=Paper=
{{Paper
|id=Vol-1152/paper60
|storemode=property
|title=Application of dGPS to Harvesting Date and Precision Viticulture in Slovenia
|pdfUrl=https://ceur-ws.org/Vol-1152/paper60.pdf
|volume=Vol-1152
|dblpUrl=https://dblp.org/rec/conf/haicta/LakotaS11
}}
==Application of dGPS to Harvesting Date and Precision Viticulture in Slovenia==
https://ceur-ws.org/Vol-1152/paper60.pdf
Application of dGPS to Harvesting Date and Precision
Viticulture in Slovenia
Miran Lakota, Denis Stajnko
1
Department of Biosystems Engineering, University of Maribor, Faculty of Agriculture and
Life Sciences, Slovenia, e-mail: miran.lakota@uni-mb.si
Abstract. In 2002, the maturity of grapevine was researched on the basis of
sugar content, total titratable acidity and pH at seven locations with an
undulating topography in four varieties 'Chardonnay', 'Riesling',
'Welschriesling' and 'Sauvignon'. All sampling points were geo-referenced
simultaneously with DGPS for creating sugar maps. The significant
relationship between the varying altitude above sea level (from 395 m to 505
m) and the concentration of sugar and the total titratable acidity of grapes was
estimated during the maturity. The results of the study indicate that a great
improvement of the grapevine quality is possible in the future by harvested it
separately on the basis of site-specific maps.
Keywords: vineyard, sugar map, GIS, GPS
1 Introduction
Precision agriculture has been described as a continuous cyclical process of data
collection, followed by interpretation and evaluation of the information acquired and
implementation of management decisions in response to it (Cook and Bramley 1998).
The chosen technologies vary greatly depending on demands of individual farms
(Blackmore 1994).
Recently, only a few studies have been reported concerning the opportunities of
precision viticulture to adapt production of grapes and wine according to the
vineyard performance and desired goals in terms of yield and quality, although the
altitude, orientation of the slope and its angle was already reported to affect the heat
gain significantly (Horney 1973; Becker 1978; Hoppmann 1978; and Hoppmann et
al. 1997).
The grape wine quality and its interaction with yield and soil properties is of
greater importance than might occur in arable farming (Bramley and Proffitt 1999,
2000). Therefore, management strategies need to be developed so both yield and
quality can be optimized. The first investigation of relationships between the yield,
grape berry quality and soil properties, studied at two vineyards, showed that an
improved understanding of the input to the grape production system was required.
For mapping of selected soil and vine indices Bramley (2001) used a modification of
the HarvestMaster grape yield monitor. In another study, Bramley and Williams
________________________________
Copyright ©by the paper’s authors. Copying permitted only for private and academic purposes.
In: M. Salampasis, A. Matopoulos (eds.): Proceedings of the International Conference on Information
and Communication Technologies
for Sustainable Agri-production and Environment (HAICTA 2011), Skiathos, 8-11 September, 2011.
697
(2001) successfully implemented a protocol for grape yield map production for two
years in Coonawarra, Australia. However, it was proved that the commercial yield
monitoring equipment has not been matched for making useful maps, because of the
lack of associated support tools. Thus, it is suggested for wine producers to apply
robust methodologies for production of yield map and other vine attributes.
In Europe, as the most important vine producer in the world, the vineyard
managers still have not access to a reliable methodology for updating their
inventories of vineyard distribution on their territory and technical means to exploit
this knowledge for supporting their decision in land management in grape producing
(Montesinos 2002). To develop a methodological approach for defining and testing a
vineyard database structure and spatial analysis procedures between years 2002 and
2005 the EU has founded the BACCHUS project.
Regrettably, till now, no comparable research has been conducted in Slovenia
neither our wine producers are jointed in European projects, because the holdings are
extremely fragmented and most of them are less than five hectares. However,
although Slovenia is one of Europe’s smaller countries, the landscape and climate is
very diverse, causing by the variety of climatic (Alpine, Panonian, Mediterranean
and transitional) and geological conditions which contribute to the use of a wide
variety of grapevines and consequently a large assortment of vines in our wine–
growing regions.
The eastern Slovenian region contains about 9000 ha of vineyards, with good
yields, but the individual vineyards are small too, with very steep slopes that
influence times of ripening of grapes. Nowadays, when, according to the applied
technology, the whole area of each vineyard is harvested manually at the same time,
substantial loss of quality may result. Namely, as shown for the sub-alpine vineyards
by Bertamini et al. (1999) and Rusjan (2002) for western Slovenian vineyards, the
significant influence of increasing altitude on the sugar content of grapes was
detected due to the increasing hours of day sunshine on well exposed south- and
west-facing. However, the positive correlation was not found for the vineyards lying
higher as 550 m.
The main objective of our investigation was to produce a vineyard data base
structure and to investigate the possibility of a site-specific determination of optimal
maturity of grape berries with the respect to the varying altitude of the vines above
mean sea level (MSL).
2 Site description and sample collection
The area selected for this study was the 20.0 ha Faculty vineyard, Meranovo (Lat
= 46o 02' 53.27004" N, Lon = 14o 32' 37.36262" E). The site is divided into nine
parcels lying on differently oriented terraces and is roughly 900 m long (east-west)
by 650 m wide (north-south). It is characterized by an undulating topography with a
difference of 98 m in altitude between the highest (505 m) and lowest point (407 m).
As clearly seen from Fig. 1, rows of grapes are oriented up and down the south
(‘Sauvignon’), south-east (‘Welschriesling’ and ‘Riesling’) as well as south-west
facing slopes (‘Chardonnay’). However, in the very near history all rows were
698
oriented across the slope as it can be still noticed in the middle of the old ortho-photo
map before the last vineyard reconstruction was conducted two years ago.
Fig. 1. Position of the monitoring locations in vineyards
For investigating the influence of differences in height above mean sea level
(MSL) on the ripening of grape berries, four different parcels planted with varieties
'Chardonnay', 'Riesling', 'Welschriesling' and ‘Sauvignon’ were selected. As seen
from Tab. 1, three of those parcels were divided into a top and bottom area, while the
'Welschriesling' parcel remained undivided.
Table 1: Data of the monitoring locations
Location Variety Area [ha] Row orientation Mean altitude [m]
1 Welschriesling 0,0161 South-east 505
2 Chardonnay top 0,0055 South-west 458
3 Chardonnay bottom 0,0061 South-west 440
4 Riesling top 0,0070 South-east 435
5 Riesling bottom 0,0076 South-east 410
6 Sauvignon top 0,0041 South 423
7 Sauvignon bottom 0,0047 South 395
The quality analysis including the content of sugars (deg Brix), total titratable acidity
(g/l) and pH were performed to evaluate the effect of MSL on the process of
699
ripening, whereas the content of sugar was the most important parameter for the vine
producer.
On locations 2-7, every seven days, between August 8th 2002 and the grape
harvest determined on the sugar content of each variety separately, four samples of
each variety were taken (two from the top part of each parcel and another two from
the bottom part). Each sample included 100 randomly collected grape berries from 25
grapevines i.e. two berries from the sunny side and two from the shadow side of each
selected grapevine. The grape berries were weighed prior the pressing and the grape
juice was later analysed in the laboratory on the content of sugars (deg Brix)
refractometrically, total titratable acidity (g/l) and pH (with pH meter Mettler Tolledo
M120).
Fig. 2. Position of sampled points on the ‘Welschriesling’ variety parcel
On the location 1, planted with the ‘Welschriesling’ variety the influence of
undulating topography on the sugar content of grape berries was evaluated only at the
harvest. A regular grid (5x5 m) sampling strategy based on the row and grapevine
spacing was used (Fig. 2). On that way, approximately 1% of the total number of
grapevines was sampled. All sampling points were geo-referenced with DGPS. For
each sample, five grape berries were collected from the middle bunch growing on the
sunny side of the grapevine and five grape berries from the shadow side,
respectively. Berry quality was assessed in the same way as on the other six areas.
The DGPS measurements data (±0,5 m) were acquired using a GPS receiver CMT
700
MARCH II (Corvallis Microtechnologies Inc.). Additionally, an associated local
base-station GPS (GSR1 located in Ljubljana (Slovenia) (Lat = 46o 02' 53.27004" N,
Lon = 14o 32' 37.36262" E, h = 351.6585 m) was used to supply differential data to
correct the coordinates of the data from the receiver. The ground control location was
referenced to a Gauss-Krieger projection.
All map production and spatial analysis was conducted using the ArcView as well
as the PC-GPS software.
3 Statistical analysis
To examine the relationships between quality parameters of each grape variety
measured at different times during the ripening and the altitude (MSL), on
'Chardonnay', 'Riesling', 'and ‘Sauvignon’ parcels a correlation and linear regression
analysis as well as paired samples t-test were calculated. Contrary, on the parcel
planted with ‘Welschriesling’ only the correlation and linear regression analysis
between different altitudes across the whole area and the sugar content were
investigated. For performing the statistical analysis the SPSS Package Program was
applied.
4 Results and discussion
Changes of the content of sugar (deg Brix), total titratable acidity (g/l) and pH for
all selected varieties are represented in Fig. 3 to 5.
Fig. 3. The sugar content (deg Brix) and total titratable acidity (g/l) of the
‘Riesling’ variety from the top and the bottom of the row
701
As seen from Figure 3, showing changes in the ‘Riesling’ variety during August
8th and September 30th, lower quantities of the sugar content and higher quantities
of the total acidity were detected from the bottom part of the parcel, while higher
quantities of the sugar content and lower quantities of the total acidity were measured
on the top part of the parcel.
Sauvignon
25 30
25
20
20
deg Brix
15
g/l
15
10
10
5
5
0 0
20.aug 27.aug 3.sep 9.sep 17.sep 30.sep
Sugar - top Sugar - bottom Acidity - top Acidity - bottom
Fig. 4. The sugar content (deg Brix) and total titratable acidity (g/l) of the
‘Sauvignon’ variety from the top and the bottom of the row
The main reason for differences in crop maturity between the top and bottom of
the slope was due to the temperature differences affected by the higher sunshine
hours. Secondly, according to Žiberna (1992) a phenomena of the ‘warm thermal
belt’ lying 20-30 m above the lowest point of the vineyard, was found to be the most
important factor influencing the temperature differences in the night between the
upper and lower part of vineyards in the eastern Slovenia.
Chardonnay
25 30
20 25
20
deg Brix
15
g/l
15
10
10
5 5
0 0
20.aug 27.aug 3.sep 9.sep 17.sep 30.sep
Sugar - top Sugar - bottom Acidity - top Acidity - bottom
Fig. 5. The sugar content (deg Brix) and total titratable acidity (g/l) of the
‘Chardonnay’ variety from the top and the bottom of the row
702
Furthermore, the same interaction of slope angle, facing and altitude and their
effect on heat gain was also reported by Bertamini et al. (1999) for vineyards in the
Trento region (Italy) and Hoppmann (1978) for Rheingau and Baden vineyards in
Germany.
For the ‘Sauvignon’ and ‘Chardonnay’ varieties the same pattern in the
development of sugar and total acidity content was detected (Fig. 4 and Fig. 5),
showing the influence of the different altitude above the sea level on the ripening of
grapes.
With additional paired samples t-test statistics given in Tab. 2, 3 and 4, the
significantly higher values of sugars were analyzed from the top sub-parcels than
from the bottom ones in all grapevine varieties proving again the dominant influence
of the higher temperature on the ripening of grape berries.
Table 2: Paired sampled statistics for sugar content (deg Brix)
Pair Mean Paired differences
Std
Mean Std dev Df t p
Error
Chardonnay top-
19,51
Chardonnay 2,78 0,78 0,22 11 12,33 0,001
16,72
bottom
Riesling top- 17,61
2,16 0,69 0,18 13 11,63 0,001
Riesling bottom 15,44
Sauvignon top- 18,38
1,46 0,44 0,13 11 11,40 0,001
Sauvignon bottom 16,91
Table 3: Paired sampled statistics for total titratable acidity (g/l)
Pair Mean Paired differences
Std
Mean Std dev Df t p
Error
Chardonnay top-
12,61
Chardonnay -2,87 1,60 0,46 11 -6,21 0,001
15,49
bottom
Riesling top- 14,67
-3,15 1,31 0,35 13 -8,99 0,001
Riesling bottom 17,82
Sauvignon top- 12,27
-4,41 1,50 0,43 11 -10,18 0,001
Sauvignon bottom 16,68
703
Table 4: Paired sampled statistics for pH value
Pair Mean Paired differences
Std
Mean Std dev Df t p
Error
Chardonnay top-
3,09
Chardonnay 0,003 0,054 0,015 11 0,212 0,836
3,08
bottom
Riesling top- 2,88
0,022 0,049 0,013 13 1,669 0,119
Riesling bottom 2,85
Sauvignon top- 2,91
0,007 0,062 0,018 11 0,414 0,687
Sauvignon bottom 2,90
Contrary, total acidities were significantly higher on the bottom than on the top
sub-parcels reflecting the much known changes in the sugar and acidity development
during the ripening. Aside, the pH values did not differ substantially in any grape
vine variety.
Fig. 6: A sugar map of the ‘Welschrisling’ variety (Oe)
A sugar map based on measurements in the ‘Welschriesling’ grapevine variety is
shown in Fig. 6. According to the distribution of the sugar content, the influence of
the near-by growing forest on the screening from the afternoon sunshine can be seen
on the left side of the map. Contrary, the two outstanding picks in the middle of the
parcel were detected due to the local depression, causing the mild micro climate,
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which reflected in the higher sugar concentration during the ripening. However, a
statistically significant correlation between the elevation and the sugar content was
not estimated, probably because of the insufficient difference between the highest
(510m) and lowest measuring point (490m).
4 Conclusions
The proposed geo-referenced monitoring technique based on the GPS data
measurements can be employed to provide objective information on the ripening
process of grape wines growing on the varying altitude above sea level.
The system was used successfully during the ripening (August-September) in four
varieties 'Chardonnay', 'Riesling', 'Welschriesling' and 'Sauvignon'. In all cases when
the difference between the top and bottom part of the parcel was over 15 m, the sugar
content was significantly higher on the top part of the parcel than on the bottom one,
while the total titratable acidity was lower. The results of the research showed that
sugar maps could form the basis for forecasting an optimal harvesting time in the
future for each part of the vineyards lying on the extremely steep slopes, separately.
However, an enhanced and complex understanding of the interaction between the
vineyard, altitude, diseases and the soil variability is necessary to successful adopt
the site specific determination of optimal grape harvest, thus further work is needed
to study these particular cases also in the other growing areas.
Acknowledgement
The authors express their appreciation to G. Bilban from the Geoservis
www.geoservis.si) for his assistance in proceeding the correction of the DGPS data
according to the base station. The authors also thank Mr. Storey Lindsey for his
helpful English language review.
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