Effect of Different Soil Managements on Physical Properties and Microbial Activities in Citrus Orchard Soil

This study was performed to investigate effect of different soil managements on physical properties and microbial activities in volcanic ash citrus orchard soil. Experiment plots had managed to control weeds on soil for 4 years with clean cultivation (CCM) used with herbicide, natural sod cultivation (NSCM), kentucky blue grass sod cultivation (KBG). Soil samples were taken on October, in both 1998 and 2000 from 3 experimental plots. In NSCM, Soil hardness was lower at 11.8 mm than in CCM. And water stable Aggregation coefficient(>0.5 mm) was high at 26.7% compared with CCM. Soil bulk density and porosity showed no significant among the treatments. Soil acid phosphatase was high in sod cultivation plots and the amount of microbial biomass C was about twice higher at $525.4mg\;kg^{-1}$ in KBG than in CCM. Conclusionally, Sod cultivation improved soil physical properties such as aggregation, hardness and increased microbial activities compared with clean cultivation in citrus orchard soil. Soil total PLFA, acid phosphatase, and microbial biomass C contents were investigated on May in nonvolcanic ash citrus soil. Soil samples were collected at 5 sites each; convention cultivation grown with herbicide, natural sod cultivation grown with 1/2 chemicals, organic cultivation. That sites have been managed for 5 years over. PLFA contents were two times higher at $112.2n\;mol\;g^{-1}$ in organic cultivation than in convention cultivation. According to the PLFA indicator, Gram negative bacteria and actinomycetes in organic cultivation were high compared with convention cultivation, which were at 15.1%, 6.6%, respectively. Soil microbial biomass C contents was about twice higher in organic cultivation than in convention cultivation. Soil acid phosphatase was high at 17.6% in organic cultivation compared with convention cultivation.

초생재배가 감귤원 토양의 물리성과 미생물 활성에 미치는 영향

화산회토 감귤원에서 제초제를 사용하는 청경재배, 자연초종을 이용하는 자연초생재배, 켄터키블루그라스를 이용하는 인위초생재배를 4년간 동일한 방법으로 토양 및 시비관리를 하면서 토양의 물리성과 미생물체량, 토양인산효소 활성을 분석하였다. 자연초생재배가 청경재배보다 입단계수(>0.5 mm)는 26.7% 높았고 토양경도는 11.8 mm 낮았다. 토양의 용적밀도와 공극율은 차이가 없었다. 초생재배가 청경재배보다 인산효소 활성이 높았으며 토양 미생물체량은 인위초생재배가 $525.4mg\;kg^{-1}$로 청경재배보다 2배 이상 높았다. 결론적으로 초생재배는 입단형성이 잘되고 토양 경도가 개선되는 효과가 있었으며 토양 미생물활성이 높았다. 비화산회토 감귤농가 중 5년 이상 된 제초제를 이용하는 관행재배, 자연 초생재배 저농약, 유기농 인증 재배 감귤원 5개를 선정하여 감귤나무의 개화기인 5월에 토양을 채취 후 인지질 지방산과 토양인산효소 활성, 미생물체량을 분석하였다. 인지질지방산함량은 유기재배 감귤원이 $112.2n\;mol\;g^{-1}$로 관행재배보다 2배 이상 많았다. 인지질 지방산의 미생물지표에 따른 유기재배토양의 그램 음성세균은 15.1%, 방선균은 6.6%로 관행재배토양 보다 높았다. 유기재배 감귤원이 관행재배보다 토양 미생물체량은1.5배 정도 많았고 토양인산효소 활성은 17.6% 높았다.