Reducing the use of pesticides by early visual detection of diseases in precision agriculture is important. Because of the color similarity between potato-plant diseases, narrow band hyper-spectral imaging is required. Payload constraints on unmanned aerial vehicles require reduc- tion of spectral bands. Therefore, we present a methodology for per-patch classification combined with hyper-spectral band selection. In controlled experiments performed on a set of individual leaves, we measure the performance of five classifiers and three dimensionality-reduction methods with three patch sizes. With the best-performing classifier an error rate of 1.5% is achieved for distinguishing two important potato-plant diseases.
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Field experiments were carried out in 1991 and 1992 on sandy soil highly infested with the potato cyst nematode Globodera pallida. Half the trial area was fumigated with nematicide to establish two levels of nematode density. Three levels of soil compaction were made by different combinations of artificial compaction and rotary cultivation. Two potato cultivars were used in 1991 and four in 1992. Both high nematode density and soil compaction caused severe yield losses, of all cultivars except cv. Elles which was tolerant of nematode attack. The effects of the two stress factors were generally additive. Analysis of the yield loss showed that nematodes mainly reduced cumulative interception of light while compaction mainly reduced the efficiency with which intercepted light was used to produce biomass. This indicates that nematodes and compaction affect growth via different damage mechanisms. Nematodes reduced light interception by accelerating leaf senescence, by decreasing the specific leaf area and indirectly by reducing overall crop growth rate. Partitioning of biomass between leaves, stems and tubers was not affected by nematode infestation but compaction decreased partitioning to leaves early in the growing season while increasing it during later growth stages. The effects of nematodes and compaction on root length dynamics and nutrient uptake were also additive. This suggests that the commonly observed variation in yield loss caused by nematodes on different soil types is not related to differences in root system expansion between soils of various strength. Cv. Elles, which showed tolerance of nematodes by relatively low yield losses in both experiments, was characterised by high root length density and thick roots. These characteristics did not confer tolerance of soil compaction, since compaction affected root lengths and tuber yields equally in all cultivars. In the first experiment only, high nematode density led to decreased root lengths and lower plant nutrient concentrations. The yield loss which occurred in the second experiment was attributed to the effects of nematodes on other aspects of plant physiology. Copyright © 1995, Wiley Blackwell. All rights reserved
The current western agrifood system is highly successful in providing for human needs. However, the dominant agricultural approach of up-scaling and specialisation is put under pressure by a number of developments in the global landscape. Global developments such as population growth, pollution, soil degradation and climate change, in which agriculture plays a crucial role, make the need for a transition towards a paradigm with a broader range of values evident. Niche initiatives often develop as a reaction to needs not fulfilled by the regime. Therefore, certain niches may have the potential of driving a necessary transition. This research aims to determine if permaculture, being a niche, has this potential. The main question for this research was formulated as follows: How can a production system based on permaculture principles contribute to the agrifood transition? To answer this question, relevant current trends and global developments were used as a basis for developing a future scenario. Empirical qualitative data on permaculture businesses in the Netherlands was gathered as well, of which the results were used for a determination of permaculture’s performance in this future scenario. This was done by comparing a standardised permaculture system with a conventional potato system. As a result of this comparison, the Unique Selling Points of permaculture were identified, which determine the future potential of permaculture.
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