In silico assessment of the potential of basalt amendments to reduce N2O emissions from bioenergy crops

Elena Blanc‐Betes,Ilsa B Kantola,William J Parton,Nuria Gomez‐Casanovas,Amy L Lewis,Melennie D Hartman,David J Beerling,Evan H Delucia

doi:10.1111/gcbb.12757

Abstract

AbstractThe potential of large‐scale deployment of basalt to reduce N2O emissions from cultivated soils may contribute to climate stabilization beyond the CO2‐removal effect from enhanced weathering. We used 3 years of field observations from maize (Zea mays) and miscanthus (Miscanthus × giganteus) to improve the nitrogen (N) module of the DayCent model and evaluate the potential of basalt amendments to reduce N losses and increase yields from two bioenergy crops. We found 20%–60% improvement in our N2O flux estimates over previous model descriptions. Model results predict that the application of basalt would reduce N2O emissions by 16% in maize and 9% in miscanthus. Lower N2O emissions responded to increases in the N2:N2O ratio of denitrification with basalt‐induced increases in soil pH, with minor contributions from the impact of P additions (a minor component of some basalts) on N immobilization. The larger reduction of N2O emissions in maize than in miscanthus was likely explained by a synergistic effect between soil pH and N content, leading to a higher sensitivity of the N2:N2O ratio to changes in pH in heavily fertilized maize. Basalt amendments led to modest increases in modeled yields and the nitrogen use efficiency (i.e., fertilizer‐N recover in crop production) of maize but did not affect the productivity of miscanthus. However, enhanced soil P availability maintained the long‐term productivity of crops with high nutrient requirements. The alleviation of plant P limitation led to enhanced plant N uptake, thereby contributing to lower microbial N availability and N2O emissions from crops with high nutrient requirements. Our results from the improved model suggest that the large‐scale deployment of basalt, by reducing N2O fluxes of cropping systems, could contribute to the sustainable intensification of agriculture and enhance the climate mitigation potential of bioenergy with carbon capture and storage strategies.

Highlights

Large-scale deployment of bioenergy with carbon capture and storage (BECCS) strategies is widely proposed to be a crucial element of climate risk management (Fuss et al, 2014; Kato & Yamagata, 2014; Obersteiner et al, 2018; Smith et al, 2016)
Recognizing the dearth of empirical data demonstrating the effect of basalt on N2O emissions and other soil properties, we used the biogeochemical model DayCent to evaluate the potential of basalt amendments to reduce N losses, increase yields, and reduce climate forcing from BECCS
Model results indicate that the application of basalt could reduce N2O emissions and lower the N2O emission factor (EF) from both maize and miscanthus, but the magnitude and the mechanisms mediating this response differed by crop

Summary

| INTRODUCTION

Large-scale deployment of bioenergy with carbon capture and storage (BECCS) strategies is widely proposed to be a crucial element of climate risk management (Fuss et al, 2014; Kato & Yamagata, 2014; Obersteiner et al, 2018; Smith et al, 2016). Recognizing the dearth of empirical data demonstrating the effect of basalt on N2O emissions and other soil properties, we used the biogeochemical model DayCent to evaluate the potential of basalt amendments to reduce N losses, increase yields, and reduce climate forcing from BECCS. We performed an in silico assessment of the response of maize (Zea mays) and miscanthus (Miscanthus × giganteus) yields and N2O fluxes to two different types of basalt, a higher P/lower alkali basalt and a lower P/higher alkali basalt These two bioenergy crops have differing belowground C allocation patterns (low and high respectively), and nutrient cycling efficiencies and requirements (high and low respectively; Anderson-Teixeira et al, 2009; Davis et al, 2012; Kantola et al, 2017). With an improved ability to capture the interactions of basalt with the nitrogen cycling of agricultural systems, the research presented here represents the first step toward the full appraisal of the climate mitigation potential of a promising, albeit understudied carbon dioxide removal strategy

| MATERIALS AND METHODS

| RESULTS

Findings

| DISCUSSION