Regulation effects of carbonized apple branches on absorption, distribution, and utilization of 15N single-labeled ammonium nitrate (15NH4NO3 or NH415NO3) in Malus hupehensis

To improve the utilization of nitrogen fertilizer and orchard waste, the apple branches were separated and pyrolyzed into carbonized wood and carbonized bark, and then applied to root-zone soil of potted Malus hupehensis. The physiological characteristics of leaves and roots were detected, and the absorption, utilization, and distribution of 15NH4NO3 and NH415NO3 in plants were analyzed using the 15N isotope tracer technique. The results indicated that the net photosynthetic rate and water use efficiency of leaves, the root growth, and the activity of nitrate reductase and glutamine synthetase were greatest increased by 1.0% (w:w) carbonized bark and carbonized wood, and the effect of carbonized bark was more effective. The carbonized bark more effectively increased nitrogen derived from fertilizer (Ndff) value in all organs, the distribution of 15N in roots, and utilization of the 15NH4NO3 and NH415NO3 of Malus hupehensis compared with carbonized wood at the same application ratio, and 1.0% ratio performed better than other ratios in these terms. The Malus hupehensis treated with carbonized bark had the highest utilization ratio of 15NH4NO3 (10.54%) when the application ratio was 1.0%, and the corresponding parameter of NH415NO3 was 12.98%. The soil immobilization capacity of 15N was improved, and carbonized bark resulted in the greatest decrease in the loss ratios of 15NH4NO3 and NH415NO3 under 1.0% ratio, which decreased by 27.33% and 30.08%, respectively. For reducing nitrogen loss and improving nitrogen utilization, carbonized bark was more effective than carbonized wood, mainly because bark contained more cellulose and less lignin than wood.