Legacy Effect of Cattle Manure Application on Greenhouse Gas Emission

Beef cattle feedlot manure is often applied to land near the feeding operations. However, long-term manure application may lead to nutrient and carbon loading in the soil, increasing the risk of loss to the environment. This study compared greenhouse gas emissions from a field that received the first manure application in 1973, and has a 43 year history of manure applied at 0 and 60 Mg ha-1 yr-1, synthetically fertilized soil, and soil that received 14 and 30 annual manure applications followed by 29 and 13 years with no manure application (discontinued), under rainfed and irrigated conditions in semi-arid southern Alberta. Greenhouse gas emissions were measured for one year following manure application in autumn 2015, and soybeans were grown during the 2016 growing season. Forty-three annual manure applications led to higher (P < 0.05) CO2 and N2O emissions than non-amended soil, synthetically fertilized soil and the soil with discontinued manure applications. Soil CO2 and N2O emissions from discontinued manure applications, synthetically fertilized and non-amended soil were not different. Irrigated soil that received 43 annual manure applications emitted more CO2 and N2O than the rainfed soil receiving continuous manure. However, irrigation did not alter soil CO2 and N2O emissions for the non-amended and synthetically fertilized soil. Irrigated soil that received 43 annual manure applications was a small CH4 source, while all other treatments were CH4 sinks. The higher CO2 and N2O emissions after 43 annual manure applications, especially under irrigated conditions, corresponded with higher water-extracted soil organic C and NO3 concentrations. After manure application was discontinued, gas emissions were similar. The results suggest that available soil C and N were respired by microbes and taken up by plants at levels similar to non-amended and synthetically fertilized soil. A second year of data has been collected to further explore the potential legacy effect.