Flux intensity and diurnal variability of soil N₂O emissions in a highly fertilized cropping system

Abstract

Manually sampling N2O soil fluxes is labor‐intensive and sampling frequencies are often insufficient to capture daily variation in N2O soil flux, compromising the accuracy of emission estimates. Knowledge of the diurnal fluctuations in N2O flux has been used to choose a sampling time that maximizes the accuracy of N2O flux estimates, thereby reducing the sampling frequency required, but results from previous studies are inconsistent. We analyzed N2O soil emissions measured quasi‐continuously over 3 yr in a highly fertilized (>200 kg N ha−1) corn (Zea mays L.) system grown in southern Wisconsin. This is the first study of temporal variability in N2O flux that includes multiple difficult to measure peak emission events (“hot moments”) and estimates the relative contribution of hot moments to cumulative emissions. The relationship between the observed hourly average flux and the mean daily flux was assessed via linear regression of all measured data (≈22,000 fluxes) and data subsets grouped by magnitude. Diurnal variation in flux was closely associated with normalized flux size. During low‐emission periods, fluxes exhibited a diurnal pattern, where N2O flux measured at particular times of day, named “Preferred Measuring Times” (PMTs), were not significantly different from the mean daily flux. During high‐emission periods, N2O flux did not exhibit a diurnal pattern and there was no PMT. High‐emission periods included difficult to measure hot moments that did not exhibit a PMT and contributed up to 50% of the cumulative emissions; therefore, flux measurements with high temporal resolution were required to estimate cumulative emissions.

Soybean Yield and Nutrition Grown on the Straw of Grain Sorghum Inoculated with Azospirillum brasilense and Intercropped with BRS Paiaguás Grass

“…Nitrogen is an ephemeral element in the soil; even with frequent fertilizations and relatively high doses [ 68 , 69 ], there is usually no direct residual effect on the crops grown in succession. However, the residual effect of nitrogen fertilization can occur indirectly, through the higher biomass yield of the fertilized cover crop, in which the greater input of dry matter to the soil will result in greater input and quantities of nutrients released to the crops in succession, by being fixed in organic compounds [ 11 , 50 , 70 ].…”