ARS | Publication request: Fertilizer Application Timing Influences Greenhouse Gas Fluxes Over a Growing Season

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 9, 2009
Publication Date: June 26, 2009
Repository URL: http://hdl.handle.net/10113/31680
Citation: Phillips, B.L., Tanaka, D.L., Archer, D.W., Hanson, J.D. 2009. Fertilizer Application Timing Influences Greenhouse Gas Fluxes Over a Growing Season. Journal of Environmental Quality. 38:1569-1579.

Interpretive Summary: Greenhouse gas management and understanding the carbon emissions associated with land management decisions is a growing public concern and an increasingly important component to sustainable agricultural systems. Fertilization with nitrogen is known to influence emissions of greenhouse gases from soils. Less clear is how the timing of fertilization impacts emissions. We performed an experiment to determine if emissions could be reduced by adjustment of fertilization timing alone using a maize field in production. We found fertilization of plots with urea in the early-spring resulted in lower greenhouse gas emissions than fertilization of similar plots with urea in the late-spring. This was primarily due to greater emissions of carbon dioxide at the soil surface when fertilized at temperatures greater than 10°C. The difference between treatments, when integrated over a 5-month growing season, was 548 kg C ha-1. Yields were similar for both treatments. Fertilizing at cooler temperatures resulted in a substantial carbon “savings” without affecting yield. This study indicates fertilization timing may be a management option for reducing soil carbon losses and greenhouse gas emissions. Additional study is needed to determine if this effect is consistent across years.

Technical Abstract: Microbial production and consumption of greenhouse gases (GHG) at the soil surface is influenced by temperature and nutrients, so effects of nutrient application on GHG fluxes should be greater as conditions warm during the growing season. We designed a replicated (n=5) field experiment to test for the effect of fertilizer application timing on fluxes of methane (CH4), carbon dioxide (CO2), and nitrous oxide (N2O) for maize produced in a northern Great Plains dryland cropping system. Each 0.30-ha plot was treated similarly with the exception of fertilizer timing: five plots were fertilized with urea in early-spring (1 April) and five plots were fertilized with urea in late-spring (13 May). We hypothesized time-integrated fluxes of CH4, CO2, and N2O would be greater for the Late-Spring treatment, resulting in greater net GHG flux, as compared to the Early-Spring treatment. Data collected on 59 dates over a 5-month time course indicated CO2 fluxes were higher (P<0.0001) and CH4 fluxes were lower (P<0.05) for soils fertilized in Late-Spring. Nitrous oxide emissions were similar for both treatments. The global warming potential (GWP) estimated over the growing season was 2543 kg C ha-1 for the Early-Spring and 3756 kg C ha-1 for the Late-Spring treatment. The greenhouse gas intensity (GHGI) was 1.3 kg C kg-1 grain and 1.9 kg C kg-1 grain for Early and Late-Spring treatments, respectively. Greater GHGI for maize production occurred due to increased soil respiration following addition of N when soil and air temperatures were >10°C. Results indicate fertilizer application timing may be important to GHG management in dryland cropping systems.