Modeling Nitrous Oxide Emissions From Large-Scale Intensive Cropping Systems in the Southern Amazon

Ciniro Costa,Christopher Neill,Christine O'Connell,KathiJo Jankowski,Michael T. Coe,Marcia Macedo,Gillian L. Galford

doi:10.3389/fsufs.2021.701416

Abstract

Nitrogen (N) fertilizer use is rapidly intensifying on tropical croplands and has the potential to increase emissions of the greenhouse gas, nitrous oxide (N2O). Since about 2005 Mato Grosso (MT), Brazil has shifted from single-cropped soybeans to double-cropping soybeans with maize, and now produces 1.5% of the world's maize. This production shift required an increase in N fertilization, but the effects on N2O emissions are poorly known. We calibrated the process-oriented biogeochemical DeNitrification-DeComposition (DNDC) model to simulate N2O emissions and crop production from soybean and soybean-maize cropping systems in MT. After model validation with field measurements and adjustments for hydrological properties of tropical soils, regional simulations suggested N2O emissions from soybean-maize cropland increased almost fourfold during 2001–2010, from 1.1 ± 1.1 to 4.1 ± 3.2 Gg 1014 N-N2O. Model sensitivity tests showed that emissions were spatially and seasonably variable and especially sensitive to soil bulk density and carbon content. Meeting future demand for maize using current soybean area in MT might require either (a) intensifying 3.0 million ha of existing single soybean to soybean-maize or (b) increasing N fertilization to ~180 kg N ha−1 on existing 2.3 million ha of soybean-maize area. The latter strategy would release ~35% more N2O than the first. Our modifications of the DNDC model will improve estimates of N2O emissions from agricultural production in MT and other tropical areas, but narrowing model uncertainty will depend on more detailed field measurements and spatial data on soil and cropping management.

Highlights

Agriculture directly accounts for 10–12% of worldwide anthropogenic greenhouse gas emissions (GHG), so it is a major concern for climate change policy (Smith et al, 2014)
We developed new DNDC parameterizations to account for the hydraulic properties of tropical soils by adjusting soil hydraulic conductivity and soil porosity (Supplementary Table 1) and recalculating soil hydraulic parameters for all texture classes based on pedotransfer functions (PTFs) for Brazilian soils (Medrado and Lima, 2014) in equations for water-filled pore space (WFPS) and wilting point, respectively: WFPS = −0.01831805 x Clay %0.89935543)
Reduction of emissions from agricultural lands is a priority for many countries, including Brazil, which has a commitment under the Paris Agreement

Summary

Introduction

Agriculture directly accounts for 10–12% of worldwide anthropogenic greenhouse gas emissions (GHG), so it is a major concern for climate change policy (Smith et al, 2014). Information on GHG emissions and potential for mitigating emissions by changing management practices is badly need, in regions of rapid cropland expansion, intensification and increased fertilizer use. Agricultural soils are the largest single source of total anthropogenic N2O emissions (Smith, 2017), contributing to approximately 60% of this total (IPCC, 2019a; Tian et al, 2020). The use of N fertilizers in agriculture is the major anthropogenic source of N2O emissions from soils (IPCC, 2019a). Fertilizer induced N2O emissions are estimated to be approximately 1% of N fertilizer applied (Bouwman et al, 2002; IPCC, 2019b), but whether and how this relationship varies among regions of intensively fertilized agriculture globally is not well understood (Snyder et al, 2009; Huddell et al, 2020)

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Conclusion