Amaranthus retroflexus is a common annual weed world-wide and causes substantial yield reduction in many crops. In this research program three main objectives were fulfilled: firstly the effect of certain environmental parameters on germination and emergence of A. retroflexus collected from Iran were determined; secondly, potential pathogen strains as biological control agents for A. retroflexus were identified; and finally the activity of a candidate biological control agent against the target weed under various environmental conditions and with different formulation were evaluated. Results of several experiments showed that under controlled conditions A. retroflexus seeds are able to germinate at a wide range of temperatures, water potentials, burial depths of seeds and soil types. However, the degree of success of germination and establishment of this plant were influenced by temperature, water potential, planting depth, soil type and interactions between these factors. A. retroflexus growth as favoured by high temperature (25-35C), high water availability (0 to -1 bar), shallow burial (0.5-1 cm) and lighter soil types. The objective of the second section of this project was to find a potential pathogen as a biological control agent for A. retroflexus. Initially a culture collection of Amaranthus pathogens, collected throughout Europe and Iran, were screened. The final results in pathogenicity tests showed that A. altemata strains 423, 780 and 930 and Aposphaeria amaranthi showed the greatest pathogenicity against A. retroflexus. The fungi of A. alternata strain 423 and Aposphaeria strain were able to control 100% of A. retroflexus plants under certain environmental conditions. Ascochyta caulina and an unidentified fungal strain 5-1 (collected from Iran) caused less disease development. These results clearly indicated the potential of A. alternata and Aposphaeria amaranthi as mycoherbicides. A. alternata strain 423 was shown to be more pathogenic than strains 780 and 930. A spore concentration of 107 spores ml-1 without application of oil emulsion or 106 spores ml-1 with oil formulation was required for good disease development. A. alternata species demonstrates potential for controlling A. retroflexus only when 16 hours of high humidity/leaf wetness were provided after spore application. Also for maximum activity of A. alternata, it had to be applied at 2-4-leaf growth stages of the weed seedlings. The optimum dew temperatures for 100% mortality were between 20 and 25C. The post inoculum temperature for giving maximum disease development was between 20 and 30C. Finally, for maximum control of A. retroflexus by A. alternata there should be no delay in the occurrence of dew after inoculation. Formulation of A. alternata spores in the rape-seed oil emulsion significantly increased disease development and decreased plant vigour and dry weight of A. retroflexus. This formulation caused a reduction in minimum spore density required in the spore suspensions and the length of dew period required for disease development. However, formulations of A. alternata, need to be further improved to reduce the requirement for a long dew period. Application of granules at emergence stage gave better control of A. retroflexus plants than application at the 4-leaf stage or application simultaneously with planting. Because A. alternata granule applications needed to be applied at very high levels, it is unlikely to be economically liable. Both formulations of Alternaria (spore suspensions (liquid) and granule (solid)) caused no serious infection in sugar-beet, maize and wheat plants.

The response of white clover/perennial ryegrass and pure ryegrass swards to fertiliser N were compared under two cutting frequencies, monthly and bimonthly, between 1978 and 1981. In the first year after sowing DM yield responses under only one cutting frequency (monthly) were examined. During the two subsequent years the cutting frequency difference was imposed and finally in 1981 uniform monthly cutting was again adopted. White clover species were chosen to provide a comparison between performance of a recently introduced long-petioled cultivar, Blanca, and a standard one, S100.S23 perennial ryegrass was chosen as a companion grass cultivar due to its recognised ability to respond well to fertiliser N. Fertiliser N was applied in 100 kg N/ha increments between zero and 400 kg N/ha/an on mixed swards and up to 600 kg N/ha/an on pure grass swards. Annual fertiliser N applications to swards were supplied at uniform and V3 increments before start of growth in March and thereafter following each harvest except the last on monthly and bimonthly cutting frequencies respectively. High N application rates increased DM yield more with longer growing periods than with higher cutting frequencies. N yield in herbage was positively affected by the N application rate and not or slightly by the cutting frequency. Consistent with this, appreciably higher N concentrations (max 3.2%) were found on average in the herbage at high fertiliser N rates and frequent cuttings than at lower rates and less frequent cuttings (2.2%). Blanca 127 and S100/523 mixed swards in the absence of fertiliser N yielded on average 61% of pure grass swards receiving annually 400 kg N/ha with monthly cutting. Differences between clover cultivar DM yields in response of mixed swards to fertiliser N were small. However there was some evidence that S100 (medium-small leaved cultivar) was less tolerant to small additions of fertiliser N (around 100 kg N/ha/an) than Blanca (medium-large leaved) when more frequently cut. Under less frequent cutting conditions yields of mixed swards were consistently higher under each level of fertiliser N than under more frequent cutting regimes. Fertiliser N applications of around 100 kg N/ha/an reduced DM and N yields in mixed swards during the period of maximum clover growth in mid summer to a greater degree on more than less frequently cut plots. The influence of season and fertiliser N on the level of herbage Ca, Mg, K, P and nitrate-N were discussed with some reference to K/(Ca+Mg) and Ca/P ratios. The effects of cutting frequency and fertiliser N on the seasonal variation of nitrogenase activity in Trifolium repens (cv S100) were measured by means of weekly acetylene reduction assays on clover grown in association with Lolium perenne (cv S23) over two seasons. Acetylene reduction activity (ARA) was drastically reduced after defoliation; recovery being considerably faster in May than later in the season. The seasonal pattern of ARA was significantly affected by the defoliation frequency of the sward. With only 3 cuts per year ARA of the more mature clover plants was significantly less prior to cutting than plants subjected to 6 cuts per year. The role of associated ryegrass competition for light with clover in a mixed sward was discussed. The response of ARA of white clover plants to fertiliser N varied during the two seasons. Fertiliser N generally reduced ARA but had little effect in the early months of 1978 when N treatments were first imposed. The decline in ARA associated with N applications was generally greater in the second year of fertilisation than the first. Cutting frequency of the sward significantly reduced the response of ARA to fertiliser N only under the infrequent cutting/ high fertiliser N regime suggesting that clover N fixation is affected by increased ryegrass competition in mixed swards. The molar ratio of acetylene reduced to nitrogen accumulated by clover plants during 4 week growth periods on control plots varied between 8.6 and 2.5:1. In May of 1978 and 1979 the molar ratio greatly exceeded 8.6:1. Only after July did the molar ratio approach the theoretical value of 3:1 of acetylene reduced to N fixed. It was concluded that the AR technique whilst suffering from a high degree of sampling variation and difficulties in estimating actual amounts of N fixed by clover plants can be useful in amassing quickly quantities of data that can lead to reliable comparisons between many types of imposed treatments.

The literature on the non-additivity of feedstuffs, their existence, occurence and possible causal mechanisms including factors affecting' fibre and starch digestion and feed energy utilisation by ruminants, was reviewed. Six experiments were designed to provide information on how these effects occur, to conclusively demonstrate the existence of associative effects and to identify possible methods whereby they may be either avoided or alleviated. The reduction in the rumen pH (to 6.0-6.1) in sheep given roughage led to the inhibition of cellulolysis and partial destruction and washout of the rumien microflora. Dry matter (DM) degradation In the rumen and dry matter intake (DMI) were also depressed. Increasing the rumen pH of sheep offered the concentrate diet did not alter greatly the rumen microflora, nor did it increase cellulolysis, DM degradation or DMI. It was concluded that both the type of substrate present in the rumen and the rumen pH influence ruminal cellulolytic activity. It was found that the amount and proportion of barley necessary to depress rumen pH, DM degradation and cellulolysis depended on the availability of the readily fermentable barley attach to the rumen microorganisms and was therefore influenced by the degree of proceeding. A pH threshold of 6.0-6.1 was obtained blow which cellulolysis was totally inhibited. It was observed that the extent of deprecation of fibre degradation was influenced by both the rumen pH and the rate of solubilisation of the concentrate supplement. This effect was further confounded by the degradability of the roughage, since the percentage reduction in the rate of cellulolyais was greatest with those roughage with a low DM degradability. It was concluded that in order to maintain rumen cellulolysis when roughages are supplemented with a readily fermentable carbohydrate, the rumen pH has to be maintained above 6.0-6.1. It was found that the diurnal variation in pH increased with the level of supplementation and degradability of the supplement and decreased as the frequency of feeding increased. Although the rumen pH of the diets supplemented with Harley was reduced to a similar extent to that or diets containing glucose, the pH was depressed over a longer period of time. It was also observed that the extent of fibre degradation was fairly similar for both glucose and barley diets, which confined that there degradation, namely the presence of readily fermentable carbohydrates. In the last two experiments the effect of offering diets containing various proportions of hay and barley, with and without the addition of bicarbonate salts, on the voluntary intake and digestibility of dietary components was examined. In the fifth cameramen fixed amounts of barley were given with hay freely available, while in the final experiment fixed proportions of hay and barley were offered ad libitum. Grinding the hay was found to increase the daily DMI, in both experiments, when the hay was offered alone or supplemented, but decreased the digestibility of the DM, organic matter (OM) and said detergent fibre (ADF) component of the diets. The addition of barley depressed the digestibility of ADF of both the ground and chopped hay based diets but increased DM and OM digestibilities. In the sixth and final experiment, it was found that although DM and OM digestibilities increased linearly with the proportion of barley in the diet, there was found to be an additional quadratic trend - the digestibility values obtained were significantly less than those calculated by the summation of the weighted sum of the separately determined digestibilities of the component feedstuffs, i.e. associative effects or the non-additivity of feedstuffs were shown to exist. A measure of the magnitude of these effects was obtained by considering the extent to which the digestibility of the diets was depressed when compared with calculated values. The maximum deviation from linearity, was obtained when the diet containing ground hay: pelleted barley (1:2) was offered, the \ DM digestibility depressed by over 9%. This represented: a loss in the faeces of about a tenth of the calculated digestible material ingested. This diet also reduced the digestibility of the hay fraction to the greatest extent, to 31.2%, compared with 51.0% when hay was given alone - a depression of 38.0%, i.e. nearly 40% of the digestible material offered as hay was excreted. It was concluded that associative effects could be largely avoided if the rumen pH was maintained above that level inhibitory to cellulolysis. It was suggested that this could be achieved by offering roughage portion of the diet either long or chopped, so as to stimulate rumination and salivation, by offering the concentrate in such a way as to minimise the risk of depressing material, such as bicarbonate salts, in the diets.

This thesis examines soil fertility management strategies in dry season irrigated vegetable production (DSIVP) in peri-urban areas of Jos, Nigeria. Farmers have developed a complex strategy of mixing inorganic fertilisers with organic manure and town refuse ash (produced by open burning, and sorting for non-combustible components). The thesis aimed to gain insights into the sustainability (in terms of nutrient supply) of the local agricultural system, acquire an understanding of past and present fertiliser practices and the rationale behind them, provide an appreciation of the role played by urban waste ash and the risks attached to its use, and place the problem of soil fertility in a wider context of farming problems. An inter-disciplinary approach was adopted so the methods used are: chemical analysis of soil and inputs (i.e. refuse ash), questionnaire surveys, semi-structured interviews (with farmers and PADP, JMDB, FUA etc.) and participant observation. The thesis observed that farmers have in-depth, but informal, empirically-derived knowledge about fertiliser application, which explains their past success in soil fertility maintenance. The tremendous increase in DSIVP in the last decade, though, has brought about a scarcity of organic amendments; farmers are increasingly reliant on inorganic fertilisers, probably over-applying them. Although this is not an immediate threat to the stability of the system, it may lead to soil acidification in the near future. Urban waste ash can counteract soil acidification (high pH and base cations), but certain batches can be contaminated by heavy metals, and indeed there is some indication of accumulation in the crops of the study farms. The problem of soil fertility needs to be addressed, however, farmers' short-term concerns (particularly access to credit facilities) need to be solved first. It is imperative that the Nigerian Government should take note of these issues and rapidly take steps to solve them.

The potential for a quantitatively produced garlic oil for use as an insecticide was investigated. The study assessed the garlic oils efficacy in the laboratory and in the field, as well as its physiological effect on three key enzymes noted for their involvement either in toxicity, or detoxication of exogenous toxins in two Dipteran pests; Delia radicum (L. ) and Musca dornestica (L. ). The garlic oil absorbed onto wood flour pellets (prills) had no significant repellent effect on D. radicum, in choice tests when presented with artificial oviposition sites. Exposure of 24hr old D. radicun, eggs to garlic prills placed on the substrate significantly reduced egg hatch, whilst exposure to vapours of the prills had no significant effect. When used in the field, damage to swede plant roots by D. radicum was reduced in a dose dependent fashion, with the highest application rate (140 kg ha') providing control comparable to that of the 'current best practice' organophosphonis pesticide. In liquid form the garlic oil had a dose dependent effect on the mortality of all life stages (egg, 2''1 instar larvae, and adult) of D. radreum and M. domestica, and corresponding LC5o values were calculated. A 5% concentration had comparable mortality rates to the 'current best practice' organophosphorus pesticide. Field application reduced swede root damage in a concentration dependent fashion with mean root damage scores in the 0.5% and 2% concentration treatment plots significantly lower than those of the control, but not significantly different to those in the organoplhosplhorus pesticide treatments. The liquid had no significant effect on swede root circumference at any concentration, thus not significantly affecting potential crop yield. Exposure of pure extracts of acetylcholinesterase,c arboxylesterasea, nd glutathione S-transferaset o a series of garlic oil concentrations inhibited carboxylesterase activity and glutathione S-transferase activity in a dose dependent fashion; no significant inhibition of acetylcliolinesterase activity was noted. No significant inhibition of the three enzymes studied was noted In vitro or in vivo exposure of larvae and adults of both Dipteran species. Quantitative assessmenot f the glutathione and lactate pools indicated that there was generally a net loss of glutathione with increasing garlic oil concentration and no significant correlation between lactate levels and concentration in the larval and adult life-stages of U. radicum and M. donaestica. It was concluded that the garlic oil studied, both in liquid form and in prill form could be used as an insecticide against the two Dipteran pests studied, although the mode of action is still unclear. Implications for use of the products and the potential mode of action are discussed. IV

The nutritive values of twelve samples of different UK wheat cultivars from two different growing years were assessed. A series of chicken feeding experiments were conducted to examine the relationships between chemical composition, grain quality and energy content of the wheat samples and the growth performance of broiler chickens when fed these wheat samples as part of nutritionally complete diets. The efficiency of utilization of apparent metabolisable energy (AMEn) of wheat samples as a source of net energy (NE) was studied. Step-wisc multiple regression analysis indicated that the content of total starch in the wheat samples and the arnylosea: mylopectin ratio in the starch were the main predictors of growth, feed intake and FCR of the broilers. Increasing starch and arnylose content in the wheat cultivar samples gave increasing weight and feed intakes. The Hagberg falling number was also significantly (P < 0.05) positively related to broiler chicken growth and food intakes. Two further experiments indicated that there was a growth response to increasing the amylose: amylopectin ratio, but that the response was specific only to the variations in amylose: amylopectin ratio by using an extracted starch from a high amylose maize cultivar. Variation of the amylose: amylopectin ratio by using different rice cultivars gave no (p > 0.05) differences in broiler growth performance. The influence of different amylose: amylopectin ratios on the physical nature of the starch granule may therefore be more important than their effects in changing the total dietary supply of those starch components. Although the net energy concentration of a wheat sample was related (p < 0.05, r2=0.42) to its determined AME, there was still unexplained variation (about 60%) in the cilicicncy of utilization of AME as a source of NE. A proportion of this variation was, however, explained (p < 0.05, r2=0.40) by differences in the water-extract viscosity of the wheat samples. Different ileal viscosities, due to feeding different wheat cultivars, may result in variation in the amount of intestinal fermentation of nutrients and so altcr the NENE ratio of whcat-based diets.

The chemical control of the potato cyst nematode (PCN) by granular nematicides when applied and incorporated into potato seed beds was investigated to assess problems connected with incorporation using bed cultivation machinery. Fluorescent tracer granule work using a range of granular nematicide incorporation methods suggested that differences exist between the incorporation methods in terms of placement of the fluorescent granules in the planted potato bed. Incorporation of tracer initially by a bed tiller followed by a second incorporation by a stone and clod separator produced a distribution of tracer greater than 40cm deep in the planted bed. Incorporation of tracer by a stone and clod separator with application of tracer halfway up the first web produced concentrated bands of tracer in the sides of the planted bed. No visible differences in tracer distribution occurred between other treatments. The differences observed between incorporation techniques during the fluorescent tracer granule work were shown not to be important in terms of PCN control or yield in the first year's field experiments. The second year of field experimentsa ssessedth e incorporation of the granular nematicide Vydate (10G) before, during or after stone and clod separation of potato beds. These field experiments suggested that timing of nematicide incorporation in relation to stone and clod separation had no effect on potato yield or control of PCN. As in the first year's experiments, significant differences occurred between plots treated or not treated with a granular nematicide, but not between incorporation methods. Work describing the field concentration of oxamyl immediately after planting showed similarities to the distribution of tracer granules observed in the soil hall studies. The subsequent distribution of oxamyl 3 weeks after planting showed no redistribution of the nematicide in the potato bed. The depth of potato planting is thought to be responsible for the uniformity of PCN control and crop response to nematicide treatment regardless of incorporation method as seed was planted below the nematicide treated layer. Evaluation of a diagnostic kit used for detecting oxamyl in soil showed that the kit was well suited for this purpose and its use is discussed in the light of the findings of this study.

No description available.

No description available.

No description available.