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.
SCANNING ELECTRON MICROSCOPE (SEM) OBSERVATIONS OF SOIL STRUCTURE CHANGES INDUCED BY SODIUM-CALCIUM EXCHANGE IN RELATION TO HYDRAULIC CONDUCTIVITY
Direct SEM observations indicate that reduction in hydraulic conductivity of soils leached with mixed NaCl-CaCl2 solutions of low electrolyte concentrations are related to fine particle dispersion and the formation of a more continuous network of these particles at higher SAR values. This causes blockage of the larger pores in the soil and reduces the rate of water flow by increasing the proportion of small size pores. The changes in a sandy and in a clayey soil were quite similar. Dispersion of the fine particles seems to start at low SAR values (less than 8), but the formation of the network becomes apparent only at SAR greater than 16. /Author/
Nuclear spin-lattice relaxation in transition metal compounds with local tetragonal symmetry.
We report on the various contributions to the total spin-lattice relaxation rate in metallic materials with local tetragonal symmetry. The analytical formulae are given in the tight-binding approximation. The calculations show the relation between various partial electron densities of states and corresponding contributions to the relaxation rates. The presented formulae can be used to compare theoretically calculated electron band structure parameters with those obtained from NMR spin-lattice relaxation time measurements.