The importance of ‘Irrigation Scheduling’ for your vineyard

13 February, 2008

Climate change seems to be providing New Zealand with hotter, drier summers. These conditions are ideal for producing ripe fruit, but not if you don’t have enough water to maintain vines in an optimum condition for harvest. Scheduling of irrigation is becoming of increased importance in viticulture management for New Zealand grape growers.

The main objective of scheduling irrigation is to target the effective root zone to enable the uptake of water to the vine. Although vines need water to survive, the effective use of water through irrigation is often over-looked by those tending the vineyard. There are many variables in the vineyard that will affect how and why we irrigate including soil type, soil variability and environmental factors.

The benefits of irrigation scheduling are widespread, particularly if these decisions are aided by soil moisture monitoring. Cost efficiencies can be made on electricity, labour, water buying costs, soil health, nutrient retention and any detrimental environmental side effects such as nutrient leaching can be minimised.

Scheduling irrigation based on regular vineyard inspection; environmental data and information from moisture sensors will help improve the quality of the fruit delivered to the winery. Soil moisture tools enable the monitoring of field capacity. Moisture probes profile the soil at selected depths showing the change in soil moisture over time. Continuous logging from each section of the profile is graphed and the rate of soil moisture loss can be determined.

Evapotranspiration

During early spring when the evapotranspiration rate (the combination of transpiration by plants and the evaporation of water from the soil surface) is low, irrigation scheduling is limited, unless soil texture or shallow root zones are present such as in new developments.

Evapotranspiration is usually expressed in millimetres and is influenced by climate (particularly temperature, humidity, wind velocity and sunlight), the availability of water in the root zone and the growth stage of the vine.

As the canopy starts to grow and the basal leaves reach maturity, stomatal conductance increases. The vines start to draw more water through the roots and this water is lost by transpiration through the leaves. In other words the evaporative demands and increased transpiration rate reduce soil moisture levels.

Soil type, texture, variation in the soil profile throughout the vineyard and irrigation volumes will govern how quickly the soil profile can be refilled. The aim is to irrigate sufficiently to refill the root zone to a desired level and then to maintain this level. Winter rainfall should recharge the soil profile, giving what is termed field capacity. At this point any further moisture would lead to saturation, in which case soil moisture is either lost through run-off or infiltration below the rootzone.

Over irrigation

Excessive irrigating is fraught with problems including water logging which reduces soil temperature, the leaching of nutrients and reduced oxygen in the soil. All of these factors can lead to conditions including spring fever, which will slow the rate of vine growth. Research shows that vines subjected to prolonged water saturation, are at risk from root rot diseases. Conversely, inadequate water supply will impact growth, yield and quality. Vines are particularly sensitive to water stress at certain stages of development.

Refilling the effective root zone can be difficult, particularly in areas where there is soil variability. In many cases the area within the irrigation zone receives either too much or not enough water. Electro Magnetic Induction (EMI) surveys and/or Multispectral Imaging (MSI) can identify these changes in soil zones and growth variability respectively. This data can then be interpreted by winemakers and/or viticulturists to allow inferences on quality parameters such as vine health and vine quality to be undertaken.

How much do I irrigate?

This can be a difficult question, as there are a number of factors that influence the amount of available water in the soil. Soil moisture monitoring (such as the services provided by Leau Below) allow vineyard managers/viticulturists to monitor the frequency of water application and the length and depth of water penetration in the root zone. Using this as part of your daily management and assessment of vines during the growth stage, enables greater control of vine vigour during the growing season. Applying water just because it hasn’t rained for some time should not be a prerequisite for irrigating or using all of a daily water allocation. Every vineyard is different so a blanket approach is not the way forward. Considering sustainability in a vineyard you don’t just want to how much water was applied, but how well used the water was too.