عنوان مقاله [English]
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.