Abstract
The nitrous oxide (N2O) emitted from soil was monitored to investigate the effect of sugarcane straw removal on the mechanisms that make mulch a “hot spot” of N2O emissions under subtropical conditions. We conducted a field experiment with the first-ratoon sugarcane with four amounts of straw (0, 4, 8, and 12 Mg ha−1) at the soil surface combined with 0 or 100 kg urea-N ha−1. The urea-N was applied 52 days after straw application. Over the course of 1 year, we measured the N2O and carbon dioxide (CO2) emissions, mineral nitrogen (N), soil moisture and temperature, and remaining straw carbon (C) and N in the mulch. We observed two “hot moments” for N2O emissions: the first one immediately after sugarcane straw application to soil and the second one after fertilizer-N application. High amounts of straw left on the soil led to an increase in the water-filled pore space (WFPS), and both WFPS and straw-C were strongly correlated with N2O fluxes. Cumulative N2O increased from 510 (0 Mg + N) to 1055 (12 Mg + N) g N2O-N ha−1 for the fertilized straw treatments. The N2O emission factors (EFs) of the sugarcane straw N and the fertilizer-N increased linearly with straw quantity, i.e., were not constant but were lower than the IPCC default values. Over 70% of the cumulative N2O emissions measured in straw + fertilizer-N treatments for 1 year were attributed to the presence of straw mulch, which emphasized the importance of the straw layer at the soil surface as a hot spot for N2O emissions.
Highlights
Agricultural land is the main source of nitrous oxide (N2O) to the atmosphere due to two major processes that occur in soil, i.e., nitrification and denitrification, in response to synthetic-N fertilizer application and organic matter mineralization (Butterbach-Bahl et al 2013; Smeets et al 2009)
By following N2O emissions over 1 year in a sugarcane crop under four scenarios of straw removal, with and without urea-N application, we examined the effects of mulch of various thicknesses on residue decomposition and soil environmental conditions and quantified the respective effects of straw mulch and fertilizer-N and their interaction on N2O emissions
After day 68, we did not observe differences in soil temperature among treatments, which we attributed to the development of the sugarcane canopy, which decreased the relative effect of the mulch layer
Summary
Agricultural land is the main source of nitrous oxide (N2O) to the atmosphere due to two major processes that occur in soil, i.e., nitrification and denitrification, in response to synthetic-N fertilizer application and organic matter mineralization (Butterbach-Bahl et al 2013; Smeets et al 2009). Combined with reduced tillage or no-till, crop residues left as mulches after crop harvest in conservation agriculture or in semi-perennial cropping systems such as with sugarcane (Sousa Junior et al 2018) or other bioenergy crops (e.g., Peyrard et al 2016) can increase long-term soil C sequestration and CO2 mitigation potential (Lal 2004). These practices can influence emissions of non-CO2 gases, such as N2O, which alter the global warming potential (GWP) and could reduce the Bsavings^ that are promoted by C sequestration (Crutzen et al 2008; Lugato et al 2018). Uncertainties in the interactions between residue mulches and fertilization and their effects on N2O emissions (do Carmo et al 2013; Pitombo et al 2017; Siqueira Neto et al 2016) further increase the need to understand how the quantity of residues left on soil (or vice versa, the quantity removed from the field) affects soil N2O emissions
Sign-in/Register to view highlights & summary 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 callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
