Dep. de Física, Univ. Federal de Santa Maria (UFSM), Santa Maria, RS, Brazil.
Embrapa Trigo, Passo Fundo, RS, Brazil.
J Environ Qual. 2022 Sep;51(5):899-915. doi: 10.1002/jeq2.20362. Epub 2022 Jun 29.
The subtropical region of Brazil is home to 33% of the soybean [Glycine max (L.) Merr.] growing area and 90% of the wheat (Tritucum aestivum L.) growing area of this country. A soybean-wheat succession with fallow between crops is used in about 11% of the cultivated area. No study has quantified CO fluxes in annual soybean-wheat succession in this region. Hence, this study analyzed the seasonality of CO exchange (net ecosystem exchange [NEE]) in a 2015/2016 wheat-soybean succession in a commercial farm located in Carazinho, Rio Grande do Sul State, Brazil. The eddy covariance method was used to estimate the annual C balance of this system. The NEE was partitioned between gross primary productivity and ecosystem respiration to understand the dynamics of these fluxes during a year of wheat-soybean succession. Considering the net ecosystem balance between photosynthesis and respiration during the growing season, both soybean and wheat absorbed CO from the atmosphere (NEE wheat: -347 ± 4 g C m ; NEE soybean: -242 ± 3 g C m ). The fallow periods between growing seasons, however, acted as a source of 156 ± 2 g C m , reducing the C absorbed by the crops by 27%. For 1 yr, the net biome productivity was -50 g C m yr . The results obtained here demonstrate that the wheat-soybean succession was a net C sink under these specific climatic conditions and field management practices and that the long fallow period between crops limited the agroecosystem from becoming a more efficient CO sink.
巴西的亚热带地区是该国 33%的大豆[Glycine max (L.) Merr.]种植区和 90%的小麦(Tritucum aestivum L.)种植区的所在地。约有 11%的耕地采用大豆-小麦轮作休耕的方式。在该地区，还没有研究量化过年度大豆-小麦轮作中的 CO 通量。因此，本研究分析了位于巴西南里奥格兰德州卡拉齐尼乌市的一个商业农场 2015/2016 年小麦-大豆轮作中 CO 交换（净生态系统交换[NEE]）的季节性。采用涡度相关法估算了该系统的年度碳平衡。将 NEE 在总初级生产力和生态系统呼吸之间进行划分，以了解一年中这些通量的动态。考虑到生长季光合作用和呼吸作用之间的净生态系统平衡，大豆和小麦均从大气中吸收 CO（小麦的 NEE：-347 ± 4 g C m ；大豆的 NEE：-242 ± 3 g C m ）。然而，生长季之间的休耕期则作为 156 ± 2 g C m 的 CO 源，减少了作物吸收的碳量的 27%。在 1 年内，净生物群区生产力为-50 g C m yr 。本研究结果表明，在这些特定的气候条件和田间管理实践下，小麦-大豆轮作是一个净碳汇，而作物之间的长休耕期限制了农业生态系统成为更有效的 CO 汇。
