【摘要】 <正> 最近的研究工作证明,作物生长与土壤物理环境有密切关系。一般水稻土有水、旱两作过程,土壤随着淹水、排水和落干的变化相应地发生膨胀、分散、凝聚和收缩。水稻土的物理环境不是固定不变的。耕作形成的土壤环境是暂时的,在没有机械扰动的情况下,土壤物理环境也在自然地向适合或妨碍植物生长的状态发展,而土壤的结构特性左右更多还原

【Abstract】 The present paper deals with the morphological characteristics of soil structure and their relations to shringkage and swelling. Four paddy soils used in the study were collected from Taihu lake region. The content of clay in the soils ranged from 20—40%. Plough layer and plowpan of clayey paddy soil are characterized by puddling and compactness. Weathering may advance the formation of structural pores of the soil. There are internal relations between behaviors of soil shrinkage and swelling and regime of soil structure. There are three shrinkage stages of a clyey soil clod in the drying process, i. e., structural shrinkage, normal shringkage and residual shrinkage. The ratios of tre change of soil volume to volume of water lost from soil in the three stages are <1,1 and <1 respectively. When structure of clod is destroyed, the structural shrinkage disappears and normal shrinkage develops. Therefore the characteristics of soil shrinkage can reflect the regime of soil structure.The process of alternate wetting and drying may develop pore of structure. Only the water content is lowered below the plastic limit can the cohesion of clay particles become stable. Development of structure can contribute to hydration and swelling of soil colloidal material, and hence may improve the compactness and rigidity of soil clod. The poor structure of soil clod is characterized not only by small swelling, but also by shorter time duration of swelling. Soil under reduction condition can weaken the cohesion of particles, but the structure is more stable and can persist in long time, if it is not disturbed.Based on the data of our experiment, discussion on the problem of conventional tillage is made, the necessary conditions and the principle of tillage for structure development are suggested. It is also suggested that though no-tillage is favourable for the development of soil structure, it has its disadvantages.更多还原