NITROUS OXIDE PRODUCTION IN TROPICAL SOILS UNDER DIFFERENT MOISTURE REGIMES AND N-APPLICATION RATES

Nitrous oxide (N2O) is a potent trace gas responsible for approximately 6% of the current greenhouse gas (GHG) effect with 60 to 80% of total global emissions originating from the agricultural sector. Within this sector, the majority of N2O emissions come from soils arising mainly from N fertilizer additions. In the Caribbean, no studies have been conducted to quantify the N2O flux from our soils, although this information is crucial in gaining a better understanding of how to manage N fertilizers, such as urea, to minimize N2O fluxes. In our region, urea represents approximately 80% of N-fertilizer used. In this laboratory study, the effects of ureaN rate and soil moisture on N2O, CH4 and CO2 flux were investigated on three soils from Trinidad. The18 treatment combinations were arranged in a completely randomized design with four replicates (72 experimental units). The equivalent of 220 g oven dried soil were placed in 1L mason jars and incubated at 50% Water Filled Pore Space (WFPS) for 7 days. Then, urea-N solutions of 0, 75 and 150 kg N/ha were applied and the soil moisture was further adjusted to 60% and 90% WFPS. Jars were then sealed and headspace air was sampled using a syringe via a rubber septum on the lid at regular intervals: three times on day 1 and then once per day for the next two weeks. Gas samples were injected into evacuated exetainers and analyzed for N2O, CO2 and CH4 concentrations using a gas chromatograph equipped with a Flame Ionization Detector (FID) and an Electron Capture Detector (ECD). Increases in N-fertilizer application rate did not have a significant effect on N2O production however it must be noted that N2O emissions were greater as N-applicate rate increased. Soil moisture was significant to N2O production with highest emissions under 90% WFPS compared to 60%WFPS. Soil type also had a significant effect with the greatest emission from the Nariva peaty clay soil type. The N2O flux data presented in this paper is the first report for Trinidad soils. This study has implications for improving urea-N fertilizer use efficiency, which could enhance soil productivity while minimizing environmental pollution