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Soil profile properties affecting grapevine root growth, vine vigour and fruit yield


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Rees, SJ 2015 , 'Soil profile properties affecting grapevine root growth, vine vigour and fruit yield', PhD thesis, University of Tasmania.

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Tasmania provides one of the most diverse ranges of soil types for viticultural production
in the world ranging from alkaline heavy clay soils (Vertosols) to acidic sandy soils
(Podosols). Wide variations in yield and quality have hindered the development of the
industry in Tasmania, the extent to which these variations are influenced by soil factors is
largely unknown. This diverse Tasmanian environment provides an ideal location for the
investigation of soil - root interactions and their relationship to vine productivity.
Investigations of grapevine root distribution were undertaken within a range of soil types
across three vineyards located in Tasmania. Soil trenches were excavated to expose soil
profiles and vine root distribution with root size frequency and soil penetration resistance
recorded across the soil face. The soil profile was described for physical properties and
all horizons were sampled for chemical analysis. Vine growth parameters such as
pruning weight and fruit yield were also measured over several seasons.
The percentage distribution of roots vertically through the soil profiles was very similar
regardless of soil type. Highest root abundance occurred at 10 – 30 cm depth for all but
one of the studied profiles. Root numbers declined with depth below 30 cm, with most
profiles having 80 % of total root growth within a depth of 0 – 60 cm. Limited root
growth was observed in the upper 0 – 10 cm of the soil profile with many soil profiles
having no roots recorded in the upper 0 – 5 cm. This was despite these layers having the
highest soil fertility and lowest soil penetration resistance. Even though the majority of
the roots were in the upper 60 cm, deep profile features such as unconsolidated layers or
access to deep water tables were observed to greatly enhance vine growth.
While the vertical distribution of roots was similar between all profiles, the horizontal
distribution of roots varied considerably between soil profiles. Soil structure and soil
strength both had a primary influence on root growth. Roots consistently grew between
the structural units of the soil at all profiles, regardless of the soil type or the type of soil
structure expressed. This was particularly evident in horizons where the structural units
were coarse which resulted in root growth being confined to distinct regions of weakness
such as vertical structural cracks, sand in-fills and/or old (dead) roots and root channels.
Therefore the extent of these favourable situations determined how widely the roots were distributed across the soil profile face. Root distribution within many subsoils was also
locally constrained by soil chemical attributes including low soil pH, high ESP and/or
shallow saline watertables.
While consistent relationships were observed between soil properties and root
distribution, there was no clear relationship between vine growth and the size of the root
system. Most importantly, greater root numbers did not necessarily produce higher vine
growth nor did low root numbers always result in lower vine growth. This signifies that
the efficiency and function of the roots is more important than total root abundance per se.
Soils with differing properties will have different ‘optimum’ root numbers and
distributions for productive vine growth. Consequently soil properties need to be
considered in order to understand the influence of root distribution on vine performance.
Differences in vine vigour (pruning weight) and fruit yield were associated with differing
soil properties. Low grapevine vigour and fruit yield was associated with thin topsoils (<
20 cm), acidic subsoils (pH < 4.5, 1:5 water) and shallow (< 40 cm) and saline >5 dS/m)
watertables. In contrast, high grapevine vigour and fruit yield was associated with deep
rooting conditions, either from well-structured, friable colluvial soils or soils with overthickened
topsoil (> 40 cm) caused by clearing and burning during vineyard
establishment. No clear relationships were observed between whole soil chemical
fertility and vine growth. This suggests that the distribution of roots and their access and
supply of nutrients and moisture are a more significant controlling factor.
Root distribution with depth was relatively uniform across the study. However horizontal
root distribution was variable across many profiles which is expected to impact on vine
management. The soils showed that the variation in vine growth and yield were closely
related to variation in soil structural properties and their effect on root efficiency and
function. Root distribution generally followed preferential water movement pathways,
highlighting the importance of appropriate water management. Optimal root number for
vine productivity is soil type dependent and needs specific soil management strategies to
optimise yield – quality factors. Therefore understanding variability of soil in both the
soil profile and the landscape is important for appropriate management of the variability
in vineyard production.

Item Type: Thesis - PhD
Authors/Creators:Rees, SJ
Keywords: soil, grapes, Vitis, root systems, roots, soil depth, soil properties, spatial distribution
Copyright Holders: The Author
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Copyright 2015 the author

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