.131 cm/hr 이었고 10년이상밭일때 0.009 cm/hr 이었다. 투수속도가 0.1 cm/hr 미만일때투수등급 매우느림 (very slow) 으로정의하는데 (NIAST, 1992) 농기계사용연차 10년이상의밭은거의불투수성을나타내었다. Jung 등 (2016) 은우리나라농경지에서입자특성만으로포화수리전도도를설명하기에는한계
506 Korean Journal of Soil Science and Fertilizer Vol. 51, No. 4, 2018 Fig. 4. The penetration resistance and saturated hydraulic conductivity (K sat ) as increase of heavy agro-machine use period in upland soil types.
Effects of Agro-machine Operating Period on Soil Physical Properties in Upland Fields 507 가있으며, 대공극을파괴하는요인을더구명할필요가있다고언급하였다. 포화수리전도도는주로대공극률과공극의연결성에의해좌우된다 (McLaren and Cameron, 1996). Schaffer (2007) 는콤바인 10번주행후대공극률과공극연결성이감소된다고밝혔다. 따라서농기계사용에따른대공극률과공극연결성감소로포화수리전도도감소뿐만아니라물의이동및순환에영향이클것으로보인다. 농기계장기사용에의해대체로심토물리성이악화되었으며, 특히중점밭의경우가장심각하며작물생육저하에대한취약성도클것으로예상되었다. 다짐으로물리성이악화된밭토양의개선방법으로심토파쇄, 거친유기물혼입, 사질토객토, 심경등이있다 (Kim, 2001). 이외에도물질균형과생태계순환을고려한지렁이등의토양동물과목초류등의식물을활용한물리성개선방법이있다. 다양한작물의뿌리는토양의입단형성과수분보유와통기를위한공극분포형성에도움을준다. 특히블루그라스등의목초류는뿌리밀도가커물리성개선능력이다른작물에비해높다고할수있다 (Kay, 1990). 생물을이용한물리성개선뿐아니라물리성악화를미연에방지하는적정한토양관리가이루어지는것이중요하다. 한편농기계작업시토양수분상태를고려하여다짐의영향을최소화하기위해소성한계이하일때수행하는것이중요하다고볼수있다. Conclusions 농기계사용연차에따른토양물리성변화를평가하기위하여분포면적이넓은 29개토양통을대상으로농기계사용 10년이상인지점과 9년이하인지점을 64개소선정하여경반층특성, 경운심, 용적밀도, 공극률, 관입저항과산중식경도, 포화수리전도도등을조사하였다. 농기계사용 10년이상의밭은 9년이하의밭에비해경반층두께, 용적밀도및경도가증가하고, 표토심이감소하였다. 농기계사용 10년이상인밭에서는경반층두께 19.8 cm, 심토용적밀도 1.54 Mg m -3, 심토경도 21.8 mm, 표토심 16.9 cm 였고, 9년이하밭에서는경반층두께 15.2 cm, 용적밀도 1.48 Mg m -3, 경도 19.3 mm, 표토심 18.1 cm 이었다. 특히대형농기계의사용연차증가에따라미사식양질 (fine silty) 토양과중점밭 (heavy clayey) 에서경반층두께증가및포화수리전도도감소가뚜렷하였고, 중점밭에서농기계사용 10년이상다짐이되었을때경반층출현깊이가 10 cm 이하에서나타나경반층출현깊이가현저히낮아졌다. 농기계사용에대한물리성악화가특히점토함량이높은토양에서취약하였고, 밭의물리성관리를위해주기적인물리성개선이필요하다고판단된다. Acknowledgement This study was conducted by support of NIAS, RDA research and development project (Project no. PJ01089903). References Akker, J.J.H. and A. Canarache. 2001. Two European concerted actions on subsoil compaction. Landnutzung and Landentwicklung. 42(1):15-22. Alakukku, L. 2000. Responses of annual crops to subsoil compaction in a field experiment in clay soil lasting 17 years. p. 205-208. In: R. Horn et al. (ed.) Subsoil Compaction : Distribution, Processes and Consequences. Advances in GeoEcology 32. Catena Verlag, Reiskirchen, Germany. Cho, H.R., K.H. Han, Y.S. Zhang, K.H. Jung, Y.K. Sonn, M.S. Kim, and S.Y. Choi. 2016. Threshold subsoil bulk
508 Korean Journal of Soil Science and Fertilizer Vol. 51, No. 4, 2018 density for optimal soil physical quality in upland: inferred through parameter Interactions and Crop Growth Inhibition. Korean Journal of Soil Science and Fertilizer. 49(5):548-554. Cook, A., C.A. Marriott, W. Seel, and C.E. Mullins. 1996. Effects of soil mechanical impedance on root and shoot growth of Lolium perenne L, Agrostis capillaris and Trifolium repens L. J. Exp. Bot. 47:1075-1084. Czyz, E.A. 2004. Effects of traffic on soil aeration, bulk density and growth of spring barley. Soil Tillage Res. 79:153-166. Hartge, K.H., R. Horton, R. Horn, J. Bachmann, and S. Peth. 2016. Essential soil physics : An introduction to soil processes, functions, structure and mechanics. Schweizerbart Science Publishers, Germany. Horn, R. and H. Fleige. 2009. Risk assessment of subsoil compaction for arable soils in Northwest Germany at farm scale. Soil & Tillage Research. 102:201-208. Imhoff, S., A.P. da Silva, and D. Fallow. 2004. Susceptibility to compaction, load support capacity and soil compressibility of Hapludox. Soil Sci. Soc. Am. J. 68:17-24. Japan soil association. 1986. Agri-environment information system for food production : crop production environment indicator, 1st soil environment. (in Korean, 농업환경생산정보시스템농작물생육환경총지표제 1집토양환경 ). Japan soil association, Japan. Jo, I.S., L.Y. Kim, D.U. Choi, J.N. Im, and K.T. Um. 1983. The effects of soil physical properties on root distribution of barley. Korean J. Soil Sci. Fert. 16(2):126-130. Jo, I.S., S.J. Cho, and J.N. Im. 1977. A study on penetration of pea seedling taproots as influenced by strength of soil. Korean J. Soil Sci. Fert. 10(1):7-12. Jung, K.H., Y.K. Sonn, S.H. Hur, K.W. Han, H.R. Cho, M.J. Seo, M.H. Jung, and S.Y. Choi. 2016. Hydraulic characteristics of arable fields in Korea and applicability of pedotransper function. Korean J. Soil Sci. Fert. 49(6):655-661. Kay, B.D. 1990. Rates of change of soil structure under different cropping systems. Advances in Soil Science 12. Springer, New York, NY, USA. Keller, T. and I. Hakansson. 2010. Estimation of reference bulk density from soil particle size distribution and soil organic matter content. Geodema. 154:398-406. Kim, L.Y. and I.S. Jo. 1998. Soil physics. Korean J. Soil Sci. Fert. 31(S.I):7-18. Kim, L.Y., H.J. Cho, B.K. Hyun, and W.P. Park. 2001. Effects of physical improvement practices at plastic film house soil. Korean J. Soil Sci. Fert. 34(2):92-97. Larson, W.E., S.C. Gupta, and R.A. Useche. 1980. Compression of agricultural soils from eight soil orders. Soil Sci. Soc. Am. J. 44:450-457. Larson, W.E., S.C. Gupta, and R.A. Useche. 1980. Compression of agricultural soils from eight soil orders. Soil Sci. Soc. Am. J. 44:450-457. Lebert, M. and R. Horn. 1991. A method to predict the mechanical strength of agricultural soils. Soil Tillage Res. 19:275-286. Letey, J. 1985. Relationship between soil physical properties and crop production. Adv. Soil Sci. 1:277-294. McLaren, R.G. and K. C. Cameron. 1996. Soil Science. 2nd edition. Oxford University Press, Canada. NAS (National Institute of Agricultural Science). 2017. Soil physical methods. NAS, RDA, Korea. NIAST (National Institute of Agricultural Science and Technology). 1992. Introduction to Korean soil. Soil survey document No. 13. NIAST, RDA, Korea. NIAST (National Institute of Agricultural Science and Technology). 2000.Taxonomical classification of Korean soils. NIAST, RDA, Korea. Raper, R.L. 2005. Agricultural traffic impacts on soil. J. Terramechanics. 42:259-280.
Effects of Agro-machine Operating Period on Soil Physical Properties in Upland Fields 509 Saqib, M., J. Akhtar, and R.H. Qureshi. 2004. Pot study on wheat growth in saline and waterlogged compacted soil I. Grain yield and yield components. Soil Tillage Res. 77:169-177. Schäffer, B., M. Stauber, R. Muller, and R. Schulin. 2007. Changes in the macro-pore structure of restored soil caused by compaction beneath heavy agricultural machinery: a morphometric study. Eur. J. Soil Sci. 58(5):1062-1073. Seo, M.J., K.H. Han, K.H. Jung, H.R. Cho, Y.S. Zhang, and S.Y. Choi. 2016. Effect of temperature and plow pan on water movement in monolithic weighable lysimeter with paddy sandy loam soil during winter season. Korean J. Soil Sci. Fert. 49(4):300-309. Shierlaw, J. and A.M. Alston. 1984. Effect of soil compaction on root growth and uptake of phosphorus. Plant and Soil. 77:15-28. Smith, C.W., M.A. Johnston, and S. Lorentz. 1997. Assessing the compaction susceptibility of South African forestry soils. II. Soil properties affecting compactibility and compressibility. Soil Tillage Res. 43:335-354. Unger, P.W. and T.C. Kaspar. 1994. Soil compaction and root-growth : a review. Agron. J. 86:759-766. Voorhees, W.B. 2000. Long term effects of subsoil compaction on yield of maize. p. 331-338. In: R. Horn et al. (ed.) Subsoil Compaction : Distribution, Processes and Consequences. Advances in GeoEcology 32. Catena Verlag, Reiskirchen, Germany.