Lake Eola is an eutrophic, land-locked lake located in downtown Orlando, Florida. It has a surface area of approximately 27 acres (11 .0 Ha) and a maximum water depth of 22 feet (6.7 meters) near the center. Sediment samples were collected from the lake bottom at various water depths and analyzed for physical characteristics and phosphorus content. Lake water samples were collected and analyzed for selected parameters as related to sediment phosphorus dynamics. Phosphorus release from agitated, aerobic sediment samples was measured in laboratory batch experiments. Phosphorus release from anaerobic hypolimnetic sediments was measured by utilizing~ situ isolation chambers. Results indicate that phosphorus release from anaerobic Lake Eola sediments can be described by the Freundlich isotherm, indicating that release may be a desorption process. Phosphorus budget calculations indicate that the phosphorus that accumulates in the hypolimnion of Lake Eola has the potential for increasing productivity when overturn occurs.

The composition of a community and the environmental conditions in which they exist fundamentally influence productivity and responses of systems to change. In the Northern Gulf of Mexico (NGoM), the relationships between nutrients, salinity, and phytoplankton populations are complex and have been changing over time. This work focuses on describing and analyzing: 1) a case study of diversity and recommendations for change within an academic institution; 2) spatial and temporal trends in surface dissolved inorganic nitrogen (DIN) and phosphorus (DIP) in the NGoM over 35 years; 3) nutrient addition experiments (NAEs) to determine prevailing NGoM surface slope region nutrient limitation; and 4) NGoM surface continental slope phytoplankton community composition and dynamics. Over time, academic institutions have not made progress toward increasing diversity, equity, and inclusion (DEI) in the geosciences. The first chapter of this work serves as a roadmap for other institutions to make progress toward ingraining DEI frameworks into the foundations of our institutional systems. Toward explaining trends in nutrients from 1985 to 2019, I compiled the largest data set of NGoM surface dissolved nutrient concentrations to date and analyzed it to delineate spatiotemporal trends and identify potential drivers of nutrient change. DIP concentrations in both the Mississippi-Atchafalaya River system (MAR) and in the NGoM increased over time, but the increase of NGoM DIP exceeded the DIP loads coming from only the MAR, suggesting additional sources of P to the NGoM. To determine nutrient controls on surface slope NGoM phytoplankton growth and populations, we calculated growth rates and pigment composition using redundancy analyses and a variety of nutrient limitation criteria for each nutrient amendment over 48 hours. Nutrient limitation criteria concluded predominant NP limitation in the NGoM, though single N and P limitation and nutrient replete conditions were also present. In individual NAEs with N and NP amendments, phytoplankton pigment changes were driven by the growth of diatoms and Synechococcus (Syn). Though release from nutrient limitation stimulated responses in some phytoplankton groups, nutrient limitation of phytoplankton growth could not fully be predicted by the criteria and response thresholds evaluated in this study. Additionally, an analysis of environmental variables and phytoplankton pigments was conducted for the surface slope region of the NGoM to determine how phytoplankton community composition varies spatially with the influence of the MAR plume using group-specific chlorophyll a (Chl-a) calculations, bivariate linear regression, multivariate redundancy analysis, and cluster analysis. The largest proportion of Chl-a occurred in the nano/microphytoplankton group, followed by Syn, with both peaking at the high and low ends of the salinity gradient. Redundancy and cluster analyses showed that nutrients and salinity alone cannot predict or subdivide phytoplankton community composition; however, with the addition of pigments, we can characterize specific regions based on shared environmental variables (i.e., low salinity, high biomass) and pigment abundance. In sum, this work produced a straightforward and reproducible guide to leading a DEI task force, the largest NGoM surface nutrient data set to date, and characterizations of NGoM continental slope nutrient limitation and pigment composition and their relation to environmental variables.

Lam Lai-yee. / Thesis submitted in: November 2004. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2005. / Includes bibliographical references (leaves 124-140). / Abstracts in English and Chinese. / Abstract --- p.i / Acknowledgement --- p.vii / Table of contents --- p.viii / List of Tables --- p.xi / List of Figures --- p.xiii / List of Plates --- p.xiv / Chapter CHAPTER ONE --- Introduction / Chapter 1.1 --- Introduction --- p.1 / Chapter 1.2 --- Background and ecological impact of hill fires in Hong Kong --- p.2 / Chapter 1.3 --- Conceptual framework of study --- p.4 / Chapter 1.4 --- Objectives of the study --- p.10 / Chapter 1.5 --- Significance --- p.11 / Chapter 1.6 --- Organization of the thesis --- p.12 / Chapter CHAPTER TWO --- The study area / Chapter 2.1 --- Introduction --- p.14 / Chapter 2.2 --- Geographical setting of Hong Kong --- p.14 / Chapter 2.2.1 --- Climate of Hong Kong --- p.14 / Chapter 2.2.2 --- Geology of Hong Kong --- p.15 / Chapter 2.2.3 --- Soils of Hong Kong --- p.16 / Chapter 2.2.4 --- Vegetation of Hong Kong --- p.17 / Chapter 2.3 --- Site selection --- p.18 / Chapter 2.4 --- Grassy Hill --- p.20 / Chapter CHAPTER THREE --- Heating effect on the properties of ash / Chapter 3.1 --- Introduction --- p.23 / Chapter 3.2 --- Experimental design and methodology / Chapter 3.2.1 --- Selection of simulation heating --- p.26 / Chapter 3.2.2 --- "Heating intensity at 200°-600°C for 1,5 and 15 minutes" --- p.27 / Chapter 3.2.3 --- Field work --- p.27 / Chapter 3.2.4 --- Heating method --- p.28 / Chapter 3.2.5 --- Chemical analysis --- p.28 / Chapter 3.2.6 --- Analysis of data --- p.32 / Chapter 3.3 --- Results and Discussion / Chapter 3.3.1 --- Heating effect on ash weight and pH --- p.33 / Chapter 3.3.2 --- "Heating effect on ash organic C, N and P" --- p.33 / Chapter 3.3.3 --- Heating effect on ash available cations --- p.40 / Chapter 3.4 --- Conclusion --- p.42 / Chapter CHAPTER FOUR --- The effect of heat and ash on soil / Chapter 4.1 --- Introduction --- p.44 / Chapter 4.2 --- Methodology / Chapter 4.2.1 --- Field work --- p.48 / Chapter 4.2.2 --- Soil heating methods --- p.48 / Chapter 4.2.3 --- Chemical analysis --- p.49 / Chapter 4.2.4 --- Statistical analysis --- p.52 / Chapter 4.3 --- Results and Discussion / Chapter 4.3.1 --- The effect of heat and ash on soil pH --- p.53 / Chapter 4.3.2 --- "The effect of heat and ash on soil organic matter, N and P" --- p.55 / Chapter 4.3.3 --- The effect of heat and ash on soil cations --- p.62 / Chapter 4.4 --- Conclusion --- p.65 / Chapter CHAPTER FIVE --- Nitrogen and phosphorus mineralization after heating / Chapter 5.1 --- Introduction --- p.67 / Chapter 5.2 --- Methodology / Chapter 5.2.1 --- Heating and incubation method --- p.70 / Chapter 5.2.2 --- Laboratory methods --- p.72 / Chapter 5.2.3 --- Statistical analysis --- p.72 / Chapter 5.3 --- Results and discussion / Chapter 5.3.1 --- Temporal changes of N mineralization in heated bare soils --- p.72 / Chapter 5.3.2 --- The effect of ash on N mineralization --- p.78 / Chapter 5.3.3 --- Comparison of N mineralization with other studies --- p.79 / Chapter 5.3.4 --- Temporal changes of P mineralization in the heated bare soils --- p.81 / Chapter 5.3.5 --- The effect of ash on P mineralization --- p.83 / Chapter 5.3.6 --- Comparison of P mineralization to other studies --- p.84 / Chapter 5.4 --- Conclusion --- p.85 / Chapter CHAPTER SIX --- Vertical movement of mineral N in ash-covered soil columns / Chapter 6.1 --- Introduction --- p.87 / Chapter 6.2 --- Methodology / Chapter 6.2.1 --- Package of soil columns --- p.89 / Chapter 6.2.2 --- Water addition and extraction of pore water --- p.90 / Chapter 6.2.3 --- Statistical analysis --- p.92 / Chapter 6.3 --- Results and Discussion / Chapter 6.3.1 --- Mineral N in the pore water --- p.92 / Chapter 6.3.2 --- The effect of ash on mineral N in pore water --- p.97 / Chapter 6.3.3 --- The leaching loss of mineral N --- p.98 / Chapter 6.3.4 --- Comparisons with other studies --- p.103 / Chapter 6.4 --- Conclusion --- p.105 / Chapter CHAPTER SEVEN --- Integrative discussion / Chapter 7.1 --- Summary of major findings --- p.107 / Chapter 7.2 --- Clarifying some misconceptions about the effect of fire --- p.110 / Chapter 7.3 --- Estimated losses of N and P from heating --- p.112 / Chapter 7.4 --- Nutrient supplying capacity of soils after heating --- p.115 / Chapter 7.5 --- Why are repeatedly burnt areas reduced to grassland? --- p.118 / Chapter 7.6 --- Implication on the restoration of fire-affected areas --- p.119 / Chapter 7.7 --- Limitations of the study --- p.121 / Chapter 7.8 --- Suggestions for future research --- p.122 / References --- p.124 / Appendices --- p.141

Liu Wing Ting. / Thesis submitted in: November 2004. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2005. / Includes bibliographical references (leaves 141-156). / Abstracts in English and Chinese. / Abstract (English) --- p.i / Abstract (Chinese) --- p.iii / Acknowledgments --- p.v / List of Tables --- p.vii / List of Figures --- p.ix / List of Plates --- p.x / List of Appendices --- p.xi / Chapter CHAPTER 1 --- INTRODUCTION / Chapter 1.1 --- Urban ecological environment and the urban parks in Hong Kong --- p.1 / Chapter 1.2 --- Conceptual framework of the study --- p.4 / Chapter 1.3 --- Objectives of the study --- p.9 / Chapter 1.4 --- Scope of the study --- p.10 / Chapter 1.5 --- Significance of the study --- p.11 / Chapter 1.6 --- Organization of the thesis --- p.12 / Chapter CHAPTER 2 --- LITERATURE REVIEW / Chapter 2.1 --- Introduction --- p.13 / Chapter 2.2 --- Urban parks and urban soils --- p.13 / Chapter 2.3 --- Urban soils: properties and problems --- p.14 / Chapter 2.3.1 --- Overseas studies about urban soils --- p.15 / Chapter 2.3.2 --- Urban soils in Hong Kong --- p.16 / Chapter 2.4 --- Nitrogen dynamics --- p.22 / Chapter 2.4.1 --- The internal N cycle and N transformations in soil --- p.22 / Chapter 2.4.2 --- Factors affecting nitrogen dynamics in soil --- p.24 / Chapter (i) --- "Soil moisture and temperature, seasonality and spatial variation" --- p.24 / Chapter (ii) --- Soil pH and texture --- p.26 / Chapter (iii) --- Litter quality and C:N ratio --- p.26 / Chapter (iv) --- Disturbance --- p.27 / Chapter (v) --- Fertilizer input and management intensity --- p.27 / Chapter 2.4.3 --- N dynamics in urban areas --- p.28 / Chapter 2.4.4 --- Research of N dynamics in Hong Kong --- p.29 / Chapter 2.5 --- Phosphorus dynamics --- p.30 / Chapter 2.5.1 --- Gains and losses of P from soil system --- p.30 / Chapter 2.5.2 --- Forms and transformations of phosphorus in soil --- p.31 / Chapter 2.5.3 --- Factors affecting P dynamics in soil --- p.34 / Chapter (i) --- Fluctuations of soil moisture --- p.34 / Chapter (ii) --- Liming and pH adjustment --- p.34 / Chapter (iii) --- Cultivation and management intensity --- p.35 / Chapter (iv) --- Vegetation cover and disturbances --- p.35 / Chapter 2.5.4 --- P dynamics in urban areas --- p.36 / Chapter CHAPTER 3 --- STUDY AREA / Chapter 3.1 --- General situation of Hong Kong and the study locations --- p.37 / Chapter 3.2 --- Background of the two parks: Kowloon Park and Tin Shui Wai Park --- p.40 / Chapter 3.3 --- Climate --- p.43 / Chapter 3.4 --- Park vegetation --- p.45 / Chapter 3.5 --- Park soils --- p.47 / Chapter 3.6 --- Park management and horticultural routines --- p.47 / Chapter CHAPTER 4 --- BASELINE STUDY OF URBAN PARK SOIL PROPERTIES / Chapter 4.1 --- Introduction --- p.52 / Chapter 4.2 --- Methodology --- p.54 / Chapter 4.2.1 --- Sampling --- p.54 / Chapter 4.2.2 --- Soil texture --- p.55 / Chapter 4.2.3 --- Soil reaction --- p.55 / Chapter 4.2.4 --- Total Kjeldahl nitrogen (TKN) --- p.55 / Chapter 4.2.5 --- Mineral nitrogen (ammonium and nitrate nitrogen) --- p.55 / Chapter 4.2.6 --- Total phosphorus --- p.56 / Chapter 4.2.7 --- Available phosphorus --- p.56 / Chapter 4.2.8 --- Organic carbon --- p.56 / Chapter 4.2.9 --- "Exchangeable cations (K, Na, Ca, Mg)" --- p.57 / Chapter 4.2.10 --- Carbon: nitrogen ratio and carbon: phosphorus ratio --- p.57 / Chapter 4.3 --- Statistical analysis --- p.57 / Chapter 4.4 --- Results --- p.58 / Chapter 4.4.1 --- Texture --- p.58 / Chapter 4.4.2 --- Soil pH --- p.58 / Chapter 4.4.3 --- Organic matter --- p.59 / Chapter 4.4.4 --- Total Kjeldahl nitrogen and C:N ratio --- p.60 / Chapter 4.4.5 --- Ammonium nitrogen and nitrate nitrogen --- p.61 / Chapter 4.4.6 --- Total phosphorus and C:P ratio --- p.62 / Chapter 4.4.7 --- Available phosphorus --- p.64 / Chapter 4.4.8 --- Exchangeable cations --- p.65 / Chapter 4.5 --- Discussion --- p.66 / Chapter 4.5.1 --- Park soils under different vegetation covers --- p.67 / Chapter 4.5.2 --- Duration of park management and influence of land use outside the parks --- p.72 / Chapter 4.5.3 --- Quality of substrates in Kowloon Park and Tin Shui Wai Park --- p.76 / Chapter 4.5.4 --- C:N ratio and C:P ratio --- p.83 / Chapter 4.6 --- Conclusion --- p.84 / Chapter CHAPTER 5 --- NITROGEN DYNAMICS OF URBAN PARK SOILS / Chapter 5.1 --- Introduction --- p.87 / Chapter 5.2 --- Methodology --- p.89 / Chapter 5.2.1 --- In situ incubation --- p.89 / Chapter 5.2.2 --- "Determination of N mineralization, leaching and uptake" --- p.91 / Chapter 5.3 --- Results --- p.94 / Chapter 5.3.1 --- "Net ammonification, NH4-N leaching and uptake" --- p.94 / Chapter 5.3.2 --- "Net nitrification, NO3-N leaching and uptake" --- p.95 / Chapter 5.3.3 --- "Net N mineralization, N leaching and uptake" --- p.96 / Chapter 5.4 --- Discussion --- p.97 / Chapter 5.4.1 --- Nitrogen mineralization and immobilization --- p.98 / Chapter 5.4.2 --- Comparison with other studies --- p.100 / Chapter 5.4.3 --- Nitrogen leaching and uptake --- p.103 / Chapter 5.5 --- Conclusion --- p.108 / Chapter CHAPTER 6 --- PHOSPHORUS DYNAMICS OF URBAN PARK SOILS / Chapter 6.1 --- Introduction --- p.110 / Chapter 6.2 --- Methodology --- p.112 / Chapter 6.3 --- Results --- p.113 / Chapter 6.4 --- Discussion --- p.115 / Chapter 6.4.1 --- Phosphorus mineralization and immobilization --- p.115 / Chapter 6.4.2 --- Phosphorus leaching and uptake --- p.118 / Chapter 6.4.3 --- Comparison with other studies --- p.120 / Chapter 6.5 --- Conclusion --- p.122 / Chapter CHAPTER 7 --- CONCLUSION / Chapter 7.1 --- Summary of findings --- p.124 / Chapter 7.2 --- Implications of the study --- p.128 / Chapter 7.2.1 --- Chemical characteristics of urban park soils and their relationship to management --- p.128 / Chapter 7.2.2 --- Management practices for different vegetation types and species --- p.133 / Chapter 7.3 --- Limitations of the study --- p.136 / Chapter 7.4 --- Suggestions for future study --- p.139 / REFERENCES --- p.141 / APPENDICES --- p.157

A study of phosphorus loading and water quality implications was conducted for the Oregon coastal lakes. The study was based on existing data for lake total phosphorus concentrations and for watershed land uses. A phosphorus mass-balance model was developed to predict lake total phosphorus concentrations from estimated phosphorus loading from land uses within the lake's watershed. Uncertainty in total phosphorus concentration estimates are included in the model, and model predictions are considered to be moderately to highly reliable. The Oregon coastal lake phosphorus mass-balance model was calibrated from data for 12 Oregon coastal lakes. Land use phosphorus loading coefficients for forestry, the coastal dunal aquifer, and precipitation were derived from data specific to the Oregon coastal region, while other phosphorus loading coefficients were estimated based on correlations between literature values and Oregon coastal conditions. The model may be used as an aid for land use management decisions by estimating water quality effects of projected land use changes. A case study of Mercer Lake was used to illustrate the model application. / Graduation date: 1994

No description available.

Thesis (MSc. Agriculture(Soil Science) -- University of Limpopo, 2018 / Soil acidity is one of the abiotic stress factors that greatly limit the productivity of crops on farmers’ fields. A greenhouse study was carried out over two summer growing seasons to evaluate the effect of lime and phosphorus (P) application rates on the growth, yield and root attributes of a determinate cowpea variety on acid soil. The experiment was laid out as a 4x5 factorial arrangement with 4 replications. Treatment factors comprised of variable rates of Vaalburg dolomitic lime (0, 2, 4 and 6 t ha-1) and P (0, 15, 30, 45 and 60 kg ha-1) using single super phosphate, 10.5% P. The two treatment factors were combined resulting in a total of 20 treatment combinations. Data collected included cowpea growth parameters, crop phenology, yield attributes and root characteristics. While cowpea plants with no P application consistently gave the least plant height, stem diameter, number and length of trifoliate leaves, the 6 t ha1 lime rate appears to be completely disadvantaged for all measured parameters with generally lower values than in soil filled pots without lime application. Results showed that soil pH was increased with 6 t ha-1 lime application while soil electrical conductivity (EC), percent of organic matter (OM) and total organic carbon (TOC) were all increased with increasing P and lime rates. All measured cowpea growth attributes such as plant height, stem diameter, number of trifoliate leaves, and leaf area were significantly increased (p≤0.05) with increasing P and lime rates. During the two planting seasons, P and lime application resulted in reduced (p≤0.05) duration to flowering, pod formation and physiological maturity. The 6 t ha-1 lime application produced higher number of pods (2.50) compared to the other rates. Application rates of 45 kg P ha-1 and 6 t ha-1 of lime produced superior number of seeds per pod with high values of (13.71) and (12.85), respectively. However, cowpea root attributes namely number of nodules per plant, the third branching root diameter, angle of adventitious root, tap root diameter at 5 and 10 cm, shallow and deep score were significantly increased at moderate P rate of 30 kg P ha-1. Overall, findings of this study revealed that application of both P fertiliser and lime were able to ameliorate the negative effect of P deficiency from soil acidity on the evaluated cowpea variety and promoted increased yield. Keywords: Acid soil, grain cowpea, P fertiliser, lime, growth, root characteristics, yield / National Research Foundation (NRF) and Department of Agriculture, Forestry and Fisheries (DAFF)

A greenhouse study was carried out to investigate the effectiveness of soil-applied silicon (Si) with that of foliar applications for sorghum growth. Silicon sources were soil-applied as calmasil (calcium silicate) at two rates (4 and 8t/ha) and foliar applied Si including pure K-silicate, K-humate and K-fulvate (all three foliar treatments at rates of 300 and 600 ppm). Another treatment included soil applied calmasil plus low rate of foliar applied K-humate. The soils used for the greenhouse trial were Cartref, Glenrosa, Nomanci and Fernwood. Results indicated that application of calcium silicate to the soil before planting increased sorghum yield and Si uptake in three of the four soils. Silicon uptake from different experimental treatments followed the order: Calmasil 8t/ha > calmasil 4t/ha ~ calmasil + 300 ppm K-humate> K-humate = K-fulvate = pure-K silicate = control. Foliar sprays were ineffective at increasing yield, Si content of the plant tissues or Si uptake. The concentrations of exchangeable Ca, Mg as well as soil pH were significantly increased by calmasil treatments. Extractable AI concentrations were also reduced due to the Iiming effect of calcium silicate and also possibly formation of insoluble aluminosilicates. The yield response to applied calmasil seemed to be primarily related to its Iiming effect and reductions in extractable AI in the Cartref, Glenrosa and Nomanci soils. The dry matter yield was highest in Fernwood and lowest in Cartref soil. However, there was no significant yield response to calmasil in Fernwood soil which had an initial pH of 5.8 and insignificant extractable AI concentrations. Therefore application of calcium silicate had no significant effect on extractable AI concentration in this soil. Yield response to calmasil may also have been partly due to direct positive effects of applied Si on crop growth through mechanisms such as increased photosynthetic rate and reduced transpiration rate, Addition of calmasil increased the concentrations of Si in the plant tissues and reduced those of N, P and Kin Nomanci and Fernwood soils respectively. This indicates that nutrient interactions were occurring in the plant. It was concluded that foliar-application is not an effective way of applying Si to a Siresponsive crop such as sorghum when growing in soils low in extractable soil Si. This is because Si is accumulated in plant tissues in similar amounts to macronutrients. It was also concluded that in future, studies of crop response to applied Si should include the use of non-Iiming source of Si (e.g. silicic acid) so as to separate a liming effect of calcium silicate from effect of applied Si. In a laboratory study, the effects of applied silicic acid, calcium silicate and calcium hydroxide on levels of extractable P in two Si-deficient soils were investigated. Two soils (Fernwood and Nomanci soils) were treated with two rates of P and three soil amendments (calcium silicate, calcium hydroxide and silicic acid) and incubated for six weeks at room temperature. Phosphorus was extracted using Truog, AMBIC and resin methods, and levels of exchangeable and solution AI and extractable and solution Si were also measured. Application of calcium silicate and calcium hydroxide increased soil pH in both soils while silicic acid additions had no significant effect compared with the control. The pH increase was much greater in the Fernwood than Nomanci soil because of the low buffering capacity of the sandy Fernwood soil. Exchangeable AI and concentrations of monomeric and total AI in soil solution generally followed the order: control ~ silicic acid> calcium silicate> calcium hydroxide. The lowering of soluble AI concentrations in the silicic acid treatments was attributed to formation of insoluble aluminosilicate compounds while that in the calcium silicate and calcium hydroxide treatments was attributed to their Iiming effects causing a rise in pH. Concentrations of Si in soil solution were lower in the calcium hydroxide than the control treatment suggesting the solubility of Si decreased with increased pH. Additions of both Si sources increased Si concentrations in solution and the effect was more marked for the calcium silicate treatment. This was attributed to formation of insoluble aluminosilicates in the silicic acid treatment. Concentrations of H2S04extractable Si with treatment did not closely follow the same trends as those for Si concentrations in soil solution. That is, levels of extractable Si were very much higher in the calcium silicate than silicic acid treatment in both soils. In addition, concentrations of extractable Si in the calcium hydroxide treatment were similar to control in the Nomanci soil, while for the Fernwood soil, concentrations in the calcium hydroxide treatment were exceptionally high. It was suggested that liming with calcium silicate or calcium hydroxide had rendered some Si-containing compounds in the soil acid-extractable and that the nature of acid-extractable Si fraction need further study in future. The quantities of P extracted from the two soils by the various extractants followed the order: Truog> AMBle> resin. The greatest increase in extractable P induced by additions of P was recorded for Truog P and the least for resin P. The effects of Iiming (addition of calcium silicate or calcium hydroxide) on extractable P levels differed depending on the soil and extractant used with increase, decrease or no effect being recorded. Such results confirm the complexity of lime and P interactions which occur in acid soils. Additions of silicic acid had no effect on levels of extractable P, compared to control. It was suggested that the reason for this was that phosphate is adsorbed to AI and Fe oxide surfaces much more strongly than silicate. As a result, additions of Si are ineffective at increasing extractable P levels. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2006.

Soil phosphate is essential for the development and maturity of crops. Plants absorb phosphate from the soil solution which is continuously replenished by fertilizer application and/or desorption from the soil solid phase. Anion exchange membranes (AEMs), act in a similar way to plant roots, adsorbing P from soil solution. Desorption of available P was studied in 1997 on two Gleysolic soils rich in P, a Ste. Rosalie clay soil and a Duravin sandy loam soil, using fluoride-saturated AEMs let in soil suspension for various contact periods. Determination of available P using these AEMs was compared to P extraction using the Mehlich III extractant for predicting P availability to soybean (Glycine max L.). Desorption from both soils, and subsequent adsorption by AEMs was found to decrease with time. A high P desorption rate was calculated for both soils with the Elovich equation. Different chemical and physical characteristics such as pH, Mehlich III extractable Al, Fe and Ca, sand and clay content were in some cases, positively correlated and in other cases, negatively correlated with various contact periods for both soils. The use of AEMs better predicted P availability than the Mehlich III extractant, although the most important asset of using AEMs is that they showed the desorption effect over time on P availability. It was observed that P remobilization from the vegetative part to the grain was reduced due to the high P concentration in both soils.

Due to recent research suggesting that water table management (WTM) can significantly reduce nitrate (NO3") loads in agricultural drainage, a study was carried out in 2001 and 2002 in Coteau-du-Lac, 60 km west of Montreal, to investigate the effect of water table management on the migration of phosphorus (P) via tile drainage and surface runoff. The second main objective was to study the influence of WTM on grain corn yields. Two drainage treatments were compared: conventional free drainage and WTM (combined controlled drainage and subirrigation) with a design water table depth at 0.6 m below the ground surface. Tile drainage and surface runoff were monitored and sampled automatically. Increased outflow volumes and concentrations - and therefore increased P loads - were measured in drainage water from plots under WTM. Plots under WTM also generally exhibited higher P loads in surface runoff. Higher P concentrations in surface runoff from plots under WTM were observed in surface runoff, especially during winter. Phosphorus loads from combined tile drainage and surface runoff were low compared with literature data (<0.4 kg/ha/year). However, the mean P concentrations in tile drainage were above Quebec's surface water quality standard of 0.03 mg total P/L during both growing seasons in plots under WTM, but not in plots with conventional free drainage. Mean P concentrations in surface runoff water routinely exceeded the criteria, except in plots with conventional free drainage in winter 2002. Therefore, P from tile drainage and surface runoff could contribute to the eutrophication of surface water. Based on these results, WTM increases P loads from the field, both in tile drainage and surface runoff. However, the well water used for subirrigation was found to contain P concentrations above Quebec's surface water quality standard, and this could partly explain the higher P concentrations found in water from plots under WTM. Water table management increased grain corn yields by 35% in both years. The growing seasons of 2001 and 2002 were among the driest ever recorded in Canada.