Sensitivity analysis of leaf wetness duration within a potato canopy
Jacobs, A.F.G. ; Heusinkveld, B.G. ; Kessel, G.J.T. ; Holtslag, A.A.M. - \ 2009
Meteorological Applications 16 (2009)4. - ISSN 1350-4827 - p. 523 - 532.
estimating dew duration - meteorological models - parameterization - field
A description and analysis is given of a wetness duration experiment, carried out in a potato field in the centre of the Netherlands in September 2005. The observations are used to design and evaluate a within-canopy dew model which provides the leaf wetness distribution within the canopy caused by dew processes and by precipitation. This withincanopy dew model consists of three layers (bottom, centre, top) each with equal contribution to the leaf area index. The model results compared favourably with experimental evidence. The sensitivity of the dew and precipitation interception on the amount of free water and the duration of the leaf wetness was analysed by varying the leaf area index and some important weather variables. The findings suggest that the leaf area index affects the amount of free water, but is barely sensitive to leaf wetness duration. Wind speed has hardly any effect on the amount of free water collection as well as on leaf wetness duration. The net radiation, however, appears to be sensitive to the amount of collected free water as well as the leaf wetness duration
Measurements and estimates of leaf wetness over agricultural grassland for dry deposition modeling of trace gases
Wichink Kruit, R.J. ; Jacobs, A.F.G. ; Holtslag, A.A.M. - \ 2008
Atmospheric Environment 42 (2008)21. - ISSN 1352-2310 - p. 5304 - 5316.
estimating dew duration - water films - sensor - moisture - periods - ammonia - canopy - leaves
Leaf wetness is an important and frequent phenomenon for the surface¿atmosphere exchange of some atmospheric trace gases that are well soluble in water, such as ammonia (NH3 and SO2), as well as for plant disease epidemiology. This study shows a comparison of two different techniques to measure leaf wetness; namely a painted flat-plate grid sensor and a system of four clip sensors. Although both techniques gave comparable results, the flat-plate grid sensor was favored, because of its stable signal and its ease of use. In this technique, the measurement height turned out to be of great importance for the leaf wetness duration (LWD); the flat-plate sensor at 1.0 m systematically underestimated LWD, while the flat-plate sensor at 0.1 m better represented the actual LWD. To obtain a representative signal, leaf wetness should be measured close to the surface. Using the available leaf wetness measurements, a comparison was made between three physical and four empirical leaf wetness models. Without any optimization, the physical model that calculates the potential condensation at the leaf surface gave the best results. However, after optimizing the humidity thresholds in the empirical leaf wetness models, the optimized model based on the difference between the actual and saturated specific humidity at the surface gave best results. For practical applications in atmospheric transport models, like for the calculation of dry deposition of well-soluble gases, the relative humidity (RH) threshold model might be easiest to implement. This study showed that different thresholds should be used for different vegetation types. In this study, an optimized RH threshold of 71% was derived for agricultural grassland.
Simulating of leaf wetness duration within a potato canopy
Jacobs, A.F.G. ; Heusinkveld, B.G. ; Kessel, G.J.T. - \ 2005
NJAS Wageningen Journal of Life Sciences 53 (2005)2. - ISSN 1573-5214 - p. 151 - 166.
gewasteelt - aardappelen - gewasbescherming - fungiciden - meteorologie - micrometeorologie - meteorologische factoren - neerslag - weer - dauw - relatieve vochtigheid - pesticiden - toepassing - toepassingsdatum - simulatie - modellen - simulatiemodellen - phytophthora - phytophthora infestans - crop management - potatoes - plant protection - fungicides - meteorology - micrometeorology - meteorological factors - precipitation - weather - dew - relative humidity - pesticides - application - application date - simulation - models - simulation models - phytophthora - phytophthora infestans - estimating dew duration - meteorological models - parameterization - field
A leaf wetness duration experiment was carried out in a potato field in the centre of the Netherlands during the growing season of 2003. A within-canopy dew simulation model was applied to simulate leaf wetness distribution in the canopy caused by dew and rainfall. The dew model is an extension of an earlier-developed energy budget model, distinguishing three layers within the potato canopy. To run the dew model successfully, information on the above-canopy wind speed, air temperature, humidity and net radiation as well as the within-canopy temperature and humidity must be available. In most cases leaf wetting starts in the top layer followed by the centre and the bottom layer, in that order. Leaf drying shortly after sunrise takes place in the same order. Leaf wetness lasted longest in the bottom layer. Rainfall was accounted for by applying an interception model. The results of the dew model agreed well with leaf wetness recorded with a resistance grid
Leaf Wetness within a Lily Canopy
Jacobs, A.F.G. ; Heusinkveld, B.G. ; Klok, E.J. - \ 2005
Meteorological Applications 12 (2005)3. - ISSN 1350-4827 - p. 193 - 198.
estimating dew duration - leaves - field
A wetness duration experiment was carried out within a lily field situated adjacent to coastal dunes in the Netherlands. A within-canopy model was applied to simulate leaf wetness in three layers, with equal leaf area indices, within the canopy. This simulation model is an extension of an existing model. It appeared that in most cases leaf wetness started in the uppermost layer followed by the middle and bottom layer, respectively. The same occurred during the early morning drying process. Just after sunrise the upper layer started to dry, followed by the middle and bottom layer, respectively. The longest leaf wetness duration occurred in the bottom layer. The calculated leaf wetness durations were within 10 minutes of the results obtained using a leaf wetness sensor