TERRECO WP 3-01
Comparisons of net ecosystem CO2 exchange, carbon gain, growth and water use efficiency of agricultural crops in small catchments in KoreaFrom 07/2010
Project manager: Dennis Ochuodho Otieno, John Tenhunen, Gian-Reto Walther
Coworkers: Steve Lindner
Grant: IRTG 1565 WP III TERRECO - Complex Terrain and Ecological Heterogeneity - Evaluating ecosystem services in production versus water yield and water quality in mountainous landscapes
Abstract 2011: The goal of our work is to evaluate as far as possible carbon budget components for an agriculturally dominated landscape in South Korea. In the last decades, rapid changes of land use and land cover due to economic development after the Korean War (Kim and Park, this proceedings) has certainly led to large changes in atmospheric CO2 exchange in the Haean Catchment in Gangwon Province, South Korea. Our studies represent a first step in trying to understand this change at landscape scale. We hypothesized that crops differ in their CO2 assimilation rates and also in their patterns of C allocation, thereby influencing the general patterns of CO2 exchange and production. To test these ideas, we quantified the seasonal patterns of NEE, GPP and Reco in non-irrigated, rain-fed crop ﬁelds (radish, potato, cabbage, bean) and in irrigated rice paddies during the growing seasons 2009 and 2010. It was shown that the most important climate factors for gas exchange and biomass development (radiation, temperature, precipitation) were very similar between locations within the catchment. After planting of the crops, the maximum GPP for potato and cabbage is reached in mid-June with up to 70 and 60 µmol m-2 s-1, respectively. A similar trend in the increase of GPP for rice, radish and bean with parallel development of plant biomass is evident. Significant differences in the maximum GPP between rice, radish, and bean occur in mid-August with fluxes up to 20, 40 and 55 µmol m-2 s-1, respectively. Harvest data on crop yields are reported. Future work is oriented to establishing the links between carbon gain, plant growth and yield; as well as up-scaling the plot results to landscape level.
Keywords: crop gas exchange, net ecosystem CO2 exchange, ecosystem respiration, gross primary production, allocation, agricultural yield
project description in detail from proceedings of 2011 TERRECO Science Conference GAP
Abstract 2013: Conversion of natural ecosystems to croplands is a direct manifestation of human activities within the biosphere. Land use and land cover changes modify the biophysical properties of the land surface (e.g. surface roughness and albedo), altering energy flows and biogeochemical cycles. Intensive agricultural production with input-intensive practices (fertilizer, pesticides, machinery) as witnessed in the Haean−myun Catchment of South Korea significantly influence the regional carbon (C) budget. The Haean−myun Catchment is dominated by three vegetation zones distinctively organized along an elevation gradient. Forests are distributed at the upper zone at an elevation range of ca. 750 to 1100 m, with an area of 39 km2, constituting 61 % of the total land surface area. The dryland farms, primarily growing summer vegetables, orchards and ginseng, occur at an elevation range of ca. 500 to 750 m (covering 17 km2) and constitute about 27 % of the land area. Rice paddies occur in the catchment basin, covering an area of 5 km2, which is 8 % of the land surface area. Characterizing CO2 exchange in each of these zones is important in order to discern their roles in atmospheric C fluxes and to estimate net C uptake and storage (usable agricultural yields and forest products).
Relating crop phenology to C uptake, plant productivity and agricultural yields is complex when the production phases of the crops are overlapping. In this case, information on the response of individual landscape elements is needed. This study focuses on providing such information for the major crops (radish, potato, cabbage, bean, rice) in the Haean Catchment. We hypothesized that the productivity (consumable biomass) of the agricultural crops is determined by C uptake capacity, the duration of C uptake and the pattern of C partitioning. To test these ideas, we quantified the rates of net ecosystem CO2 exchange (NEE), gross primary productivity (GPP) and ecosystem respiration (Reco) in non-irrigated/ rain-fed crop ﬁelds (radish, potato, cabbage, bean) and rice paddies during the growing seasons of 2009 and 2010, with manually operated gas exchange chambers. Aboveground biomass and total leaf area (LA) were determined for each of the crops (plots) after the gas exchange measurements. The samples were further analyzed for C/N content. The maximum GPP rates were 41, 39, 25 µmol m-2 s-1 for radish, potato and rice, respectively, while the respective Reco rates were 14, 17 and 4 µmol m-2 s-1, occurring during July. The highest NEE during the growing period occurred in July and were −27, −23, −21 µmol m-2 s-1 for radish, potato and rice, respectively. GPP and NEE varied significantly (P<0.05) during the season in response to changing biomass, while daily fluctuations were due to changing light intensities. Changes in Reco were due to changing soil temperatures. Up-scaling from plot to landscape level C fluxes using eddy covariance data and the PIXGRO−model is planned. The three levels of CO2 exchange will be related to biomass harvests and farm produce information from the local agricultural offices in order to characterize the agro-ecosystem carbon budget of the Haean catchment.
Key words: carbon dioxide exchange, carbon budget, crop productivity, biomass development, carbon allocation