Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

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Optimization of productivity and quality of irrigated tomato (Solanum lycopersicum L.) by smallholder farmers in the Central Rift Valley area of Oromia, Ethiopia
Gemechis, Ambecha O. - \ 2017
University. Promotor(en): Paul Struik, co-promotor(en): B. Emana. - Wageningen : Wageningen University - ISBN 9789463431576 - 262
solanum lycopersicum - irrigation - crop production - optimization - photosynthesis - chlorophyll - gas exchange - water use efficiency - crop yield - ethiopia - irrigatie - gewasproductie - optimalisatie - fotosynthese - chlorofyl - gasuitwisseling - watergebruiksrendement - gewasopbrengst - ethiopië

Tomato (Solanum lycopersicum L.) is a vegetable crop with high potential to contribute to poverty reduction via increased income and food security. It is widely grown by smallholders, has high productivity and its demand is increasing. Ethiopia produced about 30,700 Mg of tomatoes on 5,027 ha annually in 2014/2015. Average yields are only 6.1 Mg ha-1, below the world average yields. There is both a need and a potential to increase tomato production per unit area.

The aim of this thesis is to analyze the irrigated tomato production systems of smallholder farmers in Ethiopia, to survey and characterize the tomato in selected ecoregions and seasons, and to identify yield-limiting or yield-reducing factors and opportunities to enhance yield by using a combination of surveys and field experiments. Field experiments on optimization of yield and quality of field-grown tomato were carried out at Ziway, Ethiopia, for two seasons to study the impact of different irrigation practices applied, based on local empirical practices, deficit irrigation, or crop water requirement.

This thesis begins with a survey of tomato production systems. The survey details the area and production in various zones and for each of these zones yield- determining, yield-limiting, and yield-reducing factors and opportunities for improving yield and quality are indicated. It also avails area, production and yield data for each growing season and typifies the production systems in these zones. Low temperature (cold) from October-January and shortage of improved seeds are recognized as yield-determining factors, whereas insufficient water and nutrient (fertilizer) supply proved to be yield-limiting factors across zones. Late blight (Phytophthora infestans), Fusarium wilt (Fusarium oxysporum) and different pests and weeds are identified as yield-reducing factors in the zones. Experienced growers who have access to extension service recorded significant yield increment. Farmers Research Groups improved actual average yield with the use of improved technology (improved varieties and quality seed), and better efficiencies of water and fertilizer use. This study quantified influences of irrigation systems and strategies on growth-determining tomato features. Variation in irrigation systems and strategies accounted for variation in growth and dry matter accumulation. Greater performance for yield-related traits was obtained with drip irrigation based on crop water requirement for tomato varieties. Examination of plants showed also that local empirical irrigation is responsible for the occurrence of Phytophthora root rot, whereas deficit irrigation proved cause for occurrence of Fusarium wilt (Fusarium oxysporum), blossom end rot and broome rape (Orobanche ramosa) on roots or leaves, stems or fruits.

The experiments on irrigation scheduling with different irrigation systems and strategies gave useful indications on the possibility to improve commercial yield (CY) and water use efficiency. Promising results on CY and agronomical water use efficiency of tomato were achieved with drip irrigation based on crop water requirement, while for the biological water use efficiency higher value was obtained with deficit drip irrigation in both seasons. The findings indicate that the CY was decreased significantly for deficit by 50% in drip irrigation and deficit by 50% in furrow irrigation in both seasons. Mean CY for drip irrigation according to crop water requirement increased by 51% and 56% compared with deficit drip irrigation, whereas furrow irrigation based on crop water requirement increased by 52% and 54% compared with deficit furrow in Experiments 1 and 2, respectively. However, water use efficiency decreased with the increasing water volume.

Simultaneous measurements of rate of photosynthesis based on gas exchange measurements and the thylakoid electron flux based on chlorophyll fluorescence were used to investigate physiological limitations to photosynthesis in leaves of deficit irrigated tomato plants under open field situations. Combined leaf gas exchange/chlorophyll fluorescence measurements differentiated the treatments effectively. Reduction in rate of photosynthesis, stomatal conductance and the maximum quantum efficiency of photosystem II varied across seasons of all varieties, whereas leaf temperature was increased by deficit irrigation in all varieties. Among varieties studied, Miya was found relatively tolerant to deficit irrigation. Stomatal limitation of rate of photosynthesis increased significantly as a result of water stress suggesting a strong influence of the stomatal behaviour.

We also determined the influence of irrigation systems and strategies on water saving and tomato fruit quality. Using deficit drip irrigation was the best management strategy to optimize water use and tomato quality. Fruit dry matter content, acid content and total soluble solids were significantly higher with deficit drip irrigation than with other treatments.

From this thesis it appeared that agro-climatic conditions, access to resources and culture all contribute to the relatively low yields of tomato in the Central Rift Valley of Ethiopia. The thesis also proved that significant advances can be made in yield, quality and resource use efficiency.

Kasklimaatregeling op basis van fotosynthese-metingen: wat zijn de mogelijkheden? : verslag van het eerste werkpakket van het project " Energie besparen door sturing van licht en CO2 op basis van gewasbehoefte"
Dieleman, J.A. ; Pot, S. ; Snel, J.F.H. ; Kromdijk, J. ; Jalink, H. ; Bontsema, J. - \ 2013
Wageningen : Wageningen UR Glastuinbouw (Rapporten GTB 1270) - 26
glastuinbouw - klimaatregeling - fotosynthese - gasuitwisseling - fluorescentie - meting - gewasmonitoring - behoeftenbepaling - lichtregiem - kooldioxide - greenhouse horticulture - air conditioning - photosynthesis - gas exchange - fluorescence - measurement - crop monitoring - needs assessment - light regime - carbon dioxide
Het klimaat in een kas wordt ingesteld om een optimale gewasfotosynthese, assimilatenverdeling en plantvorm te realiseren. Om momentaan het kasklimaat aan te kunnen passen aan de behoeftes van de plant is het van groot belang inzicht te hebben in de directe gevolgen van aanpassingen in het klimaat op de plant prestaties, in het bijzonder op de fotosynthese. Dit is te doen met de volgende methodes: 1. Gasuitwisseling van bladeren: nauwkeurige metingen van de fotosynthese van een stukje blad, met draagbare meetapparatuur. 2. Plantivity: een commercieel verkrijgbare meter die de fluorescentie van een stukje blad meet. 3. Kas-in-kas: een niet-geklimatiseerde meetkamer waarin CO 2 opname van een aantal planten gemeten kan worden. 4. Fluorescentie-imaging: fluorescentie metingen op afstand aan een groter oppervlakte gewas. 5. Fotosynthese-monitor: soft-sensor waarmee de CO 2 opname van een kas berekend wordt op basis van ventilatievoud en metingen van de CO 2 concentratie binnen en buiten de kas. Uit twee workshops met telers bleek dat zij fotosynthese als een belangrijk proces beschouwen in de teelt van hun gewas, en dat zij de fotosynthese van hun gewas graag momentaan online zouden willen meten. Het is daarom wenselijk door te gaan met de ontwikkeling van een robuust en betrouwbaar meetsysteem voor de gewasfotosynthese
On-line monitoring van transpiratie en fotosynthese: de praktijk
Bontsema, J. ; Hemming, J. ; Janssen, H.J.J. ; Meinen, E. ; Rispens, S. ; Steenhuizen, J.W. ; Visser, P.H.B. de - \ 2011
Wageningen : Wageningen UR Glastuinbouw (Rapporten GTB 1091) - 65
gasuitwisseling - fotosynthese - transpiratie - glastuinbouw - kasgewassen - gewasmonitoring - on-line - gegevensverwerking - gas exchange - photosynthesis - transpiration - greenhouse horticulture - greenhouse crops - crop monitoring - on line - data processing
WUR Glastuinbouw heeft monitoren ontwikkeld voor de on-line bepaling van de verdamping en fotosynthese. Deze monitoren zijn uitgetest bij diverse vruchtgroentetelers en slatelers. In het onderzoek is ook een nieuwe transpiratiemonitor ontwikkeld, op basis van een statische energie- en vochtbalans
Systeemontwerp rendabele algen teeltsystemen
Hemming, Silke - \ 2010
algae - algae culture - cropping systems - intercropping - energy - gas exchange - water flow - biobased economy - greenhouse horticulture - light distribution
On-line monitoring van transpiratie en fotosyntheseactiviteit
Bontsema, J. ; Hemming, J. ; Stanghellini, C. ; Visser, P.H.B. de; Henten, E.J. van; Budding, J. ; Rieswijk, T. ; Nieboer, S. - \ 2007
Wageningen : Wageningen UR, Glastuinbouw (Nota / Wageningen UR, Glastuinbouw 451) - 40
gasuitwisseling - fotosynthese - transpiratie - kassen - gas exchange - photosynthesis - transpiration - greenhouses
Fotosynthese optimaliseren en kwaliteit verbeteren. Van Weel: "Ik wil vooraf de stand van de huidmondjes voorspellen"
Arkesteijn, Marleen ; Weel, P.A. van - \ 2007
Onder Glas 4 (2007)2. - p. 20 - 21.
kassen - landbouwtechniek - vernevelen - fotosynthese - gasuitwisseling - groeifactoren - kooldioxide - huidmondjes - toegepast onderzoek - milieubeheersing - klimaatregeling - glastuinbouw - greenhouses - agricultural engineering - fogging - photosynthesis - gas exchange - growth factors - carbon dioxide - stomata - applied research - environmental control - air conditioning - greenhouse horticulture
In de praktijk komt het regelmatig voor dat de kasttemperatuur te hoog is en de RV te laag. Als de huidmondjes dan dicht gaan, kan de plant geen CO2 opnemen. Deze is nodig voor de fotosynthese. Als de kas wordt gekoeld door het vernevelen van water hoeven de ramen minder open, waardoor het CO2-gehalte hoger blijft. Dit resulteert in een hogere productie en grotere energiebesparing. Onderzoeker Van Weel wil een model ontwikkelen dat inzicht geeft in de factoren die de stand van de huidmondjes beïnvloeden. Hiermee wil hij cruciale kenmerken ontdekken om de huidmondjes rechtstreeks aan te sturen
Geforceerde luchtbeweging stimuleert groei gewas
Gelder, A. de; Campen, J.B. - \ 2005
Groenten en Fruit. Algemeen 2005 (2005)36. - ISSN 0925-9694 - p. 26 - 27.
kassen - cultuurmethoden - fotosynthese - lichtrelaties - gasuitwisseling - luchtstroming - weerstand - weerstand van huidmondjes - bladgeleidingsvermogen - plantenontwikkeling - gewasopbrengst - onderzoek - glastuinbouw - greenhouses - cultural methods - photosynthesis - light relations - gas exchange - air flow - resistance - stomatal resistance - leaf conductance - plant development - crop yield - research - greenhouse horticulture
Lucht gestuurd langs planten laten bewegen, lijkt de productie te verhogen. Dit is bevestigd in theoretische berekeningen en in proeven in klimaatcellen. Het PPO in Naaldwijk gaat nu in een proefkas na welk effect luchtbeweging heeft op de productie en op de ontwikkeling van planten.
Optimaal besturen van temperatuur en CO2 op basis van fotosynthese en energie
Dieleman, J.A. ; Zwart, H.F. de - \ 2004
Wageningen : Plant Research International (Nota / Plant Research International 323) - 56
fotosynthese - milieubeheersing - kooldioxide - temperatuur - gasuitwisseling - photosynthesis - environmental control - carbon dioxide - temperature - gas exchange
Inhibition of ethylene biosynthesis in fruits by carbon dioxide : the mode of action = Remming van de ethyleenbiosynthese in vruchten door kooldioxide : het werkingsmechanisme
Wild, J.P.J. de - \ 2004
Utrecht University. Promotor(en): L.A.C.J. Voesenek, co-promotor(en): Herman Peppelenbos. - [S.l.] : S.n. - ISBN 9064643180
ethyleen - ethyleenproductie - kooldioxide - gasuitwisseling - ademhaling - remming - acc - vruchten - opslag - peren - tomaten - bewaarfysiologie - plantenfysiologie - biosynthese - pears - tomatoes - ethylene - ethylene production - carbon dioxide - gas exchange - respiration - inhibition - fruits - storage - postharvest physiology - plant physiology - biosynthesis
Measuring techniques to determine the air exchange rate during the storage of potatoes for consumption
Mosquera, J. ; Scheer, A. ; Wagemans, M.J.M. ; Schans, D.A. van der - \ 2002
Wageningen : IMAG (IMAG rapport 2002-08) - ISBN 9789054062127 - 28
aardappelen - solanum tuberosum - aardappelopslagplaatsen - emissie - carbamaten - ventilatie - gasuitwisseling - windmeters - potatoes - potato stores - emission - carbamates - ventilation - gas exchange - anemometers
Growth and productivity of cut rose as related to the rootstock
Hu, X. - \ 2001
University. Promotor(en): H. Challa; P.A. van de Pol. - S.l. : S.n. - ISBN 9789058084927 - 108
rosa - rozen - onderstam-ent relatie - onderstammen - plantenfysiologie - vergroeiing van ent en onderstam - ademhaling - gasuitwisseling - fotosynthese - snoeien - plant-water relaties - roses - rootstock scion relationships - rootstocks - plant physiology - unions - respiration - gas exchange - photosynthesis - pruning - plant water relations
<em><p>Keywords</em> : Rosa, rose, rootstock, rootstock vigour, carbohydrate, respiration, photosynthesis, pruning, shoot regeneration, water content, water potential, water conductivity, Natal Briar.</p><p>This research examines various rose rootstock effects and the relationships between them, particularly between the effect on flower productivity (defined as rootstock vigour) and the effects on other growing aspects. 5 to 8 rootstocks, both weak and invigorating, were investigated in a series of related experiments. The rootstocks affected flower production mainly by affecting the number of budbreaks in each flush cycle rather than the duration of cycle. The rootstocks also significantly affected flower qualities. Flower shoots were generally shorter and lighter on weak rootstocks than those on significantly more invigorating rootstocks. However, this observation did not apply to the invigorating rootstocks that have little differences in vigour. This is because that the stem density, which was significantly higher on invigorating rootstocks, has a strong impact on flower qualities, resulting in the relationship between the production (in number of flowers) and the quality parameters to be reversed.</p><p>The rootstock effects on shoot regeneration in darkness with respect to both the dry weight and the lifespan of the regenerated shoots, though very significant, were not correlated with rootstock vigour. The rootstocks affected the capacity of photoassimilation mainly through leaf area. The same was true for respiration. When the size effect is eliminated, neither photoassimilation nor respiration is (closely) correlated with rootstock vigour. There were little differences between the rootstocks in the concentrations of carbohydrates except for starch (at the marketable flower stage of the primary shoots). The rootstocks showed stronger effects on sucrose and starch than on glucose and fructose. In roots, sucrose and starch were generally lower in weak rootstocks than in invigorating ones. In basal stems, however, the situation is reversed. Rootstocks had significant effects on plant water relations. Shoot water content as well as leaf water potential of invigorating rootstocks was higher than those of weak rootstocks. This is corresponding to a higher water conductivity of the root system. The importance of the rootstock effect on water status in relation to rootstock vigour is addressed and discussed.</p>
Eddy covariance and scintillation measurements of atmospheric exchange processes over different types of vegetation
Nieveen, J.P. - \ 1999
Agricultural University. Promotor(en): J. Goudriaan; A.F.G. Jacobs. - S.l. : Nieveen - ISBN 9789058080288 - 122
vegetatietypen - atmosfeer - turbulentie - gasuitwisseling - bladoppervlakte-index - kooldioxide - waterdamp - covariantie - analytische methoden - vegetation types - atmosphere - turbulence - gas exchange - leaf area index - carbon dioxide - water vapour - covariance - analytical methods
<p>Introduction and objectives</p><p>Good comprehension of the energy and mass cycles and their effect on climate dynamics is crucial to understanding, predicting and anticipating ecological changes due to possible future climate perturbations. Here direct and long-term flux density measurements of greenhouse gases from various ecosystems provide means to supply such fundamental knowledge. For the global water vapour and carbon cycles, however, the interactions between different spatial scales become important, where extrapolating from canopy flux density measurements to global budgets lead to practical and theoretical problems. This thesis focuses on the direct and long-term measurement of surface flux densities and interaction processes at the canopy (&lt; 1 km scale within the framework of the Surface Layer Integration Measurements and Modelling (SLIMM) project. Furthermore, some characteristics and limitations of the scintillation technique are studied in two field experiments in New Zealand.</p><p>As indicated in Chapter 1, the <em>first objective</em> of this project was the direct and continuous long-term measurement of the surface flux densities of radiation, momentum, heat, water vapour and carbon dioxide (CO <sub>2</sub> ) to study the effect of biological and climatic processes that regulate carbon dioxide exchange of this ecosystem at the canopy scale. At the same time these data were used to study the effect of plant related and environmental conditions on the interaction of carbon dioxide and water vapour exchange, to satisfy the <em>second objective</em> of the thesis. The <em>third objective</em> focussed on the prospect of obtaining both the spatial averaged sensible heat flux density and momentum flux density from scintillation measurements.</p><p>Generally, a compromising point measurement of the mean horizontal wind speed or friction velocity is used to calculate the sensible heat flux density from the temperature structure parameter. By using two scintillometers at two heights, point measurements to obtain the atmospheric stability can be omitted. The <em>fourth objective</em> of this thesis was to study the influence of absorption fluctuations on the average sensible heat flux density derived from the scintillation technique.</p><p><strong>Carbon dioxide exchange and the effect of biological and climatic processes</strong></p><p>Carbon dioxide exchange was measured, using the eddy covariance technique, during a one and a half-year period in 1994 and 1995. The measurements took place over a former true raised bog, characterised by a shallow peat layer and tussock vegetation dominated by <em>Molinia caerulea</em> . Peat soils in the Northern Hemisphere's wetlands contain about one third of the worlds carbon pool. Many regions in the arctic tundra, however, have changed from sinks to sources for CO <sub>2</sub> over the past decade but this can not simply be generalised.</p><p>The growing season extended from May until late October, with a maximum <em>LAI</em> in August of 1.7. The carbon balance showed a net release of 97 g CO <sub>2</sub> m <sup>-2</SUP>y <sup>-1</SUP>(265 kg C ha <sup>-1</SUP>y <sup>-1</SUP>) from the peat bog ecosystem to the atmosphere. During June, July and August there was net consumption of CO <sub>2</sub> , while during the rest of the year there was net production of CO <sub>2</sub> . The maximum daytime net exchange rates were about -0.5 mg CO <sub>2</sub> m <sup>-2</SUP>s <sup>-1</SUP>(-11.3μmol CO <sub>2</sub> m <sup>-2</SUP>s <sup>-1</SUP>) with an average peak exchange rate of -0.2 mg CO <sub>2</sub> m <sup>-2</SUP>s <sup>-1</SUP>(-4.5μmol CO <sub>2</sub> m <sup>-2</SUP>s <sup>-1</SUP>), in a period where the <em>LAI</em> ranged between 1 and 1.7. A high vapour pressure deficit (&gt;15 hPa) corresponding with high temperature was found to reduce the net CO <sub>2</sub> exchange rate by on average 50%.</p><p>Apart from these factors, <em>LAI</em> and the soil temperature co-determined the net exchange of CO <sub>2</sub> . The total nocturnal respiration during the growing season was within the same order as the average daytime net photosynthetic rate. Temperature was found to be the main factor controlling soil respiration, with a <em>Q <sub>10</em></sub> of 4.8.</p><p><strong>The effect of plant related and environmental conditions on the interaction of CO <sub>2</sub> and H <sub>2</sub> O exchange</strong></p><p>The tussock grassland, dominated by <em>Molinea caerulea</em> , was covered with a dense layer of dead organic material from the previous growing seasons. During the summer months, the daytime carbon dioxide uptake often showed a single early morning maximum and a decline in uptake during the rest of the day. Surprisingly, maximum water vapour flux densities were not greatly reduced. The surface cover and the small value of the leaf area index were the main reasons for this phenomenon.</p><p>The layer of dead organic material acted as an insulating blanket to the transport of water vapour from the soil to the atmosphere. Furthermore, the canopy was far from closed with a peak leaf area index of 1.7 in early August. For both low vapour pressure deficit (&lt; 15 hPa) and high vapour pressure deficit (&gt; 20 hPa) at high surface temperatures, the vegetation showed similar behaviour resulting in a clear reduction of the daytime CO <sub>2</sub> uptake. Temperature was therefore inferred to be main the reason for a reduction in CO <sub>2</sub> exchange. The response of the stomata to atmospheric humidity was deduced to be small possibly due to the abundant availability of soil water. Instead transpiration increased with increasing vapour pressure deficit. The latter was stimulated by the surface temperature, which often exceeded the optimum temperature for photosynthesis and led to an increase in the atmospheric evaporative demand.</p><p><strong>The scintillation technique</strong></p><p>An optical or electromagnetic wave propagating through a turbulent atmosphere exhibits fluctuations in intensity known as 'scintillations'. In atmospheric turbulence, fluctuations in temperature, humidity and pressure cause density fluctuation and with it fluctuations in the refractive index ( <em>n</em> ). These refractive index fluctuations cause random refraction and absorption of electromagnetic (EM) radiation passing through the turbulent atmosphere, changing the characteristics of the wave. Scintillation of light is related to these phenomena and is experienced at a receiver as fluctuations in the light intensity caused by interference of refracted light and absorption of the light. Scintillometers measure the turbulent intensity of the refractive index fluctuations of the air from the intensity fluctuations of a received signal expressed in the refractive index structure parameter, <em>C <sub>n</sub><sup>2</em></SUP>.</p><p>The measured <em>C <sub>n</sub><sup>2</em></SUP>value is related to the structure parameters of temperature <em>C <sub>T</sub><sup>2</em></SUP>, humidity <em>C <sub>Q</sub><sup>2</em></SUP>and a covariant term <em>C <sub>TQ</em></sub> , respectively. To calculate the sensible heat flux density from <em>C <sub>n</sub><sup>2</em></SUP>compromising point measurements of the Bowen ratio,β, and friction velocity, <em>u <sub>*</em></sub> , are necessary. Generally, the deficiency in the available spatial measurement of <em>u <sub>*</em></sub> is overcome by using a point measure of the average wind speed, <em>u</em> and surface roughness, <em>z <sub>0</em></sub> , <em><sub></em></sub> but the necessity forβoften remains unresolved.</p><p>By using two scintillometers at different heights above the surface, a spatial measurement of the Obukhov length, <em>L <sub>o</em></sub> , and <em>u <sub>*</em></sub> can be derived without incorporating compromising point measurements of the friction velocity or alternatively the average wind speed combined with a measure of the roughness length. The presumption that such measurements are representative of the entire transect usually holds for homogeneous surface cover but may not be valid for patchwork terrain. The two-scintillometer technique is referred to as the <em>C <sub>T</sub><sup>2</em></SUP>-profile method.</p><p>Refraction is the result of normal and anomalous dispersion. If, however, the frequency of the emitted EM wave is close to a resonance frequency (absorption lines) of atmospheric constituents, like water vapour and carbon dioxide, absorption becomes important. To quantitatively describe the combined effect of refraction and absorption, a complex refractive index structure parameter, <em>C <sub>n</sub><sup>2</em></SUP>, is introduced. Here the phenomenon of absorption is represented by the imaginary part of the refractive index and is solely determined by single absorption lines and their corresponding absorption coefficients (β <em><sub>i</em></sub> ), resulting in a total absorption coefficient for a band of lines (Hill <em>et al.</em> , 1980). The absorption line strength is temperature dependent, while the absorption line width is temperature, humidity and pressure dependent.</p><p>The contribution of absorption fluctuations to <em>C <sub>n</sub><sup>2</em></SUP>is generally neglected, that means to have a real component only. In reality <em>C <sub>n</sub><sup>2</em></SUP>includes both a real part, <em>C <sub>nR</sub><sup>2</em></SUP>, due to refraction and an imaginary part, <em>C <sub>nI</sub><sup>2</em></SUP>, attributable to the absorption mechanism. Any additional source of scintillation such as a contribution from absorption fluctuations could conceivably corrupt the estimation of the sensible heat flux.</p><p><strong>Measuring sensible heat flux density over pasture using the C <sub>T</sub><sup>2</SUP>- profile method</strong></p><p>Two large aperture scintillometers were positioned at heights ( <em>z</em> ) of 10 and 1.5 m with beams propagating horizontally over pasture for distances of 3.1 km and 141 m respectively. From each scintillometer a half-hourly average value of the path-averaged, temperature structure parameter ( <em>C <sub>T</sub><sup>2</em></SUP>) was obtained in unstable atmospheric conditions. The result suggested <em>C <sub>T</sub><sup>2</em></SUP>to scale with height as <em>z <sup>-2/3</em></SUP>. Using the <em>C <sub>T</sub><sup>2</em></SUP>- profile method, a path averaged measure of the Obukhov length ( <em>L <sub>o</em></sub> ) was calculated for each half hour period. <em>L <sub>o</em></sub> was used to determine the friction velocity and the surface layer temperature scaling parameter, <em>T <sub>*</em></sub> . The scintillometer sensible heat flux density, <em>H <sub>sc</em></sub> , was then calculated from <em>H <sub>sc</sub></em> = <em>-ρC <sub>p</sub> u <sub>*</em></sub><em>T <sub>*</em></sub> . A time series of half-hourly averaged <em>H <sub>sc</em></sub> compared to <em>H <sub>ec</em></sub> obtained by the eddy covariance method agreed to within 10%, with R <sup>2</SUP>= 0.67, for a range of unstable conditions (-0.2≤( <em>z/L <sub>o</em></sub> )≤-0.01).</p><p><strong>Using a Large Aperture Scintillometer to measure absorption and refractive index fluctuations</strong></p><p>The contribution of refraction and absorption fluctuations to the measured scintillation were observed for a near-infrared absorption region using a NOAA designed large aperture scintillometer. The logarithm amplitude spectra were shown to decay with a frequency as <em>f</em><sup>-8/3</SUP>for both the absorption and scattering mechanism. For the absorption mechanism this is in line with similar observations made at microwave and infrared frequencies. However, for finite transmitting and receiving apertures, theory predicts a stronger decay of the scattering mechanism due to aperture averaging. The spectral shape is characterised by a region of low frequency absorption, higher frequency refraction separated by a flattish transition zone. The upper observed corner frequency ( <em>f <sub>C2</em></sub> ), compared well with the calculated values using the measured transverse wind speed ( <em>v</em> ) for a known aperture radius. The lower corner frequency ( <em>f <sub>C1</em></sub> ) position was shown to be sensitive to the ratio of the real and imaginary part of the refractive index structure parameter, ( <em>C <sub>nR</sub><sup>2</SUP>/C <sub>nI</sub><sup>2</em></SUP>) <sup>3/8</SUP>and <em>v</em> . The part of the spectrum associated with the absorption scintillations was observed to be much less than that due to refraction until the evening when decreasing <em>C <sub>nR</sub><sup>2</em></SUP>caused <em>C <sub>nR</sub><sup>2</SUP>/C <sub>nI</sub><sup>2</em></SUP>to decrease and absorption to become significant. If absorption is ignored, this may have consequences for calculating nocturnal surface heat flux densities. During unstable, daytime conditions the large aperture scintillometer is most sensitive to refractive scintillations despite having an infrared source transmitting in a lossy atmosphere. But also under these conditions, the low frequency absorption part of the spectrum is observable.</p>
An assembly for the continuous recording of CO2 exchange and transpiration of whole plants
Oorschot, J.L.P. ; Belksma, M. - \ 1961
Wageningen : [s.n.] (Mededeling / Instituut voor biologisch en scheikundig onderzoek van landbouwgewassen no. 198) - 13
katabolisme - chemie - evapotranspiratie - groeikamers - instrumenten (meters) - laboratoriumuitrusting - laboratoriummethoden - fotosynthese - plantenfysiologie - ademhaling - transpiratie - gasuitwisseling - kooldioxide - catabolism - chemistry - evapotranspiration - growth chambers - instruments - laboratory equipment - laboratory methods - photosynthesis - plant physiology - respiration - transpiration - gas exchange - carbon dioxide
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