Effects of fractionated nitrogen application on leaf senescence and <SUP>15</SUP> N-urea uptake and utilization of apple rootstock―<I>Malus hupenhensis</I>

Abstract

Aims The effects of fractionated nitrogen (N) fertilization (once, twice and thrice) on leaf senescence and nitro- gen uptake and utilization of potted Malus hupenhensis were explored using the 15 N labeling technique. Methods We measured growth parameters such as plant height, stem diameter, leaf area and chlorophyll content (SPAD), enzyme parameters such as superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) in leaves and 15 N parameters such as uptake and utilization for potted M. hupehensis under different fractionated N applications. Important findings Plant height, stem diameter, leaf area and SPAD were highest at early growth stage for once fractionated application and lower for twice fractionated application, and lowest for thrice fractionated applica- tion. At middle growth stage, twice fractionated application showed the highest values, while once fractionated application exhibited the lowest values. At the late growth stage, thrice fractionated application was the highest, while once fractionated application was the lowest. The leaf SOD, POD and CAT activities were highest for once fractionated application at early growth stage and lowest for thrice fractionated application. At the middle growth stage, twice fractionated application was the highest, whereas once fractionated application was lowest. At the late growth stage, thrice fractionated application showed the highest values, while once fractionated application had the lowest values. The 15 N derived from fertilizer (Ndff) value in different organs was significantly different. Thrice fractionated application demonstrated higher values than either of once and twice fractionated application at the late growth stage. Plant total N, 15 N uptake and N-usage efficiency were highest for thrice fractionated application at late growth stage. This indicates that thrice fractionated application not only can enhance the total N content of leaves and delay leaf senescence, but also can increase the N-usage efficiency.