Pedogenic Characterization of Alluvium Derived Soils in the Arid Region of Rajasthan, India

South eastern part of the arid region of Rajasthan (India) is an alluvial plain developed from the sediments deposited by the river _Luni _and its tributaries, arising from the Aravali hill range. Soils of the region are medium to fine textured. Mean annual rainfall ranges between 350- 400 mm, the soil temperature regime is hyperthermic and the moisture regime is aridic, which restricts pedogenic processes. The objective of the study is to characterize the uniformity of the parent material and illuviation process. Extensive field work for the study of morphological characteristics of soil profiles revealed two major types of soils viz medium texture non-calcareous and fine texture calcareous. Sand fractionation and related parameters were worked out to ascertain the uniformity of the parent material. In medium texture non- calcareous profiles medium sand (1-2 Φ) and fine sand (2-3 Φ) are dominant fractions while in fine texture calcareous alluvium, the major particle sizes are fine sand (Φ 2-3, very fine sand (3-4 Φ and coarse silt (Φ 4-5). The sorting coefficient in medium texture (1.49 to 1.61) and fine textured (1.41 to 1.81) soils indicated the well sorted nature of the sediments (values less than 2.5). In both medium and fine texture soils the depth wise uniform distribution of all size sand fractions and the sorting coefficient indicated the uniformity of the parent material. Parameters such as clay/ sand ratio, HA-carbon/ FA-carbon ratio, CEC and CaCO3 considered together, indicated that in medium texture non-calcareous soils the clay and humus fractions have moved up to 80 cm depth, whereas in fine texture calcareous soils the clay, humus fractions and CaCO3 have moved up to 60 cm depth. These observations suggest that both medium and fine texture soils have undergone the illuviation process but the process is more pronounced in fine texture calcareous soils.