SATI Beyond The Bunch 1st Quarter 2026

DEWALD KIRSTEN | LUCENTLANDS

Irrigation must be adjusted throughout the season to match the plant phenology.

A daily decision Weather drives short-term fluctuations in water demand. Theoretically, growers would track soil mois ture (tools for this are discussed below) and irrigate as needed to stay within field capacity and the refill line. In practice, pump capacity, system delivery, and water availability are often limiting factors. The goal is uniform soil moisture throughout the profile, but the root zone (top 40 cm) typically dries faster than the buffer zone (lower 40–80 cm) due to evaporation and a greater root density. Therefore, irrigation will be some combination of short events targeting the root zone and longer events targeting the buffer zone. Soil moisture must be checked in both zones to achieve the right weekly irrigation schedule. However, daily scheduling decisions can’t be based solely on soil moisture, as many growers discovered during the past season when sudden hot weather led to skyrocketing evaporation and transpiration. By the time soils had dried, the irrigation infrastructure couldn’t replenish soil moisture or keep up with plant demand, resulting in reduced berry growth and, ultimately, fewer export cartons at harvest. To avoid such losses, growers can use weather stations and evapotranspiration-demand estimates to schedule irrigation proactively ahead of hot spells. Of course, irrigation may also be adjusted in anticipation of cold spells or rain. Irrigation scheduling is a big topic, and the details are beyond the scope of this article. More information is available in the resources listed under Further reading. Feed according to need Precision grapevine nutrition addresses spatial and temporal variability. Nitrogen applications are tailored to the phenological stage and observed vigour, which

is usually assessed during flowering, when berries are pea-sized, and after harvest. Where appropriate, differential vigour within blocks can be managed by variable applications of nitrogen, compost, or mulch, keeping in mind that nitrogen is not a panacea for weak growth. With fertigation, be aware that one block may receive nutrients mixed for another block due to residual fluid in the irrigation lines. Production figures, yield targets, and soil and leaf samples must also inform fertiliser programmes. Soil and leaf samples are discussed in detail in the 2025 Q2 issue of Beyond the Bunch. Even when not fertigating, irrigation and nutrition are inseparable. Everyone is doubtless aware that over irrigating leaches soil nutrients. What is likely less well known is that nitrogen availability decreases in oxygen depleted, waterlogged soils because soil microbes convert nitrogenous compounds into forms that are lost to the atmosphere.

DEWALD KIRSTEN | LUCENTLANDS

Weather stations can help growers irrigate proactively ahead of hot conditions.

BEYOND THE BUNCH • 9 • QUARTER 1 • 2026