With current predictions indicating this summer will be long, hot and dry, what proactive measures can be taken by Top of the South viticulturists to prepare for the heat? In this article, we explain why the early application of composts or mulch to vineyard soil is highly recommended.
NIWA, the National Institute of Water and Atmospheric Research, reports that the consensus from international models is for the tropical Pacific to transition toward El Niño over the next three-months. Further, the probability for El Niño conditions being established increases as we reach into and beyond the Southern Hemisphere summer, with a 78% chance for El Niño conditions over the March – May 2019 period.
Typical El Niño impacts on the local climate include stronger or more frequent winds from the west in summer, leading to an elevated risk of drier-than-normal conditions in east coast areas, due to the barrier effect of the Southern Alps. This means there will be “above average” temperatures and drier soil conditions.
The Marlborough region is accustomed to periods of low rainfall due to its position in a rain shadow. However, sometimes extended periods of very low rainfall occur, resulting in droughts. Similarly, Nelson and the Waimea Plains are the driest areas in their region, being well-sheltered from rain-bearing systems arriving from the west and south. Dry spells of more than two weeks are quite common, particularly in eastern and inland locations.
With weather warnings in mind, viticulturists, reliant on a single harvest each year to produce income, would be wise to expect the best, but plan for the worst. So what is the best pre-emptive action that can be taken to protect vines and ensure a successful grape harvest when hot, dry conditions are predicted? Laying down mulch or compost has a multitude of benefits, many of which provide plant protection preceding dry weather.
The application of compost or mulch to the under-vine area insulates the soil and buffers soil temperature, preventing the surface from crusting in summer and protecting the roots from getting burnt. It affects drainage positively by cushioning water flow and stopping the soil from drying out. Compost or mulch also increases inherent soil-moisture retention enabling a reduction in irrigation and improving plants’ drought resistance.
Enough water should be applied to vines early in the season to ensure the development of a healthy canopy that can be maintained throughout the growing season to protect grape bunches from sun exposure. Grapevines should be irrigated before an extreme heat event to maximise transpirational cooling and prevent physiological damage.
The mid-row of a vineyard is an important source of reflected heat, even more so than the under-vine strip, due to its greater area. Studies have shown that vineyards with stubble or mown sward in the mid-rows and mulch, (mostly under-vine), suffer less heat damage than those with bare soil.
If your vineyard could benefit from improved moisture retention through improved soil structure, added beneficial microbes and better erosion and weed control, consider applying compost and mulch. These products can be important long-term investments in the health of your vineyard.
Given that NIWA warns on its website that the likelihood of an El Niño pattern is increasing with climate change, viticulturists will benefit from incorporating composting or mulching permanently into their vineyard management plans.