Soil profile properties affecting grapevine root growth, vine vigour and fruit yield
Creators: name: Rees, SJ
Publisher: name: University Of Tasmania
Year: 2023

description: 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 ‚Äö- 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 ‚Äö- 60 cm. Limited root growth was observed in the upper 0 ‚Äö- 10 cm of the soil profile with many soil profiles having no roots recorded in the upper 0 ‚Äö- 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 (&lt; 20 cm), acidic subsoils (pH &lt; 4.5, 1:5 water) and shallow (&lt; 40 cm) and saline &gt;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 (&gt; 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 ‚Äö- 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.