Intensive field measurements of nitrous oxide emissions from a tropical agricultural soil

Abstract

Abstract. The amount of nitrous oxide (N20) continues to increase in the atmosphere. Agricultural use of nitrogen fertilizers in the tropics is thought to be an important source of atmospheric N20. High frequency, highly precise measurements of the N20 flux were made with an automated system deployed in N fertilized and unfertilized agricultural plots of papaya and corn in Costa Rica for an entire corn crop growth to harvest cycle. N20 fluxes were as high as 64 ng N-N20 cm -2 h -• from fertilized versus 12 ng N-N20 cm -2 h '• from unfertilized corn and 28 ng N-N20 cm -2 h -• from fertilized versus 4.6 ng N-N20 cm -2 h '• from unfertilized papaya. Fertilized corn released more N20 than fertilized papaya over the 125 days of the crop cycle, 1.83 kg N ha -• versus 1.37 kg N ha -•. This represents a loss as N2 ¸ of 1.1 and 0.9% of the total N applied as ammonium nitrate to the corn and papaya, respectively. As has often been observed, N20 fluxes were highly variable. The fastest rates of emission were associated with fertilization and high soil moisture. A diurnal cycle in the fluxes was not evident probably due to the minimal day/night temperature fluctuations. Each chamber was measured between 509 and 523 times over the course of the experiment. This allows us to evaluate the effect on constructed mean fluxes of lowered sampling frequencies. Sampling each collar about once a day throughout the crop cycle (25% of the data set) could result in a calculated mean flux from any individual chamber that can vary by as much as 20% even though the calculated mean would probably be within 10% of the mean of the complete data set. The uncertainty increases very rapidly at lower sampling frequencies. For example, if only 10% of the data set were used which would be the equivalent of sampling every other day, a very high sampling frequency in terms of manual measurements, the calculated mean flux could vary by as much as 40% or more at any given site.

Seasonal dynamics in nitrous oxide emissions under different types of vegetation in saline-alkaline soils of the Yellow River Delta, China and implications for eco-restoring coastal wetland

“…Correlation analysis in the current study showed that there did not exist a significant relationship between air or soil temperatures and N 2 O emissions in P. australis community, but the significant relationship between N 2 O emissions and temperature was found in other three positions. Tang et al (2006) suggested that soil temperature did not have a strong effect on N 2 O emissions, which was consistent with results reported in tropical, agricultural soils (Crill et al, 2000;Kiese and Butterbach-Bahl, 2002). On the other hand, some studies showed that N 2 O fluxes were strongly correlated with soil temperature.…”

Spatial and temporal variability of nitrogen oxide and methane fluxes from a fertilized tree plantation in Costa Rica

“…Our study of spatial and temporal variability of trace gas fluxes forms part of a 3-year field experiment established to identify controls and to quantify dynamics of N20 fluxes from humid tropical soils under different agricultural management [Crill et al, 1999]. The time schedule for the main experiment and the variability study is given in Table 1.…”

“…High temporal variability of emissions from a fertilized banana plantation in Costa Rica resulted in an underestimation of mean annual N20 emissions if monthly sampled flux data are extrapolated compared to extrapolation of fluxes sampled on a fertilization event basis [Veldkamp and Keller, 1997]. Temporal variability and short-time responses of fluxes on changes in controlling factors has been demonstrated using automated sampling and analysis systems [Brumme and Beese, 1992;Crill et al, 1999].…”

“…of gas fluxes after fertilization [e.g., Matson et al, 1996;Crill et al, 1999] increases the uncertainty in gas flux extrapolations. High temporal variability of emissions from a fertilized banana plantation in Costa Rica resulted in an underestimation of mean annual N20 emissions if monthly sampled flux data are extrapolated compared to extrapolation of fluxes sampled on a fertilization event basis [Veldkamp and Keller, 1997].…”

Soil‐atmosphere nitrogen oxide fluxes: Effects of root disturbance

“…Plantations were abandoned about 1968 and secondary forest developed [Hartshorn, 1983;McDade and Hartshorn, 1994]. In 1994 this forest was cleared to establish farm plots for a 2-year study of nitrogen oxide fluxes from fertilized and unfertilized agricultural soils [Crill et al, 2000]. After forest clearing, papayas (Carica papaya) were planted in 1994.…”