No description available.

Investigations in the field of soil fertility have for a long time suggested a relationship between uptake of the so-called trace elements by plants and the presence of organic matter. The manner in which this influence is exerted is still not fully understood because of the complexity of the nature and properties of soil organic matter and its relationships with the inorganic material in soil. Progress in the study of the properties of soil organic matter is, in turn, hindered by the absence of a satisfactory method of extracting this material and purifying it to remove all the inorganic cautions especially the heavy metal ions. Existing methods of extraction are either inefficient in terms of the amount organic matter which they dissolve or open to criticism on chemical grounds. There have been few serious attempts either to investigate the possibility of employing new methods or to improve existing methods of purification. This thesis is divided into two parts: Part A consisting of four chapters, presents a brief review of the relevant literature in which an attempt has been made to report and assess the present state of our knowledge. In chapter I the evidence for complex formation between soil organic matter and metal cations is reviewed and the physico chemical methods employed in studying these complexes are surveyed. Chapter II covers the methods of extraction and the conclusion is drawn that anhydrous formic acid has many favorable advantages over the widely used conventional aqueous extractants. The Procedures for removing inorganic impurities from soil organic matter are reported in chapter III and the review shows that purification has received comparatively little attention. From the information presented in Chapter IV on the iron and copper nutrition of plants is appears that several factors influence their availability. It is well known that synthetic chelating agents increase the availability of these cations but there is very little information to hand to explain the influence of soil organic matter on their uptake. Part II records the methods used and the results obtained in the experimental studies. Chapter V Explains the experimental aims and describes the analytical procedures employed. The remaining chapters correspond to those of the review but deal with the topics in a different order. Because of the complexing ability of organic matter a chelating agent, namely acetyl aceton was included in formic acid in a attempt to achieve a better separation of the organic and inorganic compounds. A variety of purification methods were examined and finally a procedure was obtained which reduced the ash content to below 1 this allowed a study of the physico-chemical aspects of the complexing properties of relatively pure material and the influence of this material on the uptake of metals by mustard seedling grown under sterile conditions on a simple nutrient medis.

No description available.

The effect of deep ploughing indurated upland soils to 90cm was investigated at three sites in North East Scotland. The sites varied in age from recently ploughed to sixteen years old. The profile morphology, disruption of induration and change in rootable volume, the maximum depth of root extension, and root orientation were quantified. The soil moisture regime was monitored over one growing season at Glenbuchat using a series of tensiometers inserted horizontally into the profile face. The deeply buried organic matter remained moist throughout the summer. In contrast organic matter near the surface underwent fluctuating cycles of wetting and drying. The deeper soils showed little response to summer rainfall. The rate of decomposition of the buried organic matter was assessed in three ways. A litterbag study determined the effect of burial on weight loss, nutrient element loss and microbial activity. Anaerobic incubations were used to measure rates of nitrogen mineralisation and the concentration of 'Klason' lignin were used as an indice of decomposition of buried organic matter. At Glenbuchat there was a significant decrease in mineralisable nitrogen and lignin concentration with depth. In contrast the older site at Culloden had the opposite trend with a significant increase with depth. This later result was thought to be due to the death and decay of fine roots.

1. Review of the literature indicated that at low levels of potassium iron chlorosis may result in plants either from reduced uptake or from iausobllization within tissues. This condition is intensified by high levels of calcium but the influence of other ions, especially chloride and sulphate is less clear. 2. Experimental techniques in plant nutrition studies were reviewed and an analytical system was devised for determination of N, P, K, Ca, Mg and Fe in a single digest of dried plant tissue. 3. Techniques for radioactive studies were reviewed and direct solid scintillation counting of Fe in soils and plant material was 55 adoptee, using a Mairell crystal for the latter. For incomparable amounts the radiation intensities proved too lor for quantitative estimation with the available equipment, dcspit' concentration of iron in plant tissue digests by co-prccipitation with Mg(GH)p. 4. Two pot experiments were conducted respectively with Italian ryegrass and New Zealand hybrid to test the effect of four levels of potassium ranging from 2-16 me potassium as sulphate and chloride, on the uptake of Fe and K, and also N, P, Hg and Ca. Soil labelled either with Fe or Fe was used in the upper, middle or lower third of each pot to study the effect of rooting habit and soil depth on Fe uptake. 5. For both species and three successive cuts the Fe content was not influenced by chloride or sulphate, but sulphate increased N and Ar contents and decreased Ca content. Chloride increased K and P contents only in Italian ryegrass. Sulphate gave higher dry matter yields in both species and source effects on nutrient untake depended raninly on this. Increased K level generally depressed Fe content but consistently increased K content. Maximum dry matter yields were at 8 nie.K. 6. Fe uptake d-crossed with soil depth in sympathy with root intensity. For both species K content decreased and Mg content increased vith labelled depth whereas N was unaffected and, Ca and P showed variable effects. Radiation damage to roots was not evident. The apparent differential effects of labelling on nutrient content were probably indirect, due to the chelating agent DTP A used for labelling soil.

The influence of transpiration rates on leaf water potential (1 - leaf water stress) in potted sunflower plants (Helianthus annuus L.) rooted in water saturated garden soil, fine sand, silica sand, ballotini and water culture solution was investigated to evaluate the nature of resistance to water flow through the root system. It was invariably observed that the resistance to flow through the root systems varied with the change of rooting materials, watering regimes, size of pots and age of plants especially in silica sand grown plants. Both curvilinear and linear relationship between leaf water potential and transpiration rates was observed in plants grown in the same amount of silica sand under the same watering regime but at different ages. A curvilinear relationship is observed as being fundamental to, and occuring invariably in most water saturated rooting media. Whilst linearity is an artifact, evidence put forward suggesting that it results from an increased percentage of moribund and dead roots, and it is considered to be due to an interaction of coarse rooting particles, size of pots, watering regimes and age of plants. It is suggested that the cause of interaction depends on the prehistory of the plant growth conditions. A study of the hydraulic resistance of the soil: plant water relations of a physical model clearly demonstrates that the drop of pressure under steady state conditions is greatest at the soil: root interface. The magnitude of the interfacial resistance for a given rate of flow is found to vary depending on the composition of the rooting material. Interfacial resistance also changes with alteration of flux and hydraulic tension in the same rooting material. It is evident from this model study that as the interfacial resistance increases, increased stress within the plant results. Hydraulic conductivity of soil and other parameters were determined to evaluate the applicability of the hypothesis of the soil: root interface being a high resistance barrier to water flow through the soil: plant system. Other parameters measured were soil water content: soil water potential; root density; total root length and surface area of roots; transpiration rate; leaf area; leaf water potential; leaf water status and stomatal resistance of potted sunflower plants, and growing in a growth room under controlled growth conditions. The result of the present study favours the existence of an interfacial resistance and also suggest that the interfacial resistance depends on a positive feed-back since the resulting stress in the plant tissues cause tissue contraction and there is a contraction of the roots and an opening of gaps between the root surface and the soil.

No description available.

This thesis examined the relatively uncharted realm of dissolved C dynamics in upland shallow organic soils. Extensive preliminary investigations and preparatory experimental evaluations led to the successful deployment of sampling strategies at a range of spatial scales in a climosequence of matched field sites in Wales, Scotland and Iceland. These sites provided the basis for investigation of climatic and mineralogical effects upon dissolved C transformations in upland shallow organic soils. Biological assessments including novel application of modified techniques identified the responsiveness of these soils to environmental perturbations at a range of experimental scales, and over varied temporal periods. As C loss from upland organic soils requires both degradation of SOM and export of degraded C via solution percolation and flushing or gaseous exchange, the capacity of the different mineral horizons to retain degraded C, and indeed the quality of the bound C, is of consequence to soil C source-sink understanding. The combined roles of organic and mineral horizons in C turnover potential and retention capability indicate the importance of upland shallow organic soils in modelling soil C dynamics in response to climate change. This highlights the necessity of sustainable management of these upland areas within the northern hemisphere.

The agricultural economy of Syria depends to a considerable extent on the use of the land along the river Euphrates. This land is fairly flat and should, therefore, be easy to cultivate, furthermore, since the river drains the better watered catchment outside the area, the problem of irrigation should not be insuperable. This should be all the more effective following the construction of the Euphrates dam. The increasing population makes it necessary to extend all the agriculturally usable areas, but above all else it is imperative to help the local and nomadic peoples to settle, sad to provide an opportunity for development within the study area, uhich lies in the middle reaches of the Syrian Euphrates. The thesis will deal mainly with the nature and characteristics of the saline, and particularly the gypaiferous soils which are associated with any such development. An account will be given of the field survey undertaken during the period 196l»197ii. Other aspects to be considered are the relationship between soils and plant life, the influence of landscape on soil dynamics, and the reclamation of land for agricultural development. Any possible development within the study area faces major problems, one of which i3 the excessive salinity or, more specifically the gypsiferous nature of the soils, which affects plant growth and consequently limits human activity. To contribute towards a solution of the area's problems, work Was started in 1161 on the measurement and collection of information on the presence and nature of salinity, together with relevant data concerning climate, hydrology, vegetation cover and other soil properties. It was also necessary to review literature concerned with the control of analogous problems in other arid areas. Part One illustrates the point that the saline soils occupy a large part of the country. The study area is situated mainly within this saline region, and the factors affecting the formation of the soil are discussed. The distribution of important soil properties occupies a major proportion of this part, over several related subsections . Part Two gives details of the vegetation cover and the general nature of the soil groups, the distribution of soil properties and soil profile descriptions. The classification of the soils is based on U.S.D.A. w7th Approximation11 and FAO-Unesco schemes. These two parts lead into the third, which deals with the gypsiferous and other saline soils in detail. From an agricultural and engineering point of view, the most important and most dangerous problems affecting the area concern these soils. Finally, Part Four, discusses the soil productivity, the irrigation network, and the field experiments on leaching. In addition, land reclamation is discussed, and recommendations are made for land use and the development of agriculture and settlement far local and nomadic people.

It is widely accepted as an established fact that the activity of earthworms promotes soil fertility. While the mechanisms responsible for this general effect are only vaguely understood, it is reasonably certain that micro-organisms will participate in most of the processes that involve transformations of organic substances. The literature provides little information concerning the gut microflora of the earthworm or of the effect of earthworms on the micro-organisms of the soil. These problems have been investigated only by Bassalik (1913). St8ckli (1928), Dawson (1947) end Day (1950). in no case did the work penetrate deeply into the subject. The investigation to be described here had as its principal objective a study of the changes that occur in the microflora when soil passes through the alimentary tract of the worm. Information on this question is desirable for the reason that many tons of soil per acre may be passed through earthworms in the course of a year (Evans, 1948)* Another objective was the investigation of any changes in the soil microflora that the worm might produce by other means, as for example by its secretion of slime. The lack of previous experimental work made it necessary, as an initial step, to establish satisfactory methods of Investigation. As it is not possible to examine the contents of the alimentary tract of the earthworm without contact with its coelomic fluid, it was also necessary to deter* {mine the nature of the microflora of the coelom. In the limited time available, an attempt has been made to provide a preliminary investigation which may serve as a basis for future studies of these problems.