Characteristics of rainfed rice and associated non-rice shrink-swell soils in Central India

Six pedons, three representing rainfed (bunded) rice (P1, P3, P5) and others corresponding (in adjacent field) to non-rice growing soils i.e. soybean (P2, P4) and pigeonpea (P6) in Nagpur district of Maharashtra were characterized and classified. Except pedons 1 and 3 (imperfectly drained) others were moderately well drained. In general, pedons exhibited brown to very dark grayish brown colour but sub-soils of Tharsa (P3, P4) and Bhilewada (P6) had very dark grayish brown to olive brown colour (2.5Y). Rice soils of Mahalgaon (P1), Tharsa (P3) and Bhilewada (P5) had red mottles (5YR/2.5YR) in their surface horizons. Few fine Fe-Mn glaebules were observed in rice growing soils (barring the Ap horizon) but in non-rice soils (P4 and P6) these were confined in the 4th horizon onwards. Surface horizons of rice soils were associated with massive structure but sub-angular blocky in non-rice soils. Rice growing soils had wider cracks in surface horizon and slickensides (P1, P3) in deeper layers but non-rice growing soils showed the opposite trend. Except Ap horizons of P5 and P6, all the pedons had clay texture. Rice soils had relatively less smectite in clay-fraction than their corresponding soils of other land uses. Rice soils had lower pH and higher organic carbon content than their non-rice growing counterparts. Ca+2 and Mg+2 ions were dominant in both the groups of soils, but relatively lower in rice soils. XRD of total clay of surface horizons of rice soils showed the dominance of smectite and subordinate amounts of chlorite and small amounts of kaolin (smectite-kaolinite interstratified minerals) whereas non-rice soil was dominated by smectite and had only small amounts of kaolin and traces of chlorite unlike in rice soils. As per diagnostic criteria, P1, P5 and P6 are grouped under Vertic Haplustepts (fine textural family) and others as Typic Haplusterts (sub group) with fine (P3 and P4) and very-fine (P2) textural family classes.