Puddling effects on soil physical properties and rice performance under shallow water table conditions of Tarai

Experiments were conducted with rice (Oryza sativa L.) at Pantnagar in a clay loam soil associated with natural water table fluctuating around 0.25±0.15 m depth from the surface during the season. Puddling reduced water stable aggregates (WSA) of diameter 8 to 1 mm from 21.2 to 3.2% and increased WSA of diameter > 0.211 mm from 28.2 to 59.8%. Similarly mean weight diameter reduced significantly from 1.27 to 0.58 mm. Bulk density in the puddled fallow plot changed from 1.31 to 1.61 Mg m⁻³ in 0 to 0.075 m layer and from 1.35 to 1.68 Mg m⁻³ in 0.15 to 0.225 m layer whereas the corresponding changes in the nonpuddled plot were from 1.33 to 1.36 Mg m⁻³ in 0 to 0.075 m layer and from 1.37 to 1.39 Mg m⁻³ in 0.15 to 0.225 m layer. Puddling reduced hydraulic conductivity of 0.15 to 0.225 m layer by 96.1%. Similarly infiltration rate was reduced by 95.2%, and air-filled porosity by 30.9%. About 78% of rice roots in the puddled plot were restricted to 0 to 0.1 m layer as against only 59.7% in the nonpuddled plot. Depth of penetration and percentage of roots in the lower layers were greater in nonpuddled than in puddled plot. Variation in leaf xylem water potential between puddled (well-watered) and nonpuddled plots was within ±0.025 MPa. Soil moisture in 0 to 0.075 m layer was always above field capacity. Grain yield of direct seeded rice was 387 kg ha⁻¹ lower than the puddled transplanted rice but the yield of straw was 610 kg ha⁻¹ higher under former than latter.