Showing papers by "Manfred Stoll published in 2020"
TL;DR: In this article, a temperature-based model was used to predict the time to target sugar concentrations from 170 to 220 grams/L for Vitis vinifera L. The best model across all target sugar concentration was the non-linear best Sigmoid model "best SIG" model (parameters: start date (tb) = 0.1294, d =−0.1295, e ǫ = 14.87).
51 citations
TL;DR: In this paper, the suitability of leaf reflectance indices and of a handheld device for the estimation of N and chlorophyll in Vitis vinifera L. cv. Riesling leaves from a long-term fertilisation trial were analyzed for nitrogen and pigments and their spectral reflectance in the Vis/near-infrared range was recorded for two consecutive seasons.
Abstract: Background and Aims
Optical leaf sensing of plant nitrogen (N) status enables fertilisation based on plant demand. The aim of this study was to assess the suitability of leaf reflectance indices and of a handheld device for the estimation of N and chlorophyll (Chl) in Vitis vinifera L. cv. Riesling.
Methods and Results
Riesling leaves from a long‐term fertilisation trial were analysed for nitrogen and pigments and their spectral reflectance in the Vis/near‐infrared range was recorded for two consecutive seasons. In the second season the leaves were also measured with a Chl fluorescence based portable device (Dualex). Published reflectance indices and fluorescence indices were regressed against the concentration of pigment and N. Temporal changes in the Chl/N ratio complicated the indirect assessment of N via Chl. Red edge inflection points and several three‐ to four‐waveband indices allowed for a good prediction of leaf N. Fluorescence indices allowed for reliable estimation of N and Chl.
Conclusions
While leaf pigments can be analysed by simple two‐band indices, accurate N estimation requires more complex indices such as three‐band indices or indices calculated from derivative spectra.
Significance of the Study
Data from this study will assist growers to monitor non‐destructively the spatial and temporal variability of grapevine N status and thereby, improve fertilisation.
14 citations
TL;DR: Compared mechanical leaf removal with the manual removal of six leaves at the prebloom and after-bloom phenological stages over two seasons in Pinot Grigio, the results suggest that ME at PB may be used to decrease fruit loss to gray mold in dry seasons and enhance fruit Brix.
Abstract: Removal of basal leaves early in the vegetative and reproductive development of grapevines is a tool used to decrease fruit set, lower cluster rot severity, and improve fruit quality. However, the considerable time required for implementation limits its use by grapegrowers. Efficient mechanization can potentially mitigate these issues, albeit this practice has not yet been compared to manual application at prebloom and after-bloom stages in a cool and humid growing region where cluster rot is the major limitation for yield and fruit quality. The goal of this study was to compare mechanical leaf removal (ME) with the manual (MA) removal of six leaves at the prebloom (PB) and after-bloom (AB) phenological stages over two seasons in Pinot Grigio (a tight-clustered cultivar). Fruit set was only decreased in 2017 by MA of six basal leaves at PB (PB-MA); however, PB reduced cluster compactness in each season. The loss of fruit to gray mold was lowered by all leaf removal treatments in the drier 2017 season, but only MA treatments mitigated loss from sour rot in that year. This indicates that a clear fruit zone and reduced cluster compactness are both needed to lower the effect of cluster rot disease. Only PB treatments enhanced fruit quality, likely driven by a similar reduction in cluster compactness. The results suggest that ME at PB may be used to decrease fruit loss to gray mold in dry seasons and enhance fruit Brix. Nevertheless, PB-MA can be an effective means to reduce fruit loss to sour rot in drier seasons and enhance ripening in years with high precipitation during veraison. This information provides a single approach to alleviate two prominent issues facing seasonal management strategies in cool climate viticulture.
12 citations
TL;DR: Evidence is provided that eCO2 did alter some bunch and berry parameters without a negative impact on fruit quality, and higher single berry weights, higher malic acid, and lower tartaric acid were examined at some stages during development of berries under e CO2 levels.
Abstract: Carbon dioxide (CO2) as one of the main factors driving climate change is known to increase grapevine growth and yield and could, therefore, have an impact on the fruit quality of vines. This study reports the effects of elevated CO2 (eCO2) on berry development and bunch structure of two grapevine cultivars (Vitis vinifera L. cvs. Riesling and Cabernet Sauvignon) within the VineyardFACE (Free-Air Carbon Dioxide enrichment) experiment, using must analysis and non-invasive fluorescence sensor technology. Berry development was examined on five dates over three consecutive years by analyzing total soluble solids (TSS), pH, total acidity, organic acids, nutrition status, and non-invasive Multiplex measurements. Before harvest, secondary bunches were collected to examine bunch and berry parameters. Results showed that eCO2 had little impact on berry composition of Riesling and Cabernet Sauvignon during berry development, which could be related to bunch structure or single berry weight within single seasons. Elevated CO2 (eCO2) did not result in modified TSS accumulation during ripening but was directly related to the chlorophyll index SFR_R. Higher single berry weights (SBW), higher malic acid (MA), and lower tartaric acid (TAA) were examined at some stages during development of berries under eCO2 levels. Our study provides evidence that eCO2 did alter some bunch and berry parameters without a negative impact on fruit quality.
10 citations