A comparison of three methods of magnesium application to grapes

摘要

Magnesium (Mg) deficiency is common in vineyards in the Hawke's Bay, Marlborough and, particularly, Gisborne regions of New Zealand. This is thought to be due to high amounts of exchangeable potassium (K) and calcium (Ca) relative to Mg in the soil. Attempts to correct this deficiency using fertiliser have not been successful. This study investigated the fate of applied Mg fertiliser in a sandy Hawke's Bay soil and also compared fertiliser application by trunk injection and foliar sprays as techniques to increase leaf Mg concentrations. Brix and titratable acidity (TA) were also measured to determine whether Mg applications affected berry quality. Soil data showed that most of the Mg applied to this sandy soil remained in the top 30 cm of the soil 18 months after kieserite application. This may explain why the fertiliser application was not effective at increasing leaf Mg concentration - minimal water was applied to the grape vines (to reduce vigour) so much of the water (and hence nutrient) uptakemay have been from deep in the profile, which remained unaffected by the added Mg fertiliser. Chardonnay on rootstock 3309 had a higher leaf Mg concentration than chardonnay grown in immediately adjacent rows on rootstock S04. Foliar sprays increased leaf Mg concentration, although a large number of sprays would be needed if the deficiency was severe. The small increase in leaf Mg, achieved through foliar spraying, had no effect on berry quality. Trunk injection of Mg sulphate did not increase leaf Mgconcentration.