Water regime influence on trace gas emissions following spreading of waste

Waste products are valuable resources as fertilizers and suitable to be applied to crops and pastures. When concentrated into a small geographical area or applied in excessive amounts however, they can have detrimental environmental effects. Excess application, can result in enhanced CO2, CH4, NH3 and N2O emissions to the atmosphere influencing global warming and destruction of the ozone layer. These gases have long atmospheric lifetimes, are consequently fairly well-mixed and therefore of global as well as local or regional importance. They represent a most serious treat to global climate in terms of greenhouse effect. NH4 emitted following waste applications can be transported in remote areas and contribute to acidification processes. Atmospheric impact of animal waste in the Mediterranean area was never assessed and few papers can be found in the literature. Reliable inventories of emissions cannot be carried out since emission factors were never assessed locally. In order to improve understanding of trace gas emissions as a function of agronomic techniques in this environment, a study was conducted to quantify emissions of ammonia, nitrous oxide, carbon dioxide, and methane from an alfalfa field in Southern Italy. Three 35 m circular plots were established in a two-year-old crop. Two plots were fertilized with chicken manure and one plot was irrigated. Ammonia fluxes were calculated using an Integrated Horizontal Flux mass balance technique. A Photo Acoustic Infrared Detector was used to measure N2O, CO2, and CH4 fluxes from vented closed chambers. Ammonia volatilization peaked about 4.1 kg ha-1 d-1 and returned to background levels within 72 hours. Irrigation with 25 mm of water increased NH3 emission rates by about 67%. Emission rates of N2O, CO2, and CH4 were short-lived and returned to the same levels as the control plot within 7 days. Total gaseous N losses were about 19.1 and 15% of the applied N in the irrigated and non-irrigated plots, respectively.