SATI Beyond The Bunch 1st Quarter 2026

Temporal variability Soil preparation and irrigation design diminish but don’t eliminate the effects of soil variability, which will influence scheduling and fertilisation decisions throughout the vineyard’s lifespan. Therefore, although this section focuses on changes over time, spatial and temporal variability are intertwined.

Cumulative changes Temporal variability occurs at scales of hours to years. Much of this is caused by weather and vine phenology, but irrigation and nutrition requirements also change during vineyard establishment and maturation. For example, while irrigation should always maintain an oxygenated profile to promote deep, healthy root development, achieving this needs special attention in young vines. Appropriate scheduling involves juggling the lower water demands of smaller leaf areas and root systems with the higher evaporative rates from unshaded vineyard floors. Without (and sometimes despite) interventions, grape vine variability is cumulative over the lifetime of the vineyard. For example, if uncorrected soil variability or poor system design leads to over-irrigating parts of a block, the affected vines may become more vigorous, especially if the farm uses fertigation. Conversely, over-irrigation can also reduce vigour by impairing root development on heavier soils and leaching soil nutrients from free-draining soils. In the short term, vigorous vines require additional actions to control growth, which increases labour costs. In the long term, these vines may develop denser canopies that restrict light penetration, reducing bud quality. Meanwhile, excess nitrogen accumulates, further stimulating vigour. Over several seasons, such a vineyard has higher input

costs (labour), wastes resources (electricity, water, and fertiliser), and produces less and lower-quality fruit. Soil and season In any given season, a precision irrigation and nutrition strategy is built on plant phenology, and the implementation is adjusted according to weather. Throughout the season, refill lines based on soil probes should be regularly tweaked in keeping with plant phenology, with consideration of soil variability. Keep in mind that setting refill lines relative to the block’s average soil moisture may leave some areas too wet or too dry. The impact of missed irrigations due to power outages or system failures will also depend on soil variability. When aiming for slightly lower overall soil moisture, a missed irrigation could result in significant stress for vines on rapidly drying patches of soil. Precision irrigation during the season can support particular viticultural goals. For example, grapevine roots typically flush in spring and after harvest. During these periods, allowing soils to dry slightly more before refilling to optimal soil moisture will stimulate root growth. In contrast, readily available moisture from flowering to véraison promotes fruit set and development. From véraison to harvest, depending on the cultivar, soils can dry slightly more between irrigations, to enhance sugar and colour formation and discourage vegetative growth.

DEWALD KIRSTEN | LUCENTLANDS

Irrigation and nutrition affect vine growth cumulatively over time.

BEYOND THE BUNCH • 8 • QUARTER 1 • 2026