The present day knowledge of the nature and amount of the organic matter in forest soils is not very extensive, due chiefly to the empirical and arbitrary methods frequently employed by investigators rather than to neglect of the subject. The recently advocated method of proximate analysis (the Waksman method), which appears to offer many advantages over the older emperical procedures, has been used as a basis for the investigation of five forest and heath soil profiles from the North East of Scotland. For the determination of the Total organic matter in soils a modified Chromic Acid wet combustion method was devised, which gives excellent results both with pure substances and with soils when compared with either theoretical or dry combustion values. After thorough investigation, it has been found that the acid residue from this wet combustion is less satis-factory for nitrogen determinations than is the usual Kjeldahl method. The Waksman method of proximate analysis has been thoroughly tested, more particularly with regard to hemi- cellulose and cellulose determinations, and a modified procedure is recommended. The/ The study of the nature of plant and soil hemicellu- loses has shown the inaccuracy of the single determination of waksman and the need for a more precise definition of Hemicelluloses than that used by this author. Cellulose determinations made by the usual chlorine-ation method have sometimes shown wide discrepancies when compared with the hydrolytic method adopted by waksman, and an attempt has been made to explain these. The modified system of proximate analysis was then applied to the selected soil profiles. Differences in the composition of the newly fallen leaves and needles of the different profile have been demonstrated. These are reflected in the changes taking place during decomposition and humification as well as in the subsequent alteration products throughout the whole profile. These differences are discussed in the light of present day theories regarding soil organic matter, its nature, formation and role in soil-forming processes.

1) It was found that initial "air-dry" moisture content of soil and the method and period of wetting affected the proportion, obtained by wet-seiving, of water-stable aggregates of Cruden Bay soils. Tha drier the soil the slower the wetting and the shorter the period of wetting the higher was the percentage of water-stable (but not of semistable) aggregates. 2) Soil pH affected significantly the water-stable and water-semistable aggregation and the porosity of the Tillycorthie soil (Site -I) between pH 5 and pH ?s the water-stable aggregation is decreased and the water-semistable aggregation and the porosity are increased with increasing pH, and vice versa. Planting with Italian Rye Grass did not affect aggregation within tha period of 7 weeks growth, but dacreased tha porosity due to the presence of fresh roots in the soil cores. Of the chemical additives used, only V.A.IK1.A. (a miature of calcium hydroxide and a copolymer of vinyl acetate and the partial methyl ester; of maleic acid) improved the poor structure of the soil, its optimum effect being around pH 6. P?E.0. ;(PolyethyleneOxide) increased the uiater-semistabla aggregation, but decreased tha water-stable aggregation and the porosity 4,7. the optimum effect being around pH S.Calcium, iron or aluminium sulphates had no significant effects, 3)/ 3) The amount of uiatar-stable aggregates affected considerably the compactibility of tha Tillycorthie soils, while the pH effect mas small between 4 and 8, and the effects of the P.E.O. solutions were negligible* It appears that compaction measurements with the Bruca type of apparatus could be very useful for structure studies relating to the behaviour of soils under field cultivation. 4) tha shear parameters of thB Tillycorthie soil were affected by:sail moisture content The P.E.O. solutions within the concentration ranga 10-10Q0 ppm did not shout a beneficial effect on the shear parameters of the soil,apparently because of very strong absorption of the polymer from solution onto tho soil colloid surfaces.

No description available.

No description available.

The agricultural demand for inorganic phosphate fertilisers needs to be reduced whilst the dependence on more sustainable sources of phosphorus, such as sewage sludge, is increased. However, the presence of heavy metals in sewage sludge pose a threat to soil microorganisms and can inhibit the action of phosphatase enzymes if present in high concentrations. The long-term impact of Zn and Cu on soil microorganisms and phosphatase enzyme activity was investigated at four field sites from the Defra ‘Long-Term Sludge Experiment’ in order to determine the overall impact on organic phosphorus mineralisation. Following the final applications of sludge in 1997, the total concentrations of Zn and Cu at each site were comparable to the UK statutory limits for sludge amended soils. Almost 20 years later 63-91 % of the applied metal loadings still remained and total concentrations of Zn and Cu were found to be significantly higher in contaminated soils, in comparison to untreated soil, and soils receiving uncontaminated sewage sludge. A significant correlation between exchangeable and total metal concentration could still be seen in soils contaminated with Zn, whereas the solubility of Cu was found to be very low (< 1 %); though a significant percent remained bound to soil organic matter. No long-term decrease in microbial biomass carbon (Cmic) could be detected in the contaminated soils at any of the sites. However analysis of ergosterol showed an increase in the proportion of microbial biomass carbon derived from fungi. Significant changes were also observed in the PLFA profiles of microbial communities within contaminated soils, indicating the microbial community has adapted and become tolerant to the heavy metal contamination. Combining results using meta-analysis indicated that Zn and Cu caused an increase in fungal biomass carbon of approximately 25-35 % in comparison to soil receiving uncontaminated sludge. Whereas overall decreases of 16 and 8 % were seen for Cmic in soils contaminated with Zn and Cu, respectively, indicating a loss of bacterial biomass from the contaminated soils. Hence, the current UK statutory limits may not be sufficient to prevent changes in soil microbial community and a reduction in the limits set for sludge amended soils is recommended in order to protect microbial diversity. No long-term decrease in the activity of phosphomonoesterase was detectable in the contaminated soils. However combining the results using meta-analysis indicated phosphomonoesterase activity per milligram of biomass carbon was greater in soils contaminated with Cu. This may be an indication that Cu is inhibiting extracellular phosphatase enzyme activity within the soil environment, though this remains undetermined. Orthophosphate, phosphomonoesters, and pyrophosphate were the predominant forms of phosphorus within the applied sludge treatments; a broad phosphodiester signal was also present. Overall, the greatest range of organic phosphorus forms was seen in the uncontaminated sewage sludge. However, no difference in the range of organic phosphorus compounds was observed between the untreated and sludge amended soils at the field sites investigated. It was therefore concluded that the organic phosphorus content of sludge amended soils is returning to that of untreated soil, with no long-term interference caused by the presence of Zn and Cu.

Carbon and nitrogen mineralization and phosphorus and potassium status were studied during incubation of soil under constant moisture levels between air-dry and water-logging, and also when low moisture levels were raised to field capacity or water-logging and high moisture levels were lowered to field capacity, The effect of soil moisture level on carbon and nitrogen mineralization at different soil pH levels and on carbon and nitrogen mineralization and phosphorus and potassium status in the presence of added organic matter was studied in incubation tests. Total nitrogen balances were studied in incubation tests in a soil of different pH, and moisture levels, and with different organic matter and inorganic nitrogen treatments. Total nitrogen balances were also studied in pot tests under rye-grass and rice plants receiving different inorganic nitrogen treatments during growth at different soil moisture levels. The performance of the rye-grass and rice tops which had been used for the total nitrogen balance studies above was studied and so was the effect of the moisture and nitrogen treatments on the pH of the soil after cropping. The effect of the height of water of submergence on the performance of whole rice plants and the effect of the length of period of soil storage under "upland" and water-logged moisture regimes prior to transplanting on the performance of whole rice seedlings, were studied. The effect of the period of air-dry storage of soils prior to wetting and incubation or cropping on carbon and nitrogen mineralization or on rye-grass performance was studied. The effect of alternate wetting to different moisture levels during incubation and air-drying on mineral nitrogen, phosphorus and potassium status of soils and the effect of alternating soil moisture between different levels compared with maintaining constant levels on the performance of ryegrass were studied.

This investigation was an attempt to characterise and evaluate Seven soils important for agriculture and. horticulture in Eastern England. The soils, which included six mineral soils ranging from loamy sand to heavy loam and en organic peat soil, were treated with organic materials and green manures and the effects compared with the untreated soils in incubation and pot tests, The incubation tests involved the measurement of carbon dioxide and accumulation of ammonia and nitrate, The ratio of carbon to nitrogen mineralised over a given period was determined. The pot tests were carried out in three successive years using 824 Ryegrass and Maize as indicator crops in the soils treated with organic materials and 824 Ryegrass again in soils treated with green manures. The green manures were clover and mustard, leguminous and non-leguminous crops respectively these were grown, removed, ground and replaced in the soils prior to the growth of the indicator crop, Determinations were made of the dry matter in leaves and roots, uptake of R, P, K, Mg. and Ca, percentage recovery of added nitrogen and the inter-relationships of shoot:root, K:Mg and K:Mg+Ca ratios, The results of all the experiments were statistically analysed. The results of the incubation and pot tests were compared and correlations noted. The results of the pot tests were discussed in relation to the mineralogy, cation exchange capacity, percentage carbon, percentage total nitrogen and water holding capacity of the soils, Consideration was given to qualitative aspects of the results in relation to utilisation of the indicator crops for animal feeding and animal health.

The bacterial genus Bradyrhizobium is biologically important within soils, with different representatives found to perform a range of functions including nitrogen fixation through symbioses, photosynthesis and denitrification. The Highfield experiment at Rothamsted provides an opportunity to study the impact of plants on microbial communities as it has three long-term contrasting regimes; permanent grassland, arable and bare fallow (devoid of plants). The bare fallow plots have a significant reduction in soil carbon and microbial biomass. Bradyrhizobium has been shown by metagenomic studies on soil to be one of the most abundant and active groups including in bare fallow soil indicating that some phenotypes are adapted to survive in the absence of plants. A culture collection was created with isolates obtained from contrasting soil types from Highfield in addition to woodland soil, gorse (Ulex europeaus) and broom (Cytisus scoparius) root nodules. The collection’s phylogeny has been explored by sequencing housekeeping genes to determine whether soil treatment affects the core genome. One grassland and one bare fallow isolate had their genome sequenced and differences have been assessed to establish their potential for a range of functions and to direct future experiments. The functional diversity of the collection has been investigated using carbon metabolism assays to identify key substrates and determine whether the isolates group according to soil treatment. Symbiosis capacity and role in nitrogen cycling has been examined using nodulation tests, anaerobic growth on nitrate and nitrous oxide production and reduction through denitrification. A high level of diversity can be seen throughout the collection with differences being linked to niche adaptation. Understanding more about Bradyrhizobium could give clues on how above ground management impacts a key group within the soil community. Furthermore, the first assembled genomes of two non-symbiotic Bradyrhizobium strains isolated from soil provide an important resource for microbiology and soil ecology.

The main purpose of the study was concerned with changes occurring in mineral nitrogen fractions during incubation of saline and alkali soils in their original state as well as after reclamation. The soils used were typical alkali, saline alkali, highly saline and moderately saline soils from West Pakistan and the laboratory reclamation methods used were similar to those used in practice. Ammonia, nitrite and nitrate levels in the soil as well as carbon dioxide evolution during incubation were determined in original and reclaiWd soils (1) without amendment and (2) after treatment with ammonium sulphate and various organic materials. The effect of soil moisture content and addition of organic material on the loss of ammonia by volatilization from soils treated with ammonium sulphate and urea were also studied. In addition to the traditional reclamation methods used, methods involving the use of sulphur and organic materials in combination with leaching were studied in relation to the properties of the reclaimed soils as well as to nitrogen changes during subsequent incubation of these soils. The optimum pH levels for nitrogen mineralization and nitrification in the soils were determined by leaching with varying levels of sulphuric acid before incubation. Experiments were done on both original and reclaimed soils to determine the effect of various amendments on (1) denitrificatiore4osses of added nitrate and (2) non— symbiotic nitrogen fixation. A subsidiary study was made on neutral English soils on nitrogen mineralizing characteristics during incubation following treatment of the soils with varying types and levels of salts, both alone and in combination, as well as with organio amendments and also at varying soil moisture contents. The effects of flooding a soil with sea water as well as those of reclaiming the sea water—affected soil were also studied.

This thesis reports a series of experiments performed to investigate the effects of soil pH on mineralisation processes in agricultural soils. The experiments utilised a short term soil incubation assay which measured the mineralisation of a mixture of 15 uniformly 14C labelled amino acids to 14CO2• Amino acids were chosen to represent the labile pool of dissolved organic matter and their mineralisation provides a means of comparing the activity of the soil microbial population performing mineralisation of nitrogenous substrates. An examination of mineralisation in five profiles of acidic soils (chapter 4) showed that the rate of amino acid mineralisation decreased with depth and was correlated significantly and linearly with total C and total N within each profile. The profiles examined contained high levels of nitrate suggesting the presence of significant populations of acid tolerant nitrifying bacteria. A strong positive correlation between basal respiration rate and the rate of amino acid mineralisation was demonstrated within most profiles. A study investigating the impact of varying intensities of sheep grazing from three upland regions of the UK on soil mineralisation processes was undertaken (chapter 5). This showed that the soil microbial biomass was maximal at low to intermediate levels of grazing across the three regions and declined as the legacy of grazing was reduced through the long term removal of sheep. High intensity of grazing tended to reduce the phenotypic evenness (a component of diversity) of the microbial community. Net mineralisation rates were highest in mid-successional and lightly grazed treatments in all regions and were generally lowest at the extremes of grazing influence. However, the rate of amino acid mineralisation was generally lowest in the short-term ungrazed and lightly grazed treatments and were fastest at the highest grazing pressure in all regions, supporting the model that heavily grazed grassland favours fast nutrient cycles dominated by labile substrates. Multiple regression of data from all sites showed that the impact of grazing on the activity of the SMB that actively mineralises nitrogenous substrates appears to function primarily through its effect on soil pH. A field study was conducted to investigate the feasibility of decreasing nitrate leaching in cereal and grass plots by acidification of soil (chapter 6). The results from porous ceramic cup extracted soil water showed that nitrate concentrations in drainage water were greater in cereal plots than in grass plots. Soil acidification lowered nitrate concentrations in drainage water, substantially over winter and spring in grass plots and in cereal plots the effect was minimal during winter but became more substantial in spring. Data indicates that soil acidification decreased nitrification rates, causing the ammonium pool to accumulate. Soil acidification also lowered levels of dissolved organic nitrogen in soil water, usually to a greater degree in grass than in cereal plots. It was concluded that it may be possible to use careful soil pH management as a tool to control nitrate leaching without compromising the quality of drainage water, this may be more effective on grassland than on arable crops. Long term experimental plots from Rothamsted Experimental Station, Woburn Experimental Farm and the Scottish Agricultural College Craibstone Estate were sampled to investigate the effect of soil pH on a range of microbially mediated soil mineralisation characteristics and processes (chapter 7). The results showed that soil pH did not significantly affect indigenous mineral nitrogen levels at the time of sampling and had little consistent effect on levels of soluble organic nitrogen or carbon across soil types. Soil pH also did not show any great influence on net ammonification, net nitrification or net total mineralisation in a 30 d aerobic incubation. Soil pH was positively correlated with soil microbial biomass carbon and nitrogen and soil basal respiration in each soil type. The proportions of organic C and N that were biomass C and N were positively correlated to soil pH, indicating an increase in availability of the C and N present in the soil with rising pH. Glucose-C and urea-C mineralisation rates were fastest at intermediate points of the pH range studied in each soil type. Arginine-C mineralisation was positively and linearly related to soil pH. Results of chapters 5, 6 and 7 showed that soil pH had a significant impact on the rate of amino acid mineralisation. Acidity increased the proportion of added amino acid-C used in respiration and decreased the proportion used in biomass, implying an acidity-induced stress on the microbial population. Soil microbial biomass C or N, basal respiration rates, total soil C and N and dissolved organic C and N were shown not to adequately predict the rate of amino acid mineralisation over the range of soil types studied. Suggestions for further investigations into the soil pH effects on characteristics of organic substrates and how they may determine carbon and nitrogen cycling rates are made.