ANISOTROPIC MEMBRANE TRANSPORT†

Membranes consisting of two layers, one of which has a concentration-dependent permeability, may show anisotropic fluxes. In other words, the flux under a given concentration difference has a different magnitude if the direction of the concentration difference is reversed but its magnitude is unchanged. This paper develops a simple theory of this effect and verifies aspects of this theory experimentally.     

The effect of soil pH and chemical form of nitrogen fertilizer on heavy-metal contents in ryegrass

Ryegrass was grown in pots containing metal-enriched soil which was adjusted to different pH levels with acid or lime, and supplied with either ammonium sulphate or calcium nitrate as the N fertilizer.Concentrations of heavy metals in the grass tops increased with decreasing soil pH to an extent diminishing in the order: Mn, Ni, Cd, Zn, Pb, Cu, Cr.Nitrate application was the more appropriate treatment for the production of lower concentrations of heavy metals in the grass because its use by the grass increased the pH of the soil, whereas added ammonium sulphate released acid to the soil during nitrification and plant uptake of ammonium. After three successive cuttings and repeated dressings, soil pH (H₂O) was 3 units higher with nitrate than with ammonium, resulting in a marked reduction in the uptake of the more pH-sensitive metals in soils where nitrate was applied