Geeta Tewari

Allelopathic Effect of Echinochloa colona L. and Cyperus iria L. Weed Extracts on the Seed Germination and Seedling Growth of Rice and Soyabean

The present study was undertaken to assess the allelopathic effect of Echinochloa colona L. and Cyperus iria L. in relation to the germination and primary growth of Oryza sativa L. (rice) and Glycine max L. (soyabean). Effects of dichloromethane (DCM) and double distilled water soluble (DDW) fractions of E. colona L. and C. iria L. root and aerial part extracts reduced germination and suppressed early seedling growth of rice and soyabean. With increase in extract concentration from 1 to 100 mg/mL, a gradual decrease in seed germination and seedling length occurred. The highest growth of G. max seedling was recorded in DDW fraction of E. colona aerial part extract at 1 mg/mL concentration with 94% germination and the lowest length was found in DCM fraction of C. iria root extract at 100 mg/mL concentration with 65% germination. In O. sativa, the highest length was noted at 1 mg/mL concentration in DDW fraction of E. colona aerial part extract with 82% germination and the lowest length was found in DCM fraction of C. iria and E. colona root extracts with germination 57% and 62%, respectively, at 100 mg/mL concentration. The results suggested that these weeds had good allelopathic potential which reduces germination and plant growth.

Nickel chemical transformation in polluted soils as affected by metal source and moisture regime.

Abstract A laboratory incubation experiment was undertaken to study the periodic changes in the five sequentially extractable chemical fractions: water soluble and exchangeable (F1), NaOAc extractable (F2), organically bound (F3), Fe–Mn oxide bound or reducible (F4) and residual (F5) of nickel added through industrial sludge or inorganic salt in three soils (acidic, neutral and alkaline) under field capacity and flooding moisture regimes during 16 months. Most of soil Ni was present in the residual fraction (60–89%) in unamended soils. Sludge addition increased NaOAc extractable-, organically bound- and Fe–Mn oxide bound- Ni fraction but decreased the proportion of Ni in residual fraction. With inorganic salt as the Ni source, there was an increase in water-soluble and exchangeable- and NaOAc extractable- Ni fractions in acidic soil. In neutral soil, there was an increase in water-soluble and exchangeable-, NaOAc extractable- and Fe–Mn oxide bound- Ni fractions while NaOAc extractable- and Fe–Mn oxide bound- Ni fractions increased in alkaline soil. After 16-month incubation, Ni added as inorganic salt was transformed from the water soluble and exchangeable fraction into the NaOAc extractable fraction in acidic soil. In neutral soil, the water soluble and exchangeable fraction transformed into NaOAc extractable- and organically bound fractions while the water soluble and exchangeable Ni fraction transformed into Fe–Mn oxide bound fraction in alkaline soil under both moisture regimes. With sludge as the Ni source, added Ni was transformed from water-soluble and exchangeable- and residual fractions into the Fe–Mn oxide bound fraction in all soils irrespective of the moisture regime.

Chemical transformation of copper in some sludge-amended soils

In a laboratory incubation study, the periodic changes in different chemical fractions of copper (Cu) in three sludge-amended soil types (acidic sandy clay loam, neutral clay loam and alkaline clay loam) of varying soil reaction were monitored under field capacity and flooding moisture regime over 16 months. The water soluble and exchangeable fraction of Cu was very low (≤1% of total Cu) in all three soil types. At the end of incubation (16 months), the sodium acetate extractable (carbonate sorbed)- and residual-Cu fractions transformed into Fe-Mn oxide fraction, irrespective of moisture regime in all three soil types. However, the extent of transformation varied among soils.