effects of different potassium and magnesium ratios on cluster necrosis and fruit quality in grapevine cv. bidaneh sefid

vineyard management, plant nutrition, irrigation, genotype and pests and diseases are effective factors quantity and quality of crops. among mentioned factors, plant nutrition has more importance and nutrient imbalance in soil can affect crop quantity and quality. grape cluster necrosis at veraison time is important disorders in vineyard, because of lack of balance between potassium and magnesium in plant leaves. therefore this research were done in two factor randomized complete block design consist of: a- potassium with three levels 0(k1). 300(k2) and 600(k3) gram per vine from potassium sulfate source), b- magnesium with three levels 0 (mg1), 100(mg2) and 200(mg3) gram per vine from magnesium sulfate source), with three replication (three vine per replicate) in two vineyards of urmia, iran. results showed that highest chlorophyll content was obtained in t3 (k1 mg3) which was 29.4% more than control. effect of different ratios of potassium and magnesium on ta, ph and berry diameter was not significant, but control treatment showed longer berries than other treatments. berries weight was best in t4 (k2 mg1) with 30.5% increase compared to control. clusters with highest weight were observed in t8 (k3 mg2). t9 (k3 mg3) showed higher tss than other treatments and in contrast with control had 67.5% increase in tss. treatments of t6(k2mg3), t7(k3mg1) and t8 had the highest cluster necrosis due to their high potassium/magnesium ratio. cluster necrosis degree was decreased in second year compared to first year. at different ratios of potassium and magnesium, highest leaf potassium content observed in t9 which were 7% and 10% higher than those in control and t3, respectively. effect of year on potassium content of leaf was significant and in first year potassium content was 41.9% higher than that of second year. highest leaf magnesium content was observed in t3 which its potassium to magnesium ratio was low. however, it was not significantly different with control, but there was significant difference among t3, t7 and t8 which had higher potassium to magnesium ratio. in t3 treatment, magnesium content was 21 and 16% higher than that of t8 and t7, respectively. results showed that with potassium application without magnesium usage, potassium to magnesium ratio was increased because of more absorption of potassium than magnesium, balance between potassium and magnesium level was negatively affected which resulted in reduction of crop quality.