Fertilizer placement for improved nitrogen use efficiency and mitigation of N2O emissions

Abstract

Deep fertilizer placement is a promising strategy to increase crop yield and nitrogen (N) use efficiency while decreasing leached N and fertilizer-induced nitrous oxide (N2O) emissions from soil to atmosphere. The objective was to test three fertilization depth treatments to compare greenhouse gas emissions of N2O, methane (CH4) and carbon dioxide (CO2), as well as leaching and crop response. A deep fertilizer placement (Deep) at 0.20 m, a shallow placement (Shallow) at 0.07 m and a mixeddepth placement (Mixed) where the same amount of fertilizer was split between the depths of 0.07 and 0.20 m, and a non-fertilized control (Control) were evaluated. These fertilizer treatments were tested in a two-year field experiment, a five-year lysimeter experiment consisting of three years with crops, in addition to a 12-day lab incubation using labeled fertilizer. Deep placement significantly increased grain N uptake and yield and decreased N2O and CH4 emissions. CO2 emissions from bare soil were not significantly affected by fertilizer placement. Further, Deep reduced N leaching and increased crop water utilization. The tracer incubation indicated that indigenous soil N was the primary contributor to total N2O emissions in Deep, and CH4 emissions were correlated to N2O fluxes originating from fertilizer N. X-ray tomography of the incubated soil cores revealed that fluxes of N2O from fertilizer were affected by compaction level. Overall N use efficiency (NUE) was evaluated in the soil-crop system via an N balance, % NUE, agronomic efficiency of N (AEN) and the recovery efficiency of N (REN). Over the five years with crops, all indices indicated a higher N use efficiency with greater fertilizer placement depth.