Foliage application of urea in late autumn will improve growth in the following spring and fruit quality of dwarfed apple

ObjectivesIn this paper, we studied the effects of urea foliar application in late autumn on the nitrogen absorption, utilization of apple trees in the following spring and the fruits quality at the fruit maturation period of dwarfed apple, hoping to provide scientific basis for appropriate fertilization on dwarfed apple orchards and improve the nitrogen efficiency.

MethodsA field experiment was conducted uing five-year-old ‘Fuji’ 3/M26/M. hupehensis Rehd. seedlings as the experimental material. The seedlings were divided into three groups and each had 5 ones. The ¹⁵N-urea (abundance 10.22%) was diluted into aqueous solution of N 1.50%, 3.00% and 4.50%, and 60 mL of the solutions were smeared onto both sides of the whole plant leaves. Common urea control of three N concentrations were made the same as the treatments. In the next year, the leaves, branches and roots samples were collected at the full-bloom stage (April 25th), and the whole plants were destructively sampled at the spring shoot growing stage (June 15th). The N contents and ¹⁵N aboundance were determined, the chlorophyll contents and fruit quality were investigated, and the Ndff values were calculated.

ResultsThere were significant differences in Ndff in different organs, and the highest one was in tretment of N 4.50%, followed by treatment N 3.00%, and the lowest in the N 1.50% treatment. At the full-bloom stage, the Ndff in perennial branches was the highest, then in leaves, flowers and roots in turn, indicating that the nitrogen absorbed by leaves was primarily stored in perennial branches. At the spring shoot growth stage, the Ndff in leaves was the highest, followed by annual branches, perennial branches, roots and stems in turn. The plant leaf area, SPAD and the total N contents of leaves were found significantly different amongst the treatments at the fruit maturity stage. The highest values was in N 4.50% treatment, then was in N 3.00% and 1.50% treatments, and the lowest value was in the control, which was consistent with the presentation of the physiological indicators, such as mean fruit weight, yield per plant, soluble solid, fruit firmness, soluble sugar content and sugar-acid ratio.

ConclusionsFoliar application of urea on dwarfed apple trees in late autumn could improve the nutrient storage of the current year, enhance the vegetative growth and flower bud differentiation, improve the leaf area, and increase the yield and fruit quality of apples as a result. The appropriate foliar application concentration of urea is N 4.50% for the experimental apples cultivars.