effects of sulfur rates and sources on growth and fruit quality of apple var. golden delicious

sulfur (s) is an essential macronutrient influencing plant growth, nutrient efficiency, quality and health of agricultural crops. the purpose of this research was to study the effects of s rates and sources on growth and fruit quality of apple (malus domestica l.) trees of ‘golden delicious’ at west azerbaijan, iran. experiment was conducted during four seasons (2003-2007), using a factorial randomized complete block design (rcbd) with three replications. the treatments included two sources of s (organic and inorganic s with thiobacillus inoculums), each applied at three different rates (0, 2 and 4 kg s/tree). the results showed soil ph and availability of p, fe and zn were significantly influenced by s application rates. the least ph and the highest values of p, zn and fe availability in soil were achieved with 4 kg s/tree. leaf chemical analysis revealed significant relationship between s rates and leaf nutrient contents except of ca and mg. leaf n, p, k, fe, mn, zn and cu contents were increased with s application as compared with the control. the added s had no effect on fruit firmness but, the highest weight, total soluble solid and total acidity of fruit recorded in 4 kg s/tree from organic source. chlorophyll content was significantly increased with s application rates. the highest chlorophyll content obtained in 2 kg s/tree treatment from organic source. the results suggested that, s is a key nutrient which has important role in balance nutrition, fruit quality and quantity enhancement of apple orchards in calcareous soils.