Abstract
Abstract: The objective of this work was to evaluate the effects of nitrogen fertilizers on the N dynamics and grain yield in flooded rice (Oryza sativa) cultivation in Brazilian tropical wetland. The experiment was carried out in a randomized complete block design with six treatments, as follows: common and protected urea; topdressing application of N doses (30, 70, and 150 kg ha-1); and one control treatment, without N fertilization. Emissions of N2O-N, global warming potential (pGWP), emission factors (EF) for mineral fertilizers, grain yield, emission intensity, nitrate, ammonium, pH, and potential redox were quantified. Gas sampling was carried out in two crop seasons of rice cultivation and in one off-season. During the flooded period of the two crop seasons, N2O fluxes did not exceed 862.41 μg m-2 h-1 N2O-N; in the off-season, the fluxes varied from -52.95 to 274.34 μg m-2 h-1 N2O-N. Consistent emission peaks were observed in soil draining before harvest, when the highest rate of both N sources was used, and also in the control treatment in the off-season. Protected urea does not reduce N2O emissions or EF. Nitrogen increases the grain yield. Protected urea does not have any effect on the pGWP. The concentrations of NO3- and NH4+ in the soil are not related to N2O fluxes.
Highlights
Brazil is the ninth largest rice (Oryza sativa L.) producer in the world (FAO, 2020)
In the flooded period of the 2014/2015 and 2015/2016 crop seasons, N2O fluxes did not exceed 862.41 μg m-2 h-1 N2O-N, and there were no statistical differences between sources or rates
Consistent emission peaks were observed when the highest N rate was used for both sources, in draining soil before harvest
Summary
Brazil is the ninth largest rice (Oryza sativa L.) producer in the world (FAO, 2020). In 2019, rice grain production in tropical lowlands was approximately 9% of the national production, and 10% of the total was produced in flooded systems (Conab, 2020). Because of the modern cultivars, it is possible to have high-quality grain outside Southern Brazil, which contributes to economic and social development, enhancing human life quality in the Cerrado, and collaborates for national food security. This demands the increasing use of nitrogen mineral fertilizer in the rice production system that directly influences the emission rates of N2O, with direct and indirect effects on the emissions of this greenhouse gas (GHG). Nitrous oxide (N2O) is an important greenhouse gas whose global warming potential is 265 times greater than CO2 (Smith et al, 2014)
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