Two laboratory experiments were conducted to study the effects of salt and nitrogen-sulfur compounds on the transformations of nitrogen in three Arizona soils. In the first experiment the effect of NaCl in concentrations of 0 to 1 m (molal) at moisture levels of 1/3 and 15 bars was studied in the Gila and Laveen loam soils. At 1/3 moisture nitrification of urea-¹⁵N and native soil nitrogen was appreciably reduced only at 1 m salt level. At 15 bars moisture, nitrification was almost completely inhibited by the 1 m salt concentration. Mineralization of soil nitrogen was reduced more by decreasing moisture than by increasing salt concentrations. Ammonia volatilization was increased by both salt and moisture stress and was associated with inhibition of nitrification. Slight effects of salt were observed on ¹⁵N immobilization and ¹⁵N recovery (including volatilization). In the second experiment nitrogen-sulphur combinations (¹⁵N labelled) of KNO₃, KNO₃ + S, urea, urea + S, APS (ammonia polysulfide) and Thiosul (ammonium thiosulfate) were studied at field capacity (FC) and 1.5 FC moistures. In the calcareous Gila soil nitrification was suppressed by the presence of sulfur at 1.5 FC moisture. Volatilization losses were appreciable only from APS. Immobilization of ¹⁵N was greatest from treatments with the higher sulfur rate (elemental S). Denitrification was slightly increased by sulfur at FC, however, at 1.5 FC dramatic losses occurred by denitrification (autotrophic in the presence of sulfur, especially with elemental S. The nitrifying ability of the slightly acid and coarse textured Sonoita soil was low. Nitrification was suppressed more by the presence of sulfur at both moistures. Ammonia volatilization was appreciable from APS followed by urea. ¹⁵N immobilization was high from urea followed by APS. Appreciable losses by denitrification occurred only with APS. The Sonoita soil showed a lower sulfur oxidizing power than the Gila with the only appreciable rate of oxidation from Thiosul followed by APS.

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Thesis (M. Agric. (Plant Production)) -- University of Limpopo, 2018 / The evergreen Red Milkwood (Mimusops zeyheri Sond.) is being targeted as a rural and urban-greening tree in Limpopo Province, due to its excellent nutritional, pharmaceutical and aesthetic attributes. Slow growth of M. zeyheri seedlings is the main drawback in the potential domestication and commercialisation of this tree species. The objectives of this study were to determine (1) the influence of soil type on root growth and foliar nutrient elements in M. zeyheri seedlings, (2) the degree of salt tolerance in M. zeyheri seedlings and (3) the influence of vesicular arbuscular mycorrhiza (VAM) fungi on growth of M. zeyheri seedlings. Objective 1 was achieved in clay, calcareous, loam and sandy soils. At 60 days after the treatments, soil type effects were significant on plant height, leaf number, chlorophyll content of primary leaves (dicots), chlorophyll content of secondary leaves, root length, number of root branches and dry root mass, contributing 60, 72, 84, 85, 74, 80 and 40% in total treatment variation (TTV) of the respective variables. Objective 2 was achieved by exposing seedlings to 0, 2, 4, 8, 16, 32, 64 and 128 NaCl + CaCl2 mM/m3 at 3:1 ratio. At 90 days after the treatments, salinity effects were significant on leaf number, dry shoot mass, root length and leaf length, contributing 73, 60, 50 and 64% in TTV of the respective variables. Leaf number, dry shoot mass, root length and leaf length each against increasing concentration of salinity exhibited positive curvilinear quadratic relations, with 74, 91, 95 and 66% associations, respectively. Responses of essential nutrient accumulation in leaf tissues of M. zeyheri to salt treatments had significant effects on K and Na, contributing 28 and 19% in TTV of the respective variables. Potassium over increasing salt concentrations exhibited positive quadratic relations and Na over increasing salt concentrations, exhibited negative quadratic relations. The models for each relation were explained by 95 and 86%, respectively. Objective 3 was achieved by exposing seedlings to 0, 10, 20, 30, 40, 50, 60 and 70 g VAM per plant. At 90 days after the treatments, VAM effects were significant on plant height, leaf number, stem diameter and chlorophyll content contributing, 49, 65, 60 and 61% in TTV of the respective variables. Plant height, leaf number and chlorophyll content each against increasing VAM levels exhibited negative quadratic relations, with 97, 83 and 80% associates, respectively. In conclusion, the use of soil type to promote growth and accumulation of essential nutrient elements on M. zeyheri seedlings demonstrated that clay soil could be suitable for cultivation of M. zeyheri. Also chloride salt concentrations included all three phases of density-dependent growth (DDG) patterns, whereas VAM levels used in the study were already in the last two phases of DDG patterns. Vesicular arbuscular mycorrhiza treatment did not have significant effects on Ca, Fe, K, Na and Zn in leaf tissues of M. zeyheri seedlings. In conclusion, soil with high clay content could be ideal when raising M. zeyheri seedlings. However, salt concentration of 8.11 mM/m3 exhibited the stimulation of M. zeyheri seedlings growth, Therefore, lower concentration less than 8.11 mM/m3 shown to be toxic by reducing the plant growth. In contrast, 5.554 g per plant of VAM will supreme for growth and development of M. zeyheri seedlings.

Includes bibliographical references (leaves 78-86) In the Herrmanns sub-catchment in the Mt. Lofty Ranges (near Mt. Torrens) soil sodicity was the dominant factor in causing clay to disperse in the eroded area along the foot slopes, wheras in non-eroded areas of the mid-slopes and on the stream banks, the dispersive power of sodicity was attenuated by the flocculative power of other soil properties.

Copies of author's previously published articles in pocket inside back cover. Bibliography: leaves 147-160. This thesis outlines the factors affecting soil strength and structural stability and their interrelationship in salt-affected soils. The objectives of this study are to investigate the influence of clay particles on soil densification and mellowing, the mellowing of compacted soils and soil aggregates as influenced by solution composition, the disaggregation of soils subjected to different sodicities and salinities and its relationship to soil strength and dispersible clay and the effect of organic matter and clay type on aggregation of salt-affected soils.

The purpose of the study was to determine the effect of four salt concentrations and four acid levels of soil solution on the germination of Quercus emoryi and Robinia neo-mexicana seeds, and to study the effects of the cation concentration changes in solution (Na, Ca, Mg, K) and exchangeable cation concentration. The solution extracts and exchange phases of both soils, salt accumulation in the soil increased by increasing the salinity and acidity of the water applied. Exchangeable sodium was related directly to the SAR of the applied solutions. The soil responded differently to the salty water and acid water. Both soil treatments released Ca, Mg and K to the soil solution from the dissolution of the primary minerals and cation exchange reaction.

A field study was conducted for two years in three semi-arid regions of Syria in order to define, under field conditions, the wheat (Triticum aestivum L.) yield response function to irrigation water salinity and to study the process of soil salt accumulation. The three regions experience similar climatic conditions (semi-arid Mediterranean climate) but have different soil textures, varying from sandy loam to clay. The study involved 74 farms all of which had been irrigating for more than 3 years prior to this study, with well water of different salinity values (0.44 to 14.1 dS/m). All of these farms operated with similar cultural practices. / Results indicate that the wheat yield response function to irrigation water salinity differs between the three regions. The irrigation water threshold salinity value beyond which wheat yield started to decline, was found to be 6.5 dS/m, 3.5 dS/m and 1.2 dS/m in the Khabur low plains; Aleppo south plains and Shedadeh area respectively. Wheat was more salt tolerant to irrigation water salinity in sandy loam soils than clay loam soils. The three threshold values obtained in this study are different from the "universal" value of 4 dS/m which is proposed in current literature. The "universal" value was obtained from artificially salinized field plots seeded under non-saline conditions. / In addition, it was found that salt accumulation in the soil profile increases as soil clay content increases. / The results demonstrate the necessity of establishing regional water quality criteria when planning the use of saline water sources for irrigation in semi-arid regions.

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The effects of high sodium chloride (NaCl) levels on Na and nutrient retention of three soil substrates and on littleleaf linden growth in different soil substrates were studied in the laboratory and the greenhouse, within the framework of a substrate selection program for trees planted in downtown Montreal. In addition, the effects of the structural soil (SS) compaction were studied in the first greenhouse experiment. The first greenhouse experiment was established in a factorial arrangement of four soils x four salt levels in a completely randomized design with five replicates. The four soil types were (1) L with a bulk density (BD) of 1.53 g/cm3, (2) LP with a BD of 1.26 g/cm3, (3) SS with a BD of 1.8 g/cm 3 (SS1.8), and (4) SS with a BD of 2.0 g/cm3 (SS2.0). The second greenhouse experiment had a split plot design. Two fertilization levels (with fertilizer and without fertilizer) were randomly arranged as the main plots on ten benches. Within each main plot, the combinations of three NaCl levels (0, 0.5 and 1.0 g NaCl/kg soil) and three soil substrates (L with a BD of 1.40 g/cm3, LP with a BD of 1.13 g/cm 3 and SS2.0) were randomized in the sub-plots. Results from the laboratory leaching experiment indicated that SS had the fastest Na leaching rate and highest Na loss, while LP retained more Na than SS or L. (Abstract shortened by UMI.)