Cut back irrigation for maximum growth
GroGuards reduce water use
GroGuard vineguards substantially reduce vine water use.
Unirrigated establishment has proven very effective with GroGuards (See article: Unirrigated establishment in a drought: Growth of vines in their second leaf and trials with cuttings).
Because they reduce vine water use, GroGuards require a substantial reduction in irrigation rates. If irrigation is not reduced, the effects of overrigation – including reduced growth - may occur. These problems are most likely to occur in heavy soils, especially heavy plastic clays.
Overirrigation reduces water uptake and growth
Prolonged irrigation does not increase the amount of water available to the vine. It displaces more and more air from the rootzone, causing reduced water uptake and reduced growth. In severe cases, overirrigation causes spindly growth, shoot burn (because the vine cannot take up water) and even death.
Once overirrigated, it takes a considerable amount of time for some soils to dry out and let in enough air for normal water uptake and normal vine growth.
Signs of overirrigation
When overwatering occurs, the inside of the GroGuard is continually wet. Vine responses include spindly growth, shoot burn and greater risk of root rots depending on the severity of overwatering (See article: Root rots can stunt young grapevines).
Water only to the bottom of the rootzone
Water should be applied only when soil moisture measurements indicate a shortage in the rootzone.
Locating the bottom of the rootzone
Soil moisture sensors must be placed in the rootzone directly under the vine.
Immediately after planting, the bottom of the rootzone is at planting depth – exactly at the base of the vine. That is where the uppermost soil moisture sensor should be placed. Until root growth begins, irrigation should be turned off as soon as the wetted front arrives at this sensor.
As the vine grows, roots grow downwards at about the same rate as the shoot grows upwards. The exact depth of the rootzone can be established at any time by simply excavating one side of a vine with a spade and seeing where the roots have grown to.
Because the rootzone deepens as the season progresses, soil moisture sensors should be placed at intervals of about 30cm down to the bottom of the cultivated part of the rootzone (usually the bottom of the rip). This depth is best determined by a using a pentrometer.
Types of soil moisture sensor
GroGuard recommends fast acting, continuously monitored moisture sensors to ensure that irrigation is stopped as soon as the wetted from reaches the bottom of the rootzone. This saves water and reduces the period of time when the rootzone is saturated. The new CSIRO "Full Stop" wetted front detector serves well in this application.
Placement of drip emitters
Correct placement of drip emitters is important. Emitters should be placed so that the vine is on the fringe of the wetted zone so that rootzone waterlogging is minimised. Typically, that will be about 30cm to the side, but the exact distance should be established by digging around a dripper after a trial irrigation (prior to planting).
Short irrigations are best
With young vines, it is not necessary to make a continuous wetted band in the planting row. Furthermore, attempts to do so can result in serious overirrigation.
Irrigation cycles should be frequent (e.g. 2-3 times weekly) and brief (e.g. about an hour), rather than infrequent and long.
Short irrigations preserve soil structure and reduce waterlogging. This results in faster growth. Furthermore, short irrigations are usually all that is needed to wet to the bottom of the rootzone of a young vine, especially early in the season.