Sandy soils are one of the most widely distributed soils in the world. However, crop production on these soils can be problematic especially in terms of water and nutrient retention. In the face of climate change and a projected reduction in water availability, food production is likely to be particularly affected. The aim of this research is to examine if amending soils with clay and organic matter can improve their water and nutrient retention. The research approach employed laboratory column leaching experiments, rainfall simulation, Computed Tomography (CT) scanning and field trials to investigate the potential of two types of clay, Kaolin (K) and Bentonite (B), and peat (Pt), as well different combinations of clay and peat, to act as effective soil amendments. The influence of amendment materials was assessed by examining water retention, nutrient retention, soil organic carbon and changes in soil properties. Laboratory analysis was supported by field trials to examine the productivity of spring wheat. The results showed that the amendment materials increased soil water retention and availability, reduced water infiltration, increased nutrient uptake, increased spring wheat growth and yield, and improved soil carbon storage compared to an unamended control. The findings provide a further understanding of how the addition of clay and OM can affect ecological function of sandy soils and elucidate the mechanisms involved in controlling water retention and availability, as well as nutrient retention in the amended soils.

The primary aims of this project were to: i) provide a survey of selenium and iodine concentrations in the terrestrial environment and locally grown crops of Iraqi-Kurdistan; ii) gain greater understanding of the factors controlling bioavailability of these elements in the calcareous soils of the region; iii) investigate the feasibility of biofortification of selenium and iodine and test the use of isotopically enriched tracers for this purpose; iv) assess iodine and selenium dietary intake and nutritional status of the local population using dietary questionnaires and a survey of a human biomarker. A survey was conducted covering locally grown crops, matched soil samples and irrigation water including 300 plant, 100 soil and 20 water samples. The potential availability of Se and I for plant uptake was examined by quantifying the soluble and adsorbed fractions of both micronutrients and their species. The influences of soil factors on plant Se and I uptake were examined. Results indicated that total soil Se (SeTot = 309 μg kg-1) was lower than the global average (400 μg kg-1). Approximately 2.5% of soil Se was present in the soluble and adsorbed fractions with an equal proportion of selenate and selenite in the soluble fraction and mainly selenite in the adsorbed fraction. The organically-bound Se extractability ranged from 20-89% of SeTot, depending on soil pH. Plant Se content was variable between crop species and different areas within Kurdistan with mean concentration of 113,112, 69 and 49 μg kg-1dw for leafy vegetables, tubers, fruit vegetables and wheat grain respectively. Higher plant Se concentrations were observed in plants grown in soils with pH > 8. The mean concentration of total soil iodine was 4140 μg kg-1. Almost 10% of this value was present in the soluble and adsorbed fractions. Mean plant iodine concentrations were 439, 368, 140, and 12 μg kg-1dw for leafy vegetables, fruit vegetables, tubers and grains respectively. The combined concentrations of soluble and adsorbed iodine were correlated with plant iodine content. The mean concentrations of irrigation water Se and I were 0.495 and 11.9 μg L-1 respectively. The amount (%) of soil CaCO3 was strongly correlated with iodine concentration in groundwater used for irrigation and irrigation water iodine concentration was again strongly correlated with plant iodine concentrations. The feasibility of Se biofortification in calcareous soils using local vegetable genotypes from Kurdistan was examined using 10 g ha-1 77Se as a biofortification treatment (and isotopic tracer). Five commonly used vegetables, including celery, chard, lettuce, radish and spring-onion were planted in soils spiked with the 77Se application and grown for 8 weeks under controlled growth room conditions. Results indicated that, at the end of the growth period approximately 35% of applied 77Se had been transferred to a recalcitrant form in the soil which resisted extraction with 10% TMAH. Only 5% of 77Se was present within the soluble and adsorbed soil fractions combined, at harvest. The amount of 77Se taken up by plant biomass varied according to crop species; 25% for radish and 7-8% for other vegetables from the total 77Se applied. Plant 77Se concentrations varied despite growing in identical soils and, unexpectedly, plants contained more Se originating from the soil rather than the fertilizer. The ratio of Sesoil/Sefertilizer also varied between varieties reflecting different growth patterns and uptake rates against a backdrop of decreasing fertilizer Se availability during the growing season. Biofortification of iodine using a range of vegetable crops grown in calcareous soil was investigated, using soil and vegetable genotypes from Kurdistan, and employing 129I as a tracer. Vegetables were irrigated daily with water containing 5.56 and 6.89 μg L-1 129IO3- and 129I- respectively for 8 weeks. Total and fractionated iodine (127I and 129I) was conducted on moist soil (c. field capacity) and air dried soil at the end of the growing season. Plant analysis was also undertaken for 127I and 129I, using ICP-MS. Results showed that plant iodine concentrations originating from native soil iodine were variable even when grown in identical soils. Generally, iodine concentrations in roots was greater than in shoots for both 127I and 129I. Vegetables irrigated with 129I- (iodide) had considerably lower iodine concentrations (6.2-12 μg kg-1dw) than those irrigated with 129IO3- (iodate) (53.3-479 μg kg-1dw). The majority of plant iodine originated from soil iodine rather than fertilizer iodine and varied depending on 129I species applied (iodate or iodide) and the vegetable plant type grown. For vegetable shoots treated with 129I- (iodide) only 3% of the iodine of the three test plants originated from the 129I treatment. By contrast, for 129IO3- (iodate) applications 11, 22 and 58% of iodine in the shoots of celery, lettuce and chard were from the 129I additions respectively. The recovery rate of 129I from soil extracted with 10% TMAH ranged from 63-95% of total iodine applied and varied depending on vegetable variety. The 129I recoveries from pots irrigated by 129IO3- were less than from 129I- irrigated soils suggesting greater loss of iodine from the iodate irrigated system. To assess the Se and I status of the population in a region of Kurdistan, the food composition data and dietary intake of Se and I was determined for 410 volunteers using a semi- quantitative food questionnaire, including commonly used food items. To directly investigate level of nutritional status of Se and I, urine samples were also collected from each participants as a biomarker. Daily dietary intake and source apportionment of Se and I from each food item was determined using questionnaire survey. The daily intake of I from food excluding salt was 119 μg d-1. Vegetables and fruits supplied 48%, protein sources 25%, cereal and grains 9%, dairy products 8% and water 2% of daily I intake. The majority (>90%) of salt samples collected were iodised with a mean I concentration of 40 mg kg-1 and daily intake of salt was estimated as 13.5g d-1. Accounting for salt intake, average daily iodine intakes increased to 668 μg d-1, with salt supplying 82% of daily I intake. The median urinary iodine (corrected for creatinine) was 379 μg g-1CRT and 424 μg L-1 osmolality corrected. More than 90% of school age children and over 55% all participants had excessive I intake according to WHO classification. The salt I concentration consumed by each family was highly correlated with mean urinary iodine of family members. Urinary Na and I were also correlated. The iodine intake estimated according to salt intake (calculated based on urinary Na) was strongly correlated with iodine intake calculated according to urinary iodine. The daily salt intake estimated by urinary Na was 15.3 g d-1 considerably higher than WHO recommended. Mean total daily intake of Se according to the questionnaire responses was 72.9 μg d-1 with 21% of participants having a daily intake lower than recommended RDA. The mean urinary Se fell in the range of 21.2-24.8 μg L-1 depending on justification methods. The predicted Se intake from urinary Se gave a values of 59 and 42 μg d-1 according to the method used which may imply Se deficiency. To conclude, Kurdistan soils Se content was found insufficient. Despite that, Due to high pH effect in some areas plant Se content seems to be having considerably higher Se content rather than areas with lower pH. Later studies revealed that daily Se intake may not enough to address the Se requirement of population. Biofortification of Se possible but to prevent decreasing availability would be recommend to apply in med season or foliar application. Typically soil and plant of Kurdistan found in a minimum of normal range of iodine and comparable with other areas. Irrigation water was found as a main source of plant iodine uptake. The daily iodine intake from food excluding salt is not enough to meet the recommended iodine level but considering high consumption of iodized salt in that region it can be classified as an excessive iodine intake which could cause high intake iodine consumption disorders such as hyperthyroidism and in turn health issues caused by elevated Na intake such as cardiovascular disease. In current iodine nutritional status of the region plant biofortification would not be recommended.

The aim of this work was to investigate the interactions of anionic radionuclides 129I, 77Se (as a proxy for 79Se) and 99Tc with soil geocolloids under a range of conditions. These anionic fission products are of specific concern to policy makers regarding human and environmental risk assessments. Previous research has demonstrated strong links between soil organic matter (SOM) content and reduced mobility of these radionuclides. Negatively charged humic substances (HS), such as humic acid (HA) and fulvic acid (FA), may constitute 80% of organic matter and the mechanisms that allow anionic radionuclide to interaction with these HSs are not well understood. In the case of all three radionuclides, speciation plays a significant role in controlling their environmental mobility, therefore HPLC and SEC coupled to ICP-MS was used to monitor the speciation changes as the isotopes were progressively incorporated into HA. X-ray absorption spectroscopy was also employed in order to establish the solid phase speciation of Se after reaction with soil geocolloids. Surface charge development of the HA significantly affected reaction with iodate (129IO3-) and iodide (129I-). Iodide added to HA systems demonstrated slow oxidation and formation of organically bound iodine (Org-129I) predominantly at higher pH (pH 6). Conversely IO3-, was rapidly transformed to form both I- and Org-I. As pH decreased, the rate of this reduction reaction increased. Increasing HA concentration also increased the rate of IO3- reduction and formation of Org-I. Previous research has suggested that the most likely mechanism is IO3- reduction to I2 or HOI which then binds with phenolic groups on OM forming Org-I species. However, IO3- was observed to rapidly bind to HA forming Org-I species with no initial evidence of I- formation; I- concentration then increased over time as Org-I decreased. Where Fe2+/Fe3+ was present increased reduction of IO3- to I- was observed, mediated by association with HA, resulting in less Org-I formation overall. Instantaneous reaction of I- with HA was observed in the presence of Fe2+/Fe3+, with bonding via cation bridging. Some I- was subsequently re-released as I- likely due to ongoing Fe hydrolysis. Modelling of the systems alone was successful and will assist the improvement of whole soil assemblage models. Selenite (Se(IV)) reaction with HA was most rapid at low pH, with minimal/no reduction occurring at > pH 6. Reduction of selenate (Se(VI)) also occurred but this was less than for Se(IV), at low pH. No formation of Se(VI) from Se(IV) was observed, suggesting no oxidation took place, however some formation of Se(IV) from Se(VI ) was observed, also the formation of an unknown Se species suspected to be organic in nature. Humic acid concentration had no significant effect on the rate of Se(IV) or Se(VI) reduction, suggesting that HA itself was not responsible for the reduction. X-ray absorption spectroscopy (XAS) demonstrated the potential for significant reduction to Se(0) at pH 4 and bonding through a Se-O-C chain. The role of microbial communities on Se(IV) and Se(VI) reduction in the HA systems was demonstrated through the use of soil inoculum and glucose additions in sterile and non-sterile systems. No reduction of Se(IV) or Se(VI) and bonding to HA was observed in filter and -irradiation systems. Additions of inoculum and glucose increased the rate of reduction. Additions of Fe2+ did not increase reduction of Se(IV) or Se(VI) when compared to non-sterile HA systems, however XAS analysis demonstrated formation of HA-Fe cation bridges. No reaction of pertechnetate (99Tc(VII)) with HA was observed in these aerobic systems. An unknown Tc species was occasionally observed (< 0.005 μ L-1) and it is possible that this is an organic-Tc species. Significant incorporation of Tc into the solid phase was observed in aerobic soils, with most Tc(VII) being retained in soils with high OM contents and low pH. The mechanisms considered here build upon the basic processes considered in current biosphere models for I and Se. Assemblage models must be used in order to reliably model the interactions of elements within soils due to the complexity of the systems. In order to understand the long-term radiological risks associated with geological repositories, the fine-scale mechanisms must be understood geochemically across a range of different soil types and conditions. The effect of I and Se speciation on bioavailability in soils determines both the potential transfer of radioactive isotopes to the food chain from GDF’s and from aerial sources of contamination. Alongside this, the work also has significant implications for advising on cost-effect fertiliser application methods for both I and Se, in order to tackle nutrient deficiencies worldwide.

Conservation Agriculture (CA) has potential benefits to the soil, crop yield, and the environment including reducing runoff, enhancing water retention and preventing soil erosion, in addition to increasing soil carbon sequestration and reducing greenhouse gas (GHG) emissions. Although CA is widely adopted in some areas of the world, it is still not widely adopted by UK farmers. The first overall aim of this project was to investigate the effects of tillage practice and residue retention, on soil physical properties, crop yield and GHG emissions. For this purpose, a split-plot field experiment was established on the University of Nottingham farm between September 2014 and August 2016. The main plot treatment was residue retention while cultivation practices were applied to the sub-plots and included three different tillage systems: no-tillage, minimum-tillage and deep ploughing. We used a novel analytical tool, X-ray Computed Tomography, to characterise the 3-D soil pore network in conjunction with a number of other soil physical properties such as bulk density, penetration resistance and shear strength. A range of portable chambers were used to detect the GHG emissions from soil and from soil-plant systems as influenced by the tillage and residue treatments. Winter wheat yield was not affected by the tillage treatments or residue retention in the first year, but, in the second year, no-tillage caused a 10% reduction in triticale yield compared to minimum-tillage and traditional ploughing. Multiple regression analysis showed that the lower triticale yield was partially explained by higher soil strength in the no-tillage plots, together with lower soil moisture content in summer. Our results show that while there is potential for climate change mitigation from no-tillage when the Net Ecosystem Exchange is considered, this effect could not be observed from soil emissions only. The second aim of this project was to assess the current level of reduced tillage (RT) uptake by UK farmers and the constraints for further adoption. A postal questionnaire was conducted in January 2016. This questionnaire found that only 7.0% of the arable land in England is under no-tillage and 47.6% is under minimum-tillage. The adoption of RT increased with an increase in farm size as it was the most adopted on farms >400 ha. Moreover, RT was adopted most on combinable crop farms. Weed management and slugs were identified as main challenges for RT adopters. Increasing uptake of CA from current levels will probably require policy intervention including financial incentives for growers during the early stages of the transition from ploughing to CA. This will encourage farmers to buy RT equipment and may help them to cover any potential yield reduction, if occurred, before the CA system stabilisation.

Plants have developed elaborate defence mechanisms to protect themselves against pathogens. Recently, the ubiquitin-proteasome pathway has been proven to play important roles in regulating plant disease resistance. Previously, the tobacco (Nicotiana tabacum) ACRE276 and its Arabidopsis homolog AtPUB17 have been identified as E3 ligases that are positive regulators of the Cf-9/Avr9- and N/p50-elicited hypersensitive response (HR) in tobacco. In addition, AtPUB17 is required for the RPM1- and RPS4-mediated resistance responses in Arabidopsis. The identification of AtPUB17 signalling partners would allow us to understand the mode of action of AtPUB17 during plant defence. AtPOB1, a BTB/POZ-domain protein was isolated as an AtPUB17 interactor in a yeast-two-hybrid screen. The aim of this study was to confirm this interaction and to investigate the potential involvement of AtPOB1 in mediating disease resistance responses. The analysis of the Atpob1 knock out plants revealed a novel BTB/POZ protein implicated in plant defence. Atpob1 plants rapidly accumulated reactive oxygen species (ROS), induced the expression of pathogenesis related (PR) genes and developed spontaneous necrotic lesions upon infection with a virulent pathogen. AtPOB1 transcript and protein levels were induced by virulent Pseudomonas syringae. And transient overexpression of AtPOB1 in Cf-9 tobacco compromised the Avr9-triggered HR. In addition, Atpob1 plants showed signs of premature senescence. These results indicate that AtPOB1 is a negative regulator of plant defence- and senescence-associated pathways. The Nicotiana benthamiana AtPOB1 homolog was also identified and its cDNA sequence was used to investigate the role of NbPOB1 and its close relative NtPOB1 in disease resistance signalling. Transient overexpression of NbPOB1 and RNA interference (RNAi)-based silencing of NtPOB1 in Cf-9 tobacco compromised and accelerated the Avr9-triggered HR, respectively. Moreover, virus induced gene silencing (VIGS) of NbPOB1 accelerated the dark-induced senescence in N. benthamiana leaves. These observations identify NbPOB1 and NtPOB1 as the orthologs of AtPOB1. The subcellular localization of AtPOB1 and NbPOB1 was analyzed by transiently overexpressing GFP-AtPOB1 and GFP-NbPOB1 fusion proteins in tobacco leaf tissue. Analysis by confocal microscopy revealed that GFP fluorescence was localized in the nucleus of leaf tissue tested. The overexpression of AtPOB1 fused with a nuclear export signal (NES) failed to compromise the Avr9-triggered HR in Cf-9 tobacco, indicating the nuclear localization of AtPOB1 is crucial for its function. The BTB/POZ domain is a highly conserved protein-protein interaction interface that mediates homo- and/or hetero-dimerization of BTB/POZ proteins. The D146A and D141A mutation in the BTB/POZ domain of AtPOB1 and NbPOB1, respectively reduces their dimerization efficiency. These mutants fail to negatively regulate the Cf-9/Avr9-mediated HR, supporting the importance of an intact BTB/POZ interface for the function of AtPOB1 and NbPOB1. Finally, yeast-two-hybrid and immunoprecipitation assays indicate that AtPOB1 interacts with AtCUL3A, a component of E3 ligase complexes, in which AtPOB1 would confer substrate-specificity. We propose that AtPOB1 (and Nicotiana POB1) negatively regulate cell death and senescence possibly through ubiquitin-mediated pathways.

Resource capture and utilisation were studied in two agroforestry systems at the International Centre for Research in Agroforestry (ICRAF) Research Station at Machakos, Kenya. The agroforestry systems examined contained two contrasting tree species, leucaena (Leucaena leucocephala (Lam.) de wit) and grevillea (Grevillea robusta), and the C3 and C4 crops, cowpea (Vigna unguiculata) and maize (Zea mays, Katumani composite). The leucaena-based trial was established in November 1989 and the trees were grown with ten maize crop rows on either side of a pruned hedgerow (HM) or unpruned tree row (LM). A sole maize control (SM) was also grown. Paired sets of treatments were irrigated to eliminate below-ground competition for water (HMI, LMI and SMI respectively). Interception of photosynthetically active radiation (PAR) by leucaena and maize was measured on a row-wise basis in all treatments at 7-10 day intervals using a sunfleck ceptometer. Sap flux was measured for the maize and both pruned and unpruned leucaena using heat balance gauges. Results are presented for the 1992 April-July rainy season. Total PAR interception was 30 % greater in LM and LMI than in the SM and SMI sole maize treatments. However, little more than 30 % of the light intercepted by the LM and LMI systems was captured by the crop component, and competition for light alone reduced maize yields by over 30 %. Total water uptake by the LM leucaena and maize comprised 60 % of the seasonal rainfall (237 mm) as compared to 30 % for sole maize. However, as for light interception, only 30 % of the water transpired in LM was used by the intercropped maize, and competition from the trees for soil water reduced maize yields at distances of over 6 m from the leucaena. The leucaena was more effective at resource capture, yet less efficient in resource utilisation since it exhibited a lower dry matter:radiation quotient and a lower transpired water:dry matter ratio than maize. Thus the leucaena in the agroforestry systems captured more of the resources that could have been used more effectively by the maize, causing the performance of the mixture to be sub-optimal; these results suggest that the two components would be best grown separately. Intensive monitoring of resource capture and use by trees and crops was subsequently transferred to the Complementarity In Resource Use on Sloping land trial (CIRUS). Although it had been intended to study both trials during the long rains of 1993, the leucaena trees were almost completely defoliated by psyllid (Heteropsylla cubana) infestation shortly before the onset of the rains: in subsequent seasons, CIRUS was studied in preference to the leucaena trial as the trees had only partially recovered. CIRUS was designed to investigate the effects of competition and the extent of complementarity between grevillea and associated crops using the following treatments; sole crops (Cg) of cowpea during the short rains and maize during the long rains, dispersed-planted trees with (CTd) and without crops (Td), and across (CTa) or on-contour-planted (CTc) tree rows with crops. Light interception and water use were monitored using a similar measurement regime to that employed in the leucaena trial. Results are presented for the 199213 and 1993/4 short rainy seasons; the failure of the 1993 long rains forced the abandonment of experimental measurements during this season. Light interception by the Td and CTd grevillea increased greatly between the two short rainy seasons. Thus, total seasonal interception of PAR was three times greater in sole cowpea than in sole grevillea during the 1992/3 short rains, but by the following short rainy season was over 50 % greater in the grevillea than in the cowpea. Cumulative interception of PAR by the CTd grevillea and cowpea combined was more than twice that of the sole cowpea and over 40 % greater than that for sole grevillea during the 1993/4 short rains. Experiments involving artificially imposed shade showed that there was no reduction in total above-ground dry matter production in cowpea until 75 % shading was imposed. To quantify the degree of below-ground complementarity in water use between grevillea and cowpea, sap flux was measured using heat balance gauges attached to the stems of young grevillea (10-18 months old), both before and after excavating the crop rooting zone (upper 60 cm of soil) around the stem base. The crop rooting zone was removed to establish the capability of the grevillea to extract water from deeper horizons. After excavation, the trees maintained sap fluxes of up to 85 % of the unexcavated values. During both short rains, soil evaporation was by far the largest component of the water balance in all treatments. However, continued extraction of water by the trees during the dry season greatly increased resource capture~ thus total water uptake was three times greater for the sole trees than for the sole crop when dry season water use was included. During the 1993/4 short rains, water use was greatest in the CTd treatment, in which 25 % of the total seasonal rainfall was transpired by the trees and crops. Although transpiration by the CTd trees exceeded interception losses, the latter may have had a greater effect on crop growth by reducing the total quantity of water available within the system. The existence of below-ground complementarity and the shade tolerance of the cowpea suggest that deep-rooted tree species and certain C3 crops may be combined successfully in the semi-arid tropics, but the sensitivity of crop yield to any reduction in water availability within the system demonstrates the need for caution when implementing such systems. The results obtained are discussed in relation to previous research on intercropping and agroforestry and their implications for the successful adoption of agroforestry systems in the semi-arid tropics.

The objective of this research was to "investigate, study, analyse, and report conditions under which Syrian "rainfed" wheat farmers live interact and adopt innovations and improved cropping practices. The purpose of this was to help in understanding forces that can influence farmers' decisions to adopt innovations and which influence their adoption behaviour. The research, also, has attempted to develop concepts and methods which have rarely been used before in Syrian conditions. The recommendations for the policy makers and the Extension organisations in Syria were based on the major findings as well as other findings which were revealed throughout the research. The study was carried out in the two largest rainfed cropping areas in the country; Aleppo province to the north and Hassakeh province to the east, the sample of farmers was distributed in First Stability Zone (Zone 1) and Second Stability Zone (Zone 2). A total sample of 60 farmers were randomly selected from both areas. Nine agricultural innovations and improved cropping practices were selected and farmers' adoption behaviour with regard to these innovations and improved practices were investigated. The nine innovations and practices were; "the use of nitrogen", the use of "phosphorus", "following the recommended time of nitrogen application", "the use of improved wheat varieties", "the degree of following the seed renewal for wheat", "the use of herbicides", "the use of pesticides", "the use of sowing machines", and "following the recommended seed bed preparation". The "Sten Score" method was adopted in order to score the adoption behaviour of farmers for the nine selected innovations and improved cropping practice. The method was modified in order to achieve the best classification of farmers on the basis of their adoption behaviour. Four major aspects and characteristics were selected, investigated and later were analysed in relation to the adoption behaviour of farmers with regard to the nine selected innovations and improved practices. These aspects and characteristics were Personal and Socio-Economic, Economic and Institutional, Communicational, and Psychological Factors. The study has concentrated on characteristics which usually have been ignored or avoided in past adoption and diffusion research. Special methods have been devised in order to help in measuring these aspects and characteristics. Special attention was paid to the role of personality and the Self-image of farmers as important aspects affecting their adoption behaviour. Until recently research into farmers' decision making to adopt or reject innovations did not pay attention to the role played by these factors at the time of taking the decision to adopt innovations. The major findings in Zone 1 revealed that the adoption of innovations and improved practice by farmers were related highly and significantly with farmers' "Self-image", the "availability of credit and cash money" and "having an Extension plot or field demonstration on the farm". The three variables together explain over 70% of the variation in the adoption behaviour of farmers. In Zone 2, the farmers' "Self-image", and the "availability of machinery and equipment on the farm" were found to be the best related variables with the adoption behaviour of farmers. The two variables together explain over 60% of the variation in the adoption behaviour of farmers. The recommendations for the policy makers and the Extension organisations in Syria were based on the major findings as well as other findings which were revealed throughout the research.

The efficacy of phytoextraction strategies were tested by pot and field trials on soil contaminated with heavy metals, including Cd, derived from long-term disposal of sewage sludge. The strategies investigated were: i) the use of hyperaccumulators; ii) chemically-enhanced uptake using arable species and iii) the use of short rotation coppice (SRC). Chemical interventions including EDTA, chloride salts, HCl and herbicide were used to enhance uptake by arable and SRC species. Tissue Cd concentrations in the Ganges population of Thlaspi caerulescens were lower than reported in other studies; the mean Cd concentration was 265 mg kg". It was deduced that Cd uptake was limited by a low Cd2+ concentration in soil and the rate at which solution Cd was replenished. High rates of plant mortality were observed, raising questions over the successful husbandry of T. caerulescens for phytoextraction. Chemical interventions produced significant increases in metal uptake by arable and SRC species. For example, Cd uptake by Z. mays following application of 10 mmol EDTA kg'' and by Salix caprea x cineria x viminalis following combined application of EDTA and HCI. However, concentrations were still well below those required for successful remediation. Furthermore downward migration of metal was observed through the soil profile following EDTA application. For example, the soil Cd concentration in the 0- 10 cm profile was reduced from 32.0 to 25.5 mg kg' seven months after application of 10 mmol EDTA kg'', yet only 1% of this reduction could be accounted for by Z. mays Cd off-take. Realistic estimates for phytoextraction timescales and costs were made in line with legislative thresholds. Overall the time required to reduce total soil Cd concentrations below 3 mg kg-1 was large and the costs were prohibitive. For example, although Cd off-take by Ganges was greater than for any of the other species tested, it was estimated that well over one century would be required to reach target metal concentrations.

1. The relevance of studies of development in crop-weather investigations is reviewed and the aims of the present work are outlined. 2. The procedures used in studying development in field crops of winter wheat are described. The developmental progress of the plants was ascertained by frequent dissections. 3. Primordium initiation at the stem apex is strongly dependent upon apex temperature, which could be accurately estimated from standard meteorological screen temperatures. Like numerous other complex biological processes, initiation has a markedly linear response to temperature: the number of primordia initiated is therefore in direct proportion to accumulated temperature (thermal time). To calculate this requires estimation of the base temperature (Tb). 4. The linear dependence upon temperature of the initiation rates of leaves, spikelets and florets (R1, Rs and Rf ) was evident. Spikelets were initiated faster than leaves ; rate changed at a distinct inflexion point, usually at about the end of leaf initiation but sometimes later. Tb = 0 grad. C for leaves but was higher for spikelets and florets. The shift in Tb apparent17 occurred because Rs and Rf were strongly influenced by the day length at inflexion point. When temperature was corrected for day length influence, Tb = 0°0 for each developmental phase. Inflexion point timing apparently depended upon interaction between vernalisation before crop emergence and photo thermal time afterwards. 5. Leaf appearance rate in thermal time was linear but apparently influenced by the direction and magnitude of day length change at emergence, with a possible secondary effect of current day length. Leaf extension was strongly related to temperature. The gradient of lamina size up the stem appeared to be ontogenetically determined. 6. Compared with early-sown or fully-fertilised crops, floret survival and grain yield was lower in those sown late or inadequately fertilised, probably on account of their smaller amount of growth per unit of developmental time.

The research described in this thesis expresses the importance of quantitative and qualitative data types and how these can be incorporated and combined to produce an agricultural management decision support system (DSS). Researchers cannot solely depend on numerical data and relationships when designing, modelling and producing decision management tools. The relevance of the social sciences and peoples interpretations of these tools is equally important. The DSS described here focuses on the management of rainwater harvesting (RWH) in Tanzania. Numerical data related to natural resources (water and nutrients) and yields of rice and maize have been collected for the production of the DSS. With regard to the social science factors, the DSS tackles the concept of common pool resources (CPR) of water and nutrients. The importance of CPR is well understood, however their inclusion in the production of models is a relatively new concept. Criteria related to social status is linked with the by laws that govern the allocation of natural resources in Tanzania to help derive a numerical method for including CPR within the DSS. The production of the DSS is a novel way of combining this research into a tool that aims to benefit all socio-economic community groups. During the production of the DSS, a single generic approach for the inclusion of quantitative and qualitative information has developed. Particular focus was on the development of a model base (programming and mathematical relationship building), database (storage of the data used for the relationships) and a dialog system (the user-interface and communication strategy). This method is termed the ‘dialog, data, and models (DDM)’ paradigm (Sprague and Carlson, 1982). From this research, a DSS has been produced that aims to optimise RWH management in Tanzania with the aim of alleviating poverty and enhancing sustainable agriculture for all community members. Also an overall strategy for the production of DSSs has been produced. It illustrates how both quantitative (numerical and physical data) and qualitative (socio-economic considerations) can be utilised individually and in combination for the production of DSSs and can be extrapolated for further research and to new areas.