Both broad-leaved trees and earthworms are often described as having an ameliorating effect on acidic podzolized soils. The role of earthworms, in particular Lumbricus rubellus, in soil changes occurring after birch colonization of heather moorland was investigated. A highly acid podzol under heather appears to have been converted to a mull or moder brown earth within one generation of birch growth. The crucial change in soil characteristics occurs after about thirty years of birch growth with a dramatic decrease in raw surface humus and consequential changes in other soil factors, such as pH, moisture and porosity. L. rubellus populations increase by about three times from birch stands of twenty-four to thirty-two years. Other earthworm species, noticeably L. terrestris increase steadily in number with increasing age of birch. Investigations into earthworm respiration revealed that the earthworms are not making a large contribution to organic matter catabolism directly by their population metabolism. However, L. rubellus seems capable of consuming much of the annual leaf litter, up to 100% in older birch areas, but it is reckoned to consume only about 1% of the annual reduction of raw mor humus occurring after about thirty years of birch growth. Even considering the stimulating effect that earthworm activities can have on microbial decomposition, it is concluded that the earthworm populations are not high enough to be decisive in mor humus reductions. Earthworms may, however, be important if conditions are intermediate between mor and mull, and also in maintaining an established mull humus system.

No description available.

No description available.

An analytical protocol for the determination of various soluble P fractions, namely: total dissolved P (TDP), dissolved reactive P (DRP), dissolved organic P (DOP) and dissolved condensed P (DCP) has been developed. The determination of DOP in soil solutions and water extracts was achieved by an improved automated photo-oxidation procedure, in which possible interferences caused by aluminium have been overcome. Partitioning of TDP into DRP, DOP and DCP fractions increased our understanding of P cycling in temperate soils. A combination of field and laboratory studies indicated that management factors such as soil acidity and fertiliser P additions greatly influenced the amount and distribution of soluble P between fractions. Natural climatic processes such as freeze/thaw and wetting/drying cycles have been shown to greatly affect soil P cycling. Fractionation of TDP into DRP, DOP and DCP components highlighted the problems associated with attributing the `freezing and drying effect' to any single process. The significance of these observations are discussed in terms of plant nutrition and possible contribution to P leaching and surface water quality.

The objective of this study was to compare the effects of ammonium and nitrate sources of nitrogen on the growth and chemical composition of rye (Scale cereale) in the presence and absence of potassium ethylxanthate (KEtX) as a nitrification inhibitor, and the effects of acidity and metal ions on nitrification in soils. Results showed that application of nitrogen caused a significant increase in dry matter yield and offtakes of N and Mn but reduced P and Fe contents at various levels. Addition of the inhibitor increased N and Mn content and offtake, and decreased P level and offtake significantly. Different forms of nitrogen showed no significant differences either in foliage yield or nutrient content except stimulation of Fe uptake by nitrate-N. Ca, Mg, K and nitrate-N in tissues remained practically unaffected. Nitrification in acid peat was stimulated by adding lime but suppressed by Cd as sulphate and Al, Fe, Mn, Co, Ni, Cu and Zn when added as chlorides. Generally, inhibition increased with metal addition. Al (200 μg g⁻¹), Fe and Mn (100 μg g⁻¹) promoted nitrification. Addition of all the metals up to 3000 μg g⁻¹ peat depressed the process and the extent of suppression depends on the type and concentration of metallic ions. Among the metallic ions studied, Cd was the most toxic. The critical concentrations of Cd; Al; and Fe, Mn, Co, Ni, Cu and Zn were 500, 1000 and 2000 μg g⁻¹ peat respectively. However, results provide evidence that nitrification can proceed slowly at pH 3.4 to 4.0 in the absence of metals. Although nitrification was suppressed, general microbial activity was not repressed even in the presence of 3000 pg Al g⁻¹ peat.

The objectives of this research were: (i) to investigate the phosphorus and zinc status of Iraqi calcareous soils, (ii) to describe the characteristics of both phosphate and zinc fertilizer reactions in such soils, and (iii) to test the nature of phosphate-zinc interactions in soils and on plant growth. Six soil samples were studied: three alluvial calcareous soils from the Lower Mesopotamian Plain and three desert calcareous soils from the southern desert region. Chemical and physical examination showed that the alluvial soils were generally more fertile than the desert soils. However, poor structure and high salinity of the alluvial soils limit their agricultural potential. Reaction of fertilizer P with soils involved initial rapid adsorption of P, followed by a gradual change in solution composition toward equilibration with octocalcium phosphate (OCP). Hydroxyapatite was unlikely to be involved because of its very slow rate of formation. Dicalcium phosphate dihydrate (DCPD) could be produced initially in all soils, but it was less persistent in the alluvial soils than in the desert soils, suggesting that persistence of DCPD was greater in a soil low in salts and/or carbonate. It was further shown that an increase in calcium ion concentration enhanced DCPD hydrolysis as evidenced by the formation of OCP. Formation of amorphous zinc silicate (Zn2SiO4) may play a major role in controlling Zn solubility in such soils. ZnCO3, Zn(OH)2 and Zn3(PO4)2.4H2O are too soluble to account for the zinc concentration. The solubility of Zn was somewhat higher in the desert soils than in the alluvial soils. P/Zn interactions in soils and plants were observed, but the reaction in the soil external to the plant is not adequate to explain crop effects. P-induced Zn deficiency in maize caused by imbalance in P/Zn ratio is basically a consequence of the differential translocation rates of P and Zn from the root to the top.

The characteristics of water-soluble organic material in soil solutions has been studied extensively 'in situ'. Relatively little attention has focused on isolation of such material, particularly when comparison of a number of samples has been attempted. In this study the water-soluble organic acids leached from the soil horizons beneath eight different tree species were isolated by adsorption onto macroporous resins. Amberlite XAD-8 and XAD-4 resins were used in series therefore two samples, labelled as 'hydrophobic' and 'hydrophilic' acids were obtained. Practical amounts of free organic acids for characterisation purposes were isolated from each resin. Elemental analysis (carbon, nitrogen and sulphur) and acidity (measured by potentiometric titration) reflected the probable state of oxidation of the material. Lower molecular weight material was more abundant with depth. Copper binding ability correlated well with the acidity generally but a group of samples isolated from similar horizons and resin showed high acidity and poor metal binding ability. This was probably due to the inability of the acidic sites to be involved in chelation reactions. Metal binding was measured using gel filtration, dialysis and an ion-exchange method. Chromatography in gel filtration was monitored by direct feed of column effluent into an atomic absorption spectrophotometer, a technique attempted but not used successfully before. The method measured directly metal bound and required only 0.2 mg of sample <I>per </I>determination. For these reasons this method was used for routine analysis whereas dialysis and ion-exchange were only used for comparison purposes. As expected the samples isolated on each resin were very different. Comparison of samples from the horizons showed clearly the increased state of oxidation with depth. It was possible to establish differences in the organic material in the soil horizons on the basis of whether the stands were coniferous or deciduous trees but the similarities between the samples were perhaps equally striking.

Preliminary effects of application of dolomitic limestone on growth and nutrient status of two different <i>Camellia sinensis</i> L. (tea) species, and on soil status in two Sri Lankan acid soils were investigated. The concentration of Mg in the leaves of TRI 206 species, grown under low-country climatic conditions, increased but Mg concentration was unaffected in CY9 species, grown under up-country climatic conditions. Dolomitic limestone had no effect on the yield of bud, and first and second leaves which are harvested for the production of made-tea. Ten representative profiles of Sri Lankan acid tea soils overlying dolomitic mineral belts and six profiles from different climatic regions were subjected to a detailed mineralogical investigation. No Mg bearing minerals were found to a depth of 75 cm, even at dolomitic sites. The release of Mg from six Sri Lankan acid tea soils was measured by intensive cropping with ryegrass. A minimum one fifth of total Mg uptake was obtained from non-exchangeable Mg forms in the soil, except St. Coombs top soil. Soils that contained less than 9 mg Mg kg^-1 initial extractable Mg released 2.0 to 13.2 mg non-exchangeable Mg kg^-1 of soil. The effect of Mg and Ca addition supplied in liming and non-liming materials on the growth of <i>Camellia japonica</i> in an acid soil was studied. Magnesium was taken up by <i>Camellia japonica</i> plants in preference to Ca when Mg and Ca were added. The amounts of soil nutrients extracted with mixed resin and ammonium acetate solution were compared with their uptake by <i>Camellia japonica</i> plants. Both methods extracted similar amounts of Mg and Ca but in limed soil the amount of Al taken up by plants was more closely related to ion-exchange resin Al values than ammonium acetate solution adjusted to the pH of the soils.

Phosphorus inputs are essential to achieve satisfactory levels of crop production in many parts of the world. In this context the use of rock phosphate is an attractive option because it is considerably cheaper than water-soluble traditional commercial P fertilisers. However, the low solubility of rock phosphate is the major limitation to its use specially for short growing crops such as rice, potato and vegetable crops. This thesis investigates the potential of poultry manure as a viable management option to increase the solubility of rock phosphate. A conventional pot experiment with dwarf French bean (<i>Phaselus vulgaris</i>) was conducted with 2 sources of rock phosphate, namely Eppawela rock phosphate (Sri Lanka) and Gafsa rock phosphate (Tunisia). Three different rates of rock phosphate (37.5, 75 and 150 kg P₂O₅ ha^-1) and poultry manure (75 kg P₂O₅ ha^-1) were combined in a factorial experimental design. Two different planting systems were imposed to investigate the effect of fallow periods and the presence of the crop on rock phosphate solubility. The solubility of rock phosphate was evaluated in terms of various parameters including plant growth, P uptake and changes in the soil P status. The application of poultry manure when combined with rock phosphate increased plant growth, P uptake and soil extractable P compared to the calculated combined individual effects of the inorganic and organic fertiliser. In addition, other parameters, such as plant Ca, N and K uptake and various soil parameters also increased in response to mixing rock phosphate with poultry manure. The same experiment was used to study solute losses. The loss of PO₄-P, NO₃-N, NH₄-N, Ca and K was increased by the addition of poultry manure with the highest losses observed during the fallow period compared to the cropping period. The leaching of PO₄-P into the drainage water increased after harvesting of bean crop. Inorganic P was the major P fraction lost into drainage water.

Roots and their associated mycorrhizal fungi have long been recognised as major determinants of nutrient cycling. Their measurement has been limited because soil limits accessibility. The use of <I>in-situ</I> camera techniques in conjunction with minirhizotrons and image analysis software now make the acquisition of accurate root longevity data possible. The current literature was reviewed in relation to root longevity - both measurement techniques and available data. Four main experiments were employed to study the root longevity of a number of tree species, grass and clover subject to differing environmental conditions and grass and clover and poplar roots with and without colonisation by Arbuscular Mycorrhizal fungi. The data was analysed in a number of different ways including the use of the powerful statistical technique for censored data - survival analysis. This technique proved to be very useful for analysing temporal changes to root longevity. The data indicate that root longevity can be extremely short but is dependent upon environment and for some species, colonisation by Arbuscular Mycorrhizal fungi. Preliminary calculations were completed to determine the role of root death in nutrient cycling and these predict that large quantities of nitrogen, phosphorus and carbon are flowing from the live to the dead root pool on an annual basis.