The Chlorophyll, Macronutrients and Carbohydrates in Apple Leaves “Crystal Variety” as Affected by the Addition of Compound Fertilizer and Humus

Abstract

Abstract The experiment was conducted on two-year-old apple trees of the ‘Crystal’ variety, grafted onto quince rootstock, planted in an orchard at the Horticulture and Landscape Engineering Department, College of Agriculture, Tikrit University. The orchard had dimensions of 3.5 × 4 meters and was irrigated by drip irrigation. The trees were fertilized with two fertilizers: first, NPK compound fertilizer at four levels - no fertilization as a control, balanced 40:40:40, high nitrogen 60:40:40, high potassium 40:40:60 - at a rate of 200 grams per tree for each. The second fertilizer was Hummix Power humus material at four levels - no addition as a control, 250, 500, 750 grams per tree. The fertilizer levels were divided into two equal doses, with the first half applied before the initiation of vegitative bud development and the second half two months later. The experiment followed a Randomized Complete Block Design (RCBD) with three replications, and one tree per experimental unit. The results indicated that the treatment with high nitrogen compound fertilizer and 500 grams per tree of humus material gave the highest values for chlorophyll content (a, b, and total) without significant difference from the treatment with high nitrogen compound fertilizer and 750 grams per tree of humus material. Meanwhile, the high potassium compound fertilizer, humus material at 750 grams per tree, and the interaction between these two factors outperformed in achieving the highest values for nitrogen, phosphorus, potassium percentages, total leaf carbohydrate content, and the carbohydrate to nitrogen ratio in the leaves.