A series of pot and field experiments was carried out in the north of Scotland in 1969 and 1970 to investigate which yield components of barley were most closely related to yield and to explain yield difference between years, sites, nitrogen and varieties. These trials were augmented by experiments in controlled-environment cabinets. The degree of correlation between yield and different yield components varied between years, sites, varieties and nitrogen. This can partly be explained in terms of intra-plant competition at different stages of growth. In general, nitrogen increased yield by increasing the number of tillers and ears but occasionally had a positive effect on other components. Splitting of the nitrogen dressing had no significant effect. There was a constancy of yield over a wide range of conditions but there were large differences in yield components which were not consistent and which could not be predicted. The only correlations which were regularly significant were those between tiller or ear number and yield within any one site. Between sites these correlations did not always apply. 4. Changes in population density altered many of the yield components but there was a constancy of yield above a certain minimum density. 5. Delaying sowing had the effect of reducing yield and also the yield components except for number of grains per ear. Sowings in May and June gave very low yields because of greatly reduced tiller number. 6. In controlled environment experiments, tiller number increased with temperature up to 23°C which was the highest temperature tested. The weight of the plant at the flag-leaf stage showed a decline below 8°C and above 18°C. At photoperiods of 24 and 16 hours, the flag-leaf was produced in 4--5 weeks from sowing but the number of tillers was low. With 8 hours light, the flag-leaf was not produced until 8 weeks after sowing but tillering was profuse. This was true even when total light intensity at 8 hours equalled that at 16 hours. These results suggest that flowering is under the control of photoperiod rather than temperature. 7. These investigations have revealed how yield components in barley affect yield but suggest that such knowledge cannot be made use of in agriculture except to suggest the use of adequate nitrogen and early sowing which is already well known. Intra-plant competition ensures a constant yield over a wide range of conditions above certain threshold values.

Experiments were carried out over a period of three years to examine the effects of a sprout inhibitor and storage temperature on the storage and post-harvest physiology of yams Dioscorea alata L. and swedes Brassica napus L. The inhibitor used was isopropyl N-(3-chlorophenyl) carbamate (CIPC or chlorpropham). It was found to be effective at a rate of 450 g/1000 kg in controlling sprout growth in swedes stored under laboratory and farm conditions but the development of rots then became the major factor limiting storage life, especially at temperatures above 10°C. CIPC did not seem to affect the normal chemical changes in stored swedes. Friesian bulls were fed CIPC-preserved swedes supplemented with 50% concentrate ration and gave satisfactory growth compared with similar bulls fed on an all-barley diet. The prospects of using CIPC granules commercially to prolong the storage life of swedes stored in conventional clamps are very slim. This is because one of the essential conditions for effective sprout inhibition by CIPC is restricted ventilation, but this also encourages rot development. Cold storage is suggested as a method which would check both sprout growth and rot development and the implications of this are discussed. In yams, CIPC treatment at both 450 and 900 g/1000 kg was without effect on sprouting at 20° and 25°C. Lower temperatures (15° and 10°C) inhibited sprouting even in the absence of CIPC. Below about 10°C, however, yams are susceptible to chilling injury. Membrane permeability changes are said to be among the causative factors. The effects of storage at chilling temperature on subsequent ion absorption, salt retention capacity and respiration confirmed that membrane damage occurred. Ion absorption and salt retention capacity were adversely affected after storage of the tubers at or below 10°C. However, respiration was markedly stimulated after storage at 10°C and became depressed only after 5°C storage. Thus, whilst respiration measurement can be a useful guide to storage history, the most straightforward and immediate check for the occurrence of chilling injury is to test salt retention or absorption against a control sample. In this way chilling injury can be detected long before visual deterioration sets in. Temperature control offers the best prospects of prolonging yam storage and the techniques used in this investigation offer a rapid method of screening yam cultivars to establish minimum storage temperatures together with those higher maximum temperatures at which satisfactory storage may be achieved; for the higher the maximum temperature the more economic cool storage of yams will be.

No description available.

In the UK, consumers and retailers demand that there be a continuous supply of onions all year round. To meet this demand, prehavest and postharvest methods are used to improve onion quality and storage life. Onions are currently cured at 28°C for 3-6 weeks to seal the neck of the bulbs thereby reducing disease incidence and esh moisture loss. Onions are then transferred to long term storage in ambient conditions or cold storage with controlled atmosphere 'storage or continuous ethylene depending on their intended storage duration. This study aimed to review and improve current UK curing and storage practises by investigating the biochemical, physiological and molecular effects these postharvest regimes have on the esh and skins of onion bulbs. Reducing curing temperatures from 28°C to 20°C was found to reduce the oxidation and degradation of avonols and anthocyanins, respectively, resulting in paler brown skins and more intense red skins. Following curing, onions intended for long term storage can be stored in continuous ethylene. This said, both ethylene and the ethylene binding inhibitor, l-methylcyclopropene (1-MCP), applied for just 24 h before or after curing reduced orion sprout growth for up to four months storage. However, onion sprout suppression beyond four months cold storage would still require continuous ethylene treatment. To elucidate the mechanisms by which ethylene and l-MCP reduce sprout growth, the rst onion microarray was developed. A cluster ofprobes were found to be down regulated in response to ethylene alone or in combination with 1-MCP. This, along with biochemical and physiological results, suggested ethylene and 1-MCP may both reduce sprout growth via different mechanisms by binding different ethylene receptors.

No description available.

The carbohydrate changes were measured dialing the cold storage of rhubarb cultivars which have differing duration of cold requirements for breaking their dormancy. During cold storage starch is broken down in both roots and crowns mainly to sucrose prior to future growth. For these carbohydrate changes to occur there is about one third increase in cold requirement of virus free plants compared with virus infected ones. The carbohydrate changes occurring during cold storage correlated closely with the cold requirement necessary to obtain a high yield when rhubarb roots are forced, so offering a method for determining when roots could successfully be forced. During cold storage an increase in the activity of phosphorylase and sucrosesynthetase in the soluble protein fraction prepared from root tissue was observed. This increase in enzymic activity could account for the breakdown of starch to sucrose during cold storage. Glucose and fructose showed very little change and invertase showed an increase in activity at later stages of cold storage. During forcing a marked decrease in sucrose occurred in the root tissue. This decrease in sucrose was partly due to its conversion into starch in the root tissue at the early stages of forcing and its translocation to the growing region for supporting growth of petioles. The main sugars in the petiole were reducing sugars. Petioles from virus free rhubarb contain more sugars than petioles from virus infected rhubarb. There was a considerable seasonal changes in dry matter and carbohydrate in rhubarb roots when growing in the field. In the spring the reserve carbohydrateswere utilized for supporting the growth of the shoot and in the summer the reserve carbohydrates were restored again.

The main problem addressed in this work is the detection of outliers in multivariate data. The practical motivation for this work is given by the desire of the Scottish Agricultural Science Agency (SASA) to automate the test of analytical purity in seed testing using machine vision. This test involves identifying any contaminant seeds in a sample of normal cereal seed. At present this test is done manually, but it is hoped that it may be possible to identify any contaminants on the basis of certain shape and size measurements recorded using image analysis. Hence the statistical problem is one of identifying outliers (contaminants) in multivariate data. A Bayesian diagnostic for outlier detection is used, and an extension to this diagnostic (involving kernel density estimation) is proposed. Both these diagnostics, as well as two other methods of outlier detection, are applied to the seed data supplied by SASA, and a comparison of the results is given. Problems encountered with high dimensionality are reported, and a solution based on principal component analysis is proposed. The use of robust estimators is also explored. An alternative approach to the problem, using discriminant analysis to classify each seed in the sample as either normal or contaminant, is reported. A comparison of the results achieved using discrimination with those of the outlier detection methods is given.

No description available.

The overall objective of this thesis work, in the Yucatán peninsula (México), was to establish a system with mixed woody species (leguminous/non-leguminous) to investigate the extent to which they increase nitrogen uptake and growth. The study tested the hypothesis that such mixtures may stimulate of N₂ fixation from the atmosphere and the transfer of N from leguminous to non-leguminous plants. Three woody species were selected: <i>Leucaena leucocephala </i>(legume), <i>Moringa oleifera </i>(non-legume) and <i>Guazuma ulmifolia</i> (non-legume). More than 80% of planted seedlings survived and grew rapidly. Total biomass (fodder) production was 1.9-7.7 ton ha^-1 for monocrops and 6-9 ton ha^-1 for the mixtures. Nitrogen yield in the fodder was higher in the <i>Leucaena</i>+<i>Guazuma </i>mixture (285 kg N ha^-1), followed by <i>Leucaena </i>monocrop and <i>Leucaena</i>+<i>Moringa</i> mixture (244 and 183 kg N ha^-1, respectively). The δ¹⁵ N of samples from non-fixing species ranged from 2.7 to 3.2‰ (mean 3.0 ± 0.45‰). The δ¹⁵ N of <i>L. leucocephala </i>(0.8‰) was significantly lower, indicating that nitrogen fixation occurred in the <i>Leucaena </i>plants. The % Ndfa in the <i>Leucaena </i>mixtures ranged from 58 to 72% while in the <i>Leucaena</i> monocrop it was 69%, at 11 months old. <i>Moringa </i>leaves decomposed most rapidly, followed by <i>Leucaena</i>+<i>Moringa, </i>and, was best described by a double exponential model. The combination of <i>Leucaena+Guazuma</i> decomposed more slowly and pure <i>Leucaena </i>leaves decomposed at an intermediate rate. Over 16 weeks, <i>Leucaena+Moringa </i>released 65-75% of the initial N, <i>Leucaena+Guazuma </i>released 46-63%, and <i>Leucaena </i>leaves alone released, on average, 54% of their N. Lignin+polyphenols and tannins had a strong negative correlation with the rate of nitrogen release. The alteration of the decomposition and N release patterns observed when mixing plant materials of different quality provides good prospects for improving synchrony between N availability and plant N uptake.

No description available.