No description available.

The efficacies ofsoil extraction methods, namely, Soxhlet, sonication, agitation, alkaline digestion and the ethyl acetate micro-method, for monitoring soil bioremediation were evaluated using three soil types, Swartland, Rensburg and Hutton, encompassing the mineralogical range prevalent in Kwa Zulu Natal. Phenol, atrazine and the BTEX component of petrol were the molecules used in this study and were extracted under different spiking concentrations, after prolonged ageing times up to 21 days and after changing the composition of the spiking solution. It was concluded that extraction methods must be validated for the specific conditions under which they would be used, taking into consideration, soil type, spiking solutions, moisture content, weathering times and the analyte(s) in question. A preliminary appraisal of atrazine degradation in a Hutton soil was then made under the conditions of sterilized, fertilized/non-fertilized and non-sterilized, fertilized/nonfertilized soils. The predominant pathway of atrazine degradation was deemed to be chemically/abiotically mediated due to the soil pH and the presence of iron and aluminium oxides as well as the high levels of manganese in the soil. The results obtained prompted further study into atrazinecatabolism using soil-slurry reactors, under the conditions of carbon-limitation, nitrogen limitation, carbon/nitrogen non-limitation and carbon/nitrogen limitation. A comparison was made between inoculated and non-inoculated bioreactors. The ability of the indigenous microbial population to return the Hutton soil to its original pristine state was confirmed. The expense of inoculation and culture maintenance could be avoided since carbon and nitrogen supplementation would be as equally effective as inoculation. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 2002.

This study examined the influence of different management practices under sugarcane production on soil chemical, biological and physical properties on a long-term (59yr) field experiment in KwaZulu-Natal. These management practices included conventional post-harvest burning of crop residues, with the tops either left on the soil surface or with tops removed, and green cane harvesting with the retention of crop residues on the soil surface as a trash blanket. Each of these treatments were either fertilized or did not receive fertilizer. The data collected was used to evaluate the effect of crop residue management on soil quality under sugarcane production. Soil organic matter content increased from 39 g C kg¯¹ soil, under conventional burning to 55 g C kg¯¹ soil in the surface 10 cm under green cane harvesting where crop residues are returned to the soil. It also resulted in greater recycling of nutrients and increases in exchangeable K and Ca and extractable P. Fertilizer application resulted in a build-up of soil nutrients in combination with trash retention. Fertilizer application induced increases in exchangeable P and also some accumulation in soil organic P. Exchangeable and non-exchangeable K concentrations were also higher in fertilized than non-fertilized treatments. However, nitrogen fertilizer application and, to a lesser degree, organic matter mineralization, resulted in soil acidification to a depth of 30 cm. Acidification in the fertilized treatments resulted in a concomitant increase in exchangeable acidity and exchangeable Al, due to the increase in H⁺ ions and solubilized Al species on exchange sites. Base cations moved into soil solution and were leaching to lower soil layers. The decrease in soil pH resulted in the surface charge conferred on the variable charge surfaces on soil colloids becoming less negative and as a result there was a decrease in ECEC. Acidification in fertilized treatment not only increased exchangeable Al but also the buffering reserve of non-exchangeable al; both that complexed with soil organic matter (CuCl₂- extractable) and that present as hydroxy - Al associated with mineral colloids (ammonium acetate - extractable). The increased organic matter content under trash retention resulted in an increase in ECEC. This enabled the soil to retain greater amounts of Ca²⁺, Mg²⁺ and K⁺ which were returned to the soil in the trash. Both residue retention and fertilizer application had a positive effect on the microbial biomass C and N and the microbial quotient increased from 0.39% to 0.86% as organic C increased from 39 g C kg¯¹ soil under burnt treatments to 55 g C kg¯¹ soil under trashed, fertilized treatments. This increase was associated with increased concentrations of labile organic material (K₂S0₄₋extractable) present as well as increased amounts of nutrients being cycled through the plant-soil system. The light fraction organic matter also increased with increasing returns of organic residues. However, the large active microbial biomass under the trashed, fertilized treatment resulted in an increased turnover rate of this fraction and consequently resulted in lower LF dry matter, C and N than in the unfertilized treatment. Aggregate stability increased with increasing amounts of organic material returned due to trash retention. Nevertheless, fertilized treatments induced a lower aggregate stability than unfertilized ones, despite the tendancy for the latter to have higher organic C and microbial biomass values. This was attributed to an increase in the proportion of exchangeable cations present in monovalent form (due to application of fertilizer K and leaching of Ca and Mg) favouring dispersion and a decline in aggregate stability. Green cane harvesting resulted in an increase in microbial activity (basal respiration, FDA hydrolytic activity, arginine ammonification rate and dehydrogenase activity) and in the activity of specific soil enzymes involved in turnover of C, N, P and S to a depth of 30 cm. Increased activities of these enzymes reflect a higher rate of turnover of C, N, P and S. The metabolic quotient decreased with increasing residue return, indicating a more metabolically efficient microbial community. Fertilizer application resulted in a variable effect on enzyme activity. Long-term fertilizer application resulted in an increase in invertase and acid phosphatase, a decrease in L-histidase and arylsulphatase and had little effect on protease and alkaline phosphatase. These variable effects were explained in terms of an interaction between fertilizer - induced increases in Corg and soil nutrient status and fertilizer - induced soil acidification. The size and activity of the soil microbial biomass was studied in the plant row and in the inter-row of a sugarcane field under burning or green cane harvesting. Soils were sampled to 30 cm depth in (i) the centre of the plant row, (ii) 30 cm out from the row centre and (iii) 60 cm out from the row centre (i.e. the middle of the inter-row area). Under burning, the only substantial input of organic matter to the soil was from root turnover in the row area where the root biomass was concentrated. As a consequence, the size (microbial biomass C) and activity (basal respiration of the soil microbial community were concentrated in the row. However, under green cane harvesting there was a large input of organic matter in the inter-row area in the form of the trash blanket itself and through turnover of crop roots that were concentrated in the surface 10 cm of the soil below the blanket. As a result, soil microbial activity was considerably higher in the interrow area under green cane harvesting than under burning. Phospholipids are essential membrane components of microorganisms and a good correlation was found between the total PLFA's extracted from soils and the microbial biomass C, indicating that phospholipids are an accurate measurement of living biomass. Mutivariate statistical analysis (PCA) was used to separate different PLFA profiles under burning versus trash retention and under different land uses (sugarcane, maize, annual and perennial pasture and undisturbed veld). Soil organic matter content contributed the greatest variance in the data along the first axis. That is increasing soil organic matter return not only increased the size of the microbial biomass, but also affected the composition of the microbial community. There was a shift in the different sub-fractions under different management practices. MUFA's are general biomarkers of Gram negative bacteria and were found to be a sensitive indicator of higher substrate availability (i.e they increased under green cane harvesting). Fungal biomarkers indicated an increased fungal biomass associated with surface application of residues. Soil physical conditions were considered to be a contributing factor to the shift in microbial community structure. Increased organic matter content improved soil physical conditions and preferentially stimulated the growth of aerobic microorganisms. In addition to this, the proportion of SATFA (gram positive bacteria) was found to increase in response to burning. This increase was attributed to the survival mechanisms of these microorganisms (i.e. endospore formation). It was found that the conversion from burning to trash management changes the composition of the soil microbial community. The effect of management practices on soil functional diversity was also evaluated using two methods (i.e. Biolog plates and substrate induced respiration (SIR)). Biolog plates are a selective technique that stimulate growth of a small proportion of the soil microbial community whereas the SIR technique measures the activity of the metabolically active microbial community in situ. As a result the SIR method separated treatments more effectively than Biolog plates (i.e. annually tilled treatments, permanent grassland sites and fertilized and unfertilized treatments). The quantity and the quality of organic C supply influenced the catabolic diversity. Conversion from burning to green cane harvesting greatly increased catabolic evenness and richness and therefore presumably also tended to increase the resilience of the soil to stress and disturbance particularly in relation to decomposition functions. It was concluded that conversion from preharvest burning to green cane harvesting results in an increase in soil organic matter content, an improvement in soil structure and soil nutrient status, an increase in the size, activity, taxonomic and functional diversity of the soil microbial community. The practice should therefore be promoted to the South African sugar industry. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 2003.

In many acid, highly leached South African soils, Na levels are very low. Applications of Na to highly leached soils may be advantageous in some situations as Na has been shown to interact with soil acidity, P availability, and K nutrition of plants. It was found that an increased level of Na at constant anion concentration in the soil solution resulted in lower soil solution pH and Al3 + activity, and improved maize root penetration into an acid subsoil (pot trial). In another pot trial, Na did not improve lucerne root growth into the same subsoil. In a field trial on a limed, low-Na soil with severe subsoil acidity, the effects off our rates of Na, three Na carriers, and three rates of gypsum on maize growth were compared. In three out of four seasons grain yield responses to the Na applications were positive, and of a similar magnitude to the response to gypsum (455-925 kg ha). In another field trial with maize, responses to Na (of up to 1027 kg grain ha) were recorded in two out of three years on plots with topsoil acid saturations of greater than 45%. The reason for the responses to Na was probably improved subsoil rooting as a result of modified soil solution composition in the presence of Na. In a field trial with Italian rye grass on an acid, highly weathered soil, the effect of sodium applications were investigated at different levels of lime and K. In the first season, 200 kg ha Na as NaCl increased dry matter yield from 11289 kg ha to 12815 kg ha , Sodium responses were possibly due to enhanced P uptake, or Na substitution for K, or a combination of the two mechanisms. No consistent lime x Na interaction was observed. Potassium and Na applications affected the mineral balance of the herbage produced. Potassium depressed herbage Ca, Mg and Na concentrations, and Na depressed herbage Ca and Mg where herbage K was low, but had no effect on herbage K. Where soil P and K reserves are marginal, rye grass pastures may benefit from Na applications. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 2000.

Abstract available on PDF file. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1978.

The relationship between soils, soil water and stream chemistry was investigated for a first order stream in a small forested watershed in the southern Laurentians, Quebec. The study was restricted to near-stream processes, particularly how the chemistry of water leaving a hillslope influenced stream chemistry. For snowmelt, 1986, a number of naturally occurring chemical elements were used to separate stream flow into three subsurface flowpaths: groundwater, solum and upwelling flow. By quantifying upwelling flow, we introduced a new approach to identify solutions forced from the groundwater up through the solum before entering the channel. In upwelling flow, we found that dissolved silicon was reactive and total aluminum, monomeric aluminum, hydronium, magnesium and fluoride were non-reactive. For spring storms, 1992, we used an end member mixing approach to describe streamwater as a combination of chemically distinct solutions from different depths in the soil. Solutions were defined by concentrations of calcium, magnesium, sodium and dissolved silicon. The contributions of water from each soil depth were estimated using the variations in end member chemistry that were measured during the storms. Hydrological reconstructions of the events were possible and it was found that the contribution of water from each depth in podzols is related to the height of the water table in the near-stream soils.

No description available.

The use of on-site wastewater treatment systems for the treatment and dispersal of domestic effluent is common in urban fringe areas which are not serviced by centralised wastewater collection systems. However, due to inappropriate siting and inadequate evaluation of soil characteristics, the failure of these systems has become a common scenario. The current standards and guidelines adopted by many local authorities for assessing suitable site and soil conditions for on-site dispersal areas are coming under increasing scrutiny due to the public health and environmental impacts caused by poorly performing systems, in particular septic tank-soil adsorption systems. In order to achieve sustainable on-site wastewater treatment with minimal impacts on the environment and public health, more appropriate means of assessment of long term performance of on-site dispersal areas are required. The research described in the thesis details the investigations undertaken for the development of robust assessment criteria for on-site dispersal area siting and design and assessment of the long term performance of soil dispersal areas. The research undertaken focused on three key research areas; (i) assessment of site and soil suitability for providing adequate treatment and dispersal of domestic wastewater; (ii) understanding sorption, purification and transport processes influencing retention and release of pollutants and the natural controls governing these processes and (iii) the development of assessment criteria for long term behaviour of soils under effluent dispersal. The research conducted was multidisciplinary in nature, with detailed investigations of the physical and chemical processes involved in on-site wastewater treatment and dispersal. This involved extensive field investigations, sampling and monitoring, laboratory and soil column testing and detailed data analysis across the fields of soil science, groundwater quality, subsurface hydrology, chemical contamination, and contaminant fate and transport processes. The interactions between these different disciplines can be complex which resulted in substantial amounts of data being generated from the numerous field and laboratory investigations and sampling undertaken. In order to understand the complex relationships that can occur, multivariate statistical techniques were utilised. The use of these techniques was extremely beneficial. These techniques not only allowed not only the respective relationships between investigated parameters to be identified, but also adequate decisions based on the correlations were able to be formulated. This allowed a more appropriate assessment of the influential factors, and the prediction of ongoing changes to soil properties due to effluent disposal. The primary outcomes for this research were disseminated through a series of peer reviewed scientific papers centred on these key disciplines. The assessment of site and soil suitability was achieved through extensive soil sampling throughout the study areas and detailed laboratory testing and data analysis. The study identified and investigated the role of influential site and soil characteristics in the treatment performance of subsurface effluent dispersal areas. The extent of effluent travel and the ability of the soil to remove pollutants contained in the effluent by adsorption and/or nutrient uptake were investigated. A framework for assessing the renovation ability of the major soil groups located throughout Southeast Queensland was also developed. The outcomes provide a more rigorous scientific basis for assessing the ability of soil and evaluating site factors to develop more reliable methods for siting effluent dispersal areas. The resulting assessment criteria developed was compared with soil column studies to determine the robustness and validity of the outcomes. This allowed refinement of the assessment criteria in developing a more reliable approach to predicting long term behaviour of soils under sewage effluent dispersal. Multivariate techniques assisted in characterising appropriate soils and to determine their long-term suitability for effluent treatment and dispersal. The assessment criteria developed included physical, chemical and sub-surface hydrological properties of a site and soil which can be used to predict suitability for long term effluent treatment and dispersal. These include:  Moderate to slow drainage (permeability) to assist the movement of effluent (percolation) through the soil profile and allow adequate time for treatment and dispersal to occur. With longer percolation times, the opportunity for exchange and transport processes increase.  Significant soil cation exchange capacity and dominance of exchangeable Ca2+ or exchangeable Mg2+ over exchangeable Na+. Although a soil dominated by Mg2+ is found to promote dispersion of soil particles to some extent, its impact is far less than that of Na+. A stable soil would have a Ca: Mg ratio > 0.5.  Low exchangeable Na+ content to maintain soil stability.  Minimum depth of 400mm of potentially unsaturated soil before encountering a restrictive horizon, to permit adequate purification to take place.  Clay type with Illite and mixed mineralogy soils being the most sensitive to Na+. In general, significant increases in ESP occur in soils with 30 to 40% clay and in the presence of illite clay. Small amounts of smectite clays enhance treatment potential of a soil. The research outcomes have significantly contributed to the knowledge base on best practice in on-site dispersal area siting and design. The developed predictive site and soil suitability assessment criteria allows more appropriate evaluation of site and soil characteristics for providing long term effluent renovation. This is generally not done in the current assessment techniques for on-site dispersal areas. The processes and techniques used in the site and soil suitability assessment, although based on the common soil types typical of South East Queensland, can be implemented in other regions, provided appropriate soil information is collected or available. The predictive assessment criteria have been developed at a generic level, allowing easy implementation into most assessment processes. This gives the framework the flexibility to be developed for other areas specifically targeting the most influential on-site dispersal area siting and design factors, and assessment of long term performance under wastewater application.

The influence of hyperaccumulator and phytostabilizing plants on soil solution chemistry and subsequent metal dynamics in the rhizosphere was investigated to gain a better understanding of the mechanisms governing metal availability and plant uptake at the soil:root interface during phytoremediation of metal contaminated soils.

The soils of Australia have extensive macro and micronutrient disorders varying greatly in their capacities to provide the chemical nutrients essential for plant growth. Assessment of nutrient availability in soils is important in order to maximise fertilizer efficiency and crop yields and to minimise environmental pollution associated with over fertilisation. Nutrient availability has proven difficult to assess due to the complexity of trace element soil chemistry and plant uptake mechanisms. The relatively new method, Diffusive Gradients in Thin Films ( DGT ), provides the potential to become an alternative soil test that could accurately predict nutrient availability. To date, DGT technology has only been designed for separate assessment of anionic and cationic species in waters or soils typically at concentrations characteristic of highly contaminated systems. In this study a new mixed binding gel ( MBL ) was developed capable of simultaneous assessment of cations and anions in a single assay at concentrations more representative of uncontaminated agricultural soils, sediments and waters. The MBL has the potential to eliminate measurement errors associated with very fine spatial scale changes in element concentrations in these environments. The MBL consisted of ferrihydrite and Chelex - 100 cation exchange resin combined together in a binding gel. Results from the MBL were comparable to experiments performed using individual Chelex gels and ferrihydrite gels that have been shown to work successfully for DGT methodology. To facilitate combined analysis of P and cations by ICP - MS, HCl ( 1 M ) was used for gel elution to minimise interferences from [superscript 14] N [superscript 16] OH or [superscript 15] N [superscript 16] O on [superscript 31] P. All elements tested ( Cd, Cu, Mn, Mo, P and Zn ) were bound successfully to the MBL. DGT measurements obtained using the MBL on agricultural soils correlated well ( r ? = 0.95 ) with measurements obtained using pure Chelex and ferrihydrite binding layers. This suggests that the MBL could be used for simultaneous measurement of cationic and anionic element availability in soils. Performance of the Diffusive Gradient in Thin Films ( DGT ) technique was compared with three other common testing methods ( Colwell, Olsen, Resin ) for available soil P in terms of the ability of each to predict wheat, canola, lupin and barley responsiveness to applied P on 21 Australian agricultural soils. DGT accurately predicted plant responsiveness in > 90 % of the soils used. In contrast the other soil testing methods failed to correctly predict plant response to P on numerous occasions. These observations reveal that the DGT technique with the newly developed MBL can predict plant available P on these soils with greater accuracy than other traditional soil P testing methods and could become a useful tool for predicting P fertilizer requirements. The DGT method using the MBL was also used to test Zn deficiency thresholds for canola and wheat in a manufactured soil ( acid washed sand ). DGT successfully determined the threshold for Zn deficiency in this soil, overcoming detection limit issues usually accompanying such low levels of Zn. This method also provides that potential to assess other micronutrients ( Mn, Cu ) and with further modification potentially assess K. Before DGT can become established as an alternative soil testing method, validation of the performance is required under field conditions. This study has shown that it out performs current common soil testing methods in glasshouse conditions but questions still remain if this will be reflected out in the field. / Thesis (Ph.D.)-- University of Adelaide, School of Earth and Environmental Sciences, 2007.