NITROUS OXIDE EMISSIONS FROM INCORPORATED AND SURFACE-APPLIED DAIRY MANURE AFTER SIMULATED IRRIGATION EVENTS

The more than 300,000 dairy cows in the Texas Panhandle generate a considerable amount of manure. This manure is a valuable fertilizer, but growing concerns with greenhouse gas (GHG) emissions has prompted research into methods for reducing GHG from land-applied manure. The objectives of this research were to 1) quantify nitrous oxide (N2O) emissions from surface-applied and incorporated dairy cattle manure, 2) determine how irrigation affects N2O emissions, and 3) determine the mechanism for N2O emissions. A laboratory study was conducted to compare N2O emissions from four treatments (TRT) consisting of commercial fertilizer (U, urea), surface-applied manure (MS), incorporated manure (MI), and soil alone (S, control). Soil and manure were placed into glass containers (4 reps per treatment) and monitored for a 14-day period, during which two simulated irrigation events were applied. Emissions were measured from each container once per hour using a multiplexer and real-time N2O analyzer. Nitrous oxide emissions were ranked (high to low): U, MI, MS, and S. While MI is often used as a best management practice to reduce ammonia emissions following land application, it produced higher N2O emissions than MS. Emissions of N2O increased immediately after simulated irrigation in all TRT. Based on initial and final soil nutrient concentrations, the N2O was most likely generated from the nitrification of ammonium to nitrate. Further research is warranted to quantify GHG emissions from land-applied dairy manure under field conditions.