Effect of exchangeable sodium percent on surface sealing
Abstract Laboratory studies were conducted to evaluate the effect of exchangeable sodium percent (ESP) on soil surface sealing and of surface sealing on infiltration and evaporation processes. Surface seals with hydraulic conductances 52.20 × 10 −3 , 49.20 × 10 −3 , 39.00 × 10 −3 , 33.00 × 10 −3 , and 17.91 × 10 −3 h −1 were attained on top of a sandy loam soil with ESP of 4 by placing a 5-mm layer of the same soil with ESP's 6, 10, 20, 30, and 60 respectively. Surface sealing increased with increasing ESP and appeared complete at ESP 30. Evaporation remained unaffected by the seals. Infiltration, however, was considerably reduced. Soil water profiles, which largely depended on the amount of infiltrated water, tended to become uniform. Equal moisture contents were also observed under evaporation.
Effects of exchangeable sodium on crusting behaviour of a sandy loam soil
Field and greenhouse studies were conducted at the Central Soil Salinity Research Institute, Karnal, India, to evaluate the effect of exchangeable sodium (ES), amount of water applied, and evaporation and temperature conditions at drying on the crusting behaviour of a sandy loam soil. The exchangeable sodium percentage (ESP) ranged from 5.8 to 30.7 in the field and from 6 to 60 in the greenhouse studies. Soil crusting behaviour was evaluated in terms of crust strength measured by a simulated seedling emergence technique. Water was applied as natural or simulated rainfall. Crust strength increased with ESP, amount of water applied, and temperature, but decreased with increasing evaporation demand. This change in crust strength was steep above ESP 30. Although drying of the crust increased its strength, beyond a certain degree of dryness the disappearance of water films surrounding the soil particles reduced strength for low ESP soils.
Unidirectional hexagonal rare-earth disilicide nanowires on vicinal Si(100)-2×1
Rare-earth disilicide nanowires grown on vicinal Si(100) with a miscut of 2–2.5° toward the [110] azimuth at 600 °C were studied by scanning tunneling microscopy and compared with those grown on flat Si(001). In contrast to rare-earth disilicide nanowires grown on flat Si(100) surfaces, the nanowires grow unidirectionally along the [01̄1] direction of the vicinal Si(100) surface. Rare-earth disilicide nanowires form bundles composed of single nanowire units on both flat and vicinal surfaces. Yet, on the vicinal surface, the bundle width is comparable to the width of the terrace. The average nanowire length on the vicinal substrate is longer than that on the flat substrate. Scanning tunneling spectroscopy shows that the rare-earth disilicide nanowires have metallic properties.