Rapid identification and large-scale mapping of salt-affected lands will help improve salinity management in watersheds and ecosystems. This study was conducted to examine spectral reflectance of soils treated with saline solutions containing NaCl, NaHCO3, Na2SO4, and CaSO4.2H2O. Spectral reflectance was measured upon salt crusts formed on two soils (Torrifluvents) subirrigated with saline solutions of 500, 1000, and 1500 mmolc L-1 with a spectroradiometer in the visible and near-infrared region (400-2500 nm). Spectral analyses revealed that samples of gypsum crusts have diagnostic absorption features near 1023, 1225, 1457, 1757, 1800, and 2336 nm, whereas halite crusts have diagnostic absorption features near 1442, 1851, 1958, and 2226 nm. Several broad absorption features were seen in the spectra of the crusts of sodium bicarbonate at 1243, 1498, 1790, 1988, and 2356 nm. The spectrum of soils treated with sodium sulfate exhibited absorption features at 1243, 1472, 1677, 1774, 1851, 1968, and 2245 nm. Crystal size or salt concentrations did not affect the positions of the absorption bands of the salt crusts. However, reflectance increased as particle sizes decreased or with increasing presence of salt crusts. Spectroscopy can be used under certain conditions to identify the presence of primary diagnostic spectral features of gypsum, nahcolite, thenardite, and halite crusts.

Urea in soil is a mobile compound which can be lost by leaching or ammonia (NH3) volatilization. This research examined the contributions of water additions and chemical reactions in explaining the behavior of applied urea.Urea [CO(NH2)2] initially moves undissociated into the soil with added water. Ammonia losses from surface‐applied urea thus decreased with increasing amounts of applied water. Ammonia losses from urea were minimal if injected into the soil 2.5 cm or more, whereas NH3 losses from (NH4)2SO4 (AS) were still high when placed 7.5‐cm deep. Application of AS produced chemically equivalent amounts of Ca and Mg whereas urea and NH4OH precipitated Ca and Mg. The amount of Ca and Mg precipitated increased with decreasing NH3 losses. Precipitation of divalent cations enhanced adsorption of NH4 on soil cation exchange sites, thereby reducing upward movement of NH4 and subsequent NH3 losses. The presence of Ca from reaction of AS with CaCO3 enhanced upward movement of NH4 and increased NH3 losses.

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The degree of salt resistance of Pistacia spp. grown in the western United States is not adequately known. This study evaluated seedling growth and ion uptake characteristics of two Pistacia spp. and one hybrid in outdoor lysimeters for two seasons. After 12 weeks, seedling stem elongation of P. atlantica Desf., P. terebinthus L. (three selections), and P. integerrima Stewart × atlantica (referred to as Gold II) was reduced by an average of 33% at soil solution salinity of 12.6 dS·m-1 (or 8.0 dS·m-1 in the saturation extract). Gold II was the most vigorous genotype and produced the greatest biomass in control and high-salt solutions. Decreases in root and stem growth (average of all seedlings combined) occurred at soil solution salinity of 13.8 dS·m-1 (or 8.7 dS·m-1 in the saturation extract). Increasing salinity resulted in a higher root to stem ratio, which was most pronounced in P. terebinthus. Comparatively small but significant differences in leaf Na and Cl concentrations between species and selections occurred. All species limited Na transport to leaf tissue up to 125 meq Na/liter in soil solution, storing the greatest amount in roots. Chloride concentrations on a dry-weight basis were substantially higher in leaves than in roots. Increasing salinity did not affect leaf K and Mg concentrations, whereas Ca was significantly reduced. Leaf Na and Cl concentrations of P. atlantica and P. terebinthus had significant correlation with Na and Cl concentrations in soil solutions (r = +0.83 to +0.94).

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