Assessment Of Soil Nitrous Oxide Emissions (N2O) In Forage Systems Fertilized With Dairy Liquid Manure.

Excessive N inputs through fertilization significantly increase the potential for large nitrous oxide (N₂O) emissions from soils. Intensive dairy production generates large amounts of liquid manure which is typically reused as fertilizer for the production of forage, together with inorganic N fertilizers. Thus, these systems typically receive high annual inputs of N, having a great potential for large N₂O emissions. The present study was carried out in three dairy forage corn production fields of the Central Valley of California representing a range of soil textures and where liquid manure was applied in irrigation water together with inorganic N fertilizers. The objectives of the study were to determine (i) the proportion of the N inputs emitted to the atmosphere as N₂O, and (ii) the main sources (manure vs. inorganic N fertilizer) of the N₂O. Total N inputs, crop N removal and N₂O emissions were assessed over two corn cropping seasons at each farm, together with soil inorganic N (NH₄⁺-N, NO₃^--N, NO₂^--N), moisture and temperature. Field data was completed with laboratory incubations of the three soils with liquid manure and ¹⁵N labeled inorganic fertilizers in order to determine the proportion of liquid manure and inorganic N in the emitted N₂O. Preliminary results show that emissions ranged from 4.7-7.4 kg N₂O-N ha^-1 in sandy soils and from 11.4-16.5 kg N₂O-N ha^-1 in a clayey soil. Also, periods of N₂O release after irrigation events were longer in the clayey than in sandy soils. Emissions represented between 0.65 and 3.53% of the initial applied N and were explained by high soil moisture and concentrations of soil inorganic N as showed by multiple regression analysis. Results of this study provide important information to understand N₂O release dynamics in dairy forage production systems which can be used to improve fertilizer management and reduce environmental impacts.