The Sri Lankan acid tea soils, collected from six different agro-ecological regions and from the long-term field experiments in St. Coombs, were subjected to a detailed mineralogical investigation with particular reference to the understanding of the chemistry of soil potassium and K fertiliser applications. These extremely weathered soils contained predominantly kaolinite, Al-chlorite, gibbsite and goethite, but K-fixing minerals like smectite and vermiculite were absent. Small quantities of micaceous minerals were only found in the fine and coarse sand fractions of these soils, except in the Hantana soil which contained substantial quantities of micaceous minerals in the clay, silt and sand fractions. The clay and silt fractions of the Scottish soils of the Countesswells and Foudland soil series comprised 60% to 70% of mica and mica-weathered products of interstratified mica/vermiculite and vermiculite/chlorite. The rate of transformation of the micaceous minerals and the concentration of hydroxy-Al 'islands' in the Countesswells soil series increased with decreasing soil pH. The Foudland soil contained more weatherable micaceous minerals, and spring barley, winter wheat, potatoes and ryegrass/clover in a crop rotation field experiment produced optimum crop yields in the absence of K fertilisers, due to the release of substantial amounts of non-exchangeable K. The Countesswells soil was unable to supply sufficient non-exchangeable K for ryegrass/clover growth in order to achieve the same yield as that with K fertiliser. A mixed NH4- and Cl- ion exchange resin method for extraction of soil K was developed, which was capable of estimating the amounts of short-, medium- and long-term K reserves that are available to ryegrass, grown in different soil types covering a wide range of soil pH and K-bearing minerals, without destroying the mineral matrix, but K-bearing minerals in both soils and pure minerals were found to either transform or dissolve progresively as mineralogical changes took place at the soil/root interface. A new perspex cell was constructed to hold a 4mm layer of soil or mineral, for in situ studies of root morphology, and for study of the mineralogical changes in soils or pure K-bearing minerals, due to the uptake of both exchangeable and non-exchangeable K by ryegrass, within a 2mm radius of the root surface. This study showed that there were more total, primary and lateral ryegrass roots growing in a soil of higher K status, compared with one of lower K status. The numbers of dead or decomposed roots were greater in the lower K status soil. Interstratified smectite, mica/vermiculite and vermiculite/chlorite minerals were formed in the soil within a 2mm radius of the root surface, due to K uptake by ryegrass. These mineralogical changes were not observed in the same soil under intensive cropping with ryegrass in the glasshouse in bigger cylindrical pots or after 21 years of continuous growth of ryegrass in the field. Dissolution of the 2:1 layer silicate mineral structure occurred in soils and vermiculite in the perspex cells, due to the production of H3O- ions, particularly where root growth was greatest. This dissolution mechanism may override the diffusion mechanism of K release to plant roots within a 2mm radius of the root surface, and may help explain the wide range of diffusion coefficients of soil K, (10-10 to 10-23)cm2 sec-1, which appear in the literature. The new techniques of extraction of soil K by use of a mixed NH4- and C1- ion exchange resin and of studying root growth in a perspex cell, which were developed in this thesis, merit further investigation.

Fertilizer nitrogen transformations in two Sitka spruce stands in northeast Scotland were studied using 15N-labelled (2.5 atom % 15N) urea at a rate equivalent to 160 kg N ha-1. The use of urea fertilizer resulted in accelerated growth of the tree crowns, and higher concentrations of total N in foliage, twigs and new wood. There was no fertilizer effect observed for bark. Despite a positive growth response by the trees to fertilizer N, only an estimated 17% of applied-N was utilized by the tree biomass. Application of urea-N resulted in a reduction in the leaching of inorganic N and certain cations (particularly Ca 2+). Gaseous losses of N were elevated following urea application, but estimated losses of fertilizer N via NH3 volatilization and denitrification were negligible. Data from both sites indicated a retention of volatilized NH3 in the tree canopy which was returned to the soil in throughfall. Urea application to the forest floor resulted in elevated pH of the LFH for a period of about 100 days. Urea application also led to a flush of acetic acid extractable PO4-P in the LFH. The addition of urea also resulted in increased counts of bacteria in the LFH. Data indicacted that elevated NO3- concentrations in the LFH may have been due to bacterial nitrification. Little effect of fertilizer N was observed for mineral soil, with a retention of the bulk of fertilizer N in the LFH.

Tree growth, litterfall and litter decomposition were measured in a stand of 39 year old Sitka spruce (Picea sitchensis, yield class 16), near Aberdeen. A split plot field experiment was used to examine the effect of nitrogen addition [200 kg ha-1 N as (NH4) 2SO4] and carbon addition (1000 kg ha 1 of soluble starch) in the main plots, and trenching in the subplots. Weight loss from litterbags was highest in the carbon treated plots (24%) while that in the nitrogen treated plots was approximately the same as that in the control (22%). Highest levels of nitrogen availability and total nitrogen concentration occurred in the litter of the nitrogen treated plots throughout the course of the experiment. Small amounts of nitrogen were immobilised in the control plots during the first 8 weeks of the experiment. A 3.5% increase in the total amount of nitrogen initially present was observed, this probably being derived from rainfall inputs. This rose to 7.1% in the carbon treated plots during the first 20 weeks, possibly as a result of increased microbial activity increasing the proportion of rainfall nitrogen being immobilised. During the same period, litter in the nitrogen treated plots immobilised 9.7% of total nitrogen initially present as a result of higher nitrogen availabilities in these plots. Rates of CO2 production were measured in the field and found to be highest in the carbon treated plots. Seasonal patterns of litterfall were identified with peaks of production occurring in June and October. Greatest amounts of litter fell in the control plots (3410 kg ha-1 y-1), although the needle litter in those plots also had the lowest nitrogen concentration (ranging from 0.75-1.14% N). Unexpectedly, trenching (the exclusion of live roots from a small plot of soil in the field) slightly decreased the rate of litter decomposition. It also increased the moisture content, availability of nitrogen, and amount of soluble organic nitrogen in the litter. Probably as a result of an adequate nitrogen status at the beginning of the experiment, little increase in tree growth was observed in response to added nitrogen. In an attempt to extend and reinforce the data obtained from the field, a laboratory experiment was designed in which pots of litter were incubated with starch and nitrogen and starch at levels comparable with those in the field. In contrast to the field experiment, nitrogen mineralisation was not increased by the addition of starch, although there was a substantial increase in the amount of KC1-extractable nitrate. The value of using measurements of CO2 evolution to estimate rates of nitrogen mineralisation are discussed.

In N.E. Scotland, the upland areas have been surveyed and classified into land facets by a number of workers. The present project attempts to evaluate the physiographic approach for land use potential and to compare the relationships between soils and physiography on the three bedrocks, granitic, metamorphic and basic rocks, in N.E. Scotland involving three areas: 1. Bennachie area: the studies were restricted to sites whose soils are derived from granitic rock. 2. Clashindarroch and Strathdon areas: the study dealt with sites whose soils are derived from metamorphic and basic rocks. Physiographic subdivision of the terrain in terms of facets was made using air photos. Eight major facets on each bedrock area were identified, involving 99, 77 and 49 sampling plots on granitic, metamorphic and basic rock types respectively. To obtain more information on the variation between physiographic units, steep and moderate slope facets were grouped together and called similar grouped facets (S.G.F.s) giving a total number of 36 facets. Ground surveys were made field data collected and sample plots established to study site and soil characteristics in the field and the laboratory. Statistical analyses of the data, using ANOVA to test the variation within and between individual facets (I.F.) and S.G.F. facets on the three bedrocks were added to validate the findings. The physiographic system has been evaluated according to topographic soil profile and soil chemical factors. The facets were significantly ranked according to the means of the variables. The results show that the physiographic system is reasonably efficient because most variables were effectively partitioned by facets. The larger facets (S.G.F.) proved to be more homogeneous and suitable than the over-defined I.F. facets, in areas of varied topographic features and more useful in reconnaissance mapping. The system was not very reliable in characterizing soil nutrient status. The results show that soil and site information can be extended to neighbouring areas and it provides a basis of land use planning and soil management.

Chapter 1: The emissions, transformation and deposition of Acid Rain are outlined in this chapter as well as the interaction of acid precipitation with vegetation and the mechanisms of soil acidification. The possible pathways for the release of aluminium in soils are discussed as well as an introduction to aqueous aluminium chemistry and aluminium speciation techniques. Chapter 2: The sites descriptions of the Loch Ard, Allt a Mharcaidh and Hoylandet catchments are presented. The methods of sample collection by field instrumentation and aluminium determination in water samples are also described. Details of soil extraction techniques applied to all the horizons of the soils in the catchments are given. The concentration of available solid phase aluminium in the soils is presented. Chapter 3: The Loch Ard catchment was used for the study of aluminium speciation in soils and surface waters of acidified catchments. Two soil types under different vegetations were examined and an aluminium budget study of input, vegetation, soil and stream waters was presented. Chapter 4: Aluminium speciation in three soil types in the Allt a Mharcaidh catchment was studied. An absolute budget of Al release was not presented but variations in Al species in waters from soil and streams over the sampling period were presented. Chapter 5: Episodic events at both Hoylandet (Norway) and Loch Ard (Scotland) were studied. The event in Norway was due to spring snowmelt while the event at Loch Ard was rainstorm event. The chemical response to large fluctuations in percolating waters through soils resulting in increased stream flow as monitored over short time periods, particularly in relation to changes in aluminium species. Chpater 6: A laboratory controlled leaching experiment on an alpine podzol and peaty podzol soil from the Allt a Mharcaidh catchment was undertaken using both mineral (sulphuric) and organic (citric) acids. The purpose of the experiment was to determine the potential release of aluminium from soil horizons acidified by different acidic inputs. It also investigated the possible soil mechanisms resulting in the release of aluminium, particularly sulphate saturation and cation exchange reactions. Chapter 7: The response of stream sediment to release aluminium into waters subjected to increased acidification was studied in both laboratory and catchment-based experiments. The results indicated the valuable source of aluminium in stream beds which must be considered in determining a proper aluminium budget for a catchment study. Chapter 8: A preliminary study of the organic complexation of aluminium with naturally occurring organic acids and three different fulvic acids is presented. The study outlines the difficulty in predicting complexation particularly for fulvic acids where major molecular structural differences account for the degree of complexation. Chapter 9: Summary and conclusions.

Some soils set to a hard structureless mass on drying and this behaviour may limit crop productivity. The purpose of this study was to assess the extent to which soil management and soil properties influence hard-setting behaviour in order to identify those soil properties which are most appropriate to characterise the limitations to management and crop growth imposed by hard-setting. Five sites from four vegetation zones of Nigeria were investigated. Within each site soils were sampled from no-till or forested plots and these were contrasted with cleared (deforested) amd ploughed plots. Hard-setting behaviour was determined by measuring the unconfined compressive and tensile strengths of small undisturbed cores (minicores) which had been equilibrated at a range of matric potentials. Rooting potential was assessed both by measuring needle penetrometer resistance or cores equilibrated at potentials of -6 and -100 kPa; and also by measuring penetrometer resistance in the field at a range of moisture contents. Soil bulk density, organic matter concentration, soil friability, aggregate stability and amounts of water suspendable solids were also measured to assess soil properties that are likely to be diagnostic of hard-setting behaviour. The limitations imposed by hard-setting behaviour on rooting and yields of maize and cowpea were assessed at IITA. The minicore strengths increased as the moisture content decreased but the increase was much more marked for mechanized cleared or tilled soils than for the less disturbed treatments of forestry and a no-till system. For all soils the most pronounced effects of moisture content deplection on soil strength occurred at potentials of < -100 kPa. Theoretical considerations indicated that the effective stress accounted for over half of the strength of minicores at -100 kPa and more than accounted for the strength of minicores at -1 MPa. The greater strength in tilled soils was attributed to a decrease in organic matter content, wet aggregate stability and friability and to an increase in bulk density. Needle and field penetrometer resistance results indicated that rooting potential was reduced on hard-setting soils and actual root measurements supported this view. Consequently maize and cowpea yields were reduced.

The relationship between soil structure and microorganisms is a unique two way interaction. Whilst soil structure influences microbial transport, activity and predation, microorganisms affect soil structure by playing a major role in its genesis and stabilisation. Microorganisms are largely thought to influence structural genesis and stabilisation through the exudation of polysaccharides, which act to bind soil particles together as well as microorganisms to soil particles. Filamentous microorganisms are also thought to influence structural genesis and stabilisation by enmeshing soil particles together. A laboratory-based experimental system was developed whereby the structural heterogeneity of soil cracking patterns, generated from homogeneous soil slurries, was quantified using fractal concepts. A fractal approach was used because it provided a theoretical framework in which structural heterogeneity could be quantified and linked to soil processes such as gaseous diffusion, water movement and microbial population dynamics. This study demonstrated the potential of fractal geometry to functionally quantify soil structure. A greater understanding was gained of some of the processes acting to direct the formation of particular structural geometries. The latter is particularly important since it is the geometry of soil structure which will regulate processes such as gaseous diffusion and water movement. Microbial activity (mainly through the production of polysaccharides) was shown to have a significant effect on the generation of soil structure as well as on its water retention properties. The nutritional management of the microbial population was also shown to be a key factor regulating its contribution to structural genesis. Microorganisms can play a significant role in structural genesis ultimately impacting upon all aspects of the soil-plant-microbe ecosystem. It will be essential to understand how to effectively manage the indigenous microbial population if their potential as soil conditioners is to be fully reached.

The requirement of zinc (Zn) for normal plant growth was first recognized in the late nineteenth century, but acceptance of this element as an essential plant nutrient did not occur until the early 1930s. Since then, Zn deficiency has been identified throughout the world on numerous crops grown on widely varying soils under a variety of management practices. Many soils contain appreciable amounts of Zn that plants are unable to utilize. The addition of Zn compounds to soils can also prove to be of limited benefit, as most of the Zn becomes "fixed" by soil components. The mechanisms responsible for Zn "fixation" or "release" have not been fully elucidated. An understanding of the controls on the concentration of Zn in soil solutions is of great significance to the art of maintaining and improving the fertility of soils, and is of rapidly growing importance in understanding the development of Zn deficiency in plants. Certainly a better understanding of soil Zn chemistry and availability, and plant-soil relations will help improve agronomic practices for efficient crop production. With a better understanding of the Zn-deficiency problem in crops in mind, a project has been undertaken on 'zinc reactions and availability in soil'. The work in the project concentrates mainly on evaluation of zinc extractants, identification of soil variables responsible for Zn unavailability, mechanisms involved in Zn fixation at elevated pH and response of barley to Zn and Cu application.

Long-term changes in soil profile characteristics and important soil physical, chemical and biological properties were evaluated and compared at 4 paired sites in NE Scotland, 44-61 years after the afforestation of agricultural soils planted with either Norway spruce (Picea abies (L.)) or Scots pine (Pinus sylvestris (L.)). At each paired site five profiles were studied in the afforested and five in the control agricultural soils. Comparison made between various properties in the pairs of soils showed a number of significant changes, which are summarised in Tables 2.18-2.20. The surface (O) horizon of the afforested soil could be differentiated into L, F and H horizons. The O horizon was rich in organic matter, crumb structured, porous and well-drained and was differentiated from the A horizon below by an irregular boundary. The A horizon was moderately well to excessively well-drained with a subangular blocky to crumb structure. This horizon was differentiated from the B horizon below by an irregular boundary. The agricultural soil profile was characterised by compact O and A horizons with a subangular blocky structure; each horizon was separated from the one below by a gradual, smooth horizon boundary. Afforestation increased the combined thickness of the O and A horizon by 0.21 cm yr-1. It caused a significant decrease in bulk density and had no effect on particle size distribution. At most sites % organic matter, C, C/N ratio, CEC and NH4+ concentration were higher and extractable P concentration lower in the O horizon and most of the A horizons of forest soils, compared to the agricultural soil. The concentration of N increased significantly in the O horizon. Soil pH, exchangeable Ca, Mg and K and % base saturation decreased significantly in most forest soil horizons compared to the agriculated soils. Exchangeable Na concentration increased in the B horizon. Accumulation rates of each element since afforestation were also calculated.

The objective of this work was to study the decomposition of five species of blue-green algae under varying environmental conditions in soil and to examine the availability of nitrogen and other nutrients supplied through the growth of blue-green algae to rice growing in pots. In the initial phase attempts were made to grow the blue-green algae on nutrient solution and culture conditions were tested to provide optimum growth. The results of pot experiments showed that growth of all five species of blue-green algae produced an increase in dry matter yield of rice significantly higher than the controls but for four species the yield was less than the lowest addition of fertilizer nitrogen. The fifth species, Anabaena variabilies produced the highest yield in pots supporting blue-green algae but it was lower than the best yields obtained by addition of fertilizer. There was little difference in yield produced by the two fertilizers, ammonium sulphate and urea, and both increased yield with increasing addition up to the third rate (90 mg N pot-1). Nitrogen addition influenced the nutrient content of the dry matter but the growth of blue-green algae appeared to cause a small but not significant competition for nutrient uptake.