Thesis (Ph. D.) -- University of Adelaide, Dept. of Soil and Water, 2000. / Includes bibliographical references (leaves 173-207). Also available on the Internet.

2 pp.

Bibliography: leaves 173-207 / xxiv, 211 leaves : ill., map ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Soil and Water, 2000

Improving productivity of sodic soils has become a concern in North Dakota because of the desire for more land for producing crops. Field and incubation studies were conducted to determine the impacts of different amendments (flue-gas desulfurization gypsum, sugar beet processing by-product lime, and langbeinite) on the chemical and biological properties of two sodic soils. The field study evaluated the amendment effects on the chemical conditions of the soil and the impact on alfalfa yield and quality. Differences were not observed in percent sodium (%Na) in the first 17 months and alfalfa yield was not impacted by the treatments except for the high rate of langbeinite. The incubation study investigated the effects of amendments on both the chemical and biological properties of the soil. Spent lime increased the cumulative respiration but was not impacted by gypsum or langbeinite. Labile carbon (C) was negatively correlated with %Na and electrical conductivity (EC). / North Dakota Soybean Council

Thesis (M.Ag.Sc.)--University of Adelaide, Dept. of Soil and Water, 2002. / Includes bibliographical references (leaves 78-86).

Bibliography: leaves 147-170. Aims to determine the influence of sodicity on the nature and decomposition of organic matter; and the influence of organic matter and its components on the structural stability of sodic soils.

[Abstract]: Scarcity of fresh water has led to use of low quality waters (high sodicity and salinity) that were considered unsuitable for irrigation in the past. Mismanagement of irrigation using this water can increase the potential for soil degradation and limit crop production in the long term. Irrigation using highly saline-sodic water requires appropriate management to avoid long term development of sodicity and salinity problems. The main factors that control the sodicity and salinity problems are maintenance of sufficientleaching and avoidance of soil structure degradation due to sodicity. The management options are determined by complex factors such as soil type and condition, water quality, irrigation practice and crop type.Investigating the management options for using highly saline-sodic water in irrigation experimentally is costly and time consuming. However, it could be done using anappropriate modelling tool that can handle the degradation of soil structure due to sodicity along with the chemical reaction system within the soil profile. UNSATCHEM has been widely used to model sodicity and salinity effects under irrigation. It has a feature to deal with soil structure degradation along with water and solute movement, major ion chemistry, CO2 production and movement and heat transfer under sodic conditions. It uses a hydraulic conductivity reduction function torelate the change of chemical properties to the change in hydraulic properties of the soil. However, the evaluation of the hydraulic conductivity reduction function underhigh sodicity during simulation has not been done. Hence, the core of this research project has been to improve quantification of soil structure degradation under sodicconditions and enhance the modelling of water and solute movement under sodic conditions. The hydraulic conductivity reduction function incorporated inUNSATCHEM was evaluated using data obtained from soil column experiments.Columns of two local soils were used in an experiment to investigate the effect on soil structural stability of different amendments to highly saline-sodic water rich withbicarbonates (EC = 4.6 dS/m and SAR = 117). The column experiments were used to examine the effect of reducing water pH to different levels using sulphuric acid andcombined gypsum and dilution treatments. It was found that reducing the pH of highly saline-sodic water did not enhance soil structural stability as the water applied hasnaturally high relative sodium concentrations. However, the application of diluted highly saline-sodic water amended with gypsum showed no significant effect on soil structure and permeability. It is concluded that different amendments associated with appropriate irrigation management can be applied to sustain irrigation and prevent long term salinity and sodicity problems.The data from the column experiments was used to evaluate the quantification of the soil structure degradation in UNSATCHEM. The resultant simulations for the soilcolumns showed that the estimated outflow and hydraulic conductivity were less than the experimental measurements, which suggested that the soil structure degradationwas not accounted for properly. The sodicity effect was accounted for in UNSATCHEM by a reduction function, which is a combined function of the McNeal (1968) clay swelling model and the Simunek et al. (1996) pH effect equations. The empirical pH effect equation accounts for the reduction of the conductivity due to increasing pH and clay swelling. The evaluation of UNSATCHEM under highly sodic conditions suggests that the hydraulic conductivity reduction function is limiting the UNSATCHEM performance.Consideration of the first term of the hydraulic conductivity reduction function (i.e. the McNeal (1968) clay swelling model) has highlighted the weaknesses of the McNeal model and led to develop a generic clay swelling model (GCSM). Calibration of the GCSM using the data of McNeal showed good agreement between the estimated and measured relative conductivity data. Further calibration of the GCSM using relative conductivity data obtained for five local soils also showed good agreement between the model estimation and the measured data.Coding of the generic clay swelling model into UNSATCHEM and re-simulating the column experiments showed that the modelling process is improved compared with theUNSATCHEM version containing the McNeal (1968) clay swelling model. However, the outflow and conductivity values produced were still less than measured values. This result suggested that further investigations are required to identify the effect of pH on the change of hydraulic conductivity, cation exchange capacity, and the exchangeable sodium percentage. Further research is also required regarding bicarbonate chemistry duringapplication of highly saline-sodic water.

Bibliography: leaves 147-170. / x, 170 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Aims to determine the influence of sodicity on the nature and decomposition of organic matter; and the influence of organic matter and its components on the structural stability of sodic soils. / Thesis (Ph.D.)--University of Adelaide, Dept. of Soil Science, 1998?

Thesis (Ph. D.)--University of Adelaide, Dept. of Soil Science, 1998? / Includes bibliographical references (leaves 147-170).

Thesis (M.S.)--University of Wyoming, 2007. / Title from PDF title page (viewed on June 16, 2008). Includes bibliographical references (p. 60-62).