Tal Land Soils of Bihar - III: Aggregation and Water Retention Characteristics

In tal land soils, there is higher degree of compaction due to swelling and shrinkage, leading to lower saturated hydraulic conductivity. In old alluvial region, themacro-aggregates are always higher-than micro-aggregates which increase sharply down the depth. This differential behaviour is mainly due to higher percentage of clay in the former and organicmatter in the latter. This is also confirmed by the positive and highly significant correlation of macro-and cumulative aggregates with the clay, fine Clay and organic carbon contents. A higher degree of correlation between mean weight diameter and water stable aggregates has also been noted. Soil water retention curves show that most of the soil water is released by a tension of 100–200 kPa. In these soil groups (old alluvial and young alluvial) water retention is mainly a function of amount and nature of clay and to some extent of organic mailer. But the percentage of water retention at higher tensions is mainly in fluenced by clay content.