Tillage pan is formed just beneath the plow layer in the fine-textured Brown lowland soil with soil texture of SiC or SiCL, Dystric Fluventic Eutrudept by Soil Taxonomy(1998), Eutri-Mollic FLUVISOL by WRB(1998). This causes the decrease in productivity of the fine-textured Brown lowland soil. Therefore, tillage pan breaking was conducted by the methods of subsoiling, improved subsoiling and deep plowing. The physical properties and root penetration after each tillage pan breaking treatment were also investigated. Improvement of physical properties by tillage pan breaking was demonstrated by the decrease of bulk density and the increase of the pore space filled with gravitational water. The pore space filled with easily available water could not be improved by tillage pan breaking treatments. Physical properties were favorable in the order of deep plowing ≒ improved subsoilng > subsoiling > controll. Sugar beet root penetration was controlled by the pore space filled with gravitational water until the middle growth period. Sugar beet root penetration was favorable in the order of deep plowing ≒ improved subsoilng > subsoiling > controll. The growth and yield of sugar beet were also favorable in the same order. The growth in the middle growth period influenced the growth in the latter growth period. It was considered that, the treatments of deep plowing and improved subsoiling increased the pore space filled with gravitational water, so that drainage and root penetration were superior to the other treatments. Therefore, the growth and yield of sugar beet in the treatments of deep plowing and improved subsoiling were higher than those in the other treatments, because the water uptake by root was more stable. It was confirmed that deep plowing and improved subsoiling at the time of one year after the tillage pan breaking operation was effective for ameliorating physical properities of the fine-textured Brown lowland soil as well as for improving the root penetration of sugar beet.

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The particle-size distribution of soils is usually measured by the sedimentation method based on the Storkes's law. The procedure of the sedimentation method is not complicate, but it needs much time. Recently, a laser scattering method based on Mie scattering theory has applied to determine the particle-size distribution. This laser scattering method requires smaller spacimens and shorter time, only a few minutes, for measurement than the sedimentation one. In this study, the correlation between the laser scattering and the sedimentation method was discussed by using 52 soils from paddy and upland fields. Moreover, the variation of particle-size distribution in a horizon of a paddy soil located in Syonaka-no-ko polder near Lake Biwa, which have the share of 20,000 years' sediments, was observed each 5cm in depth by the laser scattering method. The correlation between both two methods were high and the correlation coefficient, R in clay, silt and fine sand fraction was 0.83, 0.85 and 0.87, respectively. While these two methods are built under the supposition that particle shape is a sphere. The particle shape became more far from the sphere and the correlation would decrease, as the particle size became fine, in consequent. The soil texture estimated from the laser scattering method didn't clearly correspond to that from the sedimentation one. The particle-size distribution in the horizon of polder soil was varied continuously or discontinuously in each depth. This suggested that the laser method was useful for the observation of relative distribution of particle-size within the same soil-horizon.

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The influence of the addition of rice straw (Oryza sativa) or azolla (Azolla pinnata) to soil on soil aggregation, hyphal length, and microbial biomass C was compared using four different systems. RS 1 and AZ 1 systems contained smaller amounts (2g of C kg^<-1> soil) of rice straw and azolla, respectively. RS 2 and AZ 2 systems contained larger amounts (6 g of C kg^<-1> soil) of rice straw and azolla, respectively. These plant materials were amended with soil, and the mixtures were incubated at 30℃ for 3 and 28 weeks under upland conditions. The amendment with plant material of rice straw or azolla increased the amounts of the >2.0 mm aggregates and microbial biomass C and the hyphal length to a larger extent compared to the control system (without plant materials). These degrees of increases varied depending on the kind and amount of the plant materials amended and the incubation periods, and tended to be much higher for 28 weeks than for 3 weeks incubation. For example, after 28 weeks incubation, the amount of the >2.0 mm aggregates was usually 13 times larger in the RS 2 and AZ 2 systems, compared to the control system. In the rice straw and azolla systems after 3 weeks incubation, the increasing patterns of the amount of the >2.0 mm aggregates were generally similar to those of the hyphal length and the amount of microbial biomass C. On the other hand, in the rice straw systems after 28 weeks incubation, the increasing patterns of the amount of the >2.0 mm aggregates were similar to those of the microbial biomass C. Whereas, in the azolla systems, the increasing patterns of the >2.0 mm aggregates were similar to those of the hyphal length. These findings seem to suggest that during long term incubation in the rice straw systems, microbial biomass played more important role than hyphae in the formation of the >2.0 mm aggregates. In contrast, in the azolla systems, the hyphae played more important role in the formation of the >2.0 mm aggregates. These may be due to the differences of the amounts of carbohydrate and C/N ratio between the rice straw and azolla. The amendments of rice straw or azolla tended to increase the amounts of the 0.1-0.25 mm and 0.25-0.5 mm aggregates. In contrast, these amendments decreased the amounts of the 0.5-1.0 mm and 1.0-2.0 mm aggregates to some extent. In the RS 2 and AZ 2 systems after 28 weeks incubation, the amount of the <0.1 mm aggregates decreased to a large extent.

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中国吉林省の中西部に分布する5種類の土壌(湿草地性黒色土,典型黒色土,レシベ,淡色チェルノーゼム,ステップ性アルカリ土)から抽出した腐植酸について1%吸光係数(E_<600>値),元素組成,官能基組成,XAD樹脂で分画される成分組成,^1H-NMRによる各種形態水素の組成を検討した。日本の土壌腐植酸と比較した結果は以下のように要約される。1)本地域土壌の有機炭素量はいずれも18g kg^<-1>以下と低いが,本地域中では黒色土で多く,アルカリ土で非常に少ない。アルカリ土は土壌pHが高いため腐植物質が溶脱しており,残存する腐植物質の抽出割合も非常に低い。ピロリン酸を含むアルカリ溶液にも可溶化しにくい腐植物質が多く残存していると考えられた。2)土壌腐植酸のE_<600>値は,黒色土が最も高く,レシベ,淡色チェルノーゼム,アルカリ土の順に低下した。元素組成から計算されるH/C原子数比は同じ順で高い。黒色土のE_<600>値とH/C比は黒ボク土と同程度であり,他の土壌のE_<600>値は黒ボク土と褐色森林土の中間であった。3)黒色土,レシベ,淡色チェルノーゼム,アルカリ土の順に腐植酸のカルボキシル基量が減少し,アルコール性水酸基量が増加した。また,同じ順でカルボキシル性成分が減少し,脂肪族性成分が増加した。黒色土腐植酸の成分組成は黒ボク土腐植酸によく類似していた。本地域土壌のフェノール性成分はいずれも非常に少なく,これは亜寒帯土壌の特徴であると推察される。4)黒色土の腐植酸は芳香族プロトンが多く,芳香環からβ位以上の脂肪族プロトン数が少ないことから,黒ボク土と同程度に芳香環が発達し脂肪族側鎖が短いと推察された。また,黒色土,レシベ,淡色チェルノーゼム,アルカリ土の順に脂肪族側鎖の長さは長いと推察した。

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中国吉林省の中西部に分布する5種の土壌と日本の褐色森林土を用い,酸添加DMSO溶媒によって腐植物質を抽出した。腐植酸を分離し,腐植酸の抽出割合,1%吸光係数(E_<600>値),元素組成,官能基組成,XAD樹脂によって分画される成分組成,ヘキソース,ペントース,アミノ酸,リグニン含量を測定し,アルカリ抽出腐植酸と比較した。得られた結果は以下のように要約される。1)中国の5土壌から酸添加DMSO溶媒によって抽出される腐植の抽出量はアルカリ溶液による抽出量の74〜85%であり,黒色土が最も高い抽出率を示し,アルカリ土の抽出率は低かった。DMSO抽出腐植酸の抽出量はアルカリ抽出腐植酸の約85%であった。褐色森林土のDMSO抽出腐植,腐植酸量はアルカリ抽出腐植,腐植酸量の約50%であった。2)DMSO抽出腐植酸はアルカリ抽出腐植酸より,E_<600>値が高く,炭素含量,カルボキシル基量,カルボニル基量,XAD樹脂によって分画されるカルボキシル性成分が多く,水素含量,アルコール性水酸基量,脂肪族性成分量が少なかった。これらの特徴は黒色土ではあまり顕著でなく,アルカリ土,褐色森林土で著しかった。酸添加DMSO溶媒は腐植酸のカルボキシル基と水素結合によって溶媒和して腐植酸を溶解するため,カルボキシル基の多い腐植酸が選択的に抽出されたと考えられる。3)DMSO抽出腐植酸とアルカリ抽出腐植酸のH/C,O/C比および官能基組成を検討し,黒色土は腐植酸のほとんど全てにカルボキシル基が多量に存在し,脱水反応が進んでおり,レシベ,淡色チェルノーゼムの腐植酸は全体として脱メチル化をすでに受けているが,DMSOで抽出されるE_<600>値の高い部分のみに多量のカルボキシル基が付加していることを推定した。アルカリ土,褐色森林土では腐植酸全体にわたり脱メチル化があまり進行しておらず,カルボキシル基量も少ないと推定した。4)DMSO抽出腐植酸中の中性糖,アミノ酸,リグニン含量は,アルカリ抽出腐植酸より少なかった。酸添加DMSOに溶解した中性糖の一部とタンパク様物質はDMSOを中和しても溶解しており,沈殿する腐植物質から分離するため,非腐植物質の混入の少ない腐植酸が得られたと考えられる。

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