Higher than expected N2O emissions from soybean crops in the Pampas Region of Argentina: Estimates from DayCent simulations and field measurements

Authors: DELLA CHIESA, TOMAS - Universidad De Buenos Aires; PIÑEIRO, GERVASIO - Universidad De Buenos Aires; Del Grosso, Stephen - Steve; PARTON, WILLIAM - Colorado State University; ARAUJO, PATRICIA - Universidad De Buenos Aires; YAHDJIAN, LAURA - Universidad De Buenos Aires

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/16/2022
Publication Date: 4/22/2022
Citation: Della Chiesa, T., Piñeiro, G., Del Grosso, S.J., Parton, W.J., Araujo, P.I., Yahdjian, L. 2022. Higher than expected N2O emissions from soybean crops in the Pampas Region of Argentina: Estimates from DayCent simulations and field measurements. Science of the Total Environment. 835. Article e155408. https://doi.org/10.1016/j.scitotenv.2022.155408.
DOI: https://doi.org/10.1016/j.scitotenv.2022.155408

Interpretive Summary: In developing countries, agriculture generally represents a large portion of greenhouse gas emissions reported in National Inventories and emissions are estimated using simple International Panel on Climate Change (IPCC) guidelines. However, field data and simulation models can improve estimation accuracy. In this study, we quantified the anthropogenic soil nitrous oxide emissions from the main crop (corn, soybean and wheat/soybean ) and unmanaged grasslands of Argentina (Pampas Region) through field measurement, model simulations and the IPCC method. We evaluated the DayCent ecosystem model and then simulated different weather and management scenarios. The DayCent model accurately simulated annual nitrous oxide emissions. Measured and simulated emissions in soybean were higher than in corn and wheat/soybean crops. Simulated gross emissions ranged from 1.4 to 5.1 kg N ha-1 yr-1 for current environmental (soil and weather) and management (crops and fertilizer doses) conditions. Background emissions ranged from 1.1 and 1.3 kg N ha-1 yr-1, and therefore net anthropogenic emissions ranged from 0.3 to 4.0 kg N ha-1 yr-1. Emissions under soybean were 5 times greater when estimated by DayCent (0.53 kg N ha-1 yr-1) compared to the IPCC guidelines. However, IPCC estimates for corn and wheat/soybean crops were similar to modeled or measured values. Our results suggest that nitrous oxide emissions from the vast 58 million ha of soybean croplands in southern South America may be substantially underestimated using typical methods.

Technical Abstract: In developing countries, agriculture generally represents a large fraction of GHG emissions reported in National Inventories and emissions are usually estimated through Tier 1 IPCC guidelines. However, field data and simulation models can improve the estimation accuracy. In this study we aimed to quantify the anthropogenic soil N2O emissions from the main crops of Argentina through field measurement, model simulations and the IPCC method estimations. We measured N2O emissions and their controlling factors in 62 plots of the Pampas Region with corn, soybean and wheat/soybean crops and from unmanaged grasslands. We accounted for gross emissions from crops and background emission from unmanaged grasslands to calculate net anthropogenic emissions from crops as the difference between them. We calibrated and evaluated the DayCent model and then simulated different weather and management scenarios. Finally, we applied IPCC guidelines to estimate anthropogenic N2O emissions at the same plots. The DayCent model accurately simulated annual N2O emission (RMSE = 1.4 kg N ha-1 yr-1). Measured and simulated emissions in soybean crops were higher than in corn and wheat/soybean crops. Simulated gross emissions ranged from 1.4 to 5.1 kg N ha-1 yr-1 for current environmental (soil and weather) and management (crops and fertilizer doses) conditions. Background emission ranged from 1.1 and 1.3 kg N ha-1 yr-1, and therefore net anthropogenic emissions ranged from 0.3 to 4.0 kg N ha-1 yr-1. IPCC Tier 1 emission factors underestimated N2O releases from soybean (0.53 kg N ha-1 yr-1), that were on average 4.87 times greater when estimated with simulation models. On the contrary, IPCC estimates for corn and wheat/soybean crops were similar to modeled or measured values. Our results suggest that N2O emissions from the vast 58 million ha of soybean croplands in southern South America may be substantially underestimated.