N Utilization, Residual and Loss Characteristics of Spring-Topdressing (15N-urea) Pear Orchards in the Old Course of the Yellow River Area

Abstract

In the old course of the Yellow River area, most orchards are over-applied with nitrogen (N) fertilizers. To improve N management in this area, a 15N tracing experiment was conducted to investigate the absorption, distribution and loss of spring-topdressing urea in pear orchards from March to August 2019. The 7-year-old Sucui 1 pear was used as the test material, and 277.5 g of ordinary urea and 15 g of 15N-urea N were evenly applied to each plant. The N absorption, distribution and utilization efficiency of different organs from the flowering stage to the post-harvest stage were analyzed, and the residual and loss of N in the soil were also discussed. The N fertilizer utilization rate increased with the advancement of the phenological period. The N fertilizer utilization rate in the full bloom period is 10.39%, which is the fastest growing period, and reached a maximum of 23.62% in the post-harvest stage. In the young fruit stage, the amount of N derived from labeled fertilizer (%Ndff) of the fruit was only 1.02%, and most of the new vegetative organs were above 1%. Residual amount in the 20–40 cm soil layer was significantly higher than that in other soil layers. Direction of N fertilizer is N fertilizer loss>soil residue>tree absorption. N loss in the fruit expansion stage and the harvest stage is higher, which are 3.76 g and 3.74 g, respectively. N utilization rate in this area is low throughout the year. There is nutrient competition between reproductive growth and vegetative growth, which can be effectively alleviated by spring top-dressing. The N loss during fruit expansion and harvesting is serious. Attention should be paid to split fertilizer application and the timely supplementation of an appropriate amount of N fertilizer to improve N use efficiency.