Different undervine practices provide both pro's and con's in terms of balancing for (1) a soil depth and composition
that promotes root development, ensures access to a large reserve of nutrients and water and; (2) the reserves of nutrients and water, are not consumed excessively by competing vegetation.
Here we consider three different undervine practices; mulched, tilled and bare soil and the effect on soil moisture during the height of the summer growing period (January to March), in Victoria, Australia.
Keywords: undervine, viticulture, soil mositure, mulching, tilling, herbicides, irrigation
The primary goals of ground management practices in any vineyard include weed supression, soil conservation and improvement, soil nutrient
and water management, enhanced biodiversity, fostering refugia for beneficial insects, and moderating resource availability (i.e., nutrients, water) to control vine vigour.
These all contribute to how the vine and fruit evolve over the season, and therefore have tangible implications for wine quality.
The best practice for each vineyard will be influenced by the vine's age, vineyard design, soil type, and site climatic conditions. Environmental regulations and public perceptions, regarding the use of different management approaches, also influence the best practices for a given site.
Below is short summary of the relatively advantages and disadvantages of three common ground management practices:
Improved and more even water infiltration
This case study took place on a block of Pinot noir (Vitis vinifera) in a Yarra Valley, Australia vineyard (37.7340° S, 145.3830° E, elevations; 50 - 430m, rainfall; 750-950mm) between Febuary and March 2017. Three thirdEYE wireless viticulture probes were installed across three rows with different undervine management practices applied (i.e. R08; bare soil, R10; mulch applied, R12; tilled to a depth of 100mm).
ThirdEYE probes are capable of measuring soil tension at depths of 150mm, 300mm, 500mm and 700mm and also record soil temperature (@150mm), canopy temperature and humidity and leaf wetness.
Measurements were taken at 15 minute intervals during the period. Soil tension (kPa) for different depths are presnted in the chart sliders below (use the left and right arrow icons on the charts to switch depths). Data has been average to 6 hourly intervals. Rainfall and temperature data for the same period is also shown.
The first set of charts show a stacked view of tension through the soil horizon (150mm down to 700mm) for the three different practices (rows). Narrowing of the bands suggests higher moisture availability and widening of the bands drier conditions. The second set of charts presents the same data as a set of line charts. The last chart constrasts soil temperature at a depth of 150mm across the three study rows
Not surprisingly bare soil showed the greatest moisture definciencies and significant variability in tension. This is confirmed in the box a whisker plots below, (where the size of the box and extension of whisker represent the range of values for tension arcross the treatments)
Soil temperature was also considerably more variable compared with mulching and tilling.
Mulching providing both consistent and significant impacts upon both soil moisture and soil temperature.
Tension values where around 60% lower than bare soil and around 40% compared with tilled areas, for the key depths of 300 and 500mm.
Observations showed vine and and leaf growth was larger and more vigourous and leaf colour a deeper green.
Tilling demonstrated improved infiltration and this clear from responses to rainfall events during the study period.
Tilling was also beneficial in regulating soil temperature, though not to the same degree as mulching, and most likely via improved airflow and solar attenuation.
Ther grower's observations also confirmed tilling's effectiveness in surpressing weed competition.
Click the charts to see a larger version of each chart. In box-and-whisker plots, the ends of the whiskers represent the max and min values, the notch is the median value (i.e. middle value in the data set and not be confused with the mean), and the ends of the box are the upper and lower quartiles. This means the box covers obervation values which include all those greater than the smallest 25% and less than the largest 25% of observed values, this is it covers the middle 50% of all observations.
Both mulching and tillage demostrated effectiveness in moderating soil mositure, improving water infiltration and stablising soil temperature. Their effect upon vigour and yield, as observed and noted by the grower, lends weight to its use within vineyard management, and a demostratable return on investment.
As an extension, studies in South Australia, showed an appoximate $9000/ha ROI for a $1000/ha investment in mulching, via improved yields, as well as significant water and energy savings, you can read more about the trial here.
In another Australian trial, this time over 3 years in Central NSW, mulching signfiicantly increased berry potassium and pH. The study concluded that increases of ~1t/ha were possible in lower yielding areas, and raised the possibiltity of using mulching to reduce yield variability across the vineyard, read more here
Mulching, has the added benefits of both suppressing weed competition and protecting undervine soils from erosion. Whilst tilling has similar benefits, including reducing herbicide use, it must be done with the risk of soil erosion in mind, since the soil is obviously loose and more mobile.
Bare soil provides the least attactive approach, with the exception of perhaps cost, in terms of managing water stress, weed condition and soil integrity.
Australian Wine Research Institute - Mulch in Vineyards
Influence of Floor Management Technique on Grapevine Growth, Disease Pressure, and Juice and Wine Composition: A Review