Impact of Different Nitrogen‐Horizontal Placements on Greenhouse Gas Exchange in an Apple Orchard

Abstract

Nitrogen (N) placement can impact nitrogen use efficiency, but its effect on greenhouse gas (GHG) emissions remain unclear. The objective of this study is to compare the effects of four different N horizontal placement methods (i.e., annular canal (An), radial canal (Ra), band (Ba), and nest fertilization (Ne)) with urea broadcast (Br) on nitrous oxide (N2O), methane (CH4), and soil heterotrophic respiration carbon dioxide (CO2) emissions from an apple orchard to assess the seasonal and spatial variations in these gas emissions. The total cumulative GHG emissions are determined through spots that are differentiated as fertilized or unfertilized. A field simulation study is conducted in an apple orchard, and all N sources have an application rate of 300 kg N ha−1. In the spots with fertilizer application, the N2O emissions from the Br treatment are significantly lower than those of other treatments, and the emissions from the Ne treatment are 1.7‐fold higher than those of the Br treatment. Surprisingly, the cumulative N2O emissions from the Br treatment are significantly higher than those of the other four treatments. N horizontal placement does not significantly influence the soil CH4 sink. The CO2 emissions in the Br treatment are higher than in other treatments. High N2O emissions in the Br treatment result in a significantly higher GHG exchange than in other treatments, while the Ne treatment significantly reduces the GHG exchange throughout the measurement period. Therefore, optimizing N placement may serve as an effective way to reduce GHG emissions from arable soils.