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Conventional Soil Survey is described briefly and several quantitative methods of improvement proposed in the last decade discussed. Lateral or spatial variability of soil properties still remains a stumbling block to increased precision of spatial prediction. The study attempts to identify methods to overcome this problem. The problem of spatial variability is placed in a stochastic framework allowing variation to be an intrinsic part of the modelling process. Concepts of stationarity and spatial dependence of random functions and regionalised variables are introduced and the semi-variogram is shown to be a useful robust descriptor of continuous spatial variation. The statistical and practical aspects of semi-variogram modelling are discussed in detail and several and varied practical examples given. An alternative approach using ARMA models is briefly discussed. These approaches represent a significant improvement in our ability to model soil variability but some practical problems remain including tests for stationarity and confidence limits for semi-variogram estimates. The problems of spatially predicting soil properties are discussed along with various interpolation methods. Kriging, an optimal spatial predictor, has very desirable properties, especially those of minimum and known predicted estimation variance and the ability to take into account the spatial variation information contained in the semi-variogram. Ordinary point and block kriging are used successfully on several data sets to produce isarithmic maps. Block kriging seems particularly useful. A comparison of the predicted estimation variances of kriging with those of Conventional Soil Survey shows kriging to be much more precise. The techniques of semi-variogram estimation and kriging are extended from single properties to situations where there are two or more spatially interdependent ones. The cross semi-variogram is introduced and models fitted. Co-kriging is described in the context of spatially predicting a variable from measurement of it plus data on one or more spatially cross-correlated properties that have been sampled more intensively. For a real example, co-kriging gives more intricate contour maps and lower estimation variances than kriging, which in turn is more precise than Conventional Soil Survey. Knowledge of the semi-variogram and the cross semi-variogram can be utilised to design optimal sampling schemes, in the sense of maxium precision for a given sampling effort, for estimating the regional mean and for local spatial prediction using kriging and co-kriging. In all cases certain triangular grids are shown to be optimal with certain rectangular grids only slightly less so. The techniques of semi-variogram and cross semi-variogram analysis, kriging and co-kriging, and optimal sampling strategies can be combined into a single methodology called Geostatistical Soil Survey. It is shown that Geostatistical Soil Survey is largely complementary to Conventional Soil Survey because of differences in aim, scale and number of properties examined. There is some overlap however. It is concluded that Geostatistical Soil Survey is most useful for medium to large scale surveys with specific aims and where a few properties provide the required soil information. Furthermore, the firm statistical basis provided by Geostatistical Soil Survey makes it possible to apply with confidence further quantitative methods to improve the value of soil survey operations. Suggestions for further work include testing of the Geostatistical Soil Survey methodology and research into improved geostatistical methods. Finally, the use of geostatistics in the design and analysis of field experiments is discussed briefly.

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.