Abstract
Winter cover crops are sources of C and N in flooded rice production systems, but very little is known about the effect of crop residue management and quality on soil methane (CH4) and nitrous oxide (N2O) emissions. This study was conducted in pots in a greenhouse to evaluate the influence of crop residue management (incorporated into the soil or left on the soil surface) and the type of cover-crop residues (ryegrass and serradella) on CH4 and N2O emissions from a flooded Albaqualf soil cultivated with rice (Oryza sativa L.). The closed chamber technique was used for air sampling and the CH4 and N2O concentrations were analyzed by gas chromatography. Soil solution was sampled at two soil depths (2 and 20 cm), simultaneously to air sampling, and the contents of dissolved organic C (DOC), NO3-, NH4+, Mn2+, and Fe2+ were analyzed. Methane and N2O emissions from the soil where crop residues had been left on the surface were lower than from soil with incorporated residues. The type of crop residue had no effect on the CH4 emissions, while higher N2O emissions were observed from serradella (leguminous) than from ryegrass, but only when the residues were left on the soil surface. The more intense soil reduction verified in the deeper soil layer (20 cm), as evidenced by higher contents of reduced metal species (Mn2+ and Fe2+), and the close relationship between CH4 emission and the DOC contents in the deeper layer indicated that the sub-surface layer was the main CH4 source of the flooded soil with incorporated crop residues. The adoption of management strategies in which crop residues are left on the soil surface is crucial to minimize soil CH4 and N2O emissions from irrigated rice fields. In these production systems, CH4 accounts for more than 90 % of the partial global warming potential (CH4+N2O) and, thus, should be the main focus of research.
Highlights
The mitigation of greenhouse gases (GHG) emissions from agricultural soil, which is estimated at about 20% in the word and 80% in Brazil (Cerri et al, 2009), is fundamental to decrease the contribution of agriculture and land use changes to global warming, which is estimated at about 20 % in the world and 80 % in Brazil (Cerri et al, 2009)
In the South, the region of the majority of paddy rice fields in Brazil, flooded rice fields contribute to 12 % of the total CH4 emissions and this relative contribution increases to 18 % in Rio Grande do Sul State, the largest rice producer in Brazil, where summer rice is grown on more than 1.1 million hectare (CONAB, 2010)
Concerning the effect of management and composition of crop residue on the CH4 and N2O emissions, the results indicated that residues left on the soil surface can potentially mitigate emissions from flooded soil by up to 60 % compared to emissions from soil with incorporated residue (Figure 8)
Summary
The mitigation of greenhouse gases (GHG) emissions from agricultural soil, which is estimated at about 20% in the word and 80% in Brazil (Cerri et al, 2009), is fundamental to decrease the contribution of agriculture and land use changes to global warming, which is estimated at about 20 % in the world and 80 % in Brazil (Cerri et al, 2009). Methane (CH4) is a major issue in flooded rice (Oryza sativa L.) fields, where this source accounts for 10– 40 % of the global CH4 emissions (Le Mer & Roger, 2001; Dalal et al, 2008). In the South, the region of the majority of paddy rice fields in Brazil, flooded rice fields contribute to 12 % of the total CH4 emissions and this relative contribution increases to 18 % in Rio Grande do Sul State, the largest rice producer in Brazil, where summer rice is grown on more than 1.1 million hectare (CONAB, 2010). Understanding the effects and interactions of soil and irrigation management practices under different conditions is crucial for developing effective strategies of CH4 emission minimization (Stepniewski & Stepniewska, 2009)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
