[Effects of split combined application of organic-inorganic fertilizers on plant growth, ¹⁵N absorption, utilization and loss of Gala apple tree]

Fifteen-year-old 'Gala'/M. hupehensis Rehd. trees and ¹⁵N trace technique were used to explore the effects of split combined application of organic-inorganic fertilizers on plant growth, ¹⁵N absorption, utilization and loss. The main results were as follows: compared to control, combined application of organic-inorganic fertilizers significantly increased the root-shoot ratio, chlorophyll content, total nitrogen content of leaves and mean fruit mass. The effects of split combined application of organic-inorganic fertilizers treatment were more obvious than one time combined application. Combined application of organic-inorganic fertilizers treatment improved the capacity of ¹⁵N derived from fertilizer (Ndff) of different organs, with the effects of split combined application of organic-inorganic fertilizers treatment being more significant. The Ndff value of fruits in different treatments were the highest, followed by leaves, biennial branches, fine roots, large roots and perennial branches, and lowest in trunks. Total N content of plant and ¹⁵N-urea utilization rate of the split combined application of organic-inorganic fertilizers treatment were 395.39 g and 28.4% respectively, which were obviously higher than the treatments of one time combined application (342.77 g and 21.1%) and no organic fertilizer application (296.41 g and 14.6%), while ¹⁵N loss rate was 51.3%, which was obviously lower than the treatments of one time combined application (57.5%) and no organic fertilizer application (60.6%).