Soil CH4 and N2O Emissions from Rice Paddy Fields in Southern Brazil as Affected by Crop Management Levels: a Three-Year Field Study

Abstract

Rice yield increases in response to improvements in crop management, but the impact on greenhouse gas (GHG) emissions in the subtropical region of Southern Brazil remains unknown. A three-year field study was developed aiming to evaluate the impact that an increase in crop management levels (high and very high) has on soil methane (CH 4) and nitrous oxide (N 2 O) emissions, as compared to the level (medium) currently adopted by farmers in Southern Brazil. Differences in crop management included seed and fertilizer rates, irrigation, and pesticide use. The effect of crop management levels on the annual partial global warming potential (pGWP = CH 4 × 25 + N 2 O × 298) ranged from 7,547 to 17,711 kg CO 2 eq ha-1 and this effect was larger than on the rice grain yield (9,280 to 12,260 kg ha-1), resulting in approximately 60 % higher yield-scaled GHG with the high crop management level compared to the current level. Soil CH 4 emissions accounted for 98 % of pGWP in the flooded rice season, whereas N 2 O prevailed during the drained non-rice season (≈65 %). Although it was impossible to relate emissions to any individual input or practice, soil CH 4 emissions in the rice season were linearly related to the biomass produced by the rice crop (p<0.01) and by ryegrass in the previous non-rice season (p<0.1), both of which were possibly related to the supply of labile C for methanogenesis. A future increase in rice yield as a result of the adoption of improved crop management may require additional agricultural practices (e.g., intermittent irrigation) to offset the increased GHG emissions.

Application of the Kolmogorov-Smirnov Test to Compare Greenhouse Gas Emissions Over Time

“…In a recent work developed in the South of Brazil, its authors observed that changes in the management of flooded rice crops have resulted in higher increases in GHG emissions than in crop yields (ZSCHORNACK et al, 2018). The authors recommended that in order to avoid growth in GHG emissions associated to increase in rice yield, agricultural practices used to mitigate emissions should be sought; and they listed the intermittent irrigation systems as promising candidates for this aim.…”

Challenges and opportunities in productivity and sustainability of rice cultivation system: a critical review in Indian perspective

“…The agriculture sector has been a major source of methane (CH 4 ) and nitrous oxide (N 2 O) emissions, primarily driven from flood-based rice cultivation (Kritee et al 2018), use of synthetic fertilizers (Zschornack et al 2018) and residue burning practices (Jain et al 2014). Such emissions can raise the global warming potential to 10 times in rice season than winter (Zschornack et al 2018). It is estimated that agriculture is the largest sector, contributing about 44% of anthropogenic methane emissions (Janssens-Maenhout et al…”

Soil conservation practices and greenhouse gases emissions in Brazil

“…Segundo a Embrapa (1998), somente a Região Sul, em 1994, contribuiu com 77,3% das emissões de CH4, devido principalmente ao manejo adotado de alagamento contínuo. As emissões de CH4 representam mais de 90% do potencial de aquecimento global parcial nesse sistema de cultivo, logo as estratégias de mitigação devem se concentrar quando a cultura está implantada, pois nessa época o potencial de aquecimento global é 10 vezes maior em relação ao período sem arroz (Zschornack et al, 2018). Solos alagados cobrem apenas cerca de 8% da área terrestre no mundo, contudo esses locais são extremamente importantes, visto que se apresentam como fonte expressiva na emissão de CH4 para a atmosfera, sendo responsáveis por metade da emissão do gás CH4 emitido globalmente (Sposito, 2008).…”